OXIDATION OF HYDROCARBONS .9. OXIDATION OF ALKYNES BY POTASSIUM-PERMANGANATE

A study of the oxidation of nonterminal alkynes by potassium permanganate has revealed that the reaction can be directed along any one of three different pathways : (i) In aqueous solutions, cleavage of the carbon-carbon triple bond, with formation of carboxylic acids, is the main reaction, (ii) In anhydrous methylene chloride solutions, the phase transfer assisted reaction leads to formation of α-diketones in good yields, (iii) In methylene chloride solutions in contact with aqueous permanganate, the phase transfer assisted reaction gives α-diketones plus cleavage products. In the last case, the cleavage reaction results in the loss of one carbon atom, indicating that it proceeds by way of an enol (RCOC(OH)̿CHRʹ) to an α-ketocarboxylic acid which subsequently undergoes an oxidative decarboxylation. The assumption that a-diketones are intermediates in the cleavage reactions was substantiated by a study of the oxidation of 8, 9-hexadecanedione and 7, 8-tetradecanedione under a variety of conditions. © 1979, American Chemical Society. All rights reserved.