Preparation of mono- and diacetyl 4,4′-dimethylbiphenyl and their corresponding carboxylic acids: Reactivity, selectivity and isomer distribution studies via Lewis acid catalyzed Friedel-Crafts acetylation/oxidation

Abstract

Shape selective acetylation of 4,4′-dimethylbiphenyl using anhydrous aluminum chloride as catalyst is an effective route for the production of mono- and di-acetyl-4,4′-dimethylbiphenyl. Preparations, characterization and a catalytic study of the Friedel-Crafts acetylation of 4,4′-dimethylbiphenyl, involving use of the Perrier addition procedure are carried out in a range of solvents and under a variety of experimental conditions. The obtained ketones are isolated and identified by various physico-chemical techniques. Mono acetylation of 4,4′-dimethylbiphenyl afforded a mixture of two isomeric acetyl dimethylbiphenyls. In chloroalkane or carbon disulfide solvent, the yields of isomers were in the order: 2 -> 3-; in nitromethane 3-isomer predominated. On the other hand diacetylation of the hydrocarbon gave only the 2,3′-diacetyl isomer. The mono- and di-ketones are converted to the corresponding carboxylic acids. 2-Acetyl-4,4′-dimethylbiphenyl was prepared by indirect multi-step synthetic routes. 3-D molecular modelling supports the positional assignment of the acetyl group with the results obtained from the electronic spectra. © 2007 Elsevier B.V. All rights reserved.