THE KINETICS OF THE OXIDATION OF ALCOHOLS BY BROMINE IN THE PRESENCE OF SILVER SALTS IN NON-AQUEOUS SOLUTION

The kinetics of the reactions of alcohols with bromine and silver salts in carbon tetrachloride at 25(DEGREES)C have been studied. Alcohols studied included cyclohexanol, 2-hexanol, 3-hexanol, 3-methyl-3-hexanol, 2-methyl-2-hexanol, 2-pentanol, 3-pentanol, and 2-octanol. Three silver salts (silver carbonate, silver acetate, and silver trifluoroacetate) have been investigated, with sodium carbonate used to neutralize the acid formed in the reaction. Reaction mixtures were analyzed by iodometric and spectrophotometric methods. In the case of the reactions employing silver carbonate and silver trifluoroacetate, spectrophotometric analysis indicated the presence of free bromine initially which decreased with time and the build-up of a hypobromite intermediate. When silver acetate was employed spectrophotometric analysis indicated only the presence of a hypobromite initially and no free bromine. First order rate constants for the decomposition of the hypobromites produced by the action of bromine and the silver salts have been determined in all cases from titrimetric kinetic data and, in some cases, also from spectrophotometric kinetic data. Differences in rates have been explained in terms of the stabilities of the hypobromite intermediates and available reaction pathways. Experimental evidence has also been found for an intermediate that forms prior to the hypobromite in the reactions employing silver acetate and silver trifluoroacetate. The intermediate is an acyl hypobromite, acetyl and trifluoroacetyl hypobromite, respectively. The intermediate can be explained by analogy to the Hunsddiecker reaction (see R. G. Johnson and R. K. Ingham, Chem. Rev., 56, 219 {1956}). The acyl hypobromite undergoes a facile exchange with the alcohol to convert it to its hypobromite. Acetyl hypobromite forms immediately, while trifluoroacetyl hypobromite forms more slowly resulting in an induction period. The kinetics of the oxidation of cyclohexanol, 2-hexanol, 3-hexanol, 2-pentanol, and 3-pentanol by bromine in the presence of sodium carbonate in carbon tetrachloride at 25(DEGREES)C have also been investigated. These reactions were found to be first order with respect to bromine. First order rate constants have been determined from titrimetric kinetic data.