Singh, H. S.

Singh, L. N.

Singh, R. N.

English

NOPR

The rate expression (4) is in accordance with theexperimental observations.Refer-ences1. HOUSE, D. A., Chem. Rev., 62 (1962), 185.2. 'WILMARTH, ,V. H. & HARIM, A., Mechanism of oxidationby peroxydisulphate ions in peroxide reaction mechanism,edited by J. O. Edwards (John Wiley, New York).1962, 175.3. SABESAN, A. & VENKATASUBRAMANIAN, N., Indian J.Chem., 9 (1971), 942.4. SABESAN, A. & VENKATASUBRAMANIAN, N., Indian J.Chem., 8 (1970), 251.5. SRIVASTAVA, S. P., ]\iAHESWARI, G. L. & SINGHAL, S. K.,J. Indian chem: Soc., 49 (1972). 235.6. SRIVASTAVA, S. P. & SINGHAL, S. K., J. Indian chem. Soc.,46 (1969). 705.7. SANTAPPA, M. & PADMA, S., Proc. Indian A cad. Sci.,(1969), 7.8. RADHAKRISHNA MURTI, P. S. & SWAMY, B. R. K., IndianJ. cu-«, (in press).9. GUPTA, Y. K. & SENGAR, H. G. S., J. Indian chem, Soc.,44 (1967), 769.Kinetics & Mechanism of Ag+-catalysedOxidation of Glyoxal & Glyoxaiic Acid byPeroxydisulphate in Aqueous MediumR. N. SINGH, L. N. SINGH* & H. S. SINGHDepartment of Chemistry, University of AllahabadAllahabadReceived 16 February 1977; accepted 21 June 1977Silver(I) ion-catalysed peroxydlsulphate oxidationsof glyoxal and glyoxalic acid follow first order kineticswith respect to peroxydisulphate and zero order withrespect to each substrate. A direct proportionalityof the reaction velocity on [Ag"] is observed. Theaddition of some inorganic salts decreases the reactionrate. On the basis of the results, a probable mecha-nism has been proposed.THE kinetics of Ag+-catalysed peroxydisulphateoxidations of several organic substrates havebeen extensively investigated":", The kinetic resultspertaining to the Ag(I)-catalysed oxidation ofglyoxal and glyoxalic acid by pero~ydis~lphate,hitherto not reported, are presented In this noteand a mechanism for the oxidation reaction hasbeen proposed.All the chemicals except glyoxal (40% solution,Riedel) were of either AR (BDH) or GR (E. Merck)grade. Their solutions were prepared in redistilledwater. The stock solution of peroxydisulphate wasalways prepared fresh.The kinetics was followedl? by estimating theamount of unconsumed peroxyclisulphate at definiteintervals of time iodometricallv+'. Self-decompositionof peroxydisulphate in the presence of silver(I) ionand absence of the substrate has also been observed.The reaction is first order with respect to [per-oxydisulphate] (Table 1). In Table 1 i, representsfirst order velocity constant, kd gives the first ordervelocity constant for the decomposition of peroxy-.Present address; Department of Chern istry, Varanasi221005.NOTESdisulphate itself and k = (ka -kd) represents thevelocity constant for the oxidation process. Thefirst order velocity constants were calculated fromthe slope of the plots made between logarithmof the volume of thiosulphate solution consumed(which is proportional to the concentration of S20~-)and time.A close examination of the data in Table 2clearly substantiates the direct proportionality of thereaction rate on [Ag(I)]. The rate constant isindependent of the concentrations of glyoxal andglyoxalic acid (Table 3).The kinetic study has also been performed atdifferent temperatures and the energy of activation(Ea) for the oxidation of glyoxal (14·6 kcal mole+)and glyoxalic acid (12·3 kcal mole=] have also beencalculated from the slope of the Arrhenius plot.The addition of inorganic salts such as KN03 andK2S04 into the reaction vessel decreases the rate ofreaction (negative salt effect).Mechanism - Thus on the basis of the observedkinetic results, the rate law (1) is suggested for theTABLE 1 - EFFECT OF VARYING THE CONCENTRATION OFPEROXYDISULPHATE IN THE Ag(I)-CATALYSED OXIDATION OFGLYOXAL AND GLYOXALIC ACID[S 0'-1 X 10'• 8Mka x 10'min"!k X 10'mirr ![GA] = 0'048M;0·500·751·001·502·00[G] = 0'03M;0'500·701·001'502·00[Ag+] = l'OxlO-3M; TEMP.= 35° ± 0·1°4·61 1'33 4·483·76 1·28 3·634·35 1'21 4·23~~ l·W 3·n4'30 0·97 4·20[Ag+] = l'OxlO-3M; TEMP.= 35° ± 0.103'21 1'33 3·082·93 1·28 2·803·06 1·21 2·943·02 toz 2·912·88 0·97 2·78GA = glyoxalic acid; and G = glyoxal.TABLE 2 - EFFECT OF VARYING [Ag+] ON THERATE CONSTANT FOR THE OXIDATION OF GLYOXAL ANDGLYOXALIC ACID BY l'EROXYDISULPHATE{[SoOn = O'OlM; temp.= 35° ± 0'1°}[Ag+] x 103 ka X 10' kd X 103 k X 10' k/[Ag+]M mirr< mirr ! min-1 M:» mirr?[GA] = 0'048M0·25 1-42 0'32 1'39 5'550'50 2'28 0·67 2'21 4·430·75 2·98 0·92 2·89 3·851·00 4'35 1'21 4'23 4·231'50 6'35 1'82 6·17 4·11[G] = 0'03M0'50 2·19 0·67 2·12 4·251·00 3·06 1'21 2·94 2·941·25 3·68 1·54 3·53 2·821'50 4'67 1'82 4·49 2·991'75 5·30 2·16 5·08 2·902·00 5·76 2'57 5·50 2·75Ul7INDIAN J. CHEM., VOL. 15A, DECEMBER 1977The formic acid was identified-" as the finalreaction product in the oxidation of glyoxal andglyoxalic acid both.Further, on comparing the rate constant values(Table 2) and also the value of Arrhenius energy ofactivation, one can easily conclude that the ratesof oxidation of glyoxalic acid and glyoxal follow theorder glyoxalic acid> glyoxal. The higher ratewith glyoxalic acid might be due to the carboxylicgroup which would ease the formation of CHOradical.One of the authors (RN.S.) is very grateful tothe UGC, New Delhi, for financial support.TABLE 3 - EFFECT OF VARYING [SUBSTRATE] ON THERATE CONSTANT FOR THE OXIDATION OF GLYOXAL ANDGLYOXALIC ACID BY PEROXYDISULPHATE{[S,O:-] = O·OlM; [Ag+] = l'Oxl0-3M; temp.= 35° ± 0'1°}[Glyoxalic ka x 10· [Glyoxal] X 10' ka X 10'acid] X 10' mirr ! M mirr !M0·80 4·57 1·0 3·23HO 5·20 2·0 3·123'20 4·41 3·0 3·064·00 4-17 4·0 3·114·80 4·35 6·0 2·905-60 4·17 8·0 3·07oxidation of both glyoxal and glyoxalic acid- d[Sd~~-J = k; [Ag+][S20~-] ... (1)where k, is specific rate constant which is equalto k([Ag+]M-I min<. The rate law (1) suggests thatrate determining step between S20~- and Ag+ ionyields one or more intermediates which subsequentlyoxidizes the substrate in fast steps. The negativesalt effect also indicates that the interaction oftwo oppositely charged species might take placein the rate determining step-".In order to explain the rate law (1), the mecha-nism shown in Scheme 1 is suggested. This is validfor both the organic substrates.»;s,oi- + Ag+ --+ Ag'+ + SO;- + SOl- ... (i)k,SO~- + Ag- --+ Ag2+ + SO~- ... (ii)k, .CHO.COOH + Ag'+ --+ CHO + Ag" + H+ + CO. . .. (iii)• k,CHO + S20;- + HOH --+ HCOOH + HSO. + SO~- ... (iv)• k,CHO + SO~- + HOH --+ HCOOH + HS04 ... (v)Scheme 1The evidence for the existence of Ag2+ and S0,i-as the reactive intermediates in the peroxydisulphateoxidations have been given by several workersI3-15.Thus, the rate of disappearance of peroxydisul-phate might be given by Eq. (2)- d[S~~~-]= kl [Ag+][SzO~-]+k4[CHO][SzO~-] ... (2)Considering the steady state conditions, one ob-tains the relationship· (klk2)![CHO] = k4k5 [Ag+]From Eqs. (2) and (3), the rate law becomes- d[S20~-]= k, [SzO§-][Ag+]dt(klk2)~where k; = kl+k4 k4kS •Thus derived, rate law (4) clearly explains theobserved kinetics ..... (3)... (4)1118References1. SABESAN, A. & VENKATASUBRAMANIAN, N., Indian J.Chem., 9 (1971), 942.2. GUPTA, Y. K. & GHOSH, S., Proc. nat. Acad. Sci., 27(1958), 258.3. SENGAR, H. G. S. & GUPTA, Y. K., Indian J. Chem.,6 (1968), 119.4. GUPTA, Y. K. & NIGAM, R. K., J. Indian chem. Soc.,37 (1960), 125.5. PRASAD, B. N., SINGH, R. N. & SINGH, N. P., J. scient.Res. BHU, XXIV (1973), 6.6. SRIVASTAVA, S. P., MAHESWARI, G. L. & SINGHAL, S. K.,J. Indian chem, Soc., 49 (1972), 235.7. SRIVASTAVA, S. P. & SINGHAL, S. K., J. Indian chem,Soc., 46 (1969), 705.8. KHANDUAL, N. C. & NAYAK, P. L., J. Indian chem. Soc.,50 (1973), 194.9. KHAN DUAL, N. C. & NAYAK, P. L., J. Indian chem. Soc.,50 (1973), 786.10. SINGH, R. N., SINGH, L. N. & SINGH, H. S., Indian J.Chem., 15A (1977), 40.11. KOLTHOF, 1. M. & CARR, E. M., Analyt. Chem., 25(1953), 298.12. LAIDLER, KEITH J., Chemical kinetics (Tata-McGraw-Hill, India), 1965, 220.13. BAWN, C. R. H. & MARGERISON, D., Trans. FaradaySoc., 51 (1955), 925.14. HIGGINSON, W. C. & MARSHALL, J. W., J. chem. Soc.,(1957), 447.15. MENGHANI, G. D. & BAKORE, G. V., Indian J. Chem.,7 (1969), 786.16. FRITZ FEIGL, Spot tests: Organic applications, Vol. 3(Elsevier, New York), 1954, 245.Cerimetric Determination of Boron asBorotartrateB. MADHAVA RAODepartment of ChemistrySardar Vallabhbhai Regional College ofEngineering & Technology, Surat 395007Received 18 December 1976; accepted 27 June 1977An indirect cerimetric method for the estimation ofboron is developed. Boron is precipitated as bariumborotartrate complex in which boron to tartaric acidratio is 1: 2. The amount of Ce(IV) consumed by thecomplex gives a measure of tartrate ion and indirectlyfurnishes the boron content.RECENTLY Gopala Rao et al.1 have developedan accurate method for the determination oftartaric acid using ammonium hexanitratocerate(IV)as an oxidizing agent. This procedure has beenextended for the determination of tartrate ioncomplexed as borotartrate, since conditions have

Kinetics & Mechanism of Ag+-catalysed Oxidation of Glyoxal & Glyoxaiic Acid by Peroxydisulphate in Aqueous Medium

http://nopr.niscair.res.in/bitstream/123456789/53325/1/IJCA%2015A%2812%29%201117-1118.pdf

Kinetics & Mechanism of Ag+-catalysed Oxidation of Glyoxal & Glyoxaiic Acid by Peroxydisulphate in Aqueous Medium

Abstract

Similar works

Full text

Available Versions

NOPR