CATALYSIS BY PHOSPHORUS AND SILICON COMPOUNDS IN THE SYNTHESIS OF OXYNAPHTOIC ACID ANILIDES

Catalysis of the acylation of aniline with 3-­hydroxy-2-naphthoic, 1-hydroxy-2-naphthoic, 2-hydroxy-1-naphthoic and 1-hydroxy-4-naphthoic acids by phosphorus P(III) and silicon Si(IV) compounds leads to the formation anilides of the corresponding hydroxy­naphthoic acids under mild conditions (ortho-xylene, 146.5–147 °C) in almost quantitative yield. Among P(III) phosphorus trichloride and tribromide; phosphorous, 1-hydroxyethyli­de­ne-di­phos­phonic, pyrophosphorous and me­ta­phos­phorous acids; trimethyl-, dimethyl- and diethylphosphites; phosph(III)azan proved to be active catalysts; among Si(IV) – tri­chloro-(methyl)silane, dichloro(ethyl)silane, dichloro­(dimethyl)silane, tetrachlorosilane and tet­ra­ethoxysilane are active. The catalysts were used in an amount of only 2% mole. from hydroxynaphthoic acid, which is 15–35 times less than the conventional use of the same compounds as condensing agents in the synthesis of carboxylic acid arylamides. P(V) compounds, thionyl chloride, and sulfuryl chloride practically do not exhibit catalytic activity. The presence of catalytic activity only in P(III) compounds, capable of forming phosphorous acid in the reaction mass, does not contradict to the previously proposed mechanism of P = O-nucleophilic catalysis for the reaction of substituted benzoic acids with aniline catalyzed by PCl3. In general, the use of P(III) and Si(IV) compounds as catalysts in the preparation of hydroxybenzoic and hydroxynaphthoic acid anilides successfully complements the range of catalysts, based on Ti(IV) compounds, previously used in the formation of substituted benzoic and naphthoic acid anilides (containing no aromatically bonded hydroxy group), allowing to create a universal method for their synthesis.