Intramolecular catalysis. Part III. Hydrolysis of 3′- and 4′-substituted phthalanilic acids [o-(N-phenylcarbamoyl)benzoic acids]

Abstract

Hydrolysis of 3′- and 4′-substituted phthalanilic [o-(N-phenylcarbamoyl)benzoic] acids between pH 0.63 and 5.08 proceeds via undissociated carboxy-group participation at a rate which shows a linear correlation with the pK_b of k_obs=(k₁+k₂[H⁺])/(1 +K_a/[H⁺])(i) the aniline leaving group. The hydrolysis follows equation (i). In 1.0M-hydrochloric acid phthalanilic acid is hydrolysed nearly 4 × 10³ times faster than benzanilide. The rate controlling step is the breakdown of the tetrahedral intermediate, which can be generated independently from N-phenylisophthalimide. N-Phenylisophthalimide has a half-life of ca. 7 s at 24.6° in 0.1 M-hydrochloric acid and is hydrolysed to phthalanilic acid ca. 500 times faster than phthalanilic acid itself and 12–13 times faster than phthalic anhydride. The effect of added dioxan and of increasing acidity on the experimental rate constant for the hydrolysis of phthalanilic acid is reported.