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

T he 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. ‎