Oxidation of tertiary amines by chromium(VI) oxide diperoxide

Abstract

The oxidation of tertiary amines Et₃N and p-McOC₆H₄NMe₂(DMPA) by (L)CrO(O₂)₂(1″) and by (OPN₃Me₆)MeO(O₂)₂(1′) in CHCl, has been investigated. Although the amines are converted into the corresponding N-oxides in good (70–95%) yields in 2:1 stoicheiometry with respect to the peroxide, the oxidation of DMPA by (1″) also produces p-MeOC₆H₄NHMe. The rate law observed and the inhibitory effect of added OPN₃Me₆(hexamethylphosphoric triamide) suggest a mechanism involving preliminary co-ordination of the amine to the metal; this is also supported by ³¹P n.m.r. experiments. Comparison of the oxidation rates of the amines with those of organic sulphides, e.s.r. experiments, and the observed appreciable competitive dealkylation of DMPA, all point to a mechanism having some single-electron-transfer (SET) character.