Studies in chromic acid oxidation of napthalene and its derivatives

Abstract

The thesis entitled “Studies in Chromic Acid Oxidation of Naphthalene and Its Derivatives” is divided into two chapters. The first chapter briefly reviews the mechanisms of chromic acid oxidation of various functional groups such as alcohols, aldehydes, and the –OH bonds of aromatic side chains and aromatic rings. The literature coverage is up to December 1974. The review is not exhaustive, but every attempt has been made to include the main features of investigations by various groups of workers which have led to the present level of understanding. The second chapter describes investigations carried out by the candidate on the mechanism of chromic acid oxidation of naphthalene and substituted naphthalenes to naphthoquinones. A second?order dependence on Cr(VI) (HCrO??) and a first?order dependence on both naphthalene and [H?], complicated by kinetic consequences of substantial complex formation between the reactants, were observed: Complex ? Products The role of water in the medium and substituent effects have been investigated. The kinetics of oxidation of the following naphthalenes were studied, and data from the first four, along with naphthalene, fitted into a Hammett plot with ? = –3.0:

2?Bromonaphthalene 2?tert?Butylnaphthalene 2,6?Di?tert?butylnaphthalene 1?Cyanonaphthalene 2,6?Dichloronaphthalene 2,6?Dibromonaphthalene

Use of octadeuterated naphthalene and 1,4?dideuterated naphthalenes provided evidence for the involvement of an arene epoxide as an intermediate. The influence of Mn(II) ions on Cr(VI) oxidation led to an unexpected rate enhancement and also produced additional products, besides naphthoquinone, resulting from reactions of intermediate radical species with excess naphthalene. The structures of these products have been established. Using UV spectroscopy, information was obtained on the intermediacy of Mn(III) species and its role in the overall reaction sequence. The influence of radical scavengers on reaction rates has also been examined. Based on all these observations, a scheme for the reaction mechanism for the conversion of naphthalene to naphthoquinone by chromic acid is proposed. The implications of this mechanism and the possibilities of its general applicability to other aromatic hydrocarbons are discussed.