Collect. Czech. Chem. Commun. 1979, 44, 3102-3110

Kinetics of reaction of 5-phenyl-1,3,4-thiadiazol-2-diazonium ion with water

Jaromír Kaválek, Karel Janák and Vojeslav Štěrba

Organic Chemistry Department, Institute of Chemical Technology, 532 10 Pardubice


5-Phenyl-1,3,4-thiadiazol-2-diazonium ion (I) is transformed into 2-amino-5-phenyl-1,3,4-thiadiazol (II) in diluted mineral acids. The reaction rate measured in solutions of diluted sulphuric acid reaches its maximum at concentrations of 2 to 2.5M-H2SO4. The reaction intermediate is 5-phenyl-1,3,4-thiadiazol-2-diazo hydroxide (III). The rate-limiting step in formation of III consists in base-catalyzed reaction of the diazonium ion I with water; it is 4.3 times slower in 0.1M-D2SO4 than in 0.1m-H2SO4. Ratio of the rate constants of the transformation of the diazo hydroxide III into the diazonium ion I and into the amine II increases rapidly with increasing sulphuric acid concentration.