1-s2.0-138151489500029F-main

ELSEVIER

REACTIVE &

FUNCTIONAL POLYMERS

Reactive & Functional Polymers 26 (1995) 3-23

Review

Some novel aspects of cationic ion-exchange resins as catalysts

M.M. Sharma Department of Chemical Technology, Universi& of Bombay, Matunga, Bombay 400 019, India

Accepted 14 March 1995

Abstract

Cationic ion-exchange resins, particularly the macroporous variety, are versatile catalysts which offer several advantages over the homogeneous acid catalysts with respect to corrosion, product recovery, selectivity, etc. In some cases, such as etherification of phenols/naphthols with isobutylene/isoamylene, resin catalysts allow the reaction to occur, but the homogeneous catalysts fail. A noteworthy development has been the use of distillation column reactors (DCR) where the exothermicity of the reaction is usefully employed and the resin inventory, for a specified level of conversion and productivity, can be significantly reduced. The availability of methyl-tert-butyl ether and tert-amyl methyl ether allows tert-butyl and tert-amyl derivatives of phenolic substances to be produced with the attendant advantages. The removal of low concentrations of substances like formaldehyde in aqueous medium offers new opportunities for resin catalysts and methylal formation with methanol in DCR has been realized in bringing down formaldehyde concentration from 1 to 2% (wt) to as low as 0.02%. Resin catalysts are useful for oligomerization of olefins like isobutylene, isoamylene, a-methyl styrene, etc.; cross-dimerization of olefins for making precursors for synthetic musks, can also be advantageously carried out. The alkylation of dissolved polyvinyl phenol with isobutylene, with resin catalysts is interesting in several ways. Many close-boiling substances, such as isomeric and non-isomeric phenolic substances, can be separated through selective reactions based on resin catalysts.

Keywords: Catalysis; Cationic ion-exchange resin; Distillation column reactors; Bisphenol; Methyl-tert-butyl ether (MTBE); Ethyl-tert-butyl ether (ETBE)

1. Introduction

Cationic ion-exchange resins, particularly the macroporous variety, offer distinct advantages over homogeneous catalysts, both from the standpoint of catalysis as well as engineering of reactions for commercial purposes. Resin catalysts can be used in batch or semi-batch reactors or continuous fixed, expanded or fluidized bed reactors; even loop reactors can be employed. The heterogenized acidity can far exceed the value of 100% H$304. Table 1 gives Hammett acidity function (H,) for various acids used as

catalysts [1,2]. The use of heterogeneous acid catalysts allows a corrosion-free atmosphere, and no washing of the homogeneous acid, which leads to bad effluents, is required. The resin matrix allows reactions to be conducted in aqueous as well as non-aqueous, polar or non-polar media, and this is quite unusual. It is generally not feasible to use acid-activated clays in aqueous medium. It is even more striking that dilute aqueous solutions containing reactants can be handled and this is greatly facilitated if reaction-distillation or extractive reaction modes can be adopted. Resin catalyst can often lead

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4 M.M. Sharma I Reactive & Functional Polymers 26 (1995) 3-23

Table 1 Values of Hammett acidity function (H,)

Acid H,

p-Toluenesulfonic acid Montmorillonite

Natural Cation exchanged

Amberlyst-15 Sulfuric acid (40%) Sulfuric acid (100%) Nafion HY Zeolites WW204 and cS2.5H0.5Pwl2040 (HP&

Lanthanum and cerium exchanged HY zeolites

Fluorosulfonic acid Sulfated zirconia HS03F-SbFS

<

+0.55

1.5 to -3.0 -5.6 to -8.0 -2.2 -2.4

-12.3 -11 to -13 -13.6 to -12.7 -13.16

-14.5 -15.07 -16 -20

to high selectivity in reactions and sometimes the selectivity can be exploited for the separation of close-boiling isomeric and non-isomeric mixtures. The manufacture of methyl-tert-butyl ether (MTBE), along with ethyl-tert-butyl ether (ETBE), methyl-tert-amyl ether (TAME), and ethyl-tert-amyl ether (ETAE) has provided an extraordinary fillip to the use of resin catalysts, which, so far, are exclusive catalysts used for these reactions. The worldwide capacity of these ethers is expected to exceed 20 million tonnes per annum very soon and by turn of the century may cross 40 million tonnes per annum.

The author, along with Chakrabarti, pub- lished in 1993 [l], an extensive review on this subject, the subject matter of which will be considered as being already known for this invited lecture.

2. Resins as selective catalysts

A number of examples have been cited by Chakrabarti and Sharma [l] and the example of etherification of phenol, substituted phenol, cresols, naphthols, etc., with isobutylene and isoamylene may be emphasized where homogeneous catalysts lead to essentially C- alkylated products. A recent example reported by Takeshi et al. [3] refers to monoacylation of

HO(CHZl,OH RCOQH ??

RCOZ(CHZ,,,OH + [RCO&Hz),OCORI,

R:Allly,gm”p

Scheme 1. Acylation of 1,2-ethanediol to 1,16-hexadecane- dial.

R NH-Z-0CH3 + HCHO -

H3CO-~HN+H2~NH-!-W~ + Hz0

Scheme 2. Condensation of methyl-Wphenyl carbamate with formaldehyde.

diols from 1,2-ethanediol to 1,16-hexadecanediol (Scheme 1); transesterification in ester/octane solvent mixtures with strongly acidic resin catalysts give higher selectivity for the mono versus diacylated product compared to the use of homogeneous catalyst like methanesulfonic acid.

Kim and Lee [4] have shown that alkylation of 2-methyl hydroquinone with isobutylene using Amberlyst-15 gives 2-methyl-Qert- butyl-hydroquinone (at 338 K) with 93.8% selectivity; the 2,6-isomer was obtained at the 6.2% level. By contrast, a homogeneous catalyst like 98% H$SOd gave 2,5- and 2,6-isomers at 82.2 and 17.8% levels. They have also referred to an additional example of condensation of methyl-N-phenyl carbamate (MPC) with formaldehyde using ethyl acetate and toluene as solvents (Scheme 2). Here the products are 4,4’-methylene diurethane (MDU), trimeric ure- thane and N-benzyl compound; with the resin catalyst, the selectivity was for 4,4’-MDU. By contrast, with 50% H2S04, the selectivity for 4,4’-MDU was 86% and 9.8% N-benzyl derivative was obtained. The difference in regioselectivity can be attributed to steric hindrance imposed on fixed protons in the solid catalysts, which caused higher selectivity towards the less hindered positions.

A similar example of regioselectivity in the alkylation of methyl salicylate with isobutylene and isoamylene, carried out in the author’s laboratory, may be cited. Here, during alkylation

M. M. Sharma /Reactive & Functional Polymers 26 (1995) 3-23 5

HCHO + CO + Hz0 ----, HWHZCOOH

Scheme 4. Carbonylation of formaldehyde.

Q (a: CoecHJ W3bC

ti

CCXXH~ OR G

CW3l3

Lp product, (c- prod”c1,

Scheme 3. Regioselectivity in the alkylation of methyl salicylate with isobutylene and isoamylene.

Scheme 5. Hydrolysis of poly(glycidyl methylacrylate-co-ethylene dimethacrylate).

with isobutylene, in the presence of Indion- 130 (a macroporous sulfonated polystyrene- divinylbenzene resin with an acidity of 4.7 mEq H+/g and crosslinking of 14%) 100% regioselectivity with respect to methyl [Qert-butyl] salicylate was realized at 403 K and methyl [3-tert- butyl] salicylate was not obtained (Scheme 3). It is striking that in this case of alkylation with 3% (w/w) of p-toluene sulfonic acid as a homogeneous catalyst, no alkylation was realized [5,6].

around 62%. This difference appears to come from different swelling characteristics and percentage DVB content, hence different pore diameter. 1,CDioxane was found to be a good solvent. The side products were methyl formate, methyl methoxy acetate and some high molecular weight unidentified products.

An interesting example of etherification of close-boiling cis- and trans-2-tert-butyl- cyclohexanol with isoamylene, carried out in the author’s laboratory, may be cited. At 353 K, and Indion-130 as catalyst at 10% loading, about 94% selectivity for the c&isomer was realized with a feed consisting of about 68.5% cis- and 31.5% truns-isomers [7].

Smigol et al. [lo] have hydrolyzed the epoxide functionalities of macroporous poly(glycidyl- methacrylate-co-ethylene dimethacrylate) to diol groups with an acid catalyst (Scheme 5). The influence of the catalyst size on the extent of reaction has been clearly demonstrated as full hydrolysis has been achieved with sulfuric acid, while only 11% hydrolysis has been observed for the ion-exchange resin catalyst, PSSA 1200.

In alkylation of phenol with MTBE to give tert-butyl phenol, the regioselectivity depends on the catalyst and the operating conditions. With Amberlyst-15 and p-toluene sulfonic acid catalysts, with phenol to MTBE mole ratio of 2 : 1 and temperature of 329 K, the product ratio of 2-tert-butyl phenol to 4-tert-butyl phenol, at close to 30% conversion of phenol, was 1.45 and 1.08, respectively [8].

A glossary of some of the commercially available cation-exchange resins is given in Appen- dix I.

3. Reactors for resin catalyzed reactions

For batch and semi-batch reactions mechan- ically agitated reactors are widely used; loop reactors can also be advantageously used. The mechanical strength of the catalyst is sufficiently good to withstand fairly high agitation intensity.

Carbonylation of formaldehyde using triox- The large scale manufacture of MTBE/ETBE ane as a source, with CO, followed by esterifica- etc. has provided tremendous impetus to the tion with methanol to methyl glycolate has been development of novel continuous reactors. The studied by Lee et al. [9] (Scheme 4) at tem- use of distillation column reactors is referred peratures between 373 and 408 K, in the pres- in the next section of the text. Chakrabarti and ence of different cationic resin catalysts. With Sharma [l] have summarized the different types Amberlyst-36, higher selectivity of about 88% of reactors, including the expanded bed reactors. was realized; Amberlyst-15 gave a selectivity of For packed column type of reactors there may

6 M.M. Sharma /Reactive & Functional Polymers 26 (1995) 3-23

be some advantages in adopting the downflow mode as the direct mass transfer from gas to solid becomes significant [ 111.

4. Distillation column reactors (DCR)

DCR offer distinct advantages of exploiting the exothermicity of reactions, such as in alky- lations, etherifications etc., for supplying heat required for distillation, lower mole ratio of reactants and yet get over the thermodynamic limita- tions encountered in simple reactors, lower resin inventory etc. compared to common single stage reactors. DCR are now commercially exploited for MTBE, ETBE, etc. Independently, with zeolites as catalysts, DCR are used for making ethyl benzene from benzene and ethylene. With homogeneous acid catalysts, DCR have been used for making esters like n-butyl acetate, dibutyl phthalate, etc. and the recent very successful example of Eastman Kodak process of making methyl acetate may be cited, where not only the utilities consumption was brought down substan- tially, but also the capital cost and the number of distillation columns were brought down.

The form of the catalyst is important. The standard size of the bead catalyst (OS-2 mm) is not very suitable and techniques such as the use of tea bags have been considered. Resin catalyst in the form of the random packings like Raschig rings have also been made available [12]. In the recent past, regular packings, also called structured packings, have also been claimed to be efficacious. A key factor in the use of resin catalysts is the limitation with respect to temperature as the stability of catalysts, based on styrene-divinylbenzene, above 403 K is poor due to desulfonation. Perfluorinated resins offer not only much higher acidity, but can also be used up to 473 K. However, they are very expensive and serious attempts are being made to use supported catalysts; supports could be activated carbon, alumina, etc. In the case of styrene-divinylbenzene type resins, silica sup- port has been considered and some results from the author’s laboratory will also be reported. Sil-

ica gel reacted with dichloro-diphenyl silane and sulfonated, has been reported, but this ,is likely to be expensive. It is necessary to have good mechanical, thermal and chemical stability of the packings. The importance of osmotic swelling should be recognized as it can cause enormous mechanical stress resulting in the breakage of the resin which is very undesirable in DCR. Fur- thermore, the pressure drop should be low and external wetting efficiency should tend to unity.

Catalysts can be confined in porous cloth bags tied in the form of bundles, along with corru- gated wire screens to provide passage for vapor flow, as reported by Yuxiang and Xien [13] for MTBE production. Resin catalyst packings have also been molded from resin particles and a thermoplastic powder in a furnace, as reported by Fuchigami [14] for hydrolysis of methyl acetate which is obtained as a by-product in the manufacture of polyvinyl alcohol from polyvinyl acetate and where recycle of acetic acid to make vinyl acetate is desirable. It is also possible to mold inactive polymeric components in the required shape and then the surface is suitably activated. For styrene-divinylbenzene-type resins, further improvement in the acidity of the catalyst can be realized through fluorination. Fiber composites as packings can also be considered.

The modeling and simulation of DCR is very fascinating and challenging and a lot of scope for optimization exists. An early study was made by Neumann and Sasson [15] on recovery of dilute acetic acid by esterification in a packed column. It was possible to realize high conversion of acetic acid and pure methyl acetate was obtained as the product.

In view of the great commercial importance of MTBE, TAME, etc., some very good papers have appeared in the last couple of years. The importance of internal and external multicom- ponent mass and heat transfer phenomena on the catalyst, under boiling conditions, has been stressed by Sundmacher and Hoffmann [16]. An important finding of these authors is that the ef- fectiveness factor of the catalyst varies along the column length.

MM. Sharma i Reactive & Functional Polymers 26 (1995) 3-23 7

Bravo et al. [17] have reported results from a pilot plant having a column of 0.15 m i.d. and a height of 11 m for producing TAME. Aspects of chemical equilibrium, kinetics, mass transfer, and hydraulics have been studied. The amount of methanol in the feed to the experimental column was found to be the most significant variable with respect to operation, conversion, and recovery. The interaction between the vapor-liquid equilibria and reaction can lead to flat concentration profiles for large portions of the column under certain conditions.

In the case of alkylates for gasoline where isobutane reacts with 1-butene or 2-butene to give iso-octane which can further react with butenes to give the unwanted Ci2H24, the removal of iso-octane, as it is formed, by reactive distillation would improve the selectivity. The complexity of reactive distillation systems makes computer simulation an extremely important tool for design and scale-up [18]. In the manufacture of TAME, the catalytic distillation column reactor allows more than 95% conversion of isoamylenes [19].

Asselineau et al. [20] have very recently ex- plored the use of DCR and have recommended them for the manufacture of tert-alkyl ethers by reacting iso-olefins and aliphatic alcohols and for alkylation of benzene with olefins. In another patent, Marker [21] has claimed a catalytic distillation process to manufacture ethers of C5_s tert-olefins which allows a smaller processing unit and a higher overall conversion. It contains an adiabatic etherification section and a catalytic distillation unit. The overhead stream which contains the unreacted olefins and alcohols is fed into the adiabatic etherification section and the effluent from that zone is fed back into the catalytic distillation section.

Removal of 1% formaldehyde from aqueous 2-butyne-1,4-diol or similar solutions by batch reactive distillation with methanol or ethylene glycol (Scheme 6a) in the presence of Indion- 130 as catalyst was carried out in the author’s laboratory; 98% conversion of formaldehyde was obtained by reactive distillation when 7 times

HCHO + ZCH~OH - CH2WH3l2 + H*O

HCHO + y+zOH ~ 7”2”\

CH2OH CH20/ CH2 + H20

Scheme 6. Reaction of formaldehyde with methanol or ethylene glycol.

H2CWH3l2 + 9 --, SHCHO + Hz0

Scheme 7. Oxidation of methylal.

the stoichiometric quantity of methanol was used compared to 15% conversion obtained in a closed system. 97% conversion of formaldehyde was obtained by reactive distillation when 3 times the stoichiometric quantity of ethylene glycol was used compared to 8% conversion obtained in a closed system [22] (Scheme 6b).

Masamuto and Matsuzaki [23] have given a description of the commercial production of methylal by reactive distillation. Oxidation of methanol yields 1 mol of water per mol of formaldehyde (Scheme 7), but by contrast oxidation of methylal yields 3 mol of formaldehyde per mol of water, and therefore 70% formaldehyde can be directly produced by the oxidation of methylal.

For making methylal, formaldehyde and methanol are reacted in the presence of a resin catalyst, via reactive distillation by using multi reaction units and a distillation tower. The middle portion of the distillation tower was furnished with stages from which the liquid components were withdrawn and pumped to the reactor units, and after reaction were returned to the distillation tower. Nearly 100% conversion of methanol and formaldehyde was realized.

Methylal was also produced by reactive distillation in the author’s laboratory by using cation- exchange resin made from supporting sulfonated styrene-divinylbenzene or divinylbenzene on silica of size 2-4 mm [24]. A single reactive distillation column was used. Up to 95% conversion of formaldehyde could be obtained by using 1.5 times the stoichiometric requirement of


17 0-C-CH3 OH

c + C,H@H G====+

b

1: + CH+OC4Hg

Scheme 8. Tkansesterification of cyclohexylacetate with n-butanol.

R o--C--R

0 I + RCDOH --=t 0 _.,S*, R o--C--R OH

c + Hfl G====== 0 + RCOOH (WI,

Scheme 9. Cyclohexanol from cyclohexene via cyclohexyl formatelbenzoate.

methanol; 80-90% methylal was obtained as dis- tillate [22].

A variety of transesterification reactions can be advantageously carried out in DCR. Thus cyclohexyl acetate can be transesterified with n-butanol to give cyclohexanol and n-butyl acetate [25] (Scheme 8); methyl acetate/acrylate can be transesterified with n-butanol to give IZ- butyl acetate/acrylate.

An unusual example is the purification of phenol to make a better material, for instance, bisphenol A of polycarbonate grade, where car- bony1 compounds (acetone, mesityl oxide, hy- drotropaldehyde, etc.) as impurities have to be reduced from a few hundred parts per million (or even 3000 ppm) to vanishing level (< 10 ppm). A continuous distillation column reactor, containing Nafion resin packings has been claimed as a versatile method to achieve the above objective WI.

A very recent interesting and potentially useful example to industry is the conversion of cyclohexene to cyclohexanol through an ester and subsequent hydrolysis (Scheme 9). Consider the use of, for example, 80-85% formic acid, where cyclohexyl formate is first formed and then hydrolyzed. Similarly, benzoic acid and water mixture may allow cyclohexanol to be formed via cyclohexyl benzoate [27].

A CHs-CH-CH2 +

F”*“” H20 e CH-OH

AH,

Scheme 10. Synthesis of propylene glycol from propylene oxide.

CHO

CHO + ZCH$HO d

Scheme 11. Formation of bis (cyclic acetal) of glyoxal with acetaldehyde.

A process for clean ethyl acetate of con- stant quality has been described by Savkovic- Stevanovic et al. [28] using the DCR, where there are no problems of waste water or corrosion. DCR has also been employed for the reaction of isomerization of 2-hydrocarbyl-1-alkenes into 2-hydrocarbyl-2-alkenes using Amberlyst-15 as a catalyst [29].

For the synthesis of propylene glycol by hydration of propylene oxide in a DCR, low water to propylene oxide ratio can be employed thus eliminating the concomitant high costs involved in water removal [30] (Scheme 10).

Successful removal of glyoxal from solutions of glyoxalic acid has been claimed by Nippon Syn. Chem. Ind. [31] via the addition of acetaldehyde which forms bis (cyclic acetal) having a low boiling point (Scheme ll), in the presence of ion-exchange resin catalyst, so that distillation works.

5. Use of molecular sieve in ion-exchange resin catalyzed reactions

Reactions such as etherification of alcohol with olefin, esterification of alcohol with acid etc. are generally reversible in nature. Although these reactions can be advantageously carried out in the presence of ion-exchange resins, in order to realize appreciable levels of conversion, one of the products has to be continuously removed from the reaction mixture. This problem is generally overcome by resorting to reactive distillation when one of the products is low

MM Sham IReactive &Functional Polymers 26 (1995) 3-23 9

boiling as compared to the reactant(s). In the cases where reactive distillation is not a prac- tical proposition, this problem can be circum- vented by using molecular sieves such as zeolite A, which selectively adsorbs one of the products.

During the alkylation of phenols with MTBE, zeolite 4A was advantageously used to remove methanol formed, resulting in an increased equilibrium conversion of phenols and overall rate of reaction. In the alkylation of p-cresol with MTBE (1: 1 mol ratio), in the presence of 5% (w/w) of Indion-130 as catalyst, the maximum conversion of p-cresol obtained was 60% after 4 h. When 5% (w/w) 4A zeolite was added as adsorbent, 60% conversion of p-cresol was obtained in 2 h and maximum conversion obtained was 67% after 4 h [32].

6. Ion-exchange resin catalysts in production of bisphenols

Bisphenols are industrially important inter- mediates, used in the manufacture of epoxy resins and polycarbonates. Generally, bisphenols are made by reaction between phenols and car- bony1 compounds in the presence of acidic catalyst; bisphenol will soon account for more then 30% use of phenol worldwide. The literature is replete with examples using both homogeneous acids and ion-exchange resins as catalysts. However, for polycarbonates high purity bisphenols are required which can be advantageously made by using ion-exchange resins as catalysts (Scheme 12).

For bisphenol production, ion-exchange resins are not used directly. The cation-exchange resin is reacted with a mercaptoalkylamine (mercaptoethylamine), and treated with p-toluene sulfonic acid [33-361. It is claimed that even

Scheme 12. Synthesis of bisphenol A from phenol and acetone.

after 500 h, the conversion of phenol dropped from 11.6 to 10.3%. Nakagawa et al. [37] have recently claimed that by limiting the divinyl benzene content of the resin to 6 wt%, long-lasting activity of the catalyst can be obtained. The resin catalysts were used as packings in the reactor.

Mitsubishi Petrochem. Co. has recently patented a process for preparation of colorless bisphenol A with high purity using Amberlyst- 31 partially modified with mercaptoethylamine as catalyst [38]. Rhone-Poulenc has claimed that mercaptomethyl benzylamines are useful as pro- moters in the preparation of bisphenols from phenols and ketones using acid catalysts [39]. In another patent by Berg et al. [40], cysteamine modified sulfonated ion-exchangers are reported to have given high yield and selectivity of bisphe- no1 A.

A very recent Japanese patent has claimed to use a layered type reactor for the production of bisphenol A in high yield [41]. The reactor consists of a PTFE coil, filled with 333 K water for heat removal, sandwiched between a sulfonic acid type cation-exchanger (K1221) layer and a 2-mercapto-ethylamine-modified K1221 layer.

Simultaneous removal of water by pervapo- ration through a polyamide or polyimide membrane during the condensation reaction of phenol and acetone to give bisphenol A, has been reported to enhance the rate reaction [42,43].

Bisphenols based on substituted cyclohex- anones have been patented by Bayer AG (Scheme 13). 3-Methyl cyclohexanone based bisphenol can be made via catalysis with cationic ion-exchange resin, such as Lewatit SC-102H, modified with j3-mercaptopropionic acid and 83% yield has been claimed. However, 3,3,5- trimethyl-1-cyclohexanone, obtained from selective hydrogenation of isophorone, gives only an 8% yield [44].

Shell Oil Co. claimed that tetra phenolic compounds such as tetrakis (hydroxy phenyl) ethane can be made by condensing glyoxal, phenol and methanol in the presence of ion-exchange resins (e.g. Lewatit SC-102) as catalyst at 353 K [45]. In another patent, _

10 MM. Sharma I Reactive & Functional Polymers 26 (1995) 3-23

20 6 Scheme 13. Synthesis of bisphenol based on substituted cyclohexanone.

F HO

7 + CHO

Scheme 14. Tetraphenolic compounds from dials and phenols.

Shell has claimed that phenol can be reacted with terephthaldehyde, in the presence of cation-exchange resins (e.g. Lewatit SC-102), to give tetraphenol derivative of xylene, i.e., 1,6bis[bis(hydroxyphenyl)methyl]benzene [46] (Scheme 14).

7. lkansallqlations

Olah and co-workers [47,48] have studied the transalkylation reaction in the presence of Nafion-H catalysts (Scheme 15). Usually, these reactions are carried out in the presence of AlCls catalyst. However, they found that for truns- tert-butylation of aromatic compounds with 2,6- di(tert-butyl) p-cresol, more than molar equivalent of AlCls-nitromethane catalyst was required. On the other hand, 10% (w/w) of Nafion-H affected smooth conversion to corresponding tert-butylated aromatic compounds and p-cresol. Similarly, they carried out de-tert-butylation of aromatic compounds using toluene and diphenyl as butyl acceptor. They found that the tert-butyl group can serve as a convenient positional pro- tective group in aromatic substitutions allowing high regioselectivity; its deprotection via Nafion- H is easy.

Effenberger [49] carried out transalkylation between tetrabromobisphenol A and toluene, in the presence of trifluoro-methane sulfonic acid to get 2,6-dibromophenol (Scheme 16). Surpris-

AH3 CH3 \ WH3)3

Scheme 15. Trans-reti-butylation of 2,6-di-tert-butyl-p-cresol with toluene.

$1 + $_ 2$3r+ $ ar CWCH3)2

otl

Scheme 16. Pansalkylation between tetrabromobisphenol and toluene.

A

ingly, Nafion-H did not catalyze the reaction effectively.

A translakylation reaction of bisphenol A with an excess of diphenylether in the presence of methanesulfonic acid at room temperature yielded transalkylated products. However, in the presence of Nafion-H at 373 K, 6,6’-dihydroxy- 3,3,3’,3’-tetramethyl-l,l’-spirobiindan was obtained [50].

8. Reaction of ethylene carbonate with methanol

Ethylene carbonate can be transesterified with methanol in the presence of ion- exchange resins containing sulfonic acids groups (Scheme 17). Texaco Inc. has patented this process for producing ethylene glycol and dimethyl carbonate [51].

9. Higher olefins to secondary alcohols

a-Olefins and internal olefins (>Cio) are readily available. Attempts to hydrate these

CH2-OH 2CH3OH w Ln,-on + W~W2

Scheme 17. Transesterification of ethylene carbonate with methanol.

M.M. Sharma I Reactive & Functional Polymers 26 (1995) 3-23 11

KJC\ +o

H,-P,,,,,, ROH G==- CH$XXJR + p”

H3C-CH-C,0H2,

ter: AMS, at 333 K, around 30% conversion of AMS was realized [55].

IR = CHt. C4Hgl 11. Acetals and ketals Scheme 18. Transesterification of 2-dodecyl acetate with alcohols. The formation of acetals of acetaldehyde with

methanol/ethanol is a relevant example. These acetals can be conveniently cracked to alkyl vinyl ethers. The catalysis of acetal and ketal reactions with cationic resins have been reported (e.g. [56]) (Scheme 21). The formation of methy- la1 from formaldehyde and methanol in DCR has been covered in the section on distillation column reactors. Some interesting features are encountered when we deal with aqueous solutions as in the case of glyoxal and substituted glyoxals.

olefins directly have been unsuccessful. In the author’s laboratory, acetate esters have been formed in high yields and at high rates using ion-exchange resin catalysts. These esters can be transesterified with methanol/n-butanol etc. to give the corresponding secondary alcohols which are also expected to be useful in making detergents [52] (Scheme 18).

10. Hydration of acrolein and a-methyl styrene (AM9

Acrolein is a cheap petrochemical as it is obtained by selective oxidation of propylene. Hy- dration of acrolein gives hydropropanaldehyde via anti-Markovnikov addition which in turn can be hydrogenated to 1,3-propanediol. Thus, Amberlite ICR-718, having iminodiacetic acid group or Duolite C467 containing phosphonate group, catalyze the hydration of acrolein [53,54] (Scheme 19).

Hydration of AMS to give dimethyl phenyl carbinol (DMPC) is a reaction of some practi- cal interest (Scheme 20). When hydration was carried in the liquid-liquid-solid mode with Amberlyst-51 as the catalyst, there was hardly any conversion of AMS. However, with isopropanol as cosolvent and 8 : 1 mol ratio of wa-

CHycHCHO 4 Hz0 - HOCHfiH$HO

Scheme 19. Hydration of acrolein.

Scheme 20. Hydration of AMS to give dimethyl phenyl carbinol.

Performance of cationic ion-exchange resins (e.g. Indion-130) for the reaction of glyoxal with alcohols having low solubility in water, such as II- butanol, isoamyl alcohol and 2-ethylhexanol was evaluated [57] (Scheme 22). The reactions were tried in solid-liquid-liquid mode for the possible enhancement in the equilibrium conversions as well as in the rates of the reactions. Since resins have more affinity towards water, it was expected that the reaction would take place in the aqueous phase and the products formed, being non- polar, would be extracted by the non-aqueous phase. However, no significant enhancement was observed. Similar results were obtained for the reactions of glyoxalic acid with these alcohols. This can be attributed to the low solubility of the alcohols in the aqueous phase.

CH3CH0 + 2Ra)H -= CHSCHIOR)? + Ii20

,R : Me, Et,

Scheme 21. Formation of acetal of acetaldehyde with methanol/ethanol.

FHO + ZR-OH d 0HCCH(OR)2 + H20 . . ..A za, CHO

CHO +

LO

4RG-l d lR012HCCH(OR)2 + 2H*O . . . ..22b.

Scheme 22. Reaction of glyoxal with alcohols,

12 h4.M. Sharma /Reactive & Functional Polymers 26 (1995) 3-23

HCHO + C,HQoii # CH2fcqHQ)Z + “*cl

Scheme 23. Reaction between formaldehyde and n-butanol.

Another interesting example of reactions carried out in solid-liquid-liquid mode is the reaction of formaldehyde with n-butanol (Scheme 23). When reaction of 1% formaldehyde was carried out with stoichiometric quantity of n-butanol in solid-liquid-liquid mode, 18% conversion of formaldehyde was obtained, which increased to 69% when solid-liquid-liquid mode of operation was used with 8 times stoichiometric quantity of butanol [58]. Similarly, up to 93% of formaldehyde can be removed from aqueous 2-butyne-1,4-diol solution initially containing 1% formaldehyde, by internal acetal formation with 2-butyne-1,4-diol to give poly(2-butyne-1,4- dioxymethylene) in the presence of Indion-130 as catalyst at 393 K [22].

Asahi Chemical Co. [59] have claimed that the condensation of aqueous formaldehyde with ethylene glycol in the presence of strongly acidic cation-exchange resin with continuous extraction of one or more of the products into benzene can lead to high conversions (Scheme 24). In the author’s laboratory, some experiments have been carried out in the presence of Indion-130 as a catalyst, in batch mode as well as with simultaneous removal of dioxolane by distillation. In the batch mode with an ethylene gly- co1 to formaldehyde mole ratio of 2: 1, at 363 K, the equilibrium conversion of formaldehyde was found to be 52%. Whereas, simultaneous removal of dioxolane led to formaldehyde conversion greater than 99% and the concentration of formaldehyde in the reactor still less than 0.1% w/w. In another case, reaction between diethylene glycol and paraformaldehyde with Indion-130 as catalyst, gave 85% conversion of paraformaldehyde to the corresponding acetal [60].

Kampe and Kiessling [61], have developed a process for the preparation of 2,2-dimethyl- 4-(hydroxymethyl)-1,3-dioxolane by acetalization of acetone with glycerol in the presence of acidic

0

HCHO + F”ZM Ctlpl d 0 + Hz0

0

Scheme 24. Condensation of formaldehyde with ethylene glycol.

Scheme 25. Acetalization of acetone with glycerol.

ion-exchange resin at 313-323 K in a fixed bed reactor (Scheme 25). With a contact time of 120 s, 45% conversion has been claimed.

12. Dimerization of isoamylene and cross-dimerization of isoamylene with AMS

The dimers of isoamylene have wide appli- cations in perfumery and flavor industry. Cross- dimerization of isoamylene with AMS gives in- termediates for synthetic musks which have been the target of extensive research over the years mainly due to the conservation order placed on the musk deer. Synthetic musks are very good perfumery substances for laundry detergents.

These reactions have been carried out in the presence of ion-exchange resins and acid- treated clays by Sharma and co-workers [62,63]. In the case of isoamylene dimerization, yields of more than 90% were achieved in the temperature range of 333-373 K (Scheme 26). In the cross-dimerization reaction, with 1.2-2 mol ratio of isoamylene to AMS, 60% selectivity towards the cross-dimers, viz. 1,1,2,3,3_pentamethylindan and 3-ethyl-1,1,3_trimethylindan, was obtained at 353 K (Scheme 27). In both cases, ion-exchange resin was found to be a better catalyst as far as the activity was concerned. These reactions can be complicated as individual olefins undergo oligomerization to unsaturated and saturated dimers and isomerization of unsaturated oligomers. An elaborate modeling has been reported by Shah et al. [63].

M.M. Sharma / Readve & Functional Polymers 26 (1995) 3-23 13

CH3CH2C=CH2 or

c “3 CH3CH ‘Y”3 -

C”3

F”3 WC” -~;~J;-CHJ

qH3 + cHf~-~H-~~CHZCH3

3 CH3 CH) CH3

F”3 + CH3CH==-CH-_F-CH3

FH3

CH3 c “3 C”3

+ CHQCH-T-CH2 -y-CH2CH3

CH3 CH3

Scheme 26. Dimerization of isoamylene.

9 0

Scheme 27. Cross-dimerization of isoamylene with AMS.

13. Reactions with polymeric substances or resulting in polymeric substances

Cationic ion-exchange resins can be conveniently employed for reactions involving polymeric substances. AIkylation of poly(p- vinylphenol) with tert-butanol has been claimed in the presence of Amberlyst-15 as a catalyst [64]. The preparation of phenolic polymers, based on dicyclopentadiene (DCPD), which are useful as thermosets, hardeners for epoxy resins, has been claimed using acidic ion-exchange resins such as Lewatit K-2611 as catalysts [65]. Polymers based on the reaction of phenol with terpenes are commercially produced.

Sun and Wang [66] have claimed that phenol, bisphenol A,p-tert-butyl phenol etc., can be poly- merized with formaldehyde or acetaldehyde in the presence of resin catalyst, using toluene as a solvent under refluxing conditions.

The cracking of bisphenol A in the presence of activated clay catalyst to give p- isopropenylphenol dimers, useful for epoxy resins and polycarbonates has been reported [67] (Scheme 28). Ion-exchange resins can possibly serve the purpose with some added advantages.

14. Separation of close-boiling substances

The selectivity offered by the available cationic ion-exchange resins can be exploited

2 OH +

C”3

Scheme 28. Cracking of bisphenol to p-isopropenylphenol.

to carry out difficult separations; further manip- ulations are possible through designing catalysts with controlled pore sizes, acidity etc. The classic example of the selective removal of isobutylene from Cd olefinslparaffins (and the corresponding example of isoamylenes from Cj olefins) should be cited as the difference in the reactivity of isobutylene and butene-1 is enormous and the selective etherification to give MTBE (ETBE) allows manufacture of not only pure MTBE, but also, through multi-stage reactors, raffinate with a negligible amount of isobutylene so that polymer grade butene-1 can be obtained by straight distillation. Further, the outgoing gases, containing saturated amounts of methanol, can possibly go through a selective membrane to remove methanol so that purification of butene-1 of polymer grade is facilitated [68]. MTBE can be cracked to give pure polymer grade isobutylene; similarly, methyl-tert-amyl ether can be cracked to give pure isoamylenes.

Sharma and co-workers [69,70] have brought out the efficacy of resin catalysts in selective etherification of p-cresol in the presence of the close-boiling 2,6-xylenol, phenol in the presence of o&o-chlorophenol, /3-naphthol in the presence of a-naphthol etc., with isobutylene (Scheme 29). Here an added advantage is that the products often have different boiling points thereby further facilitating the separation. The ethers can be conveniently cracked to give the original phenol substance and isobutylene can be recycled.


Scheme 29. Etherification of p-cresol with isoamylene.

Jayadeokar and Sharma [71] have also reported separation of mixtures of primary/ secondary/tertiary alcohols via selective etherification with isobutylene. Here also, the ethers usually have different boiling points and separation is further facilitated.

o- and m-Nitrobenzaldehydes can possibly be separated by condensing the mixture with acetic anhydride in the presence of an ion-exchange resin as a catalyst, followed by separation of the acetylated mixture by crystallization, and subsequent hydrolysis of the isolated fractions. This separation has also been realized by the formation of a cyclic acetal with ethylene glycol, in the presence of resin catalyst, when the m- or p-isomer selectively reacts. The mixture on crystallization from toluene gives pure m-isomer which is subsequently hydrolyzed with a resin catalyst [72].

15. Esterification of amino acids and alkanolamines

Esterification of the compounds containing amino group in their structures, is an interesting example of acid-catalyzed reactions. These reactions are different from other esterification reactions as the basic amino group may inter- act with the acid catalyst and create undesirable complications. Hence, it would be interesting and useful to manipulate reaction conditions in order to obtain maximum yields and conversions.

15.1. Esterijication of amino acids

Esterification of amino acids (Scheme 30) is an important step in the synthesis of the cor-

responding peptides. The literature is replete on the esterification of amino acids such as glycine, lysine, serine, etc. in the presence of homogeneous acids such as dissolved hydrogen chloride, p-TSA, sulfuric acid, etc. (e.g. [73]). Most of the reactions have been carried out with azeotropic removal of water simultaneously during the course of the reaction.

Catalysis with cationic ion-exchange resins for these reactions, has been the subject of scant attention. Some experiments in this direction have been performed by Jain et al. [74,75]. They have carried out the esterification of glycine, lysine, etc. at around room temperature. Higher temperatures were required for the amino acids with side chains in their structure. Water formed in the reaction was removed simultaneously using anhydrous calcium sulfate as a dehydrat- ing agent. Yields close to 90% were realized. The catalyst loading required was approximately equal to the equivalents of the amino groups present in the reaction mixture. At the end of the reaction, product was eluted from the resin using acidified methanol.

Though the use of ion-exchange resins in the reaction eliminates the problem of catalyst removal, requirement of high catalyst loading and dry hydrogen chloride gas might prove to be undesirable from process point of view. Hence further work is desirable and the use of zeolites may be more attractive than calcium sulfate to absorb water.

15.2. Esterijication of alkanolamines

Esterification of alkanolamines with organic acids (Scheme 31) is of commercial importance (e.g. for making dimethyl amino acrylate). The reaction is somewhat complicated as side products such as amides (when primary and sec-

Scheme 30. Esterification of amino acids.

M.M. Sharma /Reactive & Functional Poiymers 26 (1995) 3-23 1s

!i> NCH~CH+~I + CH2=CH2COOH R d ~>N-ct4Z~~Z~c~=c~2 + ~~0

Scheme 31. Esterification of alkanolamines.

ondary amino groups are present), salt com- plexes of the amino alcohol and organic acid are likely to form in the reaction.

Alcohols having tertiary amino group in their structure, such as NSJ-dimethyl (or diethyl) amino ethanol, undergo esterification with acrylic acid in the presence of acid catalysts like aluminum isopropoxide, tetrabutyl titanate, etc. [76,77]. The reaction was carried out in the presence of a solvent capable of removing water azeotropically.

Attempts are being made in the author’s laboratory to study in detail the applicability of ion-exchange resins for the esterification of different amino alcohols, notably dimethyl amino ethanol, and diethyl amino ethanol with acetic acid and n-propionic acid. Some preliminary experiments indicate that dimethyl amino ethanol can be esterified with acetic acid at temperatures above 433 IS in the presence of toluene as a solvent. However, it is doubtful whether, at such temperatures, there is any significant effect of resin catalyst [78].

16. Hydrolysis of proteins and peptides

Acidic ion-exchange resins such as Dowex-50, have been found to be very effective for the hydrolysis of proteins and peptides. Hydrolysis of protein (e.g. casein) has been carried out by Paulson et al. [79]. They have reported a conversion near to 100% after refluxing the protein with 0.05 N hydrochloric acid in the presence of Dowex-50. The type of ion-exchange resin and the protein have a major effect on the reaction rates.

In the reaction of hydrolysis of peptides such as glycylglycine, Whitaker and Deatherage [80] found that Dowex50 was much more effective than an equivalent amount of hydrochloric acid in terms of reaction rates. They have also re-

ported in another publication [81] that Dowex-50 requires a free amino group in the reactant for its catalytic activity. They found that glycylglycine and aspargine, which contain a free amino group in their structure, split more rapidly than acetyl- glycine and acetamide, respectively. This was attributed to the formation of a complex between the charged resin and the free amino group so that the peptide bond is placed under a strain which permits easier splitting of the bond. The nature of peptide, ion-exchange resin, temperature, pH, etc. are the parameters which affect the reaction rate.

17. Alkylation of aromatic amines

The alkylation of aromatic amines, such as anilines, toluene diamines, diphenyl amine etc., with olefins like isobutylene, diisobutylene, styrene, a-methyl styrene, etc., is of consider- able commercial importance (Scheme 32). Thus dicumyl diphenyl amine is sold as an antioxi- dant. These alkylation reactions are difficult and a variety of catalysts have been studied. The successful use of zeolites has been reported. In the author’s laboratory, alkylation of dipheny- lamine with diisobutylene and a-methyl styrene, in the presence of macroporous resin catalysts (e.g. Amberlyst-15), was found to be unsuccessful even up to 393 K [82]. However, properly treated acid-activated clays are very useful catalysts. The life of the catalyst, in this application, is short.

18. Resins as catalysts in cyclohexene based processes

As the selective hydrogenation of benzene to cyclohexene has been recently commercialized by Asahi Chemical Co., Japan, cyclohexene- based processes are gaining a lot of importance. Cyclohexene can be used as a starting material for many industrially important chemicals like cyclohexanol, cyclohexanone (for manufacture of caprolactum via oximation), cyclohexyl esters and ethers (perfumery chemicals), cyclo-


. . . . ..(32C)

Scheme 32. Alkylation of aromatic amines with olefins.

hexene epoxide (an important intermediate for pharmaceuticals, agrochemicals and perfumery chemicals).

Ion-exchange resins can be used as catalyst for converting cyclohexene to cyclohexanol. It was observed that when direct hydration was carried out, conversion of cyclohexene was 8% in the presence of Amberlyst-15 as catalyst, whereas, in the presence of aqueous acetic acid (70%), overall conversion of cyclohexene was 65% with a selectivity of 35% to cyclohexanol and 65% to cyclohexylacetate, under otherwise identical conditions [25]. To overcome the problems of low solubility of cyclohexene in water, Panneman and Beenackers [83,84] have used co-solvents like sulfolane. They found that, during packed bed studies, the rate of hydration shows a strong dependence on the concentration

Scheme 33. Synthesis of phenyl cyclohexyl ether.

CH~CH(OHpzH*OH + - CH3CH(OH)CH20 -0 Scheme 34. Reaction of propylene glycol with cyclohexene.

of sulfolane. Cyclohexene can be reacted with phenol in the presence of ion-exchange resin to obtain cyclohexyl phenols or phenyl cyclohexyl ether depending on the reaction conditions [85] (Scheme 33). Cyclohexyl phenols are also precursors for phenyl phenols, while the ether can be used in perfumery formulations.

Propylene glycol can be reacted with cyclohexene at 393 K and 1.8 atm, with Nafion as a catalyst, to give 99% selectivity for the mo- noether at 36% conversion [86] (Scheme 34).

The hydration of cyclohexene oxide to give 1,2-cyclohexanediol can be conducted in excess water, in the presence of cationic ion- exchange resin (DIANON-PK 228; 14% crosslinking; area 0.15-0.2 m’/g; 10% pore volume) [87] (Scheme 35).

The alcoholysis of cyclohexene oxide is potentially attractive. Thus with methanol, 2-methoxy cyclohexanol is obtained, with resin catalyst (e.g. Nafion) and this substance on dehydrogenation on a modified supported noble metal catalyst gives guaiacol, an important intermediate for drugs, agrochemicals, perfumery chemicals, etc.

A similar process for manufacture of o-ethoxy phenols from cyclohexene via cyclohexene oxide has been claimed by Matsuoka [88]. 2-Ethoxy cyclohexanol was dehydrogenated to afford o- ethoxyphenol (Scheme 36).

Scheme 35. Hydration of cyclohexene epoxide.

M.M. Sharma /Reactive & Functional Polymers 26 (1995) 3-23 17

0 G OH

0 + C2H50H w- . . . . ..(3W

C=2”5

OH

a - cl O

/OH

2% + 3H2 __.___( 36b) OWS

Scheme 36. Alcoholysis of cyclohexene epoxide.

Olah et al. [89] have reported the hydrolysis and alcoholysis of cycloalkene oxide in the presence of Nafion-H catalyst to get cycloalkanediol and derivatives.

19. Reactions of olefins with acetic anhydride

Olefins such as diisobutylene, diisoamylene react with acetic anhydride in the presence of acid catalyst to give unsaturated methyl ketones which are valuable perfumery intermedi- ates (Scheme 37). Conventional methods using Lewis or protonic acid catalysts require the use of nearly stoichiometric quantities of the catalyst, which pose problems during separation of the products and effluent disposal. These reactions were carried out in the author’s laboratory, in the presence of ion-exchange resins and acid-treated clay as catalysts, with their attendant advantages [90]. With 5 : 1 mol ratio of acetic anhydride to DIE and 5% (w/w) loading of Amberlyst-15, at 363 K, 80% conversion of DIB was realized.

w4,co,,o ____,

+ CH ,R,"~:H-~H 3 I I 3

CH3 CH3 CH3 CH3

Scheme 37. Reactions of olefins with acetic anhydride.

Amberlyst-15 was found to be a better catalyst as compared to acid-treated clay so far as activity and selectivity towards the desired trans-isomer was concerned.

20. Clean processes for perfumery compounds

The use of cation-exchange resin catalysts for perfumery syntheses will gain more importance in the years to come. Resin catalysts with their attendant advantages including ease of separation of catalyst, mild operating conditions etc., enable the synthesis of perfumery compounds with less contamination.

Some work done in the author’s laboratory in this field will be cited. 2-Phenylethanol (PEA) is a perfumery compound widely used in the cos- metics and food industry. Ethers and esters of PEA also possess perfumery and flavoring value. A common ether of PEA, methyl ether, pos- sesses the fragrance of oil of screw pine or Pan- dunusfasciculuris, found in India. The synthesis of the methyl ether involves the use of dimethyl sulfate or methyl halide as alkylating agent. The presence of unreacted alkylating agent and undesirable by-products, even at ppm levels, is of detrimental value for the product. The separation of the impurities contributes to the cost of production of the ether. The direct etherification of PEA with isobutylene and isoamylene to give the respective tert-alkyl ethers is a very convenient and clean method (Scheme 38). The odor of tert-butyl ether resembles the fragrance of the oil of screw pine. The tert-amyl ether has a mild and pleasant floral odor.

The ease of synthesis of the above ethers is the greatest advantage. At 308 K, 100% conversion of PEA was obtained during the etherification with

Scheme 38. Etherification of phenylethanol with olefins.

18 MM. Sharma /Reactive & Functional Polymers 26 (1995) 3-23

CHZOH CH+H

+ H20 - Scheme 39. Hydration of citronellol.

isobutylene in 3 h. In the etherification of PEA with isoamylene, equilibrium conversion of 67% with respect to PEA was obtained in 2 h [91].

Hydroxycitronellal is an important perfumery material. Substantial quantities of hydroxycitronellal are manufactured by the hydration of citronella1 available from naturally occur- ring sources. The synthetic route for the synthesis of hydroxycitronellal consists of hydration of citronellol and subsequent oxidation to hydroxycitronellal. The first step of the synthetic route, i.e., hydration (Scheme 39), was carried out by Wasker and Pangarkar [92], in the presence of Amberlyst-15 as catalyst. They observed that at 12 : 1 mol ratio of water to citronellol, at 353 K, -55% conversion of citronellol was obtained.

21. Aldol condensation of cyclohexanone

Aldol condensation of cyclohexanone in the presence of acid catalyst gives 2-(l-cyclohexen-l- yl)cyclohexanone (Scheme 40) which is an intermediate for manufacturing o-phenylphenol. This reaction was carried out in the author’s laboratory using ion-exchange resin and acid-treated clay as catalyst [63]. Although ion-exchange resin was found to be more active, acid-treated clay gave a selectivity of 98%, as compared to 82% for the desired product in the presence of ion- exchange resin as catalyst. Aragon et al. [93]

or G=b Scheme 40. Aldol condensation of cyclohexanone.

Hoe + CHIC++ - "O&H,

have studied the deactivation of ion-exchange resin catalyst for the same reaction. They found

k”’ 2 ?&To1 Scheme 41. Synthesis of methyl glucoside.

that deactivation of the catalyst can be attributed to 3 factors: (1) inhibition by water; (2) fouling and poisoning; and (3) hydrolysis of sulfonic acid groups.

22. Methyl glucoside

Methyl glucoside is an excellent raw material used in the manufacture of drying oils, plasticiz- ers, non-ionic surface-active agents, etc. It may also serve as a modifier for amine and pheno- lit resins. It is a good mold release agent for thermoset plastics.

The usual procedure for manufacturing methyl glucoside (Scheme 41) using strong homogeneous acids did not lend itself to commer- cialization due to corrosion problems and low yields. Cationic ion-exchange resin has been suc- cessfully employed to get a yield of around 80% and a product having higher quality, good color and free of other impurities [94].

23. Prins reaction

Reaction of olefins with formaldehyde to give 1,3-dioxanes (Scheme 42) can be carried out under mild experimental conditions in the presence of ion-exchange resin catalysts. A clear il- lustration of the Prins reaction has been given by Delmas et al. [95]. Isoeugenol was con- densed with paraformaldehyde in the presence of Lewatit SP-120 or SPC-118 to give quanti- tative yield of 4-(4-hydroxy, 3-methoxy-phenyl)- 5-methyl-1,3-dioxane at remarkably high selectivity. For macroporous resins the cross-linking density had no significant effect on the reaction yields, but for gel resins, the yields de-

M.M. Sharma /Reactive & Functional Polymers 26 (1995) 3-23 19

R Km 4 HCHO + RCH=CH~ - CH2 0, r-7”

I %/JJ CHpi

Scheme 42. Prim reaction: reaction of olefins with formaldehyde.

creased as the percentage of DVB content was increased.

24. Difficult alkylation reactions

There is hectic activity in having a stable, active and heterogeneous catalyst for alkylation of benzene with C12 olefin-paraffin mixture, with the olefins present below 15%. This step is very important for making linear alkyl benzene, the sulfonate of which is a ‘work horse’ in laundry detergents. In the well-established process, HF is used, and the toxicity of HF has been act- ing as a deterrent. A number of zeolites and pillared clays have been patented and commercial versions have been announced. In principle, resin catalysts can be useful. However, information is almost non-existent in the available literature.

The alkylation of isobutane with isobutylene/ butenes/propylene also falls in the above cate- gory, where 100% sulfonic acid is also used as a catalyst.

The alkylation of toluene with ethylene to givep-ethyl toluene has been very successful with zeolite catalysts. However, to date, efficient resin catalysts have not been developed.

25. Some engineering aspects of the use of cationic ion-exchange resins as catalysts

A number of authors have brought out the salient differences between wet and dry resins when reactions are conducted in a non-polar medium. Thus the protocol for drying of the resin catalyst should be properly followed and a reference be made to the brochures of suppliers and papers by Buttersack et al. [96,97]. A recent publication on this subject by Iborra et al. [98] merits attention. They have shown that drying

of ion-exchange resins by methanol percolation leads to lower moisture content as compared to that in other methods. The dissolved moisture content of organic reactants should be assessed and its possible impact on the rate of reaction be ascertained.

Many alkylation reactions, particularly with tert-olefins, give products which are ultrasensi- tive to extremely low concentration of dissolved acidity which arises out of desulfonation of the resin catalyst. In subsequent purification by distillation, even though conducted at pressures below 20 mm Hg, the alkylated product can crack. Thus it is prudent to have a guard bed of anionic exchange resin for the alkylated products to go through before distillation is taken.

Any impurity in the feed which can adversely affect the resin catalyst should be removed. Thus the residual acetonitrile in CJ olefins, after removal of butadiene via extractive distillation with acetonitrile as a solvent, can hydrolyze on the resin and give acetic acid and ammonia, and the later can neutralize the acidity of the catalyst and adversely affect the performance of the reactor. The diolefinic compounds can be selectively hydrogenated to mono-olefinic compounds with a supported Pd catalyst. Any ionizable in- organic compounds exchange with the acid sites and reduce the activity. It is reversible in nature, though.

26. Reactions in microemulsion media

The use of co-solvents, such as isopropanol, to form a microemulsion is well known. In the simultaneous hydration and etherification of isoamylene using sub-azeotropic ethanol, in the presence of resin catalyst, the effect of microemulsion phase has been studied [99]. It was found that the selectivity towards the formation of the ether increased. This fact was attributed to the change in distribution of water and ethanol in the resin phase due to the presence of isopropanol. However, when tert-butanol was used as a co-solvent no change in the conversion and selectivity was observed.


27. Development of ion-exchange resin catalysts: recent trends

A reference was made to the supported styrene-divinyl benzene based catalysts under distillation column reactors. This area should witness increased activity in the coming years.

Weaver et al. [loo] have shown the advantages of using supported fluorocarbon sulfuric acid (FCSA), as not only these compounds, which have an unusually high acidity, are expensive, but the polymer material also does not permit ready accessibility to the acidic group. The supported FCSA catalysts appear to be very promis- ing due to high activity, thermal stability, long life, etc.

The development of perfluorosulfonic acid ion-exchange resin is being pursued with high surface area fibers, employing organopolysilox- ane substrates rather than polystyrene to boost their activity and heat resistance [loll.

Du Pont has claimed that perfluorinated resins, Nafions, diluted with perfluorinated dilu- ents, such as Teflon, are more active for oligomerization of isobutylene [102]. Waller has patented a process for preparation of N- substituted carbamic acid esters using the above- mentioned catalyst [103]. In another patent, Du Pont has claimed that Nafion, on calcined coke, with a pore diameter greater than 1000 A, is a good catalyst for oligomerization of olefins, hydration of olefins, etc. [104].

Allied-Signal has claimed that directly fluo- rinated hydrocarbon ion-exchange resins have higher acidity and can be used for alkylation of toluene with ethylene, isobutane with isobutylene etc. which is currently made using liquid HF or HzS04 as catalysts [105].

Cationic ion-exchange resin in the form of membrane has been used for the reaction of aqueous hydroxylamine sulfate and cyclohexanone to give the oxime [106].

Pellicular resins, which consist of a thin layer of a functional polymer grafted onto an inert core, are gaining importance as they can provide high surface area and larger particle size of the

catalyst. An acidic catalyst has been prepared from porous silica having an area of 78 m2/g by polymerizing potassium styrene sulfonate using an azo initiator. This catalyst was found to be comparable to Amberlyst-15 for alkylation of phenol with 1-dodecene [ 1071.

Cationic polymeric micelles may offer some advantages of high activity, high interfacial area, favorable distribution coefficient, etc. [108]. The use of high flux ultrafiltration membranes would enable the polymeric micelles to be removed from the product stream and then recycled. There is hardly any information in the literature on catalysis in such systems.

a-Olefin sulfonates are cheap and readily available. The use of oligomers of these sulfonates would be worth investigating.

The supported catalysts offer a number of advantages and, as pointed out under distillation column reactors, even structured packings can be made.

The use of catalyst in the form of woven fibers merits attention.

28. Concluding remarks

The drive for clean, safe and selective processes will lead to more extensive adoption of cationic exchange resins as catalyst for small, medium and large scale production of a variety of speciality and bulk chemicals. There is scope for further improvement in the stability of the catalysts, particularly at temperatures higher than 403 K. Supported catalysts are likely to be commercialized. In particular, catalysts in the form of packings for distillation column reactors are likely to make an impact. The modelling and simulation of distillation column reactors offer many challenges; the reaction engineering aspects need further investigation.

The manufacture of MTBE, ETBE and TAME will dominate the use of resin catalysts. Alternative catalysts based on acid-activated clays, pillared clays and supported heteropoly- acids are expected to make a dent in some niche areas of application of resin catalysts.

M. M. Sharma /Reactive & Functional Polymers 26 (1995) 3-23 21

Appendix I: Properties of some commercially available resin catalysts

Catalyst Size Internal Weight

(mm) surface area capacity ~ I

(m*k) (mEq H+/g)

Amberlyst-15 ’ Amberlyst-31 a Amberlyst-36” Amberlyst

XN-1010 a Diaion PK-228 h Indian 130” Lewatit SC- 102’ Lewatit SP-120d Lewatit SPC-118’ Dowex-50’

0.5 55 4.1 0.42-1.2 * 4.9 0.42-1.2 35 5.3

20-50 mesh 5 i70 3.3 0.4-0.55 0.15-0.2 2.05 0.55 4.8 _ 0.1 5.1 0.3-l .5 75-85 1.2 _ 35 4.65 0.3-1.2 * 0.6

Catalyst Porosity

(%)

Temperature stability

(“C)

Amberlyst-15 a 36 Amberlyst-31 a * Amberlyst-36 a 30 Amberlyst

XN-1010 a 47 Diaion PK-228 h 10 lndion 130’ _

Lewatit SC-102’ - Lewatit SP-120d 45-50 Lewatit SPC-118d - Dowex-50’ *

120 120 150

150 140 120

120

-3 data not available; *, not applicable due to gel-type structure. il Rohm and Haas Data Sheet. h Mitsubishi Chemical’s Data Sheet. c Data Sheet of Ion Exchange India Ltd. d K. Dorfner, Ion Exchangers, New York (1991).

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