ABSTRACT
Abstract One of the most efficient methods for oxidation of primary alcohols to either aldehydes or carboxylic acids is the one, commonly known as the Anelli oxidation. This reaction is carried out in a two-phase (CH2Cl2/aq.buffer) system utilizing TEMPO/NaBr as a catalyst and NaOCl as the terminal oxidant The new system described here is an extension of the Anelli oxidation, but surprisingly, does not require the use of any organic solvents and replaces the KBr co-catalyst with the more benign, Na2BB4O7 (Borax). The use of the new cocatalyst reduces the volume of the buffer solution and eliminates completely the need of a reaction solvent. The new system was successfully applied in the industrial synthesis of the 3,3Dimethylbutanal, which is a key intermediate in the preparation of the new artificial sweetener Neotame. Introduction The selective oxidation of alcohols to the corresponding carbonyl compounds is one of the more important transformations in synthetic organic chemistry. A large number of oxidants have been reported in the literature but most of them are based on the use of transition metal oxides such as those of chromium and manganese (1,2). Since most of the oxidants and the products of their transformation are toxic species, their use creates serious problems concerning their handling and disposal. For these reasons, the search for an efficient, easily accessible catalysts and ”clean” oxidants such as hydrogen peroxide or molecular oxygen for industrial applications is still a challenge (3-6). A particularly convenient procedure for the oxidation of primary and secondary alcohols is reported by Anelli (4). The oxidation has been carried out in a two-phase system (CH2Cl2-water) utilizing 2,2,6,6tetramethylpiperidinyl-1-oxyl (TEMPO) as a catalyst, NaBr as a cocatalyst and cheap and readily accessible NaOCl as an oxidant. The aqueous phase is buffered at pH 8.5-9.5 using NaHCO3 (Scheme 1). In another development of the same procedure, the ethyl acetate-toluene mixture has been used to replace the CH2Cl2 (7)
Despite the extensive work reported in the area of the selective oxidation of primary alcohols, there is still a continuous need for developing efficient and
economical oxidation methods which do not require bromine based catalysts, can be carried out with environmentally friendly oxidants and avoid the use of organic solvents.
