Molar heat capacities and standard molar enthalpy of formation of 2-amino-5-methylpyridine

The heat capacities (C (p,m)) of 2-amino-5-methylpyridine (AMP) were measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 398 K. A solid-liquid phase transition was found in the range from 336 to 351 K with the peak heat capacity at 350.426 K. The melting temperature (T (m)), the molar enthalpy (Delta(fus) H (m) (0) ), and the molar entropy (Delta(fus) S (m) (0) ) of fusion were determined to be 350.431 +/- 0.018 K, 18.108 kJ mol(-1) and 51.676 J K(-1) mol(-1), respectively. The mole fraction purity of the sample used was determined to be 0.99734 through the Van't Hoff equation. The thermodynamic functions (H (T)-H (298.15) and S (T)-S (298.15)) were calculated. The molar energy of combustion and the standard molar enthalpy of combustion were determined, Delta U (c)(C(6)H(8)N(2),cr)= -3500.15 +/- 1.51 kJ mol(-1) and Delta(c) H (m) (0) (C(6)H(8)N(2),cr)= -3502.64 +/- 1.51 kJ mol(-1), by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. The standard molar enthalpy of formation of the crystalline compound was derived, Delta(r) H (m) (0) (C(6)H(8)N(2),cr)= -1.74 +/- 0.57 kJ mol(-1)