Effects of Mixed H 2 O—CH 3 CN and H 2 O—HCONMe 2 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.