Solubility of Benzimidazoles in Alcohols

The solid−liquid equilibrium (SLE) has been measured from 270 K to 445 K for 10 binary mixtures of benzimidazoles (benzimidazole and 2-methylbenzimidazole) with alcohols (1-propanol, 1-butanol, 2-butanol, 2-methyl-2-propanol, 1-hexanol) using a dynamic method. The melting point, enthalpy of fusion, and heat capacity change at the melting temperature were determined by differential scanning calorimetry (DSC). The solubility of benzimidazoles in alcohols (C3−C6) is higher than in water and in 1-octanol and generally decreases with an increase of the alkyl chain length of the alcohol. The intermolecular solute−solvent interaction is higher for the 1-alcohol than for the secondary or tertiary alcohol. The solubility of 2-methylbenzimidazole in alcohols (C3−C6) is higher than that of benzimidazole. Experimental results of solubility were correlated by means of the Wilson, UNIQUAC ASM, and NRTL 1 equations utilizing parameters derived from SLE results. The existence of a solid−solid first-order phase transition in benzimidazole and 2-methylbenzimidazole has been observed in the DSC measurements and has been taken into consideration in the solubility calculation. The best correlation of the solubility data has been obtained by the NRTL 1 equation.