CS261191B1 - 2-amino-4-carbamoylbenzoic acid and a process for its preparation - Google Patents

Abstract

The solution relates to 2-amino-4-carbamoylbenzoic acid of formula I and a method of its preparation consisting in that the methyl ester of 2-nitro-4-carbamoylbenzoic acid of formula II is hydrolytically cleaved by the action of an equivalent of sodium or potassium hydroxide in an aqueous medium in the temperature range of 20 to 90 °C, the obtained solution of alkali salts of 2-nitro-4-carbamoylbenzoic acid is acidified and the precipitated 2-nitro-4-carbamoylbenzoic acid is reduced.

Description

The invention relates to 2-amino-4-carbamoylbenzoic acid and to a process for its preparation.

2-Amino-4-carbamoylbenzoic acid is a novel semi-finished product based on amino-terephthalic acid derivatives suitable for the synthesis of organic dyes, especially azo dyes. The esters and amides of aminoterephthalic acid have received considerable attention in recent years. The preparation of valuable organic dyes from the mono and diesters of amino-terephthalic acid, obtained by nitration of dimethyl terephthalate, partial hydrolysis of nitrodimethyl terephthalate and reduction of the nitro group to the amino group, has been described (cf. AO 201 945). Similarly, the reaction of nitrodimethyl terephthalate with ammonia has been described to give a mixture of 2-nitro-4-carbamoylbenzoic acid, 3-nitro-4-carbamoylbenzoic acid and nitroterephthalic acid diamide (U.S. Pat. No. 2,316,459, U.S. Pat. No. 4,399,303). Furthermore, the preparation of valuable azo pigments from 2-amino-4-carbamoylbenzoic acid methyl ester obtained by reduction of 2-nitro-4-carbamoylbenzoic acid methyl ester (NSR Pat. 1 199 905) has been described.

It has now been found that 2-nitro-4-carbamoylbenzoic acid methyl ester can be used to prepare a new dyeing intermediate, 2-amino-4-carbamoylbenzoic acid. A process for the preparation of 2-amino-4-carbamoylbenzoic acid of the formula I

COOH

The NH ₂ (I) conk ₂ according to the invention is characterized in that 2-nitro-4-carbamoylbenzoic acid methyl ester of the formula II

COOCH3

NO ₂

CONH 3 is hydrolytically cleaved by treatment with an equivalent of sodium or potassium hydroxide in an aqueous medium between 20 and 90 ° C, the resulting solution of 2-nitro-4-carbamoylbenzoic acid alkali salts is acidified and the precipitated 2-nitro-4-carbamoylbenzoic acid is reduced. The reduction may be carried out after isolation of 2-nitro-4-carbamoylbenzoic acid or directly in suspension or solution prior to acidification, either by catalytic hydrogenation, or by iron in a neutral medium or with tin (II) salts. The advantage of this process is the uniform course of the two reaction steps, so that the final product is a technically pure isomer-free and other impurity-free substance.

2-Amino-4-carbamoylbenzoic acid is characterized by high thermostability and properties suitable for the synthesis of organic dyes, especially azo dyes. For example, it can be used in known dyes instead of the anthranilic acid, or as a component for the preparation of new dyes, including combinations capable of forming salts or metal complexes such as acetoacetarylides, 2-hydroxy-3-naphtharylides, 1-phenyl-3-methylpyrazole- 5-one and benzimidazolone derivatives.

This preparation method can be illustrated by the following example.

Example 1

To an aqueous suspension of 22.5 g of 2-nitro-4-carbamoylbenzoic acid methyl ester at 75-80 ° C, with good stirring, is gradually added the equivalent of sodium or potassium hydroxide as a solution of c (NaOH or KOH) = 2 mol / l as disappears alkaline to brilliant yellow. The solution obtained is acidified at 40 ° C with an excess of hydrochloric or sulfuric acid c (HCl or SO 2) = 5 and 5, respectively. The 2-nitro-4-carbamoylbenzoic acid (2.5 mol / l) which has precipitated is filtered off, washed with water and dried as necessary. 19.59 g of chromatographically pure 2-nitro-4-carbamoylbenzoic acid are obtained. Purification from water gave a melting point of 246-252 ° C. Analysis for C ₈ H ₉ N ₂ Og (mol.% 210.142) calculated: 45.72% C,

H, 2.88; N, 13.33. Found: C, 45.67; H, 3.10; N, 13.15.

7.8 g of 2-nitro-4-carbamoylbenzoic acid are reduced with a solution of stannous chloride in concentrated hydrochloric acid and the obtained 2-amino-4-carbamoylbenzoic acid hydro-chloride (yield about 70% th.) Is treated with an alkali such as bicarbonate or sodium hydroxide, converts to the corresponding amino acid. 97% yield, based on hydrochloride. The obtained 2-amino-4-carbamoylbenzoic acid of the formula I is characterized by a high melting point of 275 DEG-280 DEG C. (with decomposition) and a blue fluorescence of an aqueous alkaline solution. Sodium nitrite is readily converted to the diazonium salt, coupled with various passive components, to the corresponding azo dye. The composition of the product of formula I was confirmed by mass spectroscopy and elemental analysis. For ΟθΗθΝ ₂ Ο ₃ (m / m 180.158) calculated: 53.33% C, 4.48% N, 15.55%, found: 53.94% C, 4.65 H, 15.30% N.

Example 2

The preparation of 2-nitro-4-carbamoylbenzoic acid was carried out as in Example 1. Then 14 g of iron shavings were etched with boiling 4.5 ml conc. of acetic acid and then an aqueous suspension of 10.5 g of 2-nitro-4-carbamoylbenzoic acid is added under stirring and gentle boiling. The reaction was completed by the addition of an additional 1.5 g of iron and 0.5 ml of acetic acid, the dissolved iron being precipitated with sodium bicarbonate or magnesium oxide with the addition of sodium dithionite. The iron sludge is hot filtered and 2-amino-4-carbamoylbenzoic acid is precipitated from the filtrate by acidification with conc. acetic acid. Obtained as a yellow sand-like substance, m.p. 275 ° C.

Claims (4)

of the invention A 2-amino-4-carbamoylbenzoic acid of the formula I COOH NH ₂ (i) CONH ₂ 2. A process for preparing 2-amino-4-karbamoylbenzoové acid of formula I according to claim 1, characterized in that the methyl ester of 2-nitro-4-karbamoylbenzoové acid of formula II CONH ₂ equivalents hydrolytically cleaved by the action of sodium or potassium hydroxide in aqueous medium in the temperature range of 20 to 90 ° C, the obtained 2-nitro-4-carbamoylbenzoic acid alkali salt solution is acidified and the precipitated 2-nitro-4-carbamoylbenzoic acid is reduced. 3. A process according to claim 2, wherein the reduction is carried out after isolation of 2-nitro-4-carbamoylbenzoic acid or directly in suspension or solution prior to acidification. 4. Process according to claim 2 or 3, characterized in that the reduction is carried out with iron in neutral medium or with salts of divalent tin or by catalytic hydrogenation.