Thermodynamics of the Hydrolysis of N-Acetyl-L-phenylalanine Ethyl Ester in Water and in Organic Solvents

Thermodynamics of the hydrolysis of 3,4,5-trihydroxybenzoic acid propyl ester (n-propylgallate) to 3,4,5-trihydroxybenzoic acid (gallic acid) and propan-1-ol in aqueous media and in toluene

“…While, we cannot explain this difference, we believe that the statistical uncertainty assigned to the value of D r H°m obtained from the results of Vega and Bates (21) for reaction (8) is fortuitously small, and that a more realistic uncertainty would be in the range2(0.2 to 0.5) kJ·mol −1 . This would bring the two results for D r H°m for reaction (8) into agreement.…”

“…Standardized NaOH(aq) {concentration c = (2.00 2 0.02) mol·dm −3 , M = 0.039997 kg·mol −1 } was obtained from Fisher Scientific; the vendor stated that, based upon turbidity measurements, the mole fraction n'(carbonate)/n(NaOH) in this solution was Q0.01, where n'(carbonate) is {n(CO The mass fractions of water in the reagents and in the toluene solutions were measured with a Metrohm Model 633 automatic Karl Fischer titrator as previously described. (8) The molalities of n-propylgallate and gallic acid were determined with a Hewlett-Packard 1090 high-performance liquid chromatograph (h.p.l.c.) equipped −3 , pH = 4.65)} and methanol.…”

“…The molality of propan-1-ol in the toluene solution was measured with a Varian 6000 g.c. as previously described; (8) butan-1-ol was used as the internal standard.…”

“…The procedure used for immobilization of the tannase on controlled-pore glass beads was identical to the method described earlier (8) for the immobilization of a-chymotrypsin. When not in use, the immobilized tannase was stored in phosphate buffer {c(K 2 HPO 4 ) = 0.1 mol·dm −3 , adjusted to pH = 7.2 with H 3 PO 4 } at T = 277 K. Equilibrium measurements were carried out by approaching equilibrium from both directions of reaction under very similar conditions.…”

“…Thus, there is a practical importance in having a quantitative understanding of the position of equilibrium of this reaction and how it can change with solvent. Because of this, and to gain a further understanding of the thermodynamics of biochemical reactions in non-aqueous media, (3)(4)(5)(6)(7)(8) we have undertaken an investigation in which equilibrium constants for this reaction were measured both in aqueous media and in toluene, an organic solvent that has a relative permittivity much less than that of water. Calorimetry was also used to measure the molar enthalpy change for this reaction in aqueous media.…”