Process for preparing 2-arylbenzimidazole-5-sulfonic acids

Details Process for preparing 2-arylbenzimidazole-5-sulfonic acids Process for preparing 2-arylbenzimidazole-5-sulfonic acids

1993-10-01

1995-12-05

Higel, Floyd D.

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

5483071, 5483101, 5483161, C07D23518, A61K 31415

Patent

active

054730791

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/EP93/00179 filed Aug. 27, 1993.
The invention relates to an improved process for preparing 2-arylbenzimidazole-5-sulfonic acids of the formula I, ##STR3## in which Ar is unsubstituted phenyl or phenyl substituted by one or more C.sub.1 -C.sub.6 alkyl or alkoxy groups and between room temperature and 250.degree. C. with a benzoic acid derivative of the formula II having from 1 to 6 C atoms, COOH, COCl, COBr or CN.
2-Phenylbenzimidazole-5-sulfonic acid (Eusolex 232) is an important water-soluble UV-B radiation filter with wide application in cosmetics. Its use as a UV radiation filter is described, for example, in German Reich Patent No. 676 103.
Its preparation proceeds, according to, for example, V. G. Sayapin et al., KhGC [Chemistry of Heterocyclic Compounds] 6, 1970, 630-632, in a two-stage reaction in which 2-phenylbenzimidazole is first prepared from 1,2-phenylenediamine and the bisulfite adduct of benzaldehyde or from phenylenediamine and benzoic acid in the presence of polyphosphoric acid, and is then reacted with chlorosulfonic acid. A survey of the preparation of 2-substituted benzimidazoles can be found, for example, in Chemical Reviews Vol. 74, No. 3, 1974 p 279 ff. ##STR4##
This process nevertheless has great disadvantages: expensive. 2-phenylbenzimidazole disulfonic acids can be formed which can be separated out only with difficulty. hydrogen sulfite must be used in large excess, so that large amounts of sulfur dioxide are given off during working up; 1-benzyl-2-phenylbenzimidazole can be formed as a byproduct, which can be separated out only with difficulty. In the second process for preparing phenylbenzimidazole from benzoic acid phosphoric acid passes into the waste water, which is undesirable because Of eutrophication of water courses and lakes.
The disadvantages of the abovementioned process can be conveniently circumvented: it has surprisingly been found that in the condensation reaction of 1,2-diphenylenediamine with benzoic acid in sulfuric acid at high temperatures intermediate products are directly sulfonated, so that 2-phenylbenzimidazole-5-sulfonic acid is formed directly without isolation of an intermediate.
DE 12 82 855 describes the use of 1,3-bis-(5-sulfobenzimidazol-2-yl)benzene as a water-soluble UV-B radiation filter.
Its preparation proceeds analogously to that of 2-phenylbenzimidazole in a two-stage process.
The invention thus relates to an improved process for preparing 2-arylbenzimidazole-5-sulfonic acids of the formula I, ##STR5## in which Ar is unsubstituted phenyl or phenyl substituted by one or more C.sub.1 -C.sub.6 alkyl or alkoxy groups and between room temperature and 250.degree. C. with a benzoic acid derivative of the formula II having from 1 to 6 C atoms, COOH, COCl, COBr or CN, particularly from 4 to 7 mol of sulfuric acid are used per 1 mol of o-phenylenediamine.
The invention further relates to such a process in which the benzoic acid derivative is introduced into the sulfuric acid, o-phenylenediamine of the formula II is subsequently added, and the mixture is heated to from 150.degree. C. to 220.degree. C., or in which o-phenylenediamine and the benzoic acid derivative are introduced together into the sulfuric acid.
A further preferred embodiment is a process in which the sulfuric acid is used as solvent, particularly in which 50-100% sulfuric acid is used and/or in which the solvent contains from 1 to 50% of water.
In a particularly preferred embodiment of the process of the invention, the mixture of the reactants is stirred for about from 1 to 5 hours at temperatures between 80.degree. and 140.degree. C., subsequently heated to temperatures between 170.degree. and 250.degree. C. and stirred for another 0.5 to 5 hours.
Carrying out the process of the invention per se is simple. The sulfuric acid, preferably in the form of a 50-100% solution, in particular as a concentrated about 96% solution, forms the initial charge. In general from 1 to 10 mol, preferably from 3 to 8 mol, in particular from 4 to 7 mol of sulfuric acid are

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K. K. Preobrazhenskii, et al., "2-Alkylbenzimidazoles and their sulfo derivatives", Chemical Abstracts, vol. 84, No. 7, Abstract No. 30963t (Aug. 14, 1976), p. 454.
L. S. Efros, "Imidazole derivatives. VII. Preparation of sulfonic acids of benzimidazole by baking method", Chemical Abstracts, vol. 48, see Column 4524, (1953).

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