Copper-catalysed diacetoxylation of butadiene. Spectroscopic and physico-chemical investigations of the catalyst

The copper(II) acetate-lithium bromide catalysed diacetoxylation of butadiene has been investigated in the acetic acid-acetic anhydride system under oxygen pressure. The distribution of positional isomers (1,4/3,4) appeared to be little dependent on the reaction conditions, the 3,4-isomer (Scheme I, compound (4)) being the kinetically controlled one. A relatively slow interconversion of the isomers was observed under the reaction conditions. The catalytic system was investigated by 7Li NMR and UV spectroscopy, and the kinetics of oxygen absorption by the catalyst were determined; the roles of acetic anhydride and water at the catalyst level were thus established. The investigation of the behaviour of potential intermediates of the diacetoxylation reaction has been considered as another tentative approach to the understanding of the reaction mechanism. © 1987.