Abstract The rate of diazotization of 2-aminothiazole was measured in 65 to 75%(w/w) aqueous H 2 SO 4. The kinetic solvent isotope effect of the diazotization in 72% D 2 SO4/D 2 O was determined (k H/k D= 5.8±0.2). These data are consistent with a mechanism in which the 2-aminothiazole, protonated at the ring N-atom, but not at the NH 2 group, is attacked by the NO+ ion. The reaction does not go to completion, but to an equilibrium. The ...