Diazotization of Aniline Derivatives and Diazo Couplings in the Presence of p-Toluenesulfonic Acid by Grinding

The solid–solid reactions of electron-donor compounds, such as: barbituric acid (1a), thiobarbituric acid (1b), 1,3-dimethyl barbituric acid (1c), phenol (1d) and resorcinol (1e) with diazotized o-nitroaniline (3), m-nitroaniline (4) and p-nitroaniline (5) catalyzed by p-toluenesulfonic acid (2) afford azo dyes by grinding in good yields. This new method totally avoids the use of inorganic acids, alkalies, toxic and/or expensive solvents in diazotization and diazo coupling reactions.