Microwave Assisted Improved Syntheses of Indigoid and Anthraquinoid Dyes

Abstract

Rapid and improved approaches to indigoid and anthtraquinoid dyes have been developed using microwave irradiation. Reaction between o-nitrobenzaldehyde and acetone in aqueous sodium hydroxide yielded indigo which was further funtionalized for indigo yellow and tyrian blue. Similarly, anthraquinoid dyes have also been synthesized. Reaction between phthalic anhydride and catechol in presence of catalytic amount of concentrated sulphuric acid gave alizarin in quantitative yield. Alizarin was further functionalized to form alizarin orange. Our aim is to utilize this energy in synthesizing dyes: like indigo, alizarin which are widely used by dyers. A rapid and improved approach to indigoid and anthraquinoid dyes has been developed using microwave irradiation. The minimum usage of organic or inorganic solvents (e.g., benzene, sulphuric acid), high efficiency, safety, reduced reaction time and simpler experimental procedure make this technique environmentally friendly.