Green and efficient diazotization and diazo coupling reactions on clays and Zeolites

Azo dyes are compounds that contain azo groups linked to methine or aromatic sp2-hybridized C-atoms. The formation of diazotizing reagent starts with protonation of nitrous acid under strongly acidic conditions, and azo coupling carried out at low temperature in the presence of nucleophilic coupling components, the reactivity of a nucleophilic substrate increases with increasing basicity phenolates and amines [1]. These conventional acidebase catalyzed processes are effective for the near quantitative formation of the desired products. But the main limitation of such synthetic processes is their environmental incompatibility. The acidic and basic effluents from the laboratory and industry produce permanent damage to the environment and disturb the ecological balance [2]. In recent years, clay based catalysts are reported to be effective for performing many of the acidebase catalyzed organic reactions in a better, environmentally benign manner [3, 4]. Nowadays more and more heterogeneous Bronsted acids, e.g. zeolites are utilized, the excellent catalytic abilities are due to the presence of Bronsted and Lewis acid centers in the zeolite structure [5]. Because of its high protonic acidity and unique shape-selective behavior, ZSM HZSM-5, HY, and H-beta have been shown to be a highly active and stable catalyst for reactions