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AssigneeMerck Patent GmbH
InventorsUlrich Heywang, Ingeborg Stein, Ulrich Fechtel, Michael Casutt, Gerald Faller, Hartmut Hartner
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The invention relates to an improved process for preparing 2-arylbenzimidazole-5-sulfonic acids of the formula I, ##STR1## in which Ar is unsubstituted phenyl or phenyl substituted by one or more C.sub.1 -C.sub.6 alkyl or alkoxy groups and m is 1, 2 or 3, wherein o-phenylenediamine is reacted in the presence of sulfuric acid at between room temperature and 250.degree. C. with a benzoic acid derivative of the formula II Ar(--X).sub.m II in which Ar and m are as above, and X is COO-alkyl, where alkyl is n-alkyl having from 1 to 6 C atoms, COOH, COCl, COBr or CN, and new arylbenzimidazole acids of the formula Ia ##STR2##
A single-step process for preparing a 2-arylbenzimidazole-5-sulfonic acid of formula I ##STR7## wherein Ar is phenyl or phenyl substituted by one or more C.sub.1-6 -alkyl or -alkoxy groups, and
Dependencies are inferred from the claim text.