GB829251A - Improvements relating to the manufacture of nitrogen-containing derivatives of benzene carboxylic acids - Google Patents

Abstract

Benzene carboxylic acids, in which the carboxylic groups are not attached to adjacent carbon atoms, or their methyl or ethyl esters, are caused to react with ammonia, or a substance yielding ammonia, by heating under elevated pressure, preferably in the absence of dehydration catalysts, and the crude amide formed, which may, if desired, be first separated from the reaction mixture, is subjected to a heat treatment at 350-500 DEG C. and the products, which include nitriles or nitrile-amides, are isolated. If desired, the two reactions may take place successively in the same reaction vessel and under the same conditions of temperature and pressure. The starting substance may be benzoic acid, iso- or tere-phthalic acid, or an ester thereof. Ammonia may be added in liquid form at the start of the treatment, and the reaction with ammonia may be effected at 150-350 DEG C. in an autoclave. Instead of ammonia, urea may be used as substance yielding ammonia. When terephthalic acid is treated, the product of the first stage comprises diamide, monoamide, ammonium salts, and uncoverted acid. The crude product may be heated at 350-500 DEG C. under atmospheric pressure. Preferably ammonia or nitrogen is passed through the reaction vessel. The reaction products may be continuously distilled from the reaction vessel. The distillate comprises the dinitrile of terephthalic acid, p-cyanobenzoic acid amide, p-cyano-benzoic acid, amides and ammonium salts of terephthalic acid. Isolation of the products may be effected by fractional solution or crystallization using selective solvents, e.g. acid constituents may be extracted with bases; iso- and tere-phthalic dinitriles and m- and p-cyanobenzoic acids may be extracted by solution in hot acetone, methylethyl ketone, or ethanol. Separation of the reaction products may also be effected by fractional distillation or sublimation. In an example, terephthalic acid is heated at 250 DEG C. under 160 atm. pressure with ammonia. After removal of excess ammonia, the residue is suspended in aqueous ammonia and filtered to obtain the crude diamide. The dried diamide is heated to 400-420 DEG C. and is subjected to sublimation and distillation. The solid obtained in the collecting vessel is sludged with aqueous ammonia, filtered, washed, and dried. The product is treated with boiling acetonitrile and on evaporation of the solution a mixture of p-cyanobenzoic acid amide and terephthalic dinitrile is obtained. These two components are separated by fractional distillation from methylethyl ketone. By acidification of the ammonia filtrate and extraction of the precipitate with ether, p-cyanobenzoic acid is obtained. In another example, terephthalic acid and liquid ammonia are introduced continuously into a pressure tube heated to 350 DEG to 500 DEG C. under 160 atm., the reaction time being 6 hours, and the products being continuously removed. Further examples describe similar treatment of isophthalic acid and dialkyl terephthalates.