INDIAN J. CHEM., VOL. 20A, JANUARY 1981

3. SRIVASTAVA,M. L. & LAL, S. N., J. membrane sa., x,7(1980),21, RNHCl + SA ~ Complex

4. HELFFERICH,F., Ion exchange (McGraw Hill, New York), kl(a) 1962, 511; (b) 510. Complex ~ RNH + S'A + H+ + CI-

5. SRIVASTAVA,M. L. & LAL, S. R, Indian J. Tech., 18 (1980),~ . ~.

6. OSTERLE,J. F., Appl. Sci. Res., 12 (1964), 425. SA --+ R' + CO2

7. M(OI9R6RI5SO)N2'11Fl'A. & OSTERLE,J. F., J. chem. Phys., 43. k. ., . R' + RNHCI ~ R' Cl + RNH

8. GROSS,R. J. & OSTERLE,J. F., J. chem. Phys., 49 (1969), ._228. . . k. .

9. KEDEM, O. & CAPLAN, S. R., Trans. Faraday Soc., 61 RNH + SA ---+ SA + RNHz(1965), 1897. k.ZR' --+ R'2

Scheme 1

Kinetic & Spectral Evidence for a Novel Chloride IonEffect & of Complex Formation in Cbloramine-T-Salicylic Acid System in Aqueous Sulpburic Acid]

S. VIVEK~ANDANt, K. VENKATARAO& M. SANTAPPADepartment of 'Physical Chemistry, University of Madras

A. C. College Campus, Guindy, Madras 600 025 '

and

SP. SHANMUGANATHAN*Department of Chemistry, Pachaiyappa's College,

Madras 600 030

Received 5 April 1980; revised 28 April 1980; accepted 12 May,. ., .,' -- ,,-' 1980

Addition of (:1- increases the rate of deearboxylatlve chlori-nation of salicylic acid by chloramine- T (CAT) in aqueous H.SO ,.At concentrations comparable to that of CAT, the rate levels offindicating Michaells-Menten type of behaviour, thereby providingkinetic e!!.dence for the formation of a complex of the type'R-SO.-NCI. which is quite novel jn CAT kinetics. Spectralevidence has also been obtained.

IN continuation of our recent studies- on the.decarboxylative ~h\orinations of a;, ~-unsaturated

acids by chloramine-T (CAT), the interaction ofsalicylic acid (SA) and CAT has now been kineticallyinves~igated .. In aqueous H2S04 (0.111M), thereaction manifests an order of 1.25 on [CAT] with azero order dependence on [SA]. Added Cl", whilenot affecting .the order in [~A], introduces a squaredependence m [CAT]. This could be rationalisedusi~g t~e .dichloramine-T (DCT)-CAT equilibrium-which, IS Important at pH <2.6. The rate in thepresence of CI- levels off around concentrationsc<;>mparableto. that.of CAT ( 0.002M) quite remi- ,n!scent of ~Ichaehs-Menten (MM) type of'beha-VIOur. The Lineweaver-Burk plot" gives a value forthe MM constant as 457, well upholding the fact thatthe DCT -CI- c.o?1plex formed iIJ.the system is quite· ,stable. A POSItIve salt effect, with a slope of + 1for the log rate. versus .f; plot: has been observedm the absence of Cl-. Taking 'into account alithese results, concomitant pathways could be pro-posed for the reaction both in the absence (Scheme 1)and presence (Scheme 2) of Cl-, respectively.

+Presented at the Fifth Annual Symposium in Chemistry1980, held at the lIT, Madras duringMarch 1980. '

tPresent address: Department of Chemistry, Pachaiyappa'sCollege, Madras 600 030.,," , '

86'

I

(

K.ZRNHCI ~ RNHz + RNCl2

(PTS)Ks~ RNCl;,,

'-' 0: Cl\ ": ,/ "~

H C A~S~N ct3 "=TII I '- ,,'0: "'Cl'",,

R I

~ R ikl + Cl2

••..•(9)

, .(I)

· . (2)

· .(3),

· .(4)

· .(5)

· .(6)

· .(7)

· .(8)

k; . .,Cl2 + SA --+ SA + CI + H+ + Cl-

. k8•

Cl + SA -~ SA + Cl" + H+. kG .

Cl2 + R~-.~- R'el +CI. . ,kld

R',+ CI ~ R' CIScheme 2

~n Schemes 1 and 2 SA' = (o)OH-C6H4COO' andR' = (o)OH-C6H' 4

Applying steady state conditions, the rate expres-sions (I) and (II) could be derived for the' pathwaysshown m Schemes 1 and 2 respectively. '

d[CAT]dt

when Kl[SA]> > 1.

· ,(10)

· .(11)

· .(12)

· :(13)

...(I}

_ d [CAT] = k6K2Ka [CArp ,[Cl-]dt {I + Kalel ]} [PTS] .. (II)

when {K2 [CAT]2 / [PTS]} <<1The mixed order mechanism as per (I) is proved

by the linear plot of rate/[CAT] versus [CAT]o.5.The complex formation in Scheme 1 and 2 the kindof which is being reported here for the fi(st time isborne ~ut by spectral shifts (observed by using aCarl-ZeISS Specord UV-VIS Spectrophotometer) in·the region 230 to 234 nm. The expected rate retar-dation by p-toluenesulphonamide (PTS) as per ex-pression (II) is experimentally found not to be much .pronounced (6 % decrease in rate when [PTS] =4.2 x 10-3M) due to the low .concentration of un-protonated PTS. Further justification is providedby the absence of any significant salt effect in thepresence of Cl-. Though other studiesv! have beenmade- with substituted" phenols, deoarboxylative

r

nuclear chlorination has not been reported earlier.The pH-rate profile shows a maximum around pH3.7. The stoichiometry under kinetic conditions{[CAT] : [SA] = 1:5 to 8) obtained as -d[COOH]!d [CAT], comes out to be 1:1 but when [CAT] is in-excess further reactions set in. The positive salt·effect in the absence of CI- may be due to the.separation of oppositely charged ions from the.activated state, as found" in the neutral decornpo-:sition of peroxydisulphate ion.

S. V. thanks the UGC, New Delhi for a teacherresearch fellowship.

References1. VIVEKANANDAN, S., VENKATARAO, K, SANTAPPA, M. &

SHANMUGANATHAN, SP., Indian J. Chem., 18A (1979),503.

2. JENNINGS, V. J., CRC c-u. Rev. Anal. Chem., 3 (1974).413.

3. AsHMORE, P. G., Catalysis and inhibition of chemical re-actions (Butterworths London), 1963, 81.

4. BALASUBRAMANIAN, V. & THIAGARAJAN, V., Int. J. chem.Kinet., 7 (1975), 605.

5. MUSHRAN, S. P., SHARMA, J. & PANDEY. L. J., Curro sa.,48 (1979), 629.

,6. CHANDRA SINGH, U. & VENKATARAO, K., J. inorg. nucl.Chem.• 38 (1976), 541.

Kinetics & Mechanism of Oxidation of Cellobiose &Melibiose by Hexacyanoferrate(III) in Ammoniacal

Medium']

K C. GUPTA* & ANITA KUMARI SHARMADepartment of Chemistry, Lucknow University,

Lucknow 226 007

Received 28 February 1979; revised 26 December 1979; accepted14 April 1980.

The rates of the title reactions are independent of [Fe(CN)~-]-and directly proportional to [melibiose] and [cellobiose] andsquare root of [ammonia]. Addition of NH.CI retards the rate.'The catalytic constants kOH- and kNH3 have been calculated.A mechanism involving the formation of an intermediate enediol.anion has been proposed.

OXIDATION of reducing sugars by Cu(II) andhexacyanoferrate(IlI) have been studied by

Singh et af.1-6 in strong alkaline medium who:suggested a mechanism based on kinetic data. Similarresults were reported by Marshall and Waters",Wiberg and Nigh" and Lambert and Jones". These.authors suggested a mechanism involving the forma-tion of intermediate enediol. The present paperdeals with the kinetics of oxidation of cellobiose andmelibiose by hexacyanoferrate(IlI) in the presenceof weak base ammonia and buffered medium.

Melibiose (AR, K. light) and cellobiose (Austranalpreparate) were used. All other chemicals used wereof AR grade. The total volume of the aqueousreaction mixture was kept 50 ml in each set. Theprogress of reaction carried out in dark-colouredbottles was followed by' estimating iodometrically

, tPaper presented at Indian Science Congress, ChemistrySection, Ahmedabad, 1978.

/

(

NOTES

unreacted hexacyanoferrate(III) at different timeintervals.

One mol of reducing sugars required six mol ofhexacyanoferrate(III). The reaction showed a briefinduction period due to dissolved oxygen whichoxidised initially produced hexacyanoferrate (II).The reaction mixture was flushed with nitrogen whenthe induction period was no more noticed. Theorder of the reaction with respect to K3Fc(CN)6 wasdetermined at fixed concentrations of other reactantsand at constant ionic strength (by adding KCl). Thestandard zero-order rate constant, ks was calculatedusing Eq. (1).

ks = ko X S ( )V ... 1

6.xwhere ko = --z;;- ,S is the strength of hypo

solution and V is the volume of aliquot taken. Theresults are summarized in Table 1. The kg valuesdo not show any variation at different initial concen-trations of K3Fe(CN)6' indicating that the reactionis zero-order with respect to hexacyanoferrate(III).This was further supported by the linear plot of theconcentration of the unreacted hexacyanofcrrateiIll)versus time. The slopes of the linear plot gave ksvalues almost similar to those obtained by Eq. (1).

The data in Table 2 show that the reaction ratedecreases proportionately with the decrease in[disaccharide]. The ratio kg![ disaccharide] is practi-cally constant in each case, confirming the first-orderkinetics with respect to disaccharide.

The ks values increase with the increase in [ammo-nia]. The ratio ks/[NH3]1/2 is fairly constant (Table 3).The slight increase in this ratio at higher[ammonia] is due to catalytic activity of undisso-ciated ammonia which increases gradually. Thus therate of reaction is directly proportional to squareroot of ammonia at low concentrations.

TABLE 1- EFFECr' OF [K3Fe(CN).1 ON THE REACTION RATE

{[NH3]=20.0x lO-2M; 1J.=.035 M; [Cellobiose] = 1.00 x lO-2M;[Melibiose] = 1.66 x lo-2M; temp. 35°}

(K3F.(CN)6] X 103 k. X 10' (mol litre'< min-I)M

Cellobiose Melibiose

5.00 1.45 3.873.33 1.49 3.772.50 1.40 3.82

TABLE 2 - EFFECT OF VARYING [DISACCHARIDE] ON THEREACfION RATE .

{[K3Fe(CN)6] = 2.5 x lO-3M; [NH3] = 20.0 x lo-2M;'temp. = 35°}

[Cell 0- k. x 10' k« X .103 [Meli- k. x 10' k« X 103biose] (mol --- biose] (mol ----

102M Jitre=' [Cellobiose] 102M litre=" [Meli-min-I) min-I) biose]

2.00 2.00 4.61 2.301.66 2.30 1.38 1.66 3.82 2.311.25 1.77 1.41 1.25 2.84 2271.00 -1.40 1.40 1.00 2.34 2.34

87