Purification of indigo

US5116996A · kind A · utility

Assignee

• BASF SE

Inventors

• Reinhold Kohlhaupt · Bischofswerda, DE
• Walter Bieg · Grünstadt, DE
• Ernst Lang · Gerlingen, DE

Key dates

• Filing date: Jul 17, 1991
• Grant date: May 26, 1992
• Expiry date: Jul 17, 2011

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C09B7/02
• WIPO field: Basic materials chemistry
• WIPO sector: Chemistry

Abstract

A process for purifying indigo comprises stripping the as-synthesized aqueous alkaline indoxylate solution before its oxidation to indigo of impurities in the absence of oxygen by distillation or by passing in steam or an inert gas and then treating the indigo precipitated on oxidation of the stripped indoxylate solution with dilute hydrogen peroxide solution.