Oxidation tetrabutylammonium tribromide

Butylcalix[n]arenes can be converted into monospirodienones 43 by mild oxidation (tetrabutylammonium tribromide) under alkaline conditions.89 The structure of two examples 43a,b has been established by single-crystal X-ray analysis.90 Their chirality is mainly due to the asymmetrically substituted spiro carbon atom, however, compound 43a has also some similarity with calix[4]arenes having three different phenolic units in the order AABC (see below). Under neutral conditions the oxidation of r-butylcalix[4]arene leads to the formation of 44 which has been also confirmed by single-crystal X-ray analysis.91... 

Oxidation of thio acids by tetrabutylammonium tribromide showed Michaelis-Menten-type kinetics with respect to the thio acid. The effect of solvent composition was analysed using the Grunwald-Winstein equation. A mechanism involving the formation of an intermediate complex in the pre-equilibrium and its subsequent decomposition in a slow step is proposed.129... 

HS(CH2) SH, neat, Me2S-Br2, 65-98% yield. HBr, probably generated in situ by oxidation of the dithiol, is probably the true catalyst in this reaction. Aldehydes react selectively in the presence of ketones. This catalyst has also been used to prepare 1,3-dioxolanes. Tetrabutylammonium tribromide similarly serves as a catalyst. ... 

The tetrabutylammonium tribromide (TBATB) oxidation of p-substituted acetophenones to a-bromoacetophenone in ACOH-H2O (50% vol/vol) was first order in TBATB and the rate increased with the substrate concentration. The reactive TBATB species was Br3 ion, and its electrophilic attack on acetophenone gave a transition state which decomposed in the rate-determining step. °... 

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