Synthesis, characterization, and thermodynamic study of ammonium benzoate C 7H 5O 2NH 4(s)

Abstract

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 399 K. 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 Δ r H m ° = ( 15.59 ± 0.50 ) kJ mo l − 1 , and the standard molar enthalpy of formation of the compound was calculated as Δ f H m ° [ C 7 H 5 O 2 N H 4 ,s ] = − ( 472.65 ± 0.62 ) kJ mo l − 1 by an isoperibol solution–reaction calorimeter.