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Original Article

ECB. 2013; 2(10): 816-824


STRUCTURE-REACTIVITY CORRELATION IN THE OXIDATION OF SUBSTITUTED BENZYL ALCOHOLS BY IMIDAZOLIUM FLUOROCHROMATE

Poonam, D. Sharma, P. Panchariya, P. Purohit, Pradeep K. Sharma.


Abstract

Oxidation of benzyl alcohol and some ortho-, meta- and para-monosubstituted ones by imidazolium fluorochromate (IFC) in dimethyl
sulphoxide (DMSO) leads to the formation of corresponding banzaldehydes. The reaction is of first order with respect to IFC. A Michaelis
– Menten type of kinetics were observed with respect to the alcohols. The reaction is promoted by hydrogen ions; the hydrogen-ion
dependence has the form kobs= a + b [H+
]. Oxidation of ,-dideuteriobenzyl alcohol (PhCD2OH) has exhibited a substantial primary
kinetic isotope effect (kH/kD = 5.86 at 298 K). The reaction has been studied in nineteen organic solvents and the effect of solvent analysed
using Taft's and Swain's multi-parametric equations. The rates of oxidation of para- and meta-substituted benzyl alcohols have been
correlated in terms of Charton’s triparametric LDR equation whereas the oxidation of ortho-substituted benzyl alcohols with
tetraperametric LDRS equation. The oxidation of para-substituted benzyl alcohols is more susceptible to the delocalization effect than that
of ortho- and meta- substituted compounds, which display a greater dependence on the field effect. The positive value of  suggests the
presence of an electron-deficient reaction centre in the rate-determining step. The reaction is subjected to steric acceleration by the orthosubstituents. A suitable mechanism has been proposed.

Key words: Correlation analysis; halochromates; imidazolium fluorochromate; kinetics; mechanism; oxidation






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