Abstmd Kinetics and mechanism of oxidation of so= o&o-, pnra-and mebsubstihtted transcimumic rids by pyridinium cldomch~ @CC) in pmsmca of oxalic acid has beea tied. The main product of oxidation is corrsspoldino bmualdebyde and glyoxalic tid. The astim is fmt onk with twpect to [PCC] md [oxalic acid]. The oxidatioo follows fractional order in [sum] and [H+]. The thermodymmic pmmetm am alao dwmined. Both the electron-rslersing lad ekctnm-wi~albetitwn~, fhcilitata tlwNteofoxid8tion. t2mmhthwitll Hamma sxmtu~tsyieldaa'V'sbrpsdcuwe. Asuitablezmchismb~. Intbe.hausitionstatethe formation of cub&on, for electron-witbdming and cubonium ion for electron relcashg substitucrrts is discussed. Kinetics and mechanism of oxidation of several organic substrates by PCC'" are well documented. Only few studies& are available for oxidation of substrates by Cr(VI) in presence of oxalic acid. But there is no systematic kinetic reports on the oxidation of trans-cinnamic acid by Cr(V1) complexes.
-Chromium(W) functions both a one and two-electron oxidant depending on the substrate and experimental conditions. The intermedii valency states Cr(V) and Cr(IV) are involved in these process.
Hasan and Rocek7 reported the concept of a "three-electron transfer" process in the cooxidation study of isopropyl alcohol and oxalic acid by chromic acid, when (30 get directly reduced to Cr(III).
Interestingly both substrates undergo oxidation and the process was termed co-oxidation. This prompted us to undertake the title for investigation. RXPERIMENTAL Reagents. Pyridinium chlorochromate was prepamd by the metha of Corey and Suggs*. 'IYans-cinnamic acid and most of the substituted cinnamic acids were obtained commemially (AR, AldrichEluka) and their purity was checked by IR and TLC. Some of the substituted trans-cinnamic acids (p-fluoro, m-fluoro-, pbromo-, o-methyl, m-chloro-and o-bromo) wem prepared by litaatu~ method9. Doubly distilled water was used throughout the course of investigation. AU other chemicals used were of analytical grade.