Montedison S.p.a.

Renato Grecu

Giuseppe Ribaldone

Camillo Paffoni

Giuseppe Sironi

The present invention relates to a new class of compounds belonging to the anthraquinone series, having the general formula: ##STR1## wherein R, R', R', R'', R' are indifferently H or Chlorine, ##STR2## Such compounds exhibit a color varying from yellow to violet depending on the nature and position of substituents R, R', R', R'', R'.sup.v and, in virtue of their excellent stability characteristics, they are particularly useful as pigments and vat dyes. This invention relates furthermore to the preparation of compounds having general formula (I) and to the utilization thereof, particularly in the following applications:

Anthraquinone compounds and process for preparing same

Process for the preparation of the monopotassium salt of 1,2,5-thiadiazol-3,4-dicarboxylic acid (I). Involves double-stage saponification of 3,4-dicyano-1,2,5-thiadiazole (II), 3-cyano-4-carbamoyl-1,2,5-thiadiazole (III) is obtained from an aqueous suspension of 3,4-dicyano-1,2,5-thiadiazole (II) by catalytic hydration through the addition of aqueous KOH, desirably at a temperature of from 20.degree. to 50.degree. C. and with a molar ratio of 3,4-dicyano-1,25-thiadiazole (II) to KOH of from 1:0.01 to 1:0.8. This is followed by hydrolysis, by the further addition of aqueous KOH, desirably at a temperature of from 85.degree. to 100.degree. C., until attaining an overall molar ratio of 3,4-dicyano-1,2,5-thiadiazole (II) to KOH of from about 1:2.0 to 1:2.35, a molar ratio of 3,4-dicyano-1,2,5-thiadiazole (II) to H.sub.2 O of from about 1:20 to 1:23. Thereafter, from the resulting solution of dipotassium salt of 1,2,5-thiadiazole-3,4-diccarboxylic acid, the monopotassium salt is separated by acidification of said solution.

Method for the preparation of the monopotassium salt of

3,4-DICYANO-1,2,5-THIADIAZOLE IS PREPARED BY REACTING DIAMINOMALEONITRILE (DAMN) with thionyl chloride (SOCl.sub.2) at a temperature of 40.degree. C. up to the boiling point of thionyl chloride wherein the molar ratio of SOCl.sub.2 /DAMN is between 2:1 and 10:1.

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Cameri (Novara), Italy

Renato Grecu