Preparation of dyes derived from Eriochrome Red B and Acid Alizarin Violet N soluble in organic solvents

Both hydroxy groups of Eriochrome Red B are protected by acetylation and the sulfonic acid group is converted to the sulfonyl chloride with phosphorus pentachloride. Reaction with dibutylamine or N‐butylbenzeneethanamine followed by the deprotection gives red azo dyes 7a or 7b, readily soluble in chloroform and toluene. A similar procedure applied to Acid Alizarin Violet N gives only a multicomponent mixture. Friedel‐Crafts reaction between dibutylsulfamoyl chloride and 2‐nitrophenol gives N,N‐dibutyl‐4‐hydroxy‐3‐nitrobenzenesulfonamide (11). Reduction of the nitro group gives amine 14 which is diazotized and coupled with 2‐naphthol to give the required dye 13 giving deep‐red solutions in methanol, chloroform and acetone.