Thermodynamics of the Hydrolysis Reactions of 1-Naphthyl Acetate, 4-Nitrophenyl Acetate, and 4-Nitrophenyl Alpha-L-Arabinofuranoside

Microcalorimetry, high-performance liquid chromatography (HPLC), and liquid chromatography-mass spectrometry (LC-MS) have been used to conduct a thermodynamic investigation of the hydrolysis reactions {1-naphthyl acetate(aq) + H₂O(l) = 1-naphthol(aq) + acetate(aq)}, {4-nitrophenyl acetate(aq) + H₂O(l) = 4-nitrophenol(aq) + acetate(aq)}, and {4-nitrophenyl α-l-arabinofuranoside(aq) + H₂O(l) = l-arabinose(aq) + 4-nitrophenol(aq)}. Calorimetrically determined enthalpies of reaction Δ_rH(cal) were measured for all three reactions. However, since the positions of equilibrium for all of these reactions were found to lie very far to the right, it was only possible to set lower limits for the values of the apparent equilibrium constants K′. A chemical equilibrium model, together with pKs and standard enthalpies of reaction Δ_rH° for the H⁺ binding reactions of the reactants and products, was then used to calculate the values of Δ_rH° for chemical reference reactions that correspond to the overall biochemical reactions that were studied experimentally. The values of Benson estimates of Δ_rH° for the chemical reference reactions that correspond to the first of the above two reactions were, in all cases, within 16 kJ•mol^-1 of the results obtained in this study. Thermochemical network calculations led to Δ_fH° = -286.4 kJ•mol^-1 for 1-napthyl acetate(aq) and Δ_fH° = -364.9 kJ•mol^-1 for 4-nitrophenyl acetate(aq).