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26.1.1.2.2.1 Variation 1: With Chromic Acid in Aqueous Solution

DOI: 10.1055/sos-SD-026-00003

von Angerer, S.Science of Synthesis, (20052644.

Chromium(VI) compounds such as chromic acid, chromates, and halochromates have a dominant role as reagents for the oxidation of secondary alcohols to ketones. It is assumed that they form intermediate esters with chromic acid, which is reduced stepwise to chromium(III). Steric effects can inhibit ester formation and decrease the yields of the ketones. The rate-determining step is the abstraction of the hydrogen atom from the hydroxylated carbon atom. Good accessibility to this hydrogen facilitates the oxidation. This effect can be exploited for the selective oxidation of a single secondary hydroxy group in polyhydroxylated cyclic compounds due to different steric orientations of the tertiary ­hydrogen atoms.[‌48‌,‌49‌] The oxidation of secondary alcohols with chromium(VI) compounds is faster and gives higher yields than that of primary alcohols. Cleavage of CC bonds can occur in a competing reaction if stable carbenium ions are formed as intermediates.[‌50‌] Other oxidizable functions such as sulfanyl and amino groups can interfere with alcohol oxidation.

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