Thermal Analysis and Calorimetric Study of 4-Dimethylaminopyridine

Abstract

4-Dimethylaminopyridine (DMAP) is an important catalyst. The thermodynamic properties of DMAP were investigated through differential scanning calorimetry, thermogravimetric analysis, adiabatic calorimetry, and combustion calorimetry. The low-temperature heat capacity (Cp,m) was measured in the temperature range from (80 to 402) K with a high-precision automated adiabatic calorimeter. The melting temperature (Tm), the molar enthalpy (ΔfusHm), and the entropy (ΔfusSm) of fusion were determined to be (387.094 ± 0.002) K, (21.628 ± 0.144) kJ·mol-1, and (55.873 ± 0.372) J·K-1·mol-1, respectively. The mole fraction purity of the sample used in the adiabatic calorimetric study was determined to be 0.99964 according to the Van't Hoff equation. The thermodynamic functions [HT − H298.15] and [ST − S298.15] were derived in the range from (80 to 400) K with temperature interval of 5 K based on the heat capacity measurements. The constant-volume energy and standard molar enthalpy of combustion have been determined, ΔcU (C7H10N2, cr) = −(4232.20 ± 0.60) kJ·mol-1 and Δc (C7H10N2, cr) = −(4235.92 ± 0.60) kJ·mol-1, by means of a precision oxygen-bomb combustion calorimeter at T = (298.15 ± 0.001) K. The standard molar enthalpy of formation has been derived, Δf (C7H10N2, cr) = (52.20 ± 1.71) kJ·mol-1, from the standard molar enthalpy of combustion in combination with other auxiliary thermodynamic quantities through a Hess thermochemical cycle.