The solubility of 6-chloropyridazin-3-amine in methanol, ethanol, n-butanol, N,N-dimethylformamide, acetone, cyclohexanone, ethyl acetate, and toluene at temperatures ranging from (298.15 to 343.55) K at atmospheric pressure was obtained using a synthetic method. The results showed that the solubility of 6-chloropyridazin-3-amine in these solvents increases with rising temperature. The modified Apelblat equation and λh equation were used to correlate the experimental solubility respectively. The calculated values with equations showed good consistency with the experimental values, and the root-mean-square relative deviation was less than 4.68 %. The enthalpy of dissolution and entropy of 6-chloropyridazin-3-amine were obtained by the van't Hoff equation, and the change in Gibbs free energy was calculated.

Using a synthetic method, the solubility data of pyridazin-3-amine were obtained in methanol, ethanol, 1-propanol, 2-propanol, 1butanol, 2-propanone, ethyl acetate, and aniline at temperatures ranging from (288.05 to 333.35) K at atmospheric pressure. The fusion enthalpy and melting point were measured by differential scanning calorimetry. Modified Apelblat, λh, and Wilson models of nonideal solution were used to correlate the measured solubility data, respectively. Among them, Apelblat and λh equations have satisfying fitting effects for the experimental solubility values in all selected solvents with the rootmean-square deviation being less than 1.58 %. The activity coefficients of pyridazin-3-amine and molar dissolution enthalpy, entropy, and Gibbs free energy of the solute in methanol, 1-propanol, and 2-propanol were calculated in accordance with the parameters of the Wilson model at experimental solubility points.

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