ISBN:0-8247-0491-6This book is printed on acid-free paper.HeadquartersMarcel Dekker, Inc.270 Madison Avenue, New York, NY10016tel: 212-696-9000; fax:212-685-4540Eastern Hemisphere DistributionMarcel Dekker AGHutgasse 4, Postfach 812, CH-4001 Basel, Switzerlandtel: 41-61-261-8482; fax: 41-61-261-8896World Wide Webhttp://www.dekker.comThe publisher offers discounts on this book when ordered in bulk quantities. For moreinformation, write to Special Sales/Professional Marketing at the headquarters addressabove.Copyright 2001 by Marcel Dekker, Inc. All Rights Reserved.Neither this book nor any part may be reproduced or transmitted in any form or by anymeans, electronic or mechanical, including photocopying, microlming, and recording,or by any information storage and retrieval system, without permission in writing fromthe publisher.Current printing (last digit):10 9 8 7 6 5 4 3 2 1PRINTED IN THE UNITED STATES OFAMERICAPrefaceThis book summarizes the knowledge about the use of some nontraditional surfac-tants in detergents. The emphasis is on laundry detergents, with some discussion ofotherdetergenciessuchashard-surfacecleaningandpersonalwashing. Thesur-factants described in this volume are in the classic organic head-tail class of sur-factantsratherthanpolymersorsiliconesurfactants.Thebookoriginatedfrompresentations given by noted scientists and authors at recent World Detergent Con-ferences in Montreux, Switzerland, and at AOCS and CESIO congresses.Traditionally,powderedandliquidlaundrydetergentscontainedlinearalkylbenzene sulfonates, ether sulfates, and alcohol ethoxylates as surfactants, alongwith builders, enzymes, polymers, and possibly bleaches as additional active in-gredients.Theseformulationsdealtwellwithdifferenttypesofdirtandstainsunder a variety of water conditions.In recent years, however, a number of specialty surfactants have been developedfor use in detergents. Some of the materials are somewhat newer in a commercialsense,suchasalkylpolyglucosides(APGs)and-sulfomethylesters.Othersub-stances,suchasalkyldiphenyloxidedisulfonates,betaines,alkanolamides,andethoxylated amines, have been known for years and used routinely in other indus-tries. In this volume, these ingredients are examined closely for advantages in deter-gents. Recent process improvements in producing new specialty surfactants such asethoxylatedmethylestersandalkylethylenediaminetriacetateshavemadetheirconsideration as detergent ingredients necessary.New specialty surfactants have been investigated and some adopted commer-cially for a variety of reasonsenvironmental, safety, performance, and formu-lationproperties.Intheenvironmentalarea,supplierswantsurfactantsthatiiibiodegrade rapidly and have low aquatic toxicity. The public also desires prod-ucts with low human toxicity and minimal skin/eye irritation. There has alwaysbeen a need for surfactants that clean well overall, clean certain stains well, orare cost effective. What criteria distinguish a commodity surfactant from a spe-cialty one? In general, a specialty surfactant has these properties:1. Smaller manufacturing volumes2. Fewer producers3. Special properties in some applicationslow irritation, biodegradable,improved foam, etc.Specialty surfactants are mostly secondary surfactants, not the primary ingre-dientinaformulation,andgarnersomewhathigherpricesinthemarketplace.Normally, over time a surfactant once considered a specialty slowly becomes acommodity.However,somesurfactantclassescanhavebothcommodityandspecialtyuses.Infact,itissometimespossibletoconvertacommodityintoaspecialty. For instance, linear alkylbenzene sulfonate (LAS) is considered a com-modity. As such, it is sold either in the acid form at 96% active or as the sodiumsaltat40%to60%active.TherearemanyproducersofandapplicationsforLAS. As a specialty, the sodium salt is sold as akes at 90% active. Few produc-ers and few applications need this material, but it commands a higher price. Onemain use is for dry blending in powdered detergents for smaller manufacturers,whereitmakesitpossibletoavoidpurchaseofexpensivespray-dryingequip-ment. Here the special property is its physical form.The same is true of sodium lauryl sulfate (SLS). As a commodity, SLS is 30%active and has many producers and many applications. As a specialty, SLS is apowderthatis95%activeandfoodgrade. Again,therearefewproducersandfew applications, the main one being toothpaste. Here the special property is itsphysical form and the fact that it is food grade.In this volume, the special properties of specialty surfactants are their perfor-manceindetergents.Detergentformulationshavechangedimmenselyinthepast 10 years. Both powders and liquids are more concentrated, making for bet-ter cleaning per gram. Enzyme use has increased in detergents, requiring surfac-tantsthatarecompatiblewithenzymesorhaveasynergisticcleaningeffect.Washingmachinesthatuselesswaterandonlycoldwaterarebecomingmorecommon in North America. Washing temperatures are decreasing dramatically inEurope also. These conditions require ingredients that are low foaming and thatdisperse easily to clean well in cold water.In this volume of the Surfactant Series, originated by Martin Schick and pub-lished by Marcel Dekker, Inc., sugar-based surfactants such as alkyl polygluco-sidesarediscussedinChapter1.Anionicssuchasalkyldiphenyloxidedisulfonatesand-sulfomethylestersarepresentedinChapters3and4,andaiv Prefacenumberofnewnonionics,amphoterics,chelatingsurfactants,andmultifunc-tional ingredients in Chapters 2, 5, and 6. Special topics such as surfactants fordrycleaning,prespotters,andsoftenersareincludedinChapters7through9.The information contained herein should help the formulator choose the best in-gredients for current detergent and cleaning formulas. This volume is related tothe Surfactant Series Volumes 59, on amphoterics, and 74 on novel surfactants,which can also be consulted.Floyd E. FriedliPreface vContentsPreface iiiContributors ix1. Alkyl Polyglycosides 1Karl Schmid and Holger Tesmann2. Nitrogen-Containing Specialty Surfactants 71Shoaib Arif and Floyd E. Friedli3. Sulfonated Methyl Esters 117Terri Germain4. Detergency Properties of Alkyldiphenyl Oxide Disulfonates 145Lisa Quencer and T. J. Loughney5. Methyl Ester Ethoxylates 167Michael F. Cox and Upali Weerasooriya6. N-Acyl ED3AChelating Surfactants: Properties and Applicationsin Detergency 195Joe Crudden7. Surfactants for the Prewash Market 221Michelle M. Wattsvii8. Dry Cleaning Surfactants 239Al Dabestani9. Concentrated and Efcient Fabric Softeners 255Amjad Farooq, Ammanuel Mehreteab, Jeffrey J. Mastrull,Rgis Csar, and Guy BrozeIndex 281viii ContentsContributorsShoaib Arif Home Care, Goldschmidt Chemical Corporation, Dublin, OhioGuyBroze PersonalCare,Colgate-PalmoliveResearchandDevelopment,Inc., Milmort, BelgiumRgis Csar Personal Care, Colgate-Palmolive Research and Development,Inc., Milmort, BelgiumMichaelF. Cox ResearchandDevelopment,CONDEA VistaCompany,Austin, TexasJoe Crudden Hampshire Chemical Corporation, Nashua, New HampshireAl Dabestani Consultant, Dublin, OhioAmjadFarooq FabricCareAdvancedTechnology,Colgate-PalmoliveCompany, Piscataway, New JerseyFloydE.Friedli ResearchandDevelopmentSynthesis/FabricCare,Gold-schmidt Chemical Corporation, Dublin, OhioTerriGermain LaundryandCleaningProductDevelopment,StepanCom-pany, Northeld, IllinoisixT. J. Loughney Samples LLC, Port Orchard, WashingtonJeffreyJ.Mastrull FabricCareAdvancedTechnology,Colgate-PalmoliveCompany, Piscataway, New JerseyAmmanuelMehreteab CorporateTechnologyCenter,Colgate-PalmoliveCompany, Piscataway, New JerseyLisa Quencer Industrial Chemicals, The Dow Chemical Company, Midland,MichiganKarlSchmid ResearchandDevelopment,CognisGmbH,Dsseldorf,Ger-manyHolgerTesmann ResearchandDevelopment,CognisGmbH,Dsseldorf,GermanyMichelle M. Watts Research and Development Synthesis/Fabric Care, Gold-schmidt Chemical Corporation, Dublin, OhioUpaliWeerasooriya ResearchandDevelopment,CONDEA VistaCom-pany, Austin, Texasx Contributors1Alkyl PolyglycosidesKARL SCHMID and HOLGER TESMANNCognis GmbH, Dsseldorf, GermanyI. INTRODUCTIONA. History of Alkyl PolyglycosidesThe rst alkyl glucoside was synthesized and identied in the laboratory by EmilFischer in 1893 [1]. This process is now well known as the Fischer glycosida-tionandcomprisesanacid-catalyzedreactionofglycoseswithalcohols.ThestructureofethylglucosidewasdenedcorrectlybyFischer,asmaybeseenfrom the historical furanosidic formula proposed (Fischer projection). In fact,Fischerglycosidationproductsarecomplex,mostlyequilibriummixturesof/-anomers and pyranoside/furanoside isomers which also comprise randomlylinked glycoside oligomers (Fig. 1) [2].Accordingly, individual molecular species are not easy to isolate from Fis-cherreactionmixtures,whichhasbeenaseriousprobleminthepast. Aftersomeimprovementofthissynthesismethod[3],FischersubsequentlyadoptedtheKoenigs-Knorrsynthesis[4]forhisinvestigations.Usingthisstereoselective glycosidation process introduced by W. Koenigs and E. Knorrin 1901, E. Fischer and B. Helferich in 1911 were the rst to report the syn-thesis of a long-chain alkyl glucoside exhibiting surfactant properties [5]. Asearlyas1893,Fischerhadnoticedessentialpropertiesofalkylglycosides,suchastheirhighstabilitytowardoxidationandhydrolysis,especiallyinstrongly alkaline media. Both characteristics are valuable for alkyl polyglyco-sides in surfactant applications.Research related to the glycosidation reaction is ongoing; some of the pro-ceduresforthesynthesisofglycosidesaresummarizedinFigure2[6].ThebroadsynthesispotentialrangehasrecentlybeenreviewedinarticlesbySchmidtandToshimaandTatsuta[7]andinanumberofreferencescitedthere.1B. Developments in IndustryAlkylglucosidesoralkylpolyglycosides,astheindustriallymanufacturedproducts are widely knownare a classic example of products which, for a longtime, were of academic interest only. The rst patent application describing theuseofalkylglucosidesindetergentswasledinGermanyin1934[8]. There-after, another 40 to 50 years went by before research groups in various compa-niesredirectedtheirattentiononalkylglucosidesanddevelopedtechnicalprocesses for the production of alkyl polyglycosides on the basis of the synthesisdiscovered by Fischer.Rohm&Haaswasthersttomarketanoctyl/decylpolyglycosideincom-mercialquantitiesinthelateseventies,followedbyBASFandlaterSEPPIC.However, owing to the more hydrotropic character of this short-chain version asasurfactant,applicationswerelimitedtofewmarketsegmentsforexample,the industrial and institutional sectors.Theproductqualityofsuchshort-chainalkylpolyglycosideshasbeenim-provedinthepastcoupleofyearsandnewtypesofoctyl/decylpolyglycosideare currently being offered by various companies, among them BASF, SEPPIC,Akzo Nobel, ICI, and Henkel.At the beginning of the 1980s, several companies started programs to developalkylpolyglycosidesinalongeralkylchainrange(dodecyl/tetradecyl)withaview to making a new surfactant available to the cosmetics and detergent indus-tries. They included Henkel KGaA, Dsseldorf, Germany, and Horizon, a divi-sion of A. E. Staley Manufacturing Company of Decatur, Illinois.AftertheacquisitionofHorizonbyHenkelCorporation/USA apilotplantwent on line in 1988/1989 and was mainly intended to determine process para-2 Schmid and TesmannFIG. 1 Synthesis of glycosides according to Fischer.Alkyl Polyglycosides3FIG. 2 Summary of methods for the synthesis of glycosides. (From Ref. 6.)meters, to optimise product quality under industrial production conditions and toprepare the market for a new class of surfactants. New peaks in the commercialexploitation of alkyl polyglycosides (APG) were reached in 1992 with the inau-guration of a 25,000 t.p.a. production plant for APG surfactants by Henkel Cor-poration in the United States and in 1995 with the opening of a second plant ofequal capacity by Henkel KGaAin Germany [9].II. TECHNOLOGYAny production process suitable for use on an industrial scale must satisfy sev-eral criteria. The ability to produce products with suitable performance proper-ties and process economy are the most important. There are other aspects, suchasminimizingsidereactionsorwasteandemissions.Thetechnologyusedshould have a exibility which allows product properties and quality features tobe adapted to market requirements.Sofarastheindustrialproductionofalkylpolyglycosidesisconcerned,processes based on the Fischer synthesis have been successfully adopted. Devel-opment work over 20 years has enabled the efciency of this synthesis route tobe increased to a level where it has nally become attractive for industrial appli-cation. Optimization work, particularly in the use of long-chain alcohols, such asdodecanol/tetradecanol, has resulted in distinct improvements in product qualityand process economy.ModernproductionplantsbuiltonthebasisoftheFischersynthesisaretheembodiment of low-waste, virtually emission-free technologies. Another advan-tage of the Fischer synthesis is that the average degree of polymerization of theproductscanbepreciselycontrolledoverawiderange.Relevantperformanceproperties, for example hydrophilicity or water solubility, can thus be adapted tomeet applicational requirements. Additionally the raw material base is no longerconned to water-free glucose [1012].A. Raw Materials for the Manufacture of AlkylPolyglycosides1. Fatty AlcoholsFatty alcohols can be obtained either from petrochemical sources (synthetic fattyalcohols)orfromnatural,renewableresources,suchasfatsandoils(naturalfatty alcohols). Fatty-alcohol blends are used in the alkyl polyglycoside synthe-sis to build up the hydrophobic part of the molecule. The natural fatty alcoholsareobtainedaftertransestericationandfractionationoffatsandoils(triglyc-erides), leading to the corresponding fatty acid methyl esters, and subsequent hy-drogenation. Depending on the desired alkyl chain length of the fatty alcohol, themain feedstocks are oils and fats of the following composition: coconut or palm4 Schmid and Tesmannkernel oil for the C12/14range and tallow, palm, or rapeseed oil for the C16/18fattyalcohols.2. Carbohydrate SourceThe hydrophilic part of the alkyl polyglycoside molecule is derived from a car-bohydrate. Based on starch from corn, wheat, or potatoes, both polymeric andmonomericcarbohydratesaresuitableasrawmaterialsfortheproductionofalkylpolyglycosides.Polymericcarbohydratesinclude,forexample,starchorglucose syrups with low degradation levels while monomeric carbohydrates canbeanyofthevariousformsinwhichglucoseisavailable,forexamplewater-freeglucose,glucosemonohydrate(dextrose),orhighlydegradedglucosesyrup. Raw material choice inuences not only raw material costs, but also pro-ductioncosts.Generallyspeaking,rawmaterialcostsincreaseintheorderstarch/glucose,syrup/glucose,andmonohydrate/water-freeglucosewhereasplant equipment requirements and hence production costs decrease in the sameorder (Fig. 3).3. Degree of PolymerizationThrough the polyfunctionality of the carbohydrate partner, the conditions of theacid-catalyzedFischerreactionyieldanoligomermixtureinwhichonaveragemore than one glycose unit is attached to an alcohol molecule. The average num-ber of glycose units linked to an alcohol group is described as the degree of poly-Alkyl Polyglycosides 5FIG.3 Carbohydratesourcesforindustrial-scalealkylpolyglycosidesynthesis.DE=dextrose equivalent.merization (DP). Figure 4 shows the distribution for an alkyl polyglycoside withDP = 1.3. In this mixture, the concentration of the individual oligomers (mono-,di-, tri-, . . .-, glycoside) is largely dependent on the ratio of glucose to alcohol inthe reaction mixture. The average DP is an important characteristic with regardto the physical chemistry and application of alkyl polyglycosides. In an equilib-rium distribution, the DPfor a given alkyl chain lengthcorrelates well withbasicproductproperties,suchaspolarity,solubility,etc.Inprinciple,thisoligomer distribution can be described by a mathematical model. P. M. McCurry[13]showedthatamodeldevelopedbyP. J.Flory[14]fordescribingtheoligomer distribution of products based on polyfunctional monomers can also beapplied to alkyl polyglycosides. This modied version of the Flory distributiondescribes alkyl polyglycosides as a mixture of statistically distributed oligomers.The content of individual species in the oligomer mixture decreases with in-creasingdegreeofpolymerization.Theoligomerdistributionobtainedbythismathematical model accords well with analytical results.B. Production of Alkyl PolyglycosidesBasically, all processes for the reaction of carbohydrates to alkyl polyglycosidesby the Fischer synthesis can be attributed to two process variants, namely direct6 Schmid and Tesmann[Wt %]100 50 DP1 DP2 DP3 DP4 DP5DP= PP12 i100100P1001+ 2+. . .=ii = 1HHOHOHOOHOHOHOROOOOCH2DP-1 FIG. 4 Typical distribution of dodecyl glycoside oligomers in a DP = 1.3 mixture. R =dodecyl.synthesisandthetransacetalizationprocess.Ineithercase,thereactioncanbecarried out in batches or continuously.Direct synthesis is simpler from the equipment point of view [1517]. In thiscase, the carbohydrate reacts directly with the fatty alcohol to form the requiredlong-chain alkyl polyglycoside. The carbohydrate used is often dried before theactualreaction(forexample,toremovethecrystal-waterincaseofglucosemonohydrate = dextrose). This drying step minimizes side reactions which takeplace in the presence of water.In the direct synthesis, monomeric solid glucose types are used as ne-parti-clesolids.Sincethereactionisaheterogeneoussolid/liquidreaction,thesolidhas to be thoroughly suspended in the alcohol.Highly degraded glucose syrup (DE>96; DE=dextrose equivalents) can reactin a modied direct synthesis. The use of a second solvent and/or emulsiers (forexample,alkylpolyglycoside)providesforastablene-dropletdispersionbe-tween alcohol and glucose syrup [18,19].The two-stage transacetalization process involves more equipment than the di-rect synthesis. In the rst stage, the carbohydrate reacts with a short-chain alcohol(for example n-butanol or propylene glycol) and optionally depolymerizes. In thesecondstage,theshort-chainalkylglycosideistransacetalizedwitharelativelylong-chain alcohol (C12/14-OH) to form the required alkyl polyglycoside. If the mo-lar ratios of carbohydrate to alcohol are identical, the oligomer distribution obtainedin the transacetalization process is basically the same as in the direct synthesis.Thetransacetalizationprocessisappliedifoligo-andpolyglycoses(forex-ample, starch, syrups with a low DE value) are used [20]. The necessary depoly-merizationofthesestartingmaterialsrequirestemperaturesof>140C.Dependingonthealcoholused,thiscancreatehigherpressureswhichimposemore stringent demands on equipment and can lead to a higher plant cost.Generallyforthesamecapacity,thetransacetalizationprocessresultsinhigher plant costs than the direct synthesis. Besides the two reaction stages, addi-tional storage tanks and recycle facilities for the short-chain alcohol are needed.Alkyl polyglycosides have to be subjected to additional or more elaborate ren-ingonaccountofspecicimpuritiesinthestarch(forexample,proteins).Inasimplied transacetalization process, syrups with a high glucose content (DE>96%) or solid glucose types can react with short-chain alcohols under normal pres-sure [2125]. Continuous processes have been developed on this basis [23]. Fig-ure 5 shows both synthesis routes for alkyl polyglycosides.The requirements for the design of alkyl polyglycoside production plants basedontheFischersynthesisarecriticallydeterminedbythecarbohydratetypesusedand by the chain length of the alcohol used as described here for the production ofalkyl polyglycosides on the basis of octanol/decanol and dodecanol/tetradecanol.Under the conditions of the acid-catalyzed syntheses of alkyl polyglycosides,secondary products, such as polydextrose [26,27], ethers, and colored impurities,Alkyl Polyglycosides 7areformed.Polydextrosesaresubstancesofundenedstructurewhichareformedinthecourseofthesynthesisthroughthepolymerizationofglycoses.The type and concentration of the substances formed by secondary reactions aredependentonprocessparameters,suchastemperature,pressure,reactiontime,catalyst, etc. One of the problems addressed by development work on industrialalkyl polyglycoside production over recent years was to minimize this synthesis-related formation of secondary products.Generally, the production of alkyl polyglycosides based on short-chain alco-hols(C8/10-OH)andwithalowDP (largealcoholexcess)presentsthefewestproblems. Fewer secondary products are formed with the increasing excess of al-cohol in the reaction stage. The thermal stress and formation of pyrolysis prod-ucts during removal of the excess alcohol are reduced.8 Schmid and TesmannFIG. 5 Alkyl polyglycoside surfactantsindustrial synthesis pathways.The Fischer glycosidation may be described as a process in which, in a rststep,thedextrosereactsrelativelyquicklyandanoligomerequilibriumisreached. This step is followed by slow degradation of the alkyl polyglycoside. Inthe course of the degradation, which consists of dealkylation and polymerizationsteps,thethermodynamicallymorestablepolydextroseisformedsubstantiallyirreversiblyinincreasingconcentrations.Reactionmixtureswhichhaveex-ceeded an optimal reaction time may be described as overreacted.If the reaction is terminated too early, the resulting reaction mixture containsa signicant amount of residual dextrose. The loss of alkyl polyglycoside activesubstance in the reaction mixture correlates well with the formation of polydex-trose, the reaction mixture in the case of overreacted systems gradually becom-ingheterogeneousagainthroughprecipitatingpolydextrose.Accordingly,product quality and product yield are critically inuenced by the time at whichthe reaction is terminated. Starting with solid dextrose, alkyl polyglycosides lowin secondary products are obtained, providing other polar constituents (polydex-trose) are ltered off together with the remaining carbohydrate from a reactionmixture that has not fully reacted [28,29].In an optimized process, the concentration of secondary products formed byethericationremainsrelativelylow(dependingonreactiontemperatureandtime, type and concentration of catalyst, etc.). Figure 6 shows the typical courseof a direct reaction of dextrose and fatty alcohol (C12/14-OH).Alkyl Polyglycosides 9FIG. 6 Mass balance of the glycosidation process.IntheFischerglycosidation,thereactionparameterstemperatureandpres-surearecloselyrelated.Toproduceanalkylpolyglycosidelowinsecondaryproducts, pressure and temperature have to be adapted to one another and care-fully controlled. Low reaction temperatures (100C,typically110120C)canlead to changes in color of the carbohydrates. By removing the lower-boiling re-action products (water in the direct synthesis, short-chain alcohols in the transac-etalizationprocess)fromthereactionmixture,theacetalizationequilibriumisshifted to the product side. If a relatively large amount of water is produced perunitoftime,forexamplebyhighreactiontemperatures,provisionhastobemade for the effective removal of this water from the reaction mixture. This min-imizessecondaryreactions(particularlytheformationofpolydextrose)whichtake place in the presence of water. The evaporation efciency of a reaction stagedepends not only on pressure, but also on temperature and on the design of thereactor(stirrer,heat-exchangearea,evaporationarea,etc.).Typicalreactionpressuresinthetransacetalizationanddirectsynthesisvariantsarebetween20and 100 mbar.Anotherimportantoptimizationfactoristhedevelopmentofselectivecata-lysts for the glycosidation process so that for example the formation of polydex-troseandethericationreactionscanbesuppressed.Asalreadymentioned,acetalization or transacetalization in the Fischer synthesis is catalyzed by acids.In principle, any acids with sufcient strength are suitable for this purpose, suchas sulfuric acid, paratoluene- and alkylbenzene sulfonic acid, and sulfosuccinicacid. The reaction rate depends on the acidity and the concentration of the acid inthe alcohol.After the reaction, the acidic catalyst is neutralized by a suitable base, for ex-ample sodium hydroxide or magnesium oxide. The neutralized reaction mixtureis a yellowish solution containing 50 to 80 % fatty alcohol. The high fatty-alco-hol content results from the molar ratios of carbohydrate to fatty alcohol. This ra-tio is adjusted to obtain a specic DP for the technical alkyl polyglycosides andis generally between 1:2 and 1:6. The excess fatty alcohol is removed by vacuumdistillation. Important boundary conditions include:1. Residual fatty alcohol content in the product must be 50%, followed by the diglycosides and higher oligomers up to heptaglycosides.Smallamountsofmorehighlyglycosidatedspeciesarealsopresent.Specieswith a degree of glycosidation > 5 are not normally determined in routine analy-sisbecausetheamountsinvolvedaretoosmall. Themostimportantanalyticaltechniques routinely used for the characterization of main and trace componentsincommercialalkylpolyglycosidesarehigh-performanceliquidchromatogra-phy (HPLC) and gas chromatography (GC).1. Alkyl Polyglycoside Determination by GCThe GC technique which has proven to be particularly suitable for the analysis ofalkylmono-andoligoglycosidesishigh-temperaturegaschromatography(HTGC).HTGCusestemperaturesofupto400C,whichenablesoligomericalkyl polyglycosides up to the very high boiling heptaglycosides to be analyzed.Thehydroxylgroupsinalkylpolyglycosideshavetobeconvertedintosilyl12 Schmid and TesmannFIG. 8 Typical industrial-scale glycosidation process for C12/14-APG. FOH = fatty alco-hol.ethersbeforeanalysistopreventsampledecomposition. A typicalHTGCofacommercial alkyl polyglycoside sample is shown in Figure 9.2. Alkyl Polyglycoside Characterization by HPLCAlkyl polyglycoside characterization by HPLC is routinely performed using anisocratic reversed-phase system. In most cases, no particular sample preparationis necessary; after dissolution in the eluent, the sample solution is ltered and di-rectly injected into the system. Atypical chromatogram and the chromatographicconditions are shown in Figure 10.Theretentiontimecorrespondstothelipophilicityofthesubstancessepa-rated. Theindividualspeciesareidentiedandquantiedbytheexternalstan-dard method using commercially available alkyl glycosides for calibration. Thealkyl monoglycosides are separated cleanly enough to allow sufciently accuratequantication. Detailed determination of individual oligoglycosides and separa-tion into and anomers, pyranosides, and furanosides are only possible with amorepolarmobilephasethatrequirestediouslylonganalysistimes[37].TheanalysisofalkylglycosidesincommercialalkylpolyglycosideproductsbyHPLC provides good results for analytical tasks which do not require high reso-lution of a broad spectrum of components. Typical applications include raw ma-terialidentication,comparativealkylpolyglycosideanalysis,quantications,and calculations solely on the basis of the alkyl monoglycoside contents.III. PHYSICOCHEMICAL PROPERTIES OF ALKYLPOLYGLYCOSIDESA. Surface TensionThe surface tension of alkyl (poly)glycosides was investigated as a function ofthe alkyl chain and the degree of polymerization (DP) using samples differing incomposition. In addition to pure surfactants for characterizing the basic depen-Alkyl Polyglycosides 13TABLE 1 Composition of Two AlkylPolyglycoside SurfactantsSubstances Sample 1 Sample 2Monoglycosides 65% 51%Diglycosides 19% 19%Triglycosides 9% 13%Tetraglycosides 5% 10%Pentaglycosides 2% 4%Hexaglycosides 0% (100Na alpha olen sulfonateC14, C16 >100Source: Ref. 29.propertiescomparedtoothercommodityanionicsurfactants[29].ThesamemodiedBorghettytestasmentionedabovewasused.Thelowerthepercentsurfactant needed to disperse the calcium soap, the more effective the surfactant.Itmustbenotedthatthesurfactantsusedwerecommercialgradeandarenotpure cuts.V. USESSurfactants are used for a variety of reasonsfoaming, wetting, emulsication,etc. One of their primary functions is the removal of soil from surfaces. In thissection, the detergency properties of SMEs and sulfonated fatty acids will be dis-cussed. Included will be suggested or actual uses of the surfactants in commer-cial cleaners.A. LaundryMuch has been written on SMEs and sulfonated fatty acids potential in laundryapplications. So much so that the following only summarizes some of the manystudies that have been done.Satsuki studied sodium SME of different chain lengths in test solutions alsocontainingsodiumcarbonateandsilicate[2].HeincludedLASandSLSforcomparison. In 25C, 54-ppm hardness water, the surfactants are ranked thus fordetergency:C16SME> C18SME> LAS> C14SME> SLS> C12SME.Inharderandwarmerwater,40C,270-ppmasCaCO3,adifferentrankingwasfound: C16 SME = C18 SME > C14 SME > SLS > C12 SME > LAS. Overall,the C16 SME and C18 SME exhibited the highest detergency. All test solutionsperformed better in 25C, 54-ppm water than in the 40C, 270-ppm water.Satsuki also studied the effects of surfactant concentrations on detergency incombination with sodium carbonate and silicate. He found that less C14,16 SMEis required to obtain the same level of detergency compared to LAS [2].Satsuki then examined the effects of several anionic surfactants versus waterhardnessinphosphate-builtformulations.TheSMEoutperformedthealpha-olen sulfonate, LAS, and SLS tested at all water hardnesses other than 0 ppm. Itis believed that SMEs tolerance to water hardness ions allows for higher deter-gency [2].Rockwell and Rao show data comparing C12 SME and C13.6 SME to LASandSLSviadetergencytesting[30].InthearticletheyexplainthatthesearecommercialproductsandnotpureSMEsamples.Theydocontainsomesul-fonatedfattyacidasanactivesurfactant.ThetestingwasaccomplishedinaTerg-O-Tometer with 1 L of wash liquor and the delta reectance represents thedifference in reectance units of the L reading of the Lab scale via a HunterColorimeter.RockwelldemonstratedpoorerperformanceoftheC12SMEin130 Germainsoft water compared to the other surfactants. In hard water, the SLS and the 1:1combinationofSLSandC13.6SMEweremosteffectiveona65/35polyester/cottonblend.On100%cottonundercold-waterconditions,boththeSMEs outperformed the other surfactants in hard water.Satsukiagaincomparedvarious-chain-lengthSMEstoLASandSLSinanexperimentalsystembuiltwithsodiumcarbonateandsodiumsilicate[17].Hespecically stayed away from sequestering builders, e.g. phosphates. He evalu-atedthesurfactantsin25C,54ppmasCaCO3wateraswellasin40C,270ppmasCaCO3water.Thefabricwascottonandthesoilanarticialsoilex-plained in the article. His studies revealed that the C16 SME gave the highest de-tergency,withtheC18SMEclosebehindunderbothconditions.Furtherexperimentation by Satsuki showed that 200 ppm C16-SME could equal or out-perform 300 ppm of either the LAS or the SLS at 25C, 54-ppm water hardness.Similar results were obtained with natural facial soil.SteinandBaumannstudiedthedetergencyoftallowSMEandpalmkernelSME [5]. The testing took place in a Launder-ometer at 90C on cotton and at60C on a cotton/polyester blend. Water hardness was 300 ppm as CaCO3. Theyfound that without a builder present, the tallow SME outperformed the palm ker-nel SME, which outperformed the LAS also included in the study. It was not un-tilanonionicsurfactantandtripolyphosphatewereaddedtotheanionicsurfactants that equivalent detergency was obtained. Stein and Baumann cite thelowsensitivitytowaterhardnessasthereasonforthehighdetergencyoftheSMEs.Ahmad and colleagues studied SMEs made from palm stearin and palm fatty-aciddistillates[8].TheyconductedTerg-O-Tometerstudiesofbuiltlaundrypowders, with and without phosphate. Evaluations took place in water hardnessconditions ranging from 50 ppm to 500 ppm as CaCO3and from water tempera-tures ranging from room temperature to 60C. They concluded that there was nodifference in performance between the SME made from palm stearin and palmfatty-acid distillate. The SMEs were equal to or better than LAS in the nonphos-phate test formulation at all conditions. The SMEs were equal to or better thanLAS in both test formulations, with or without phosphate, in soft water.SchambilstudieddetergencyeffectsofchainlengthonSMEandthedis-odium salts of sulfonated fatty acid [3]. He found that as chain length increases,detergency improves in both soft and hard water. The highest performers in bothsurfactant classes were the C16 and C18 chain lengths. The sulfonated fatty acidanalogsdidnotperformaswellastheirSMEcounterparts.Increasingwaterhardness decreased the performance of both the SMEs and sulfonated fatty acidssimilarly for the C14 to C18 samples. Only the C12 SME had better detergencyin hard water than in soft water.IfZeolitewasadded,thehardwaterperformanceoftheSMEsincreasedtoequal or better performance compared to soft water conditions without the Zeo-Sulfonated Methyl Esters 131lite.Thesulfonatedfatty-acidsamplesinhardwaterwithZeoliteshowedap-proximately 85% of the remission values of the analog SME samples in soft wa-ter.Theadditionofabuildersignicantlyimprovedsulfonatedfatty-acidperformance. The Zeolite is necessary for sulfonated fatty-acid detergency per-formance due to their sensitivity to water hardness.Stirton studied the detergency properties of sulfonated fatty acids [4]. He andhis colleagues found that the di-Na C18-sulfonated fatty acid was the best deter-gent. The more soluble salts, i.e. the mono- and disodium salts of C12-sulfonatedfatty acid and the disodium salt C14-sulfonated fatty acid, gave the poorest de-tergency.Changesinchainlengthhadalargerimpactondetergencythanchanges in water hardness.Weilandhiscolleaguesstudieddifferentcationsofmonoanddisaltsofpalmityl and stearyl sulfonated fatty acid. They found that the monolithium, tri-ethanolammonium,magnesium,andcalciumsaltsgavethehighestdetergency[21].Stirton compared the disodium salt of C16-sulfonated fatty acid to SLS andLAS[31].HeconcludedthatthedisodiumC16-sulfonatedfattyacidisagooddetergent in both soft and hard water. His results show that the sulfonated fattyacid statistically outperformed the SLS and alkylaryl sulfonate in his particulartest (Fig. 14) [31].The detergency of differing ratios of the C13.6 analogs of SME to sulfonatedfattyacidwereevaluatedusingaTerg-O-Tometerwithcotton,35/65132 GermainFIG. 14 Detergency of C16 sulfonated fatty acid, SLS, LAS vs. water hardness.cotton/polyester, and polyester fabric swatches soiled with dust/sebum soil fromScientic Services in New Jersey [32]. Figures 15 and 16 show the detergencyresults on cotton and polyester, respectively. Twenty-ve percent of the total sur-factant can be the sulfonated fatty acid and not diminish detergency. Detergencytrendsweresimilaronthecotton/polyesterblend.Detergencyimprovedwithhigh water hardness on polyester. As expected from the literature, increasing wa-ter hardness decreased the detergency of the 100% sulfonated fatty acid.R.G.BristlineJr.andcolleaguesstudiedthedetergencypropertiesoftallowSME with tallow soap, with and without builders [33]. Testing was conducted in aTerg-O-Tometer with various soils on cotton swatches. The detergency of soap wassignicantly enhanced by the incorporation of the tallow SME and builders such assodium tripolyphosphate, sodium citrate, sodium metasilicate, and sodium oxydiac-etate. Sodium carbonate only affected detergency results in multiwash tests. TallowSMEwasfoundtobeaseffectiveatimprovingdetergencyasotherknownlimesoap dispersing agents, e.g., tallow alcohol ethoxysulfate and ethoxylated n-hexade-canol-10 ethylene oxide units (EO). LAS was also studied and performed poorer incomparison to the other lime soap dispersing agents (LSDA) including tallow SME.Optimumdetergencywasobtainedinmostcaseswithan80:10:10ratioofsoap:LSDA:builder.Testconditions:300ppmwater,60C,and0.2%surfactantplus builder. Detergency was measured by delta reectance.OveralltheC16andC18chainlengthsofbothSMEsandsulfonatedfattySulfonated Methyl Esters 133Terg-O-Tometer Detergency of C13.6 SME/SFADust-Sebum on Cotton18.016.014.012.010.08.06.04.02.00.00.2% total surfactant38C (100F) water temppH=87:1 SME:SFA3:1 SME:SFAall SFA0 ppm 150 ppm 350 ppmWater Hardness as CaCO3Delta Relectance15.7 15.814.113.613.010.012.713.15.3FIG. 15 SME/sulfonated fatty acid Terg at pH 8 on cotton.acids are the best detergents of these surfactant classes. The SMEs generally out-performedLASandSLSinhard-waterconditions.Inbuiltorunbuiltformula-tionstheSMEsaregooddetergents.Thedatasuggestthatalthoughthesulfonated fatty acids are not as detersive as the SMEs, they are still very goodsurfactants.Inanoptimizedformulationtheyshouldgiveacceptableperfor-mance. Withtheirlowersolubilities,theymayndmoreapplicabilityinpow-dered, bar, or paste formulations.Long-chainSMEs,C14throughC18,areusedincommerciallyavailablepowderedlaundryproductsinJapan.Theshorter-chainedSMEs,C12throughC14, have found use in liquid laundry products in the United States.B. Hand DishwashLight-dutyliquids,ofwhichhanddishwashingproductsarethemajorsubset,have seen formulation changes in the past several years. Apreviously static cate-gory,theintroductionofproductswithclaimsofantibacterialactivityhavespurred growth in North America. Ultra products have taken over the U.S. mar-ket. Microemulsion technology was introduced in Europe. Mildness and greasecutting have become key attributes of hand dishwash products. Surfactants pro-viding more than one property will have the advantage.SMEs highfoamingandhydrotropicpropertiesmakethemcandidatesur-134 Germain0.2% total surfactant38C (100F) water temppH = 816.014.012.010.08.06.04.02.00.00 ppm 150 ppm 350 ppmWater Hardness as CaCO37:1 SME:SFA3:1 SME:SFAall SFADelta Reflectance11.212.412.012.110.313.113.96.711.5Terg-O-Tometer Detergency of C13.6 Sme/SFADust-Sebum on PolyesterFIG. 16 SME/sulfonated fatty acid Terg at pH 8 on polyester.factantsforliquidhanddishwashproducts.Thistypeofproductcanbefrom10% to 45% total active surfactant. Foam actually is a more important attributethan detergency, although a claim to cut through grease on dishes helps a prod-ucts marketability.Drozd showed that substituting a C13.6 SME for a lauryl ethoxy(3)sulfateinaliquiddishwashformulationresultedinequalperformanceviatheCol-gate Mini-Plate Test [25,34]. Also, less hydrotrope was required to obtain op-timumphysicalproperties.SubstitutionwiththeC12-SMEresultedinlowerperformance.One study in France showed the foam and cleaning synergy between a C13.6SME/sulfonated fatty-acid blend and SLS [35]. In Figure 17 it can be seen thatasSMEreplacesfrom15%to46%oftheSLSactives,thenumberofwashedplates before a foam endpoint is reached is at its highest. The test method usedwas a large plate test. The soil consisted of water, powdered milk, potato akes,and hydrogenated coconut oil; 4 mL soil per plate. The test solution was 5 L of0.032% actives in 220 ppm water as CaCO3at 45C.AccordingtoRaoandassociates,theadditionofmagnesiumionscangreatly improve the dishwash performance of SMEs [18]. This is not surpris-inginlightofthepreviouslymentionedimprovedfoampropertiesandmi-celle size of Mg-SME versus Na-SME. He showed that Mg-SME washed 27Sulfonated Methyl Esters 135FIG. 17 SME/SLS large-plate test for synergy.miniplateswhereasthesodiumandammoniumanalogswashedonly13and12miniplates,respectively.Histestsolutionswere0.1%activeindeionizedwater.Using alkyl ether sulfate and SMEs together in a MgLAS/amide based formu-lationcanresultinincreasedperformance[36]. A formulationcontainingbothethersulfateandSMEwashed51miniplates,whereastheequivalentformula-tion, containing only the ethersulfate, washed 45 miniplates.Sajic and colleagues reported that the same SME/ether sulfate formulation intheabovepatentcouldoutperformleadingcommercialU.S.handdishwashproducts in the removal of lard from plastic [37]. The SME formulation was ei-ther equal to or better than the commercial products via the miniplate test.Knaggs and colleagues published data on the use of the sodium and magne-sium salts of myristic SME in hand dishwash evaluations [20]. Using the May-hewtest[38],Knaggsconcludedthatwhenformulatedwiththeproperfoamboosters,SMEsallowfortheformulationofproductsthatperformedequaltocommercial products at 50% to 60% of their concentration.C. Hard-Surface CleanersOneofthemostdiverseconsumerandindustrialproductcategoriesishard-surface cleaning. These products can contain from < 1% surfactant, as foundin glass cleaners, to > 70% surfactants, as found in some concentrated indus-trialcleaners. Theycanbehighlyacidictoiletbowlcleanersorhighlyalka-lineoorwaxstrippers.Unlikedishwashandlaundryproducts,surfactantsmaynotbethemajorityofthecomposition. Theyarecertainlykeyingredi-ents.WhilesomeworkhasbeenpublishedontheuseofSMEsinhard-sur-facecleaners,noreferencesonuseofsulfonatedfattyacidsinhardsurfacewere found.Malik presented data [27] on the detergency of C12 and C13.6 SMEs via amodied Gardner Straight Line Washability Test [39]. The test solutions con-sisted of 0.6% of the test surfactant and 0.12% tetrapotassium pyrophosphatein140ppmasCaCO3waterat25C. TheC12SMEgaveequivalentperfor-mance compared to decyl and branched dodecyl diphenyl oxide disulfonates.TheC13.6SMEslightlyoutperformedtheC12SMEbutwasnotquiteasgoodastheC810,5-moleethoxylatedphosphateesterthatwasalsoin-cluded. Both SMEs contained the analog sulfonated fatty-acid sodium salts assecondary surfactants.One study compared the performance of the commercially available C13.6SME/sulfonated fatty acid blend to a 3-mole sodium lauryl ether sulfate and toNaLAS with an average carbon chain of 11.4 [40]. Again, using the modiedGardnertest,itcanbeseeninFigure18thattheLASandSME/sulfonatedfattyacidblendgaveequalperformance.Theethersulfatewasslightlyinfe-136 Germainrior.Thetestsolutionwas2%activesurfactantindeionizedwaterwithoutbuilders present.CombiningtheSMEperformancedatawiththepreviouslymentionedhy-drotropic evaluations suggests they may be good choices as hydrotropes in hard-surfacecleaners.ThehighlyacidicandalkalineformulationswillneedtobeavoidedduetoSMEstendencytohydrolyzeinextremeconditions.Formula-tionsthatcontainhighamountsofsurfactantwherehighfoamisdesirablearealso good candidate formulations for SMEs.D. Soap BarsOne application for SMEs and sulfonated fatty acids not usually found in the lit-eratureissoapbars. Thesecanbepersonalwash/toiletbarsorlaundrybars. A1942 patent discusses the use of SMEs in soap bars [41]. SMEs are also typicallyincludedintheextendedlistofanionicsurfactantsinmorerecentbarsoappatents. However, they are rarely the focus of the patent. Sulfonated fatty acidsdopromotefeelandimprovesmearproperties[42,43].Morerecently,theuse of SMEs and sulfonated fatty acids in specic ratios was recommended [44].ThereappearstobeasynergybetweenSMEsandsulfonatedfattyacids,whichallowforimprovedfoamandfeelofasoapbarwhileretainingeaseofproduction.Existingequipmentusedtomakepuresoapbarsmaybeabletomake combo SME/sulfonated fatty acid/soap bars. Surfactants currently used incombosoapbarsincludealkylethersulfates,sodiumcocoylisethionates,alkylglyceryl ether sulfonates, and betaines. Incorporation of these surfactants gener-ally requires special equipment and processing.Sulfonated Methyl Esters 137FIG. 18 LAS, AES, SME Gardner HSC data.VI. SAFETY AND ENVIRONMENTALA. BiodegradationSMEsareeasilybiodegradedunderaerobicconditions.E.W.Maureretal.found that as the alkyl chain increases from 9 carbons to 18 carbons, percentbiodegradationincreases[45].UsinganEssocontrollednutrientprocedure,the activated sludge used was acclimated to the test samples and biodegrada-tion was measured via loss of carbon. This same article also shows that the lau-rylanalogsofSMEandsulfonatedfattyacidareequivalentinbiodegradability.DrozdpublishedprimarydegradationdataonC12andC14SMEs[25]. TheresultsshowareductionofsurfactantactivesviaMethyleneBluetitrationevaluations.After8days,>99%oftheactiveshadproceededthrough primary degradation.Mitsuteru Masuda et al. studied the biodegradation pathways of a C14 SME[46]. They found that the microbial attack began with -oxidation to form a car-boxyl group and then continued with -oxidation, removing 2 carbons at a time.Atemporary intermediary monomethyl -sulfosuccinate was formed which thenunderwent desulfonation.Unfortunately like LAS, there are reports that SMEs do not degrade quicklyunderanaerobicconditions. Anaerobicdegradationisimportantifacompounddoesnotdegradeduringsewagetreatmentandisthereforepresentinasigni-cant amount in the resulting sludge. Sewage sludge is sometimes put into land-lls and is also used as fertilizer. LAS has not been found to be an environmentalconcern via numerous studies of treatment plants and waterways [4752]. Thereis no reason that SMEs and sulfonated fatty acids should be considered any lessenvironmentally acceptable.B. ToxicityToxicity to people and the environment needs to be considered when using anychemical or product. Following is some information on the safety of SMEs andsulfonated fatty acids.1. AcuteA36% to 38% active C12 SME was found to be nontoxic orally. The LD50is > 5g/kg [25].2. AquaticAquatic toxicity of SMEs is signicantly affected by the chain length of the alkylgroup. As the chain length increases, the toxicity increases. Drozd published re-portedLC50valuesofvarioussurfactantstestedonshandinvertebrates[25].The C12 SME data ratings are practically nontoxic according to the U.S. FishandWildlifeService.Othersurfactantslisted,suchasLAS, AOS,andalcohol138 Germainethoxylates,areintherangeofmoderatelytoxic.Henkelpublisheddataonsh and invertebrate toxicity of C16/C18 SMEs [53]. The sh toxicity, LCodata,of the C16/18 SME was 0.4 to 0.9 mg/L. The C12/14 SME data showed signi-cantly less toxicity at 46 mg/L.C. MildnessSMEs are recognized as mild surfactants. The C12 SME was compared to a lau-ryl3-moleethersulfateandtoalauryl3-moleethoxysulfosuccinate[25].At10% actives the SME was as mild as the sulfosuccinate and less irritating thanthe ether sulfate. Table 4 shows mildness and toxicity data on commercial prod-ucts of SME/sulfonated fatty-acid blends [54]. An increase in alkyl chain lengthresultedinanincreaseinaquatictoxicityandinrabbitskinirritation.Humanskin irritation studies did not show the same trend.A 14-day cumulative irritation test was run [40]. The number of days it takesa product to produce irritation (score of 1) were determined. The longer it takes aproduct to reach a score of 1, the milder the product. Table 5 shows a comparisonofvarioussurfactantstosodiumlaurylsulfate,anirritatingcontrol. Ascanbeseen, the SME and sulfonated fatty-acid samples evaluated were as mild as the3-moleethersulfateandisethionatetested. Thesesurfactantsarerecognizedinthe industry as mild.Sulfonated Methyl Esters 139TABLE 4 Irritation and Toxicity Data of Commercial SME/Sulfonated Fatty-AcidBlendsAlpha-step ML-40 Alphpa-step MC-48C12 SME/sulfonatedC13.8 SME/sulfonated Evaluation fatty acid fatty acidHuman patch test for Mild Mildmildness (0.25%, 0.50%, 0.75% actives)Primary skin irritation, Slightly irritating Severely irritating (similarrabbit (10% active) to AES-3EO)Primary eye irritation, moderately irritating Moderately irritatingrabbit (10% active)Acute oral toxicity, rat LD50 >5 g/kg LD50 >5 g/kgAcute aquatic toxicity, LC50= 129 mg/L LC50= 4.7 mg/Lrainbow troutAcute aquatic toxicity, EC50= 200 mg/L EC50= 11.8 mg/LDaphnia magnaSource: Ref. 54.D. SensitizationTherehavebeenpublishedconcernsofpossibleimpuritiesincommercialpro-duction of SMEs and sulfonated fatty acids. Of specic concern are dimethylsul-fate(DMS),dimethylsulfoalkanoate(DSA),isoestersulfonate(IES)[54],andinternal unsaturated sultones (IUS) [55].Despite D.W. Roberts et al. concerns over DMS, DSA, and IES sensitizationand toxicity potentials (real or proposed), they indicate in their paper [54] that itis unlikely any of these molecules would survive through to the nished neutral-ized product. Analytical data support that DSA and DMS are not found in com-mercialproducts[40].EveninRoberts study,ifmethanolispresentpriortoneutralization, IES was not detected. It is well known in the art that methanol isrequired to control the SME/sulfonated fatty-acid ratios in nished commercialmaterial (see Process section of this chapter).A.E.Sherryspaper[55]raisestheconcernofthepotentialformationof,-unsaturated--sultones (IUS). Sherrys paper cites a paper by D.S. Conneret al. [56] that identied 1-dodecene-1,3-sultone and 1-tetradecene-1,3-sultoneassensitizersinguineapigs.Sherrysuggeststhatunsaturatedmethylestersused as feedstock for SMEs could also result in IUSs. Figure 19 shows the hy-potheticalIUSthatcouldresultfromtheunsaturatedmethylestersversustheIUS mentioned in Conners paper. The two are substantially different from oneanother.NodatawereprovidedbySherrythat1-alkyl-3-(-sulfoalkylester)-1,3-sultone causes skin sensitization. It is also unlikely any IUS that could beformed would survive the harsh peroxide conditions used during the manufac-turing of SMEs.Finally, despite the published concerns over possible byproducts in SMEs,therearenoreportsthatcommerciallyavailableSMEsorsulfonatedfattyacidshavecausedhumanskinsensitization.Studiesconductedoncommer-cialC13.6SME/sulfonatedfatty-acidblend(ALPHA-STEP MC-48)showthat the product is not a skin sensitizer in either guinea pig or human testing[57].140 GermainTABLE 5 Comparative Irritation Study via 14-Day Cumulative Irritation TestProduct Average days to produce irritationSodium lauryl sulfate 2.70Sodium cocoylisethionate 4.27C 13.6 sulfonated fatty acid 4.97Sodium lauryl ether sulfate3 moles EO 5.07C13.6 SME/sulfonated fatty acid 7:1 ratio 5.20VII. FUTURESMEs and sulfonated fatty acids are commercially available as blends for use inhousehold and personal cleaning products. As cleaning and personal-care formu-lations become more concentrated and milder, alpha-sulfo fatty derivatives willbecomeevenmoreattractive.Alsosincemethylestersareanabundantfeed-stock,theirconversiontoSMEsforuseasbulkanionicsislikelytogrow. AsquotedbyEd A.Knaggs,aformerStepanemployeeAsalreadystated,alphasulfo fatty derivatives have exceptional and unique properties which can be var-iedandtailoredtomeetanextremelywidevarietyofsurfactantapplica-tions. . . .Hence,theiracceptanceisbasicallylimitedonlybyresearch,marketing and manufacturing dedication, imagination, innovation, commitmentand support. The future potential therefore is almost limitless!ACKNOWLEDGMENTSThe author would like to acknowledge Stepan Company for access to their dataand the contributions of Marshall Nepras of Stepan Company and Teruhisa Sat-suki of Lion Corporation.Sulfonated Methyl Esters 141FIG. 19 Conners IUS versus hypothetical IUS in SMEs.REFERENCES1. JK Weil, RG Bistline Jr, AJ Stirton. 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Studies were conducted by Safepharm Laboratories Limited in the United Kingdomand Stephens & Associates Inc. in Texas, respectively.Sulfonated Methyl Esters 1434Detergency Properties of AlkyldiphenylOxide DisulfonatesLISA QUENCER The Dow Chemical Company, Midland, MichiganT. J. LOUGHNEY Samples LLC, Port Orchard, WashingtonI. INTRODUCTIONAlkyldiphenyl oxide disulfonates were rst identied in 1937 by Prahl [1] of E.I. duPont de Nemours & Company. They were produced by condensation of a sulfuricacid ester of an aliphatic or cycloaliphatic alcohol with diphenyl oxide. Because ofthe large excess of sulfuric acid ester necessary to drive the reaction to completion,reaction yields were low. Only a few investigations followed this initial work [2,3].In1958Steinhauer[4]wasabletodevelopacommerciallyviableprocess.Thismadeitpossibletoevaluatealkyldiphenyloxidedisulfonatesinvariousapplica-tions where the basic physical properties of the chemistry were hypothesized to beof value. The original observations showed that branched alkyldiphenyl oxide disul-fonates were much more soluble in electrolytes than alkylbenzene(mono)sulfonatesand were in fact more soluble than other conventional surfactants of the time. TheprocessdevelopedbySteinhauer[4]producedalkyldiphenyloxidewith1to1.3alkyl substituents on the diphenyl oxide intermediate. Reaction of this mixture witheither chlorosulfonic acid or sulfur trioxide produced the disulfonates. This reactionwas carried out as a batch process using a nonreactive solvent such as a liquid poly-chlorinatedaliphatichydrocarbon(i.e.,methylenechloride,carbontetrachloride,perchloroethylene, or ethylene dichloride) as diluent and heat exchange agent.TheDowChemicalCo.hasbeenproducingthealkyldiphenyloxidesul-fonates since 1958 under the trade name of Dowfax Surfactants. These productshave been distributed globally for over 35 years and have capitalized on the sol-ubility, rinsibility, and stability of this family of surfactants. Alkyldiphenyl oxidedisulfonates are also produced and sold by Kao, Pilot Chemical Co., Rhodia, andSanyo. In addition, a number of smaller suppliers are located in China, India, andFrance.145Traditional uses of the alkyldiphenyl oxide disulfonates include (1) emulsionpolymerization to yield faster run times with less reactor waste and smaller parti-clesize;(2)aciddyeingofnyloncarpetberaslevelingagentstopromoteaneven distribution of dye, (3) crystal habit modication to alter crystal shape andsize;and(4)cleaningformulationstoprovidesolubilizationinstronglyacidic,caustic, and bleach environments.II. STRUCTURE AND METHOD OF PREPARATIONAlkyldiphenyl oxide disulfonate surfactants are a Friedel-Crafts reaction productof an olen and diphenyl oxide using AlCl3as a catalyst, as indicated in Figure 1.Diphenyl oxide is present in excess and is recycled. The reaction yields a mix-ture of monoalkyl and dialkyldiphenyl oxide. The ratio of mono- to dialkylationcan be optimized depending on the end use of the products.The next step in the process is the reaction of the alkylate with the sulfonatingagent. This reaction (Fig. 1) is conducted in a solvent to dilute the reactant and toact as a diluent for the SO3used in the reaction. The reaction generally yields amixtureofmonosulfonateanddisulfonate.Thelevelofdisulfonationisdeter-mined by the end use of the product. Generally, the disulfonation level is >80%.The four primary components are shown in Figure 1. The predominant compo-nentinthecommercialreactionmixtureisthemonoalkyldiphenyloxidedisul-fonate (MADS).Theprocesstoproducethesetypesofmaterialshasundergoneanumberofchanges and modications over the years. The Dow Chemical Company rst de-veloped a continuous process to alkylate, sulfonate, and neutralize these materi-als, but due to operational difculties this process was abandoned in favor of abatch operation. The general process today (Fig. 2) consists of the reaction of anunsaturated hydrocarbon such as an alpha-olen in the range of 6 to 16 carbonswith diphenyl oxide in the presence of AlCl3. The ratio of mono- to dialkylationis controlled by the ratio of olen to diphenyl oxide. Recycled excess diphenyloxide is puried and reused. The rate of the reaction and the yield are controlledbytheamountofcatalystandtemperatureofthealkylation.Excessivelyhightemperatures as well as excessive amounts of catalyst yield higher levels of di-and trialkylation. Low temperatures result in a low conversion of olen. The ra-tios of concentration, catalyst, and temperature are critical in keeping the reac-tionproductsconsistentthroughouttheproductioncycle.Thecatalystisremoved from the process stream and the crude reaction mixture is then strippedof excess diphenyl oxide. Additional purication may take place prior to the sul-fonation reaction.Sulfonation is generally carried out in a solvent. The solvent is used (1) to dis-tribute the sulfonating agent such as SO3, preventing localized burning and yieldloss of the reaction product, and (2) to act as a heat removal medium, allowing146 Quencer and LoughneyAlkyldiphenyl Oxide Disulfonates147FIG. 1 Chemistry of the alkyldiphenyl oxide disulfonates. Olen = C616alpha olen or tetrapropylene.controlofthetemperatureofthereactionprocess.Thecommercialprocessroutes use sulfur dioxide (Pilot Chemical Company) and methylene chloride asthe preferred reaction solvents or air (Chemithon Corporation). The air sulfona-tion process eliminates the need for the removal and recycle of the liquid reac-tion solvent and is amenable to onsite generation of SO3. Liquid solvents requirethe use of liquid SO3that is diluted into the solvent prior to addition to the sul-fonation reactors. Sulfur trioxide and chlorosulfonic acid are the two most com-mon sulfonating agents.148 Quencer and LoughneyFIG.2 Processowsheetforthemanufactureofalkyldiphenyloxidedisulfonates.DPO = diphenyl oxide.After sulfonation, the sulfonic acid is separated from its diluent and the anhy-drous acid is then diluted with water prior to neutralization with an alkaline basesuch as sodium hydroxide. In the past, much of the product has been sold as thesodium salt because its viscosity is lower than that of the neat acid. This is the re-verseofmonosulfonatedlinearalkylbenzene,wheretheviscosityoftheneatacid is lower than that of the sodium salt. The reduced viscosity of the sodiumsalt form is hypothesized to be due to the increased solubility of the disulfonateoverthatofthemonosulfonate.Recentimprovementsinprocessandhandlingtechnology have resulted in high-active acid products.The material is then packaged and sold in drums or bulk shipments as the cus-tomer may require. Storage precautions are designed to prevent the product fromfreezing. Upon the onset of freezing, crystals form which settle to the bottom ofthecontainerand,untilthawed,willblockpumpsandvalves.Thishappensatabout 4C and the surfactant solution freezes at around 1 to 3C. Upon thaw-ing, the disulfonated surfactant becomes homogeneous with minimal agitation.III. DETERGENCY OF ALKYLDIPHENYL OXIDEDISULFONATESA. Removal of Particulate Soil with Alkyldiphenyl OxideDisulfonatesThe predominant nonmechanical mechanism of removal of particulate soil froma substrate is believed to involve negative electrical potential at the Stern layersof both soil and substrate as a result of adsorption of anions from the wash bath[5]. The presence of anionic surfactants in the wash bath aids in increasing thenegativepotentialofboththesubstrateandtheparticulatesoil. Withincreasednegativepotential,themutualrepulsionbetweenthesoilandsubstrateisin-creasedandtheenergybarrierforremovalofthesoilfromthesubstrateisde-creased.Alongwiththeloweringoftheenergybarrierforparticulatesoilremoval, the energy barrier for particulate soil redeposition is increased [6]. Theanionic surfactants added to detergent formulations for greater removal of partic-ulatesoilsaretypicallymonosulfonated.Itseemsreasonablethatadditionofadisulfonated surfactant would lower the energy barrier even further than a typi-cal monosulfonated surfactant.Figure 3 illustrates the detergency performance of a linear C16alkyldiphenyloxidedisulfonatecomparedtoatypicalmonosulfonatedsurfactant,C12linearalkylbenzenesulfonate.Thealkyldiphenyloxidedisulfonatewasobservedtoyield a higher detergency score than the monosulfonated surfactant over a broadconcentration range. The results illustrated in Figure 3 represent a direct compar-ison between a mono- and disulfonated surfactant in an unformulated system at ahardness level of 150 ppm Ca2+.Alkyldiphenyl Oxide Disulfonates 149Investigations conducted by Rouse et al. [7] and Kumar et al. [8] have shownthatmonosulfonatedsurfactantsreadilyprecipitateinthepresenceofdivalentcounterions.Incontrast,Rouse[7]foundthatdisulfonatedsurfactantsexhibitexcellentsolubilityinthepresenceofdivalentcounterionssuchasMg2+andCa2+.InvestigationsbyCoxetal.[9]haveshownthatthedetergencyperfor-mance of a monosulfonated surfactant decreases with increasing water hardnessin the absence of components such as micelle promotion agents or builders orincreasedsurfactantconcentrations.Thealkyldiphenyloxidedisulfonatewasobserved to provide higher detergency scores than the alkylbenzene(mono)sul-fonate over a broad range of hardness (Fig. 4). Moreover, the detergency perfor-manceofthedisulfonatedsurfactantactuallyincreasedwithincreasingwaterhardness.Boththecalciumandmagnesiumsaltsofthealkyldiphenyloxidedisulfonatewereobservedtoprovideimproveddetergencyperformanceoverthat of the sodium salt. Detergency scores of 7.5, 16.5, and 21.8 were obtainedforthesodium,calcium,andmagnesiumsalts,respectively.Thedetergencycomparison of the different salts was conducted on cotton, cotton/polyester, andpolyester fabrics.As long as the surfactant remains soluble, this increase in detergency perfor-mance with increasing water hardness is not unexpected in view of the degree ofbinding of the counterion. This binding increases with an increase in polarizabil-ityandvalenceofthecounterion.Increasedcounterionbindingessentially150 Quencer and LoughneyFIG. 3 Comparison of the detergency performance of C12linear alkylbenzenesulfonateandC16alkyldiphenyloxidedisulfonate.Thedetergencycomparisonwasconductedat25CusingaTergotometeranddust/sebum-soiledswatchesofcotton,cotton/polyester,and polyester. Clean swatches of each fabric type were also included to measure redeposi-tion.Thedetergencyscoreisasummationofreectancedeltasofthecleanandsoiledswatches before and after washing.makesthesurfactantmorehydrophobicinnature. AccordingtoRosen[10],inaqueousmediaforlaurylsulfatethecriticalmicellizationconcentrationde-creases in the order Li+> Na+> K+> Ca2+, Mg2+.B. Optimization of Disulfonate/Nonionic Blends forEnhanced Oily Soil RemovalWhile anionic surfactants are typically recognized for providing good particulatesoildetergencyinaformulation,nonionicsurfactantsarerecognizedforcon-tributing good oily soil detergency. Anionic and nonionic surfactants are there-foreoftenformulatedtogetherinordertooptimizetheperformanceofaformulation on both types of soils.Raney and Miller [11] related the detergency performance of alcohol ethoxy-latesystemstotheirphasebehavior.Raney[12]thenextendedthatworktodemonstrate the importance of the phase inversion temperature (PIT) in optimiz-ing a blend of nonionic and anionic surfactants for oily soil removal. A similarstudy was undertaken to optimize a blend of commercial grade nonionic surfac-tant, C12/133-EO alcohol ethoxylate, and C16alkyldiphenyl oxide disulfonate forthe removal of cetane.Alkyldiphenyl Oxide Disulfonates 151FIG. 4 Comparison of the detergency performance of C12linear alkylbenzenesulfonateand C16alkyldiphenyl oxide disulfonate at varying hardness levels. The detergency com-parison was conducted at 25C using a Tergotometer and dust/sebum-soiled swatches ofcotton, cotton/polyester, and polyester. Clean swatches of each fabric type were also in-cluded to measure redeposition. The detergency score is a summation of reectance deltasof the clean and soiled swatches before and after washing.A phase inversion plot was developed for the C16alkyldiphenyl oxide disul-fonate/alcohol ethoxylate blends at a temperature of 35C (Fig. 5). The y-inter-cept in this plot is equivalent to the optimal composition of the surfactant lm.Thiscompositionprovidesthelowestoil-waterinterfacialtensionatagiventemperature. If the ratio of nonionic surfactant to anionic surfactant is lower thanthe optimum, the system is too hydrophilic in nature and tends to form an oil-in-water emulsion. Similarly, if the ratio of nonionic surfactant to anionic surfactantishigherthantheoptimum,awater-in-oilemulsionforms.TheplotshowninFigure5wasdevelopedbyusingelectricalconductivitymeasurementsasout-lined by Raney [12] to identify the transition from a high-conductivity oil-in-wa-ter emulsion to a low-conductivity water-in-oil emulsion.Asshown,ablendof82.2%C12/133-EOalcoholethoxylateand17.8%C16152 Quencer and LoughneyFIG.5 Phaseinversioncompositionsforblendsofnonionic(C12/133-EOalcoholethoxylate) and anionic (C16alkyldiphenyl oxide disulfonate) surfactants at 35C.alkyldiphenyl oxide disulfonate is predicted to give the optimum detergency forremoval of cetane at a temperature of 35C. Asimilar plot incorporating C12lin-earalkylbenzenesulfonateinplaceofthedilsulfonatedsurfactantpredictedanoptimumdetergencycompositionof61.4%nonionicsurfactantand38.6%an-ionic surfactant. These numbers indicate that a higher concentration of monosul-fonated surfactant is required to invert the W/O emulsion to a O/Wemulsion.Figure 6 illustrates the detergency performance of blends of C12/133-EO alco-hol ethoxylate and C16alkyldiphenyl oxide disulfonate on polyester fabric soiledwith cetane. The detergency of the nonionic/disulfonated anionic blends peakedat ratios close to the predicted optimum. The lowest level of redeposition of thecetane onto the clean fabric swatches was observed to occur at the predicted op-timized blend. Ratios of nonionic to disulfonated anionic surfactant that yieldedwater in oil emulsions in Figure 5 were observed to yield the lowest detergencyscores in Figure 6. Redeposition was also dramatically increased for these highratios of nonionic surfactant. Figure 6 illustrates that oily soil can be effectivelyremoved with a blend of nonionic and disulfonated anionic surfactant. However,the ratio at which the disulfonated anionic and nonionic surfactants are blendedtogether should be carefully chosen.C. Rinsability of Alkyldiphenyl Oxide DisulfonatesIt is expected that standards for reduced energy and water usage proposed by theU.S. Department of Energy (DOE) will result in major changes in the design ofwashing machines within the United States [13,14]. These changes will requiredetergentsthatareformulatedforlowerwatervolumesandreducedwashingtemperatures. A highdegreeofsurfactantsolubilityisrequiredforbothcondi-tions. The dual hydrophilic headgroups of disulfonated surfactants enhance theirsolubility in aqueous environments and therefore should enhance their rinsabilityAlkyldiphenyl Oxide Disulfonates 153FIG. 6 Cetane removal/redeposition by blends of C12/133-EO alcohol ethoxylate and C16alkyldiphenyloxidedisulfonate. Thedetergencyevaluationswereconductedat35Cin1% NaCl with no added hardness.fromhydrophobicsurfaces.Inordertotestthishypothesis,therinsabilityofamonosulfonatedsurfactant,adisulfonatedsurfactant,andanonionicsurfactantfromacottonsubstratewerecompared.CottonskeinsspeciedinASTMD-2281-68 [15] were allowed to completely wet in 0.0125 M solutions of C12linearalkylbenzenesulfonate, C16alkyldiphenyl oxide disulfonate, nonylphenol ethoxy-late, and sodium xylenesulfonate. The sodium xylene sulfonate was included as acontrol since, because it lacks a large hydrophobe, it was not expected to adhereto the cotton substrate. After the skeins were wet in the 0.0125 M surfactant solu-tions, they were packed in chromatography columns. The void space in the chro-matography columns was lled with the equilibrium surfactant solution in whichthe skeins were prewet. Distilled water was then pumped through the columns ata rate of 5 mL/min. The efuent from the columns was collected and analyzed us-ing a UV-VIS spectrophotometer. The quantity (in mols) of each surfactant rinsedfrom the cotton substrate as a function of time is shown in Figure 7.As predicted, sodium xylenesulfonate was not substantive to the cotton sub-strate.Thenonionicnonylphenolethoxylatewasobservedtobethemostsub-stantivetothecottonberofthesurfactantsevaluated.Thedisulfonatedsurfactant rinsed more readily from the cotton ber than the monosulfonated sur-154 Quencer and LoughneyFIG. 7 Mols of surfactants rinsed from cotton skeins as a function of time. Disulfonate= C16alkyldiphenyl oxide disulfonate; monosulfonate = C12linear alkylbenzenesulfonate;nonionic=nonylphenolethoxylate(EO=9). Allrinsabilitystudieswereconductedatambient temperature.factant.Sinceallofthesurfactantswerecomparedonanequalmolarbasis,inactualusetherinsibilityofthedisulfonatedsurfactantwouldbeevenmorefa-vorablebecauseofthelargedifferenceinmolecularweightbetweenthedisul-fonated and monosulfonated molecules (643 g/mole vs. 348 g/mole). Typicallythesurfactantsareusedonaweightbasisratherthanamolebasis.Thedeter-gency performance of the two surfactants on an equal weight basis has alreadybeen illustrated in Figure 3.D. FoamingThefoamprolesofsurfactantsusedindetergentformulationswillbecomeeven more important as the anticipated changes in washing machine design oc-cur [16]. One of the anticipated changes in machine design is a switch from thetypicalvertical-axismachinesusedthroughouttheUnitedStatestodaytohori-zontal-axis machines similar to those currently used throughout Europe. The an-ticipatedhorizontalaxisdesigncoupledwithanincreasedsurfactantconcentrationduetolowerwatervolumeswillrequireformulationswithlowfoam proles. The foaming of a formulation may be reduced by either adding anantifoam agent to the formulation or by formulating with components that do notcontribute to foaming.Thealkyldiphenyloxidedisulfonatesareconsideredmoderatefoamers.While foam can be generated upon agitation of the surfactant solution, the foamprole tends to be lower than that of many other common monosulfonated sur-factants.Figure8illustratesmodiedRoss-Miles[17]foamprolesoftheC12linearalkylbenzenesulfonateandofC16alkyldiphenyloxidedisulfonate.Thedisulfonated surfactant was observed to yield a lower foam prole over the entirerangeofconditionsevaluated.Thefoamproleofthedisulfonatedsurfactant,C16alkyldiphenyl oxide disulfonate, varies with the solution in which it is solu-bilized. For example, the initial foam height of the disulfonated surfactant in thepresence of 5% sodium hypochlorite is approximately one-half of that observedin deionized water (Table 1).E. MultifunctionalityThe high tolerance of C16alkyldiphenyl oxide disulfonate to divalent cations hasbeenillustratedinaprevioussection.Becauseoftheirincreasedsolubility,theshorter-chainedalkyldiphenyloxidedisulfonates,C6andC10,showanevengreater tolerance toward divalent cations. The ability of these surfactants to with-standhard-waterconditionscanresultinareductionofadditivessuchasbuilders and chelates to a formulation. The alkyldiphenyl oxide disulfonates canalsoexhibitmultifunctionalityinaformulationbycontributingtodetergencyperformance and at the same time enhancing the solubilization of other formula-tion ingredients. Figure 9 illustrates the solubilization of nonylphenol ethoxylateAlkyldiphenyl Oxide Disulfonates 155by C6and C16alkyldiphenyl oxide disulfonates in an alkaline environment. Thelonger-chainC16alkyldiphenyloxidedisulfonateprovidesdetergencyperfor-mance to the formulation and at the same time serves to solubilize the nonionicsurfactant. Although the shorter-chain C6alkyldiphenyl oxide disulfonate is notas effective in detergency as the longer-chain C16surfactant, it is the most effec-tive coupler.F. Bleach StabilitySodium hypochlorite, bleach, has been a staple ingredient of cleaning productsfor well over a hundred years. The extensive use of bleach is due to its ability todecolorize stains, oxidize some soils thereby promoting their removal, and pro-videantibacterialactivityagainstawidevarietyofmicroorganisms.Alone,156 Quencer and LoughneyFIG. 8 Modied Ross-Miles foam heights for C12linear alkylbenzenesulfonate and C16alkyldiphenyloxidedisulfonateatvaryinglevelsofCa2+.Mono=C12linearalkylben-zenesulfonate; Di = C16alkyldiphenyl oxide disulfonate. T = 0 represents the initial foamheight. T = 5 represents the foam height after 5 min.TABLE 1 Ross Miles Foam Height Measurements for 1% Active C16Alkyldiphenyl Oxide Disulfonate in Various Solutions at 25CSolution Initial foam height Foam height at 5 minDeionized water 120 mm 40 mm5% sodium hypochlorite 60 mm 0 mm20% sodium hydroxide 63 mm 56 mm20% phosphoric acid 120 mm 45 mmbleachlacksgooddetergencyandwettingproperties.Toenhanceitsperfor-mance,itisthereforeoftenformulatedwithotheringredients,suchassurfac-tants. Addition of selected surfactants can increase the viscosity of the sodiumhypochlorite solutions which, in turn, may improve their cleaning and disinfect-ing properties as a result of longer contact times with the substrate, particularlyon vertical surfaces. To mask the distinctive chlorine odor, fragrances are oftenadded to solutions of sodium hypochlorite for both household and institutionaluse. Surfactants are useful in this context also since they promote the solubiliza-tion of fragrance into bleach solutions. Even though the addition of surfactantsand fragrances result in performance and esthetic improvements, both materialsmust be chosen with care to avoid interaction with sodium hypochlorite whichresultsinlossofboththeadditiveaswellasofthesodiumhypochlorite. Thestability of the sodium hypochlorite may also be affected by additional factors(i.e., storage temperature, metal content, pH, etc.) which vary from formulationto formulation.Thestabilityofsodiumhypochloriteinthepresenceofdifferentsurfactantswas evaluated by preparing solutions in distilled water containing 4.5% sodiumhypochlorite, 1.0% active surfactant, and 0.3% sodium hydroxide. The concen-trationofstore-brandsodiumhypochloritebleachwasdeterminedaspercentavailable chlorine according to an ASTM procedure [18]. The remaining formu-lation ingredients were then added directly to the sodium hypochlorite solution.Alkyldiphenyl Oxide Disulfonates 157FIG.9 Cloudpointmodicationofnonylphenolethoxylate(EO=9)in5%NaOHwith C6and C16alkyldiphenyl oxide disulfonates and common hydrotropes.Subsequent measurements were all recorded as percent available chlorine usingthe cited ASTM titration method. All samples were stored in the dark at 37C.As seen in Table 2, sodium hypochlorite bleach maintains excellent stabilityinthepresenceofthealkyldiphenyloxidedisulfonates,evenafter319days.Only 2-ethylhexylsulfate exhibited similar inertness to sodium hypochlorite. Thebleach solution fared moderately well with a number of surfactants to the 137-day point, but were not tested at 319 days due to the level of precipitate that de-veloped.Twoofthesurfactants,phosphateestersandalkylpolysaccharide,exhibited very poor stability.G. Detergency Properties of the Components ofAlkyldiphenyl Oxide Disulfonate Reaction MixturesThecomponents(MAMS,MADS,DADS,DAMS;Fig.1)thatmakeupthecommercial blend of alkyldiphenyl oxide disulfonates were evaluated individu-ally in both built and unbuilt formulations to determine the effect of equivalentweightondetergencyperformance(Fig.10)Measurementswereobtainedondust/sebumandground-in-claysoilsoncotton,cotton/polyester,andpolyesterfabric.The C16monoalkyldiphenyl oxide disulfonate component yielded the opti-mum detergency in the unbuilt formulation. In built formulations, the C10di-alkyldiphenyloxidedisulfonatecomponentshowedoptimumdetergency.In158 Quencer and LoughneyTABLE 2 Percent of Original Available Chlorine Upon the Aging ofSodium Hypochlorite Solutions in the Presence of Various SurfactantsSurfactant 137 Days 319 DaysNone 92.6 84.1 clearC12alkyldiphenyl oxide disulfonate 90.8 80.6 clearC6alkyldiphenyl oxide disulfaonte 88.0 76.4 clearC16alkyldiphenyl oxide disulfonate 87.0 75.8 clear2-Ethylhexyl sulfate 86.2 75.7 clearC10alkyldiphenyl oxide disulfonate 87.1 74.3 clearNonylphenolethoxylate, EO = 9 85.7 73.6 hazyAlkylnapthalenesulfonate 71.0 28.8 clearSodium lauryl sulfate 92.3 pptC12linear alkylbenzenesulfonate76.4 pptLauryl ether sulfate 54.4 pptC9C11alcohol ethoxylate, EO = 8 74.4 pptC14C16alpha olen sulfonate 57.6 pptPhosphate ester 81.8 0.0 clearC9C11Alkyl polysaccharide 0.0 0.0 clearbothformulationtypes,adisulfonatedcomponentprovidedthebestdeter-gency performance. A correlation between equivalent weight and detergencyperformancemaybeobservedforbothformulations.Theshorter-chainmonoalkyldiphenyloxidedisulfonateswithlowequivalentweightsaretoowatersolubletoprovidegooddetergencyperformance.Thehigherequiva-lent-weightmonoalkyldiphenyloxidemonosulfonatesaretoohydrophobicandyieldanegativetotalscoreindicatingthatsoilwasdepositedontothecleanfabricswatches.Becauseoftheirlowsolubilityinwater,thedi-alkyldiphenyl oxide monosulfonates were not tested.InvestigationsundertakenbyRosenetal.[19,20]haveshownthedi-alkyldiphenyl oxide disulfonates capable of enhancing the wetting propertiesofwater-insolublesurfactantsandtoprovidepropertiessuchaslowcriticalmicellizationconcentrationsandlowC20values[5].Thedetergencyproper-tiesofthedialkyldiphenyloxidedisulfonateshavenotyetbeenthoroughly investigated.Alkyldiphenyl Oxide Disulfonates 159FIG.10 Detergencyperformanceoftheindividualcomponentsofcommercialalkyldiphenyloxidedisulfonatesasafunctionofequivalentweight.MADS=monoalkyldiphenyloxidedisulfonate;MAMS=monoalkyldiphenyloxidemonosul-fonate; DADS = dialkyldiphenyl oxide disulfonate.IV. ENVIRONMENTAL/SAFETYA. Skin IrritationCommercial-gradeC16alkyldiphenyloxidedisulfonatewascomparedtocom-mercialgradeC12linearalkylbenzenesulfonatesodiumsaltandacommercialgrade sodium C12142.8 to 3.0 EO alcohol ether sulfate in a study which evalu-ated primary dermal irritation on New Zealand white rabbits. Aliquots of 0.5 mLof 10% active surfactant were applied for 4 hours to the intact skin on the backsof groups of six New Zealand white rabbits.WithC16alkyldiphenyloxidedisulfonate,nosignsofdermalirritationwereobserved up to 3 days on the test site in any of the six rabbits that were dosed.Withthealcoholethersulfate,twoofthesixrabbitsshowedslighterythemawhen the test site was unwrapped approximately 30 min after dosing. The ery-thema was resolved at the 48-hour observation. This test, too, was terminated af-ter3days.WithC12linearalkylbenzenesulfonatesodiumsalt,threeofthesixrabbitshadaslighterythemaand/orslightedemawhenthetestsitewasun-wrappedapproximately30minafterdosing.Oneofthethreeaffectedrabbitscontinuedtoshowslighterythemaand/oredemauntiltestday7.Inaddition,there was also scaling of the test site of this rabbit on test day 7, when the testwas terminated. There was no effect on the body weights of the rabbits for any ofthe three test materials.B. Degradation of C16Alkyldiphenyl Oxide Disulfonates inActivated SludgeThe degradation of commercial alkyldiphenyl oxide disulfonates was evaluatedin the semicontinuous activated sludge (SCAS) conrmatory test [21]. For boththe C10and C16alkyldiphenyl oxide disulfonates, > 90% reduction in MethyleneBluereactivesubstancesoccurredallowingclassicationoftheseproductsasbiodegradable under the conditions of the SCAS test. By contrast, the commer-cialC12branchedandC6alkyldiphenyloxidedisulfonatesdidnotachievea>90%reductioninMethyleneBluereactivesubstancesandarenotconsideredbiodegradable under this procedure.SincetheSCAStestdoesnotprovideinformationonthedegradationpath-way of the alkyldiphenyl oxide disulfonates, a study was undertaken to observethe degradation of these molecules. Because of the analytical complexities asso-ciated with the commercial mixture of alkyldiphenyl oxide disulfonates, degra-dationstudiesinitiallyfocusedonasingleisomer,theC16monoalkyldiphenyloxide disulfonate, shown in Figure 11. The choice of labeling the disubstitutedringshowninFigure11issupportedbytheexpectedbiodegradationpathwaywhich, in turn, is based on the known biodegradation pathway of linear alkylben-zenesulfonate [22].160 Quencer and LoughneyBiodegradation is expected to be initiated on the terminal carbon of the linearalkyl group (omega oxidation). Degradation of the linear chain should proceedwith consecutive losses of two carbon fragments (beta oxidation) to a carboxylicacid. Subsequent steps in the pathway are more speculative. One possible path-way would include opening of the trisubstituted ring followed by the degradationof the disubstituted ring. Thus, labeling of the disubstituted ring would permit astudyofthefateoftheC16alkyldiphenyloxidedisulfonatetothepointwhenboth aromatic rings are degraded.A ll-and-drawdesignmodeledaftertheSoapandDetergentAssociationmethod[21]wasusedtostudythedegradationoftheC16alkyldiphenyloxidedisulfonate under both acclimated and nonacclimated conditions. Municipal ac-tivatedsludge(2500mg/L suspendedsolids)wasacclimatedto20ppmC16alkyldiphenyloxidedisulfonate.Activatedsludgenotexposedtothedisul-fonatedsurfactantwasmaintainedinaparallelsystem.Followingacclimation,radiolabeleddisulfonatedsurfactantwasintroducedintoeachsystem.Primarydegradation (degradation of the parent compound) is shown in Figure 12. Eventhough rapid degradation occurred in the acclimated activated sludge, < 2% radi-olabeled CO2was collected. Figure 13 illustrates the major degradation productas determined by analysis of the efuent. This degradation product supports thehypothesized degradation pathway.ThebiodegradabilityofC16alkyldiphenyloxidedisulfonatewasevaluatedseparatelyunderaerobicconditionsusingtheSCAStest[21].Thesurfactantpassed these tests with > 90% reduction of methylene blue active substance oc-curring following 23 hours of aeration. In addition the surfactant showed 90%reduction of Methylene Blue active substance in 19 days in the OECD Screen-ing and Conrmatory Test [23]. More recently, the biodegradation of the surfac-tant was evaluated in the OECD Zahn-Wellens/EMPA test [24]. The surfactantwas shown to be inherently biodegradable according to the test guidelines since55% degradation was observed within 28 days.C. Degradation in Surface and Subsurface SoilsStandardmicrocosmswerepreparedwitheitheraquifersolids(subsurfacesandyloam)orasandyloamsurfacesoilanddosedwithradiolabeledC16Alkyldiphenyl Oxide Disulfonates 161FIG. 11 Radiolabeled monoalkyldiphenyl oxide disulfonate.* Carbon 14.alkyldiphenyl oxide disulfonate. As shown in Table 3, signicant mineralizationwas achieved in the sandy loam surface soil. The major degradation intermedi-ate detected was similar to the product identied in the activated sludge study(Fig. 13).It can be concluded that the primary biodegradation of the C16alkyldiphenyloxidedisulfonateproceedsinavarietyofaerobicenvironments(activated162 Quencer and LoughneyFIG. 12 Primary degradation of C16monoalkyldiphenyl oxide disulfonate.FIG. 13 Major degradation product of C16monoalkyldiphenyl oxide disulfonate.sludge,surface,andsubsurfacesoils).Thedegradationpathwayisconsistentwith that of the linear alkylbenzene(mono)sulfonate.D. Aquatic Toxicity of the Major Degradation IntermediateTheacuteaquatictoxicityofthemajordegradationintermediate(Fig.13)wasdetermined under static conditions on both rainbow trout and daphnid with repli-cate groups of 10 organisms. The results of this study are summarized in Table 4.As seen from these results, the control efuent had no effect on the rainbow troutorthedaphnid.ThebiodegradationproductsfromtheactivatedsludgetreatedwithC16alkyldiphenyloxidedisulfonate(20ppminitialconcentration)hadnoeffect on the rainbow trout or daphnid. The fact that the disulfonated surfactant,when added directly to the efuent, is toxic to sh is consistent with other sul-fonated surfactants [25,26].Alkyldiphenyl Oxide Disulfonates 163TABLE 3 Degradation in Soil95% Primary Mineralization*Soil ppm MADS degradation after 85 daysSubsurface sandy soil 1 10 days 100%Daphnid 48 >100% >100%Intermediate Trout 96 >100% >100%Daphnid 48 >100% >100%C16alkyldiphenyl Trout 96 0.7 mg/L 0.7 mg/Loxide disulfonate Daphnid 48 14.1 mg/L 13.5 mg/L*No toxicity.Samplesofactivatedsludgeefuentwerepreparedinsemi-continuousactivatedsludge(SCAS)units: Blank = efuent from the SCAS unit; Intermediate = feed to the SCAS unit containing 20 ppmC16alkyldiphenyl oxide disulfonate (the efuent was conrmed to contain the previously identiedmajor intermediate); C16alkyldiphenyl oxide disulfonate = efuent from the SCAS unit which wasamended with surfactant at known concentrations.ACKNOWLEDGMENTSThe authors would like to thank Stanley Gonsior, Sally Kokke-Hall, Pushpa In-basekaran, Dave Wallick, and Beth Haines of the Dow Chemical Company, andChrisMeansofKellyServices,whohaveprovideddataforinclusioninthischapter.REFERENCES1. 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