Synthesis of a New Vat Dye

Abstract

The importance of vat dyes especially those derived from indigo and its derivatives is still relevant and prompted this investigation. Disclosed hereby is the synthesis of a new vat dye from 2, 4- dinitroaniline which yielded a blue dye of indigo skeleton. 2, 4 dinitroaniline was treated with chloroacetic acid, in a base catalysed substitution nucleophilic bimolecular reaction using a high boiling non polar solvent such as nitrobenzene at a temperature above 300⁰C.The intermediate compound that resulted was purified and this in turn was treated with admixture sodium hydroxide-potassium hydroxide - sodamide in a 5:5:1 ratio at a temperature of 120⁰C to yield an indoxyl, in an intramolecular cyclization reaction. Oxidation of the indoxyl into the vat dye was brought about by treating the indoxyl with acidified solution of ferric chloride. The yield was excellent and the structure of this compound was established as 5, 5’ 7, 7’- tetranitroindigo by chemical evidence: ultraviolet, infrared, nuclear magnetic resonance spectroscopy and mass spectrometry. Reduction of this compound with sodium dithionite (sodium hydrosulphite) and the ease of air oxidation back to the original colour made it applicable as vat dye.