Thermochemistry of 2-Aminopyridine (C5H6N2)(s)

The molar enthalpies of solution of 2-aminopyridine at various molalities were measured at T=298.15 K in double-distilled water by means of an isoperibol solution-reaction calorimeter. According to Pitzer’s theory, the molar enthalpy of solution of the title compound at infinite dilution was calculated to be D_solH_m^￥ = 14.34 kJ·mol^-1Delta_{mathrm{sol}}H_{mathrm{m}}^{infty} = 14.34~mbox{kJ}cdotmbox{mol}^{-1}, and Pitzer’s ion interaction parameters b_MX^(0)L, b_MX^(1)Lbeta_{mathrm{MX}}^{(0)L}, beta_{mathrm{MX}}^{(1)L}, and C_MX^fLC_{mathrm{MX}}^{phi L} were obtained. Values of the relative apparent molar enthalpies ( ^φ L) and relative partial molar enthalpies of the compound ([`(L)]₂)bar{L}_{2}) were derived from the experimental enthalpies of solution of the compound. The standard molar enthalpy of formation of the cation C₅H₇N₂ ⁺mathrm{C}_{5}mathrm{H}_{7}mathrm{N}_{2}^{ +} in aqueous solution was calculated to be D_fH_m^o(C₅H₇N₂⁺,aq)=-(2.096±0.801) kJ·mol^-1Delta_{mathrm{f}}H_{mathrm{m}}^{mathrm{o}}(mathrm{C}_{5}mathrm{H}_{7}mathrm{N}_{2}^{+},mbox{aq})=-(2.096pm 0.801)~mbox{kJ}cdotmbox{mol}^{-1}.