Kumar, Anil

Srivastava, S. P.

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iNDIAN J. CHEM., VOL. 15A, DECEMBER 1977Kinetics & Mechanism of Ag+-catalysedOxidation of 1,3-Propanediol byPeroxydisulphate Ion - A ReinvestigationS. P. SRIVASTAVA & ANIL KUMARDepartment of Chemistry, University of RoorkeeRoorkee 247672Received 5 January 1977; accepted 13 June 1977The Ag+vcatalysed oxidation of 1,3-propanediol byperoxydisulphate ion has been found to yield3-hydroxypropionaldehyde by a first order processin the first stage, which is followed by the oxidationof this aldehyde in the next stage along with theoxidation of diol. A mechanism different from thatreported by Bakore and Menghant [Curro Sci., 37(1968), 641] has been proposed on the basis of theproduct formed and kinetic study.THE kinetics of Ag" -catalysed oxidation of 1,3-propanediol by peroxydisulphate ion was investi-gated by Bakore and Menghani! who suggested amechanism based on the formation of formaldehydeand acetaldehyde. However, a reinvestigation ofthe reaction, the results of which are reported inthis note, shows that the product formed is 3-hydroxypropionaldehyde, thus leading to a mecha-nism different from that reported by Bakore andMenghani1.The progress of the reaction was followed byestimating the unreacted K2S20s iodometricallyemploying the method of Szabo et al.2 as modifiedby Khulbe and Srivastava".The absence of HCHO as the reaction productwas confirmed by the negative chromotropic acidtest in the reaction mixture as well as ill thedistillate obtained under reduced pressure. Thesolid 2,4-DNP derivative of the distillate, preparedin HCI-H20 mixtures, melted at 1510 and was foundto be TLC pure (silica gel). That the 2,4-DNPderivative is not that of acetaldehyde was confirmedby the spectral data. Its NMR spectrum (chemicalshift in a-scale) showed a high field two-protontriplet 3·98 U = 5·0 Hz) which might be due tomethylene protons flanked on either side by ahydroxy group and another methylene group. Aquartet at 2·7 (] = 5·0 Hz) clearly confirmed thepresence of one methylene and methine groups in itsneighbourhood. The total number of ten protonsconfirmed clearly indicated that 2,4-DNP derivativeis derived from 3-hydroxypropionaldehyde[OH.CH2.CH2.CH=N -NHC6H3(N02)2(2,4-position)]The IR spectrum of the 2,4-DNP derivative showedpeaks at 3280 (v-NH) and 3600-3200 (br, v-OH).l~Formation of 3-hydroxypropionaldehyde was COn-firmed by a study of the mass spectrum of the2,4-DNP derivative. The parent ion peak at nt]«254 agrees with the molecular weight. The basepeak was found at m]« 39 (C3H;). The otherprominent peak was observed at m]« 2365,6 whichis due to loss of a water molecule as depicted inChart 1.Kinetic runs at four different temperatures showedthat the reaction consists of two independent first,order reactions: (i) oxidation of the diol to corres-ponding hydroxyaldehyde (stage-A) and (ii) oxidationof the aldehyde to corresponding hydroxy acid (stage-B). However, the rate constant for stage-B is lessthan that of first reaction which may be due toinhibition in later stages, but the exact nature ofthe inhibiting process could not be worked out.At low temperature a slight induction period wasalso observed.The specific rate at four temperatures along withthe energy parameters calculated therefrom aregiven in Table 1.The general similarity of this reaction with otherAg+-ca talyscd peroxydisulpha te reactions suggestedthat the following mechanism (Eqs. 1-6) for stage-Ais followed:k,Ag++ S20~----+ Ag2++ so; + SO~- ... (1)k.SO~ + H20 ---+ 'OH + HSO. ... (2)k.S+Ag2+--+R+Ag+ ... (3)k.S + Ag> ---+ R + H20 ... (4)k,R + S20~-----+ OH-(CH')2-CHO+ HSO. + SO~ ... (5)k.R + SO~ --+ OH-(CHz)2-CHO+ HSO. ... (6)where S stands for OH-(CH.}a-OH and R stands forOH-CH.-CH2-CH.0.Scheme 1TABLE 1 - ENERGY PARAMETERSReactionstageAB{[1,3-Propanediol]= 1·0xl0-zM; [K.S20.] = 2·0xl0-2M; [AgN03J= 1·0xl0-3M; temp.= 35°}k -:= (kobs./CAg+)X 10' t!>.E. Frequency factor (A)litres mole"! see"! kcal mole=! litres rnole"! sec-1AS.e.u.13·307·10(8·8±0·3)(11-6±0'3)(2'50±0'02) X 105(1·32±0·03) X 107(-35·90± 0·05)(-28'93±0'04)1114Steps (1) and (2) of Scheme i have beenproposed by a large number of workers7-12 and thehydrogen abstraction from the organic substrateto yield the radical is considered to be the r.extpossible step-", The formation of bivalent silver ionin peroxydisulphate redox processes has been shownby McMillan and Smaller= and the existence ofS04 and ·OH in the peroxydisulphate redox reactionshave recently been proved by the ESR studies-".It can safely be assumed that the next stage,namely the oxidation of hydroxyaldehyde to thecorresponding hydroxy acid, follows a similar mecha-nism.One of the authors (A.K.) is thankful to theCSIR, New Delhi, for the award of a junior researchfellowship.References1. MENGHANI, G. D. & BAKORE, G. V., Curro Sci., 37(1968), 641.2. SZABO, Z. G., CSANYI, L. & GALIBA, H., Z. anal. Chem.,135 (1952), 269.3. KHULBE, K. C. & SRIVASTAVA, S. P., Agra Univ. j.Res. (Sci.), 9 (1960), 177; 14 (1965), 85.4. VOGEL, ARTHUR 1., Textbook of practical organic chemistry(ELBS & Longmans, London), 1957, 1061.5. DAS, K. G. & JAMES, E. P., Organic mass spectrometry(Oxford & IBH Publishers, ew Delhi), 1976, 100.6. FRIEDEL, R. A., SHULTZ, J. L. & SHARKEY, A. G.,Analyt. Chem., 28 (1956), 926.7. SRIVASTAVA, S. P. & GHOSH, S., Proc. natn, Acad. Sci.(India), 22A (1953), 91; 23A (1954), 44.8. BAWN, C. E. H. & MARGERISON, D., Trans. FaradaySoc., 51 (1955), 925.9. BHAKUNI, R. S. & SRIVASTAVA, S. P., Z. phys. Chem.,210 (1959), 246.10. KHULBE, C. P. & SRIVASTAVA, S. P., Agra Univ. j. Res.(Sci.), 15 (1966), 27.11. KHAN, M. M. & SRIVASTAVA, S. P., j. Indian chem. Soc.,46 (1969), 574.12. SRIVASTAVA, S. P. & SINGHAL, S. K., j. Indian chem.Soc., 46 (1969), 705.13. SRIVASTAVA, S. P., SINGH, HAMBIR & KUMAR, ANIL,j. Indian chem. s».. 52 (1975), 404.14. McMILLAN, J. A. & SMALLER, B., j. chem. Phys., 35(1961), 1698.15. CHAWLA, OM P. & RICHARD, W. FESSENDEN, j. phys.Chern., 79 (1975), 2693.Kinetics & Mechanism of Ag+-catalysedOxidation of Dicarboxylic Acids by PotassiumPeroxydisulphateP. S. RADHAKRISHNAMURT! & B. R. K. SWAMYDepartment of Chemistry, Berhampur UniversityBerhampur 760007Received 25 March 1977; accepted 29 July 1977Kinetics of oxidation of saturated dicarboxylic acidsby potassium peroxydisulphate catalysed by Ag+ isreported under varying acidities, [substrate] and [Ag+].The results indicate that these oxidations are firstorder in [oxidant] and [Ag"] but show zero orderdependence on the [SUbstrate]. Catalytic influence ofCu'+ and Hg2+in H2S04, HC}O. and HC}media havealso been investigated. A mechanism and rate lawconsistent with the results obtained is postulated.THE kinetics of peroxydisulphate oxidations, bothAg+ catalysedv+ and uncatalysed", of a largenumber of organic substrates including dicarboxylicNOTESacids have been reported. We have recently reportedthe oxidation of saturated dicarboxylic acids byCe4+ catalysed by Ag+ (ref. 8). In continuation ofthis work, the kinetics of Agt -catalysed oxidationof succinic, adipic, pimelic, suberic ar.d sebacic acidsby peroxydisulphate under varying conditions arereported in this note.Standard solution of recrystallized potassium per-oxydisulphate was always prepared fresh and stan-dardized by iodometric method. Standard solutionsof recrystallized dicarboxylic acids (AR) were pre-pared by direct weighing. The reaction was carriedout by running a calculated volume of K2S20Ssolution in to the thermostated (± 0.1°) reactionvessel containing the substrate and estimatii g theunreacted K2S20S by the iodometric method. Thedecomposition of peroxydisulphate was followedseparately and necessary corrections have been madein computing the rate constants. The rate constantshave been computed by the usual tangential method.The reactions are first order in peroxydisulphateas seen by the linear plots of log (a-x) versus time,The reactions are independent of the nature of thesubstrate and [substrate], indicating zero orderdependence on the substrate (Tables 1 and 2).Though there appears to be very slight deviationin rate constants with increasing [substrate] theorder with respect to substrate comes to be 0·08which can be taken as zero order.For a threefold increase in the [acid] there isa slight decrease in the rate (Table 1) which maybe due to the increase in ionic strength. Suchslight decrease was observed earlier by Gupta andSengar? in the reaction between persulphate andsilver ion. Surprisingly the reactions are acceleratedat pH 4·5 (Table 2). Further in the absence ofAg", the reactions in H2S04 medium are verysluggish, whereas the uncatalysed reactions in thepresence of HCI proceed fairly well and first orderrate constants are reported in Table 3. Even inHCl medium and in the absence of catalyst thereactions are zero order with respect to the [sub-strate].An increase in [Ag"] increases the rate and aplot of log k vs log [Ag+] is linear with unit slopeestablishing the order as unity with respect to[Ag"]. It was thought worth while to study thecatalytic effect of Cu2+ and Hg2+. Surprisinglythere was no reaction in presence of Cu2+ andHg2+ in H2S04 or HCl04 media. But in HCImedium though there is no positive catalytic effectdue to Hg2+ and Cu2+ the reactions are facile ascompared to H2S04 and HCl04 media. Further,there is no dramatic catalysis in presence of Ag" inHCI04 medium as in the Ce4+ oxidations of saturateddicarboxylic acids in HCI04 medium reported earlier.Mechanism - Present evidences in literature pointto the fact that in aqueous acid solutions it ismore likely that Ag2+ ions exist rather than Ag3+ions. Allen and his associates have shown thatthe equilibrium 2Ag2+ .=: Ag++Ag3+ lies far to theleft. The fraction of Ag3+ (likely to exist as AgO+in solution) has been estimated to be 0·03% ofAg2+. Further, Yost has shown that Ag3+ may beformed by a direct interaction of Ag+ and S20~-followed by a rapid reaction of Ag3+ with water1115

Kinetics & Mechanism of Ag+-catalysed Oxidation of 1,3-Propanediol by Peroxydisulphate Ion - A Reinvestigation

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Kinetics & Mechanism of Ag+-catalysed Oxidation of 1,3-Propanediol by Peroxydisulphate Ion - A Reinvestigation

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