Chatterjee, Hriday R.

Gupta, (Mrs) Shipra Sen

Gupta, Kalyan K. Sen

English

NOPR

Indian J01ll'D8l of ChemistryVol. 14A, Auguat 1976, pp. 586-588Kinetics of Os(VIII)-catalysed Oxidation of Neutralized Glyoxylic &Pyruvic Acids by Alkaline Hexacyanoferrate(III)KALYAN K. SEN GUPTA, (Mrs) SHIPRA SEN GUPTA & HRIDAY R. CHATTERJEEDepartment of Chemistry, }adavpur University, Calcutta 700032Received 17 June 1975; accepted 22 January 1976In the reactions between alkaline hexacyanoferrate(III) and some a-keto carboxylate cata-lysed by Os(VIII) at [OH-]<10-sM, the rate of reaction has been found to be proportional to the[substrate] but independent of the initial [Oxidant]. The rate is also directly proportional to the[OH-] and [Os(VIII)]. The reactlons have been studied at different temperatures and activationparameters evaluated. Tentative reaction mechanism has been proposed.KINETICS of Os(VIII)-catalysed oxidation ofvarious inorganicl,1 and organic compoundss'",by alkaline hexacyanoferrate (III) have beenstudied. Some of the results have indicated thatunless catalyst is employed, the reactions are eitherextremely slow or do not occur, especially whenthe alkali concentration is very low. It has earlierbeen shown" that the oxidation of glyoxylic andpyruvic acids by hexacyanoferrate(III) do notproceed at [OH-]<1O-3M. However, the additionof a catalyst like Os(VIII) enhanced the rate ofoxidation even at low [OH-]. The present report,therefore, deals with the Os(VIII)-catalysed oxi-dation of the glyoxylic and pyruvic acids by alkalinehexacyanoferrate(III) at low [alkali].Materials and MethodsAll inorganic chemicals were either of BDH(Analar) or E. Merck (GR) grades and used withoutfurther purification. Neutralized glyoxylic and pyru-vic acids were always used for studying reactions.The chemicals employed and the procedure adoptedwere described in a previous paper".The solution of osmium tetroxide (Johnson &Matthey) was prepared by dissolving the samplein potassium hydroxide solution. Freshly preparedsodium carbonate-sodium bicarbonate buffer wasused throughout during kinetic runs.Procedure - The rate of disappearance of hexa-cyanoferrate(I1I) was folk-wed spectrophotometri-cally as mentioned earlier''. The extinction coeffi-cient (E) of ferricyanide ions at 420 nm is 1060±10M-I em-I. The initiation of the reaction wascarried out by adding the requisite quantity ofsubstrate maintained at a constant temperatures,to a mixture of oxidant, buffer and Os(VIII). Theplot of optical density against time was linear andthe slope of each plot gave initial rate (ko) whichhas been expressed in terms of concentration. Thereproducibility was more than ± 3%. The rateof loss of oxidant was followedup to 50% conversionof initial hexacyanoferrate(III). All the runs weretaken in the presence of buffer and thereby PHof the solutions were maintained constant.586Results and DiscussionStoichiometry - The.equivalents of ferricyanide ionconsumed per mole of substrate have been foundto be 2·8 and 3·2 respectively.Effect of varying [reactant]- The order withrespect to each reactant was determined from themeasurement of initial rates of reaction by keepingthe concentration, in turn, fixed in one case andvarying the other. The values of ko at various[oxidant] showed that the rate was independentof loxidant] (Table 1). Again, when the concen-tration of the reducing substrate was changed, theinitial [hexacyanoferrate(III)], [OH-] and [catalyst]were kept constant. The values of initial ratesalong with the quotients, ko/[(X-ketocarboxylate]at various [substrate] are summarized in Table 2.The rates were directly proportional to the initial[substrate].Effect of varying [OH-]- The effect of varying[OH-] on the initial rates were studied at constant[reactants] as well as [catalyst]. The ko values atdifferent [OH-] calculated from the correspondingPH values are given in Table 3. The ko/(OH-values indicated the first-order dependence on[OH-].Effect of varying [catalyst] - The [reactants] andthe PH of the solutions were kept constant, whileTABLE 1 - EFFECT OF [OXIDANT] ON THE RATE OF REACTION{(A) [Glyoxylate]=2·50xlO-3M; pH=9·8; [Os(VIII)J=5xl0-6M; ternp.=33°C. (B) [PyruvateJ=2·40xl0-sM; pH=10·2; [Os(VIII)] =5 x 10-oM; temp.=31·5°qA[Fe(CNn-J x 104M 0·499 0·999 1·50ko x 10· 2·44 2·52 2·40(M see I)2·002-262·502-45[Fe(CNtIJ x 10'M 2·00ko x 108 8·44(M sec ")B2·508·573·008·573·508·104'008·17SEN GUPTA et al.: Os(VIII)-CATALYSED OXIDATION OF GLYOXYLIC & PYRUVIC ACIDSTABLE 2 - ZERO ORDER RATE CONSTANTSAT VARYING TABLE 4 - EFFECT OF VARYING [Os(VIII)] ON THE[SUBSTRATE] REACTIONRATE{(A) [Fe(CNJ-~]=1'50;< 1O-4M; [Os(VIIlJJ =5·0 x lO'5M; pH {(A) [GJyoxylate]=2·50)( 1O-3M; [Fe(CNJ-:J =1·50 x 1O-4M;=9'8; temp.=32·5°C. (B) [Fe(CN)-:J=2'0 x 10-tM; pH=9·8; temp. = 33°C. (B) [PyruvateJ=2'40 X 10-3M;[Os(VIII)]=5'0xl0-"M; pH=10·2, temp.=30·5°q [Fe(CN)n=2'Ox 10-4M; pH=10'2; temp.=31·5°qA A[Glyoxylate] 2·50 3·75 5'00 6·25 7·50 [Os(VIlI)] 5 10 15 20 25X 10' (M) xl06Mko x 108 2·09 3·30 4-45 5·53 6·38 koX 108 2-68 5'35 8·13 11·0 13-8(M see-i) (M see-I)ko/[Substrate] 8·36 8·80 8·90 g'85 8·50 ko/[Os(VIII)) 5·36 5·35 5·42 5·50 5·52X 106(see-i) x 10' (sec'<)B B[Pyruvate] 0·599 1·20 1·80 NO 3·00 [Os(VIII)] 5 10 15 20 25x 10' (M) xl0"MkoX 108 2·06 4'35 6'41 7·97 9·98 ko X 108 6·79 14·1 20·6 26'6 34·3(M see-I) (M seer")ko/[Substrate] 3·44 3·62 3·56 3·32 3·33 ko/[OsVIII)] 1'36 1-41 1·37 1·33 1·37x 10" (sec'") X 103 (see-I)TABLE 3 - EFFECT OFpH ONTHE RATE OF REACTION((A) [Glyoxylate] =2·5 x 1O-3M; [Fe(CNt:]=1'50 x 10-4M;[Os (VIII)] =5 x 10-oM; temp.=33·5°C. (B) [Pyruvate]=2'40 X 10-3M; [Fe(CNn] =2·0 X 10-4M; [Os(VIII)] =5X 10-6M; temp.=31·5°qA)pH 9·8 10·0 10·2 10·7ko x 108 2'94 4·56 7·23 25·9(M see-I)ko/[OH-] X 104 4-66 4·56 4-57 5·17(sec-t)BpH 9·2 9·5 9·8 10·2 10·7ko X lOS 0·729 1·82 3·24 8'64 24·7(M sec'<)ko/[OH-] X 104 4·61 5·76 5'13 5·47 4·93(sec=)the [catalyst] was varied. The value; of kot[Os(VIII)](Table 4) indicated that the rate of reaction wasalso directly proportional to the [catalyst].I nftuence of varying temperature and the activationparameters - The temperature dependence of thereaction rates was studied at constant [substrate],[oxidant], [catalyst] and [OH-]. ThE values ofkl have been calculated from the relation kl = kot[substrate] at various temperatures [Table 5).The plots lc'g kl against liT were linear. Thermo-dynamic parameters 6..H and 6..5 have been evaluatedand found to be 26·2 ± 2 kcal mole? and 3·4 ± 6·0cal deg.-l mole-l for glyoxylic acid oxidation and21·8±1·5 kcal mole? and -8·9±4·5 cal deg.-lmole? for pyruvic acid oxidation.Krauss a.nd Wilken" have shown that potassiumsalt of perosmic acid exists as K2[OsO,(OH)2J. Itwas, later on, shown by Sandel et at.lO from spectro-photometric measurements in potassium hydroxidesolution that osmium tetroxide yielded a value of,......10-10for the first dissociation constant at 25°Cwhereas the second dissociation constant of theparent acid was much smaller (,....,10-16) than thatof first one. Although the exact composition ofTABLE 5 - EFFECT OF VARYINGTEMPERATUREON RATE CONSTANT{(A) [Glyoxylate] =2·5 X 10-3M; [Fe(CN)!-] =1'5 x 10-4M;pH=9'8; [Os(VIII)]=5'Ox10-6M; (B)[Pyruvate]=2'40x10-3M; [Os(VIII)] =5·0 x lo-5M; [Fe(CN)rJ =1'50 X 10-4M;pH=10'2}Temp.(0C)343540·545'546(A) Glyoxalate0·7861·893·982-665·348·48(B) Pyruvateperosmic acid was not known, the perosmate anionwhich acted as a catalyst was probably OsO/jH-and not OsO.Ht. It was, therefore, suggestedthat complex was formed by the interaction ofsubstrate (S) with HOsO-1i which was designatedby Os(VIII). The complex (X) finally reactedwith OH- to give reaction products and Os(VI).The latter was finally oxidized by two moleculesof hexacyanoferrate(III} to give Os(VIII) (Scheme 1).k'S+Os(VIII) ~X "'(1)k_,k,X+OH--~P*+Os(VI)+H20 ... (2)k,2Fe(CN)t +Os (VI)---.+Os (VIII) +2Fe(CN)3- ... (3)Scheme 1The rate of formation of complex IS given byrelation (4)d~~] = kl [S][O:;(VIII)] -k_lfX] -k2[X][OH-] ... (4)Applying steady state approximation, the[complex] is given by Eq. (5)kJ [S}[Os{VIII)][X] = (5)k-l +k2[OH-] .. ,587INDIAN J. CHEM., VOL. 14A, AUGUST 1976The rate of disappearance of hexacyanoferrate(III)is given by Eq. (6)-d[Fe (CN)t] 2k{ kll[S][Os(VIII)][OH-]-dt k-1+kll[OH-]Assuming k-l »k., i.e, step (2) to be the rate-determining, the product k. [OH-] will still bea smaller quantity, hence-d[Fe(CN) 1-] 2k;, k.[S][Os(VIII)][OH-]dt = k-l= k[S][Os(VIII)][OH-]where k = 2ktk.1 k_1.Alternatively, it could be proposed (Scheme 2)that the substrate reacts with the OH- to give anintermediate compound (X') followed by its reactionwith Os(VIII) in a slow step to give oxidationproduct (P*) and Os (VI). The latter is finallyoxidized by two moles of hexacyanoferrate(III)regenerating Os(VIII) by fast step.•.. (6)... (7)... (8),"1S+OH-~X' +H.O11.1... (9)".X' +Os(VIII)--+P* +Os(VI).•.2Fe(CN)i·+Os(VI)~s(VIII) +2Fe(CN)tScheme 2... (10)... (11)Thus a probable rate law which might be pro-posed for the oxidations of glyoxylate and pyruvateions is given by Eq. (8) and this indicates first orderdependence of reaction rate on [substrate]. [catalyst]and [OH-]. The value of k (average of five deter-588minations) comes out to be 2750 at 32·5° and.4360M-2 sec-1at 30·5°Cin the oxidation of glyoxylicand pyruvic acids respectively. The reported valuesat a particular set of conditions indicate thatkpyruvate>kglyoxylate. The activation parameterscalculated in Table 5 also support the above con-tention which indicates that more energy will be-required to oxidize glyoxylate than pyruvate ion.The observed stoichiometry of 2·8 and 3·2 forglyoxalate and pyruvate ion oxidation respectivelycan be explained considering that steps" (12)and (13)take place to the extent of 60 and 40% respectivelywhereas steps8 (14) and (15) take place to the extentof 80 and 20% respectively. The details regard-ing the formation of reaction products have beendescribed in preceding paper.References1. JINDAL, V. K., AGARWAL,M. C. & MUSHRAN, S. P.,J. chem. Soc., (1971), 622.2. JINDAL, V. K., AGARWAL,M. C. & MUSHRAN, S. P.,J. inorg, flucl. Chem., 32 (1970), 1257.3. SAXENA,B. B. L., SINGH, M. P. & SINGH, V. N., J. Am.chem. Soc., 91 (1969), 2643.4. SINGH, M. P., SINGH, H. S., SINGH, V. N. & LAL, V.,Indian J. Chem., 10 (1972), 392 .5. SONI, G. C. & MENGHANI,G. D., Tetrahedro», 38 (1972),5567.6. SINGH, N. P., SINGH, V. N. & SINGH, M. P., Aust. J.Chem., 21 (1968), 2913.7. SINGH, N. P., SINGH,V. N., SINGH,H. S. & SINGH,M. P.,Aust. J. Chem., 23 (1970), 921.8. SEN GUPTA, K. K., SARKAR,T., CHATTERJEE, H. R. &SEN GUPTA, S., Indian J. Chem., 14A (1976), 583.9. KRAUSS, F. & WILKEN, D., Z. inorg, allgem, Chem., 145(1925), 151.10. SANERBRAUNN,R. D. & SANDEL, E. B., J. Am. chem.Soc., 75 (1953), 4171.

Kinetics of Os(VIII)-catalysed Oxidation of Neutralized Glyoxylic & Pyruvic Acids by Alkaline Hexacyanoferrate(III)

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Kinetics of Os(VIII)-catalysed Oxidation of Neutralized Glyoxylic & Pyruvic Acids by Alkaline Hexacyanoferrate(III)

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