Abstract
The majority of azo coupling reactions have so far been studied by means of spectrophotometric methods. However, with respect to high absorption coefficients of azo dyestuffs these reactions must be carried out in very dilute solutions. The present paper deals with a kinetic study of azo coupling reactions of substituted benzenediazonium salts with 1-(4'-sulphophenyl)-3-methylpyrazolin-5-one under real production conditions. The method of direct injection enthalpimetry (DIE) has been used for this study. The rate constants of the reactions studied have been determined and correlated by means of the Hammett equation. The applicability of the DIE method to the study of azo coupling reactions under real production conditions has been demonstrated on the reaction of 4-chlorobenzenediazonium cation with 1-(4'-sulphophenyl)-3-methylpyrazolin-5-one. At the concentration used, the azo dyestuff formed is precipitated, and can be distinctly observed in the temperature-time curve.
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