Abstract
The reaction kinetics of 4,6-dinitrobenzofuroxan with five heterocyclic amines was investigated spectrophotometrically (UV–Vis) in acetonitrile at 20°C. It was observed that the rate constants of these reactions increased as follows: 2-aminopyrimidine>2-aminothiazole>2-aminobenzothiazole>5-amino-3,4-dimethylisoxazole>2-amino-5-trifluoromethyl-1,3,4-thiadiazole. Further, second-order rate constants (k1) pertaining to the C–N and C–C bond forming step of these complexation processes fit to the three parameter equation log k (20°C)=sN (N+E), allowing the determination of the nucleophilicity parameters (N) of the five heterocyclic amines. The heterocyclic amines were subsequently ranked on the comprehensive nucleophilicity scale defined by Mayr et al. (2003), providing a direct comparison of n-, π-, and σ-nucleophiles.