Effects of Mixed H₂O—CH₃CN and H₂O—HCONMe₂ Solvents on the Rate of Cleavage of N-Benzylphthalamic Acid

Abstract

The values of pseudo first-order rate constants, k1, for the O-cyclization and k3 for N-cyclization of N-benzylphthalamic acid 1, obtained at 0.02 M HCl and 35°C, show a respective nonlinear increase from 17.6 × 10−6 to 29.7 × 10−6 s−1 and decrease from 12.5 × 10−7 to 3.75 × 10−7 s−1 with increase in the CH3CN content from 2 to 60% v/v in mixed aqueous solvent. Increase in the CH3CN content from 60 to 90% v/v decreases k1 from 29.7 × 10−6 to 24.4 × 10−6 s−1 and increases k3 from 3.75 × 10−7 to 14.7 × 10−7 s−1. The respective values of k1 and k3 decrease nonlinearly from 16.0 × 10−6 to 3.0 × 10−6 s−1 and 14.0 × 10−7 to ~4.0 × 10−7 s−1 with increase in the content of N,N-dimethylformamide (HCONMe2) from 2 to 80% v/v in mixed aqueous solvents. These results indicate rather mild rate-retarding effects of mixed H2O—CH3CN and H2O—HCONMe2 solvents on the rates of the intramolecular reactions.