Can be Azo Dyes Obtained by Grinding under Solvent‐Free Conditions?

Abstract

Abstract The solid‐solid reactions of some electron‐donors with sulfanilic acid in the presence of solid sodium nitrite afford azo dyes by self‐catalyzed diazotization of sulfanilic acid (2) under solvent‐free conditions with moderate yields. Also the reactions of some electron‐donors with diazotization of o ‐nitroaniline (5), m ‐nitroaniline (6) and p ‐nitroaniline (7) in the presence of solid sodium nitrite catalyzed by p ‐toluenesulfonic acid (PTSA) afford azo dyes under solvent‐free conditions in good yields. This new method totally avoids the use of acids, alkalies, and toxic and/or expensive solvents in diazotization and diazo coupling reactions.