Process for preparing 2,5-dichlorophenylthioglycollic acid

US4918221A · kind A · utility

Assignee

• Cassella Aktiengesellschaft · DE

Inventors

• Wolfgang Bauer · Krefeld, DE
• Willi Steckelberg · Hofheim, DE

Key dates

• Filing date: Apr 27, 1988
• Grant date: Apr 17, 1990
• Expiry date: Apr 27, 2008

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C07C323/00
• WIPO field: Organic fine chemistry
• WIPO sector: Chemistry

Abstract

A valuable starting material for the manufacture of tetrachlorothioindigo pigments is 2,5-dichlorophenylthioglycollic acid which is prepared by: PA1 (a) diazotizing 2,5-dichloroaniline with aqueous alkali metal nitrite at acidic pH to produce 2,5-dichlorophenyl-diazonium salt, PA1 (b) reacting the 2,5-dichlorophenyl-diazonium salt from (a) with thiourea in an aqueous medium at acidic pH in the presence of a catalyst to produce 2,5-dichlorophenyl-isothiuronium salt of the formula ##STR1## wherein X.sup..crclbar. is an anion of a mineral acid, (c) hydroloyzing the 2,5-dichlorophenylisothiuronium salt from (b), without intermediate isolation, at alkaline pH to produce 2,5-dichlorothiophenol and PA1 (d) condensing the 2,5-dichlorothiophenol with monochloroacetic acid to produce 2,5-dichlorophenylthioglycollic acid.