Effects of mixed aqueous‐organic solvents on the rate of intramolecular carboxylic group‐catalyzed cleavage of N ‐(4′‐methoxyphenyl)phthalamic acid

Kinetic study on the cleavage of N ‐(4′‐methoxyphenyl)phthalamic acid (NMPPAH) in mixed H 2 O‐CH 3 CN and H 2 O‐1,4‐dioxan solvents containing 0.05 M HCl reveals the formation of phthalic anhydride (PAn)/phthalic acid (PA) as the sole or major product. Pseudo first‐order rate constants ( k 1 ) for the conversion of NMPPAH to PAn decrease nonlinearly from 60.4 × 10 −5 to 2.64 × 10 −5 s −1 with the increase in the contents of 1,4‐dioxan from 10 to 80% v/v in mixed aqueous solvents. The rate of cleavage of NMPPAH in mixed H 2 O‐CH 3 CN solvents at ≥50% v/v CH 3 CN follows an irreversible consecutive reaction path: NMPPAH PA. The values of k 1 are larger in H 2 O‐CH 3 CN than in H 2 O‐1,4‐dioxan solvents. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 316–325, 2004