Process for upgrading the color value of 3,4,9,10-tetracarboxylic acid N,N'-bis-methylimide

US4189582A · kind A · utility

Assignee

• BASF SE

Inventors

• Helmut Hoch
• Heinrich Hiller · Monsheim, DE

Key dates

• Filing date: Jun 7, 1978
• Grant date: Feb 19, 1980
• Expiry date: Jun 7, 1998

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C09B67/0001
• WIPO field: Basic materials chemistry
• WIPO sector: Chemistry

Abstract

A process for the manufacture of a red pigment from perylene-3,4,9,10-tetracarboxylic acid N,N'-bis-methylimide which has been obtained by methylating the corresponding diimide or by fusing naphthalic acid N-methylimide with an alkali metal hydroxide which comprises vatting a suspension of N,N'-bis-methylimide dye with 0.5-1.5 times by weight of an alkali metal dithionite in the presence of up to 4 times by weight of an alkali metal hydroxide relative to the quantity of the dithionite, at a temperature of from room temperature to 100.degree. C., to obtain the corresponding leuco compound, cooling the resulting solution to 20.degree.-40.degree. C., isolating and washing the leuco compound with fresh vatting solution until the solution is virtually colorless and clean and then oxidizing the leuco compound.