The kinetic study on the effects of mixed aqueous-organic solvents on the rate of O- and N- cyclisation of N-(4'-nitrophenyl)phthalamic acid

Abstract

The pseudo-first-order rate constants (kobs) for the intramolecular carboxylic group-assisted cleavage of N-(4'-nitrophenyl)phthalamic acid (1) show nonlinear decrease of ~ 17-fold and ~ 117-fold with the increase in the respective contents of CH3CN (10-80% v/v) and 1,4-dioxan (9.5-79.4% v/v) in mixed aqueous solvents. The fraction of N-cyclization of 1 leading to the formation of N-(4'-nitrophenyl)phthalimide, 2, remains almost zero at ≤40% v/v CH₃CN while it increases from 0.06 to 0.49 with increase in CH₃CN content (50-80% v/v) at 1.0×10⁻³ M HCl. However, the observed data reveal an almost absence of N-cyclization within 1,4-dioxan content range 10-80% v/v.