Linear free energy relationships in the kinetic study of oxidation of phenols by quinolinium dichromate

✍ Scribed by K. Aruna; P. Manikyamba

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 146 KB
• Volume: 29
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/(sici)1097-4601(1997)29:6<437::aid-kin5>3.0.co;2-v

✦ Synopsis

The oxidation of ortho-, meta-, and para-substituted phenols by Quinolinium Dichromate (QDC) to the corresponding Quinones in aqueous acetic acid medium is first-order with respect to [QDC] and [phenol]. There is no effect of added Quinoline on rate. The reaction is acid catalyzed. A medium of low dielectric constant favors the oxidation process, and the rate of the oxidation process changes with change in the ionic strength of the medium. Electron releasing groups on the benzene ring enhance the rate of oxidation, while electron withdrawing groups retard, compared to the unsubstituted phenol. A correlation exists between log k 2 and , the Hammett's substituent constant, with a slope of Ϫ 3.79 at 303 K. Analysis of the rate data using I and R values indicate that both inductive and resonance effects of the substituents equally influence the rate of the reaction. The free energy of activation, ⌬G ϶ , is linearly correlated with . A probable mechanism is proposed.