Synthesis, characterization, and thermodynamic study of ammonium benzoate C7H5O2NH4(s)

Benzoic acid and concentrated ammonia were chosen as reactants and a novel compound (ammonium benzoate) was synthesized using the method of liquid phase reaction. FTIR, elemental analysis and X-ray powder diffraction technique were applied to characterize the structure and composition of the compound. Low-temperature heat capacities of the solid compound were measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 399K. A polynomial equation of the heat capacities was fitted by the least-squares method. In accordance with Hess' law, a thermochemical cycle was designed, the enthalpy change of the reaction of benzoic acid with ammonium acetate was determined as Delta H-r(m)degrees = (15.59 +/- 0.50) kJ mol(-1), and the standard molar enthalpy of formation of the compound was calculated as Delta H-f(m)degrees [C7H5O2NH4,S] = -(472.65 +/- 0.62) kJ mol(-1) by an isoperibol solution-reaction calorimeter. (C) 2010 Elsevier B.V. All rights reserved.