Der Mechanismus der Alkoholoxidation durch Chromsäure

Abstract

Recent investigations concerning the oxidation mechanism of secondary alcohols with chromic acid are summarized. The reaction is initiated by the reversible formation of a chromium(VI) mono- or diester intermediate. Breakdown of the intermediate yields a ketone and a chromium(IV) species. Oxidation of a second alcohol molecule with chromium(IV) gives a radical and stable Cr(III). The radical in turn reacts with Cr(VI) to form a carbonyl compound and Cr(V), which can disproportionate to Cr(IV) and Cr(VI) or alternatively attack the alcohol by a mechanism similar to that of Cr(VI). 
The reaction rate of sterically unhindered alcohols correlates with the strain difference between ketones and the respective alcohols, as evaluated by force-fleld calculations. This correlation suggests that the properties of the carbonyl group are in part reflected in the transition state of the oxidation.