PYRAZOLONE DYESTUFF PREPARATION

See also PYRAZOLONE DYESTUFF PREPARATION, SULFUR BLACK... 

Pyrazolone dyestuff preparation, 350 Pyrophoric alloys, 350 Pyrophoric catalysts, 350 Pyrophoric iron—sulfur compounds, 351 Pyrophoric materials, 352 Pyrophoric metals, 354 Pyrotechnics, 355... 

The reaction is very common in pyrazolone chemistry. Since alkoxypyrazoles and tautomerizable pyrazolones undergo this reaction and 3-pyrazolin-5-ones, like antipyrine, do not, it is assumed that the reaction takes place at C-4 of the OH tautomer. Pyrazolone diazo coupling is an important industrial reaction since the resulting azo derivatives are used as dyestuffs. For instance, tartrazine (Section 4.04.4.1.3) has been prepared this way. 3,5-Pyrazolidinediones react with aryldiazonium salts resulting in the introduction of a 4-arylazo group. As has been described in Section 4.04.2.1.4(v), diazonium salts couple in the 3-position with indazole to give azo compounds. 

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