Post Graduate and Research Department of Chemistry, St. Joseph's College (Autf'nomous), Tiruchirappalli-620 002, Tamilnadu, India E-mail : sjcmathi@yahoo.co.uk Manuscript received 13 September 2011, accepted 21 February 2012 The oxidation of meta- and para-substituted aromatic acetals by N-bromosuccinimide (NBS) to the corresponding esters and alkyl bromide, is first-order in [NBS] and [acetal]. The effect of substituents in,the aromatic ring of some aromatic acetals [X-C6H4CH(OBu-n)2] {X = H,

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... -OMe, p-Me, p-Cl, p-NO2, m-OMe, m-CI, m-NO2} on the kinetics of above oxidation has been studied in acetonitrile medium at various temperatures by iodometric method. The rate of the reaction increases with the increase in the dielectric constant of the medium. The stoichiometry of the reaction is found to be 1 : 1. A primary kinetic isotopic effect kH/kD of 1.8 is observed, which indicates the C-H bond cleavage of the aldehydic carbon in the rate determining step. The Hammett reaction constant (σ) for the reaction is found to be -1.38 and -1.42 at 313 K and 323 K respectively. The Exner plot is found to be linear with the isokinetic temperature 132 K. The kinetic and activation parameters Ea , A, Δ H≠, ΔG≠, ΔS≠ have been calculated. A mechanism involving simultaneous loss of H+ from the aldehydic carbon and expulsion of bromide ion with the formation of carbonium ion intermediate is proposed.