IJCRR - Vol 04 Issue 05, March, 2012
Date of Publication: 30-Nov--0001
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KINETICS AND MECHANISM OF OXIDATION OF BENZOPHENONE OXIME BY BISPYRIDINE SILVER (I)
Author: J. Dharmaraja, S.Vadivel, A.Kandasamy
Category: General Sciences
Abstract:The oxidation of Benzophenoneoxime by Bispyridine silver (I) dichromate (BPSDC) has been
studied in 50% (v/v) aqueous ethanol medium at 303K. The reactions show unit order dependence with respect to [Benzophenoneoxime].The reaction is acid catalyzed, the effect of
concentration of Mangnoussulphate, sodium perchlorate and dielectric constant on the reaction
rates was studied, Thermodynamic parameters were calculated from the Eyring?s plot.
Mechanism consistent with the observed kinetic results has been proposed and the related rate
Keywords: Kinetics, mechanism, Benzophenoneoxime, Bispyridinesilver (I) dichromate.
AIMS AND BACKGROUND The Kinetics and mechanism of oxidation of Benzophenoneoxime was carried out in EtOH-H2O medium at 30oC and the rates were calculated. Further studies in this direction may be useful to understand the mechanistic aspects of the reaction. Regeneration of carbonyl compounds from their derivatives under mild conditions is an important process in synthetic organic chemistry. Several oxidative methods are available for deoximation1 , 2, 3 . Considerable research has been done in the last years on the mechanism of oxidation by the use of modified Cr (VI) regents as oxidants4-16, pyridiniumchlorochromate has been reported as an useful reagent for the formation of carbonyl compounds from the corresponding alcohols17. Bispyridine silver (I) dichromate is a recently developed Cr(VI) oxidant and has been found quite useful as an oxidant in organic synthesis18.There seems to be no report on the kinetics and mechanism of oxidation of Benzophenoneoxime by BPSDC. Hence this paper reports on the kinetics and mechanism of oxidation of Benzophenoneoxime by Bispyrinine silver (I) dichromate.
EXPERIMENTAL Benzophenoneoxime were prepared by the reported literature procedure19.Bispyridine silver (I) dichromate was prepared by the standard procedure18.Ethanol was purified as described in the litrature19.perchloric acid, manganousshulphate, acrylonitrile and sodium perchlorate were of AnalaR grade and used without further purification. All the kinetic measurements were carried out in a glass stoppered iodine flask protected from light and thermostated to within ±0.010C, Pseudo first order conditions were maintained throughout the study. Reactions were carried out in aqueous ethanol (50-50 (v/v)) medium at 303K unless otherwise stated. The course of the reaction was followed by standard iodometric procedure. The reproducibility of rate constant was checked by duplicate measurement and were found to be within ±4% error. Product analysis; Benzophenone were found to be the products. The products have been confirmed by their melting point and IR spectra.
RESULT AND DISCUSSIONS
Oxidation of Benzophenoneoxime by BPSDC.
The kinetic results for the oxidation of Benzophenoneoxime by BPSDC along with the experimental conditions are given in tables 1 and 2. The order of the reaction was found to be first with repect to the [BPSDC] as evidenced by the plot of log[BPSDC] versus time( r= 0.999). The rate constant increased with increase in the [Benzophenoneoxime]. A plot of log kobs versus log [benzophenoneoxime] gave a straight line with a slope of 1.16 (r=0.990) indicating a first order dependence of the reaction with respect to [Benzophenoneoxime].A fractional order dependence of the reaction with respect to [HClO4] has been observed .The dependence of logkobsversus log [H+ ] is a straight line with a slope of 0.53(r= 0.996) indicating fractional order. The rate of the reaction has been found to increase with the decrease in the dielectric constant of the medium. This might probably be due to the reaction between two molecules forming a polar product20.The addition of sodium perchlorate increases the rate of the reaction suggesting that the reaction may be between an ion and a dipole type21 . Added acrylonitrile has no effect on the reaction rate, i.e., the reaction did not induce polymerization of acrylonitrile indicating the absence of the radical pathway. The added Mn2+ ion enhances the rate confirming the formation of Cr (IV) in slow step. The reaction has been conducted at five different temperature and the activation parameters ?H*and ?S*were calculated; ?H* =50.224 KJ mol-1 , ?S* =- 113.3J k-1mol-1 .
CONCLUSION Oxidative regeneration of carbonyl compounds from benzophenoneoxime by BPSDC follows different mechanistic pathway. The large negative entropies of activation support the formation of a rigid cyclic intermediate complex. The oxidation of benzophenoneoxime by BPSDC in the presence of perchloric acid in aqueous ethanol medium leads to the formation of benzophenone and a biologically active compound of hypo nitrous acid as end product. R
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