Physicochemical Investigation of Interactions in the Urea – Dl-Alanine System

A comprehensive physicochemical study of the “urea – DL-alanine – water” system was carried out to determine the nature of the interactions between its components. Methods of isomolar series, X-ray phase analysis, thermal analysis, and FTIR spectroscopy were applied. It was found that molecular associates with a stoichiometry of 1:1 are formed in an aqueous solution, as evidenced by deviations in density, viscosity, refractive index, and electrical conductivity from their additive values. In the solid phase, the system represents a mechanical mixture of the initial components without the formation of new crystalline phases. The presence of hydrogen bonds of the N – H ··· O = C and N – H ··· O(COO-) types, which stabilize the molecular associate, was confirmed. The results are of practical importance for the development of stable liquid nitrogen fertilizers based on urea-ammonium mixtures modified with amino acids.