Catalytic Activity in the Hydrolysis of Phenyl Esters of α-Furoic Acid

Abstract

Hydrolysis of p-nitrophenyl-α-furoate (p-NPF), p-chlorophenyl-α- furoate (p-CPF) and phenyl-α-furoate (PF) in 5% aqueous acetonitrile is catalyzed by hydroxide ion (OH–), benzimidazole (BI), benzotriazole (BT), hydroxylmethylbenzotriazole (HMBT), phenol (PhOH), p-cresol (p-MP), p-chlorophenol (pCP), 6-hydroxy-2-picoline (HP), hydrazine (HYD), trihydroxymethylmethylamine (TRIS) and borax (BO). Brφnsted β value for varying attacking nucleophiles is obtained as 0.25. Brφnsted β value for varying leaving groups is obtained as -0.25. Hammett ρ value of +0.84 is obtained when the substituted phenyl esters are hydrolyzed by hydroxide ion. Kinetic data indicates (1) characteristic strong nucleophilic attack with asymmetric early transition state, (2) catalysis by nucleophile on carbonyl carbon of the acyl group, (3) catalysis by TRIS and BO is following general base mechanism, (4) the relative rate ratios k_OH^-/k_cat support the distinction in catalysis by attacking species, (5) the bond breaking involving leaving group is not significant in the rate determining step, (6) Hammett ρ value obtained is in keeping with the leaving group abilities of substituted phenoxides and (7) inhibition by 2,6-lutidine indicates steric inhibition.