Abstract
Mixed anhydrides of carboxylic acids and diesters of ortho-phosphoric acid are described in the literature as acylating agents. Theoretically these compounds could also be phosphorylating agents. The mechanisms of nucleophilic reactions of anhydrides of ortho-phosphoric acid - the pyrophosphates - and carboxylic-carboxylic anhydrides, differ considerably. In order to obtain a clearer understanding of the reactions of phosphoric-carboxylic anhydrides, relevant aspects of the reported chemistry of carboxylic-carboxylic anhydrides and pyrophosphates have been compared. Nine phosphoric-carboxylic anhydrides have been prepared, namely those from diethyl phosphoric acid and acetic, trifluoracetic, tri-methylacetic, triphenylacetic, benzoic, 2,3,6-trichlorobenzoic, 2,3,5,6-tetrachlorobenzoic, 2,3,4,5,6-pentachlorobenzoic acids, and the hypothetical ethylcarbonic acid. With the exception of the acetyl and benzoyl compounds these anhydrides have not been described before. They were prepared by interacting a salt and an acid chloride, and it has been shown that it is critical which moiety is present as the salt or acid chloride. In general the salt should be derived from the stronger acid. However when the carbonyl group is subject to considerable steric hindrance, e. g. triphenylacetic acid, the salt of the latter must be used. It has been shown that acetyl and trimethylacetyl diethyl phosphates exclusively acylate aniline, but as the steric hindrance at the carbonyl group increases, phosphorylation becomes more important until it is the exclusive reaction with the tetra- and penta-chloro anhydrides above. Contrary to suggestions in the literature, tri-fluoracetyl diethyl phosphate was shown to acylate aniline. A number of hitherto unreported compounds required as intermediates have been prepared, viz: 2,3,6-trichlorobenzyl acetate, 2,3,6-trichlorobenzanilide, 2,3,6-trichlorobenzoyl chloride, 2,3,5,6-tetrachlorobenzyl alcohol and the corresponding bromide and acetate, and 2,3,4,5,6-pentachlorobenzyl bromide. An improved method has been developed for the preparation of the polychlorobenzoic acids from the corresponding benzyl alcohols by potassium permanganate oxidation in pyridine.