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A kinetic approach to the oxidation of some primary perfumery alcohols using ammonium metavanadate in acidic medium
Author : Harichandra A. Parbat* and D. V. Prabhu
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ABSTRACT
Literature survey shows several reports of the oxidation of a variety of alcohols to the corresponding carbonyl compounds. But there are relatively few reports of the kinetic and thermodynamic aspects of oxidation of alcohols. This paper reports the kinetics of oxidation of primary perfumery alcohols, Nerol, Citronellol and Geraniol by ammonium metavanadate in acidic medium under first order kinetic conditions with respect to the inorganic oxidant. The oxidation was monitored by titrimetric estimation of the unreacted oxidant at regular intervals in the temperature range 303–318 K. K2SO4 was used to determine the effect of ionic strength on the oxidation rates of alcohols. The thermodynamic activation parameters have been interpreted in terms of the molecular dynamics and reaction mechanism suggested for the oxidation process. Literature study indicates extensive use of costly catalysts like Os(VIII), Cr(VI) and Ru in different oxidation states. In the present study, relatively less expensive transition metal ions of the first series, Mn(II), Co(II) and Ni(II) have been effectively used to catalyze the oxidation reaction. The sequence of oxidation rates of alcohols, Nerol > Citronellol > Geraniol has been explained on the basis of their steric, structural and isomeric features. The catalytic efficiency of metal ions follows the sequence, Mn(II) > Co(II) > Ni(II) for all the primary alcohols studied.
KEYWORD
Primary perfumery alcohols, ammonium metavanadate, oxidation, kinetics, thermodynamic activation parameters, transition metal ions,