Interactions in aqueous solutions of alkylureas. Excess enthalpies at 25• for butylurea and its isomers.

The heats of dilution in water of three isomeric alkylureas (normal-butylurea, tert-butylurea and tetramethylurea) were determined at 25°C. A comparison of the concentration coefficients of the excess enthalpies, with those of other alkylureas in water makes possible to identify, different behaviours, both determined primarily by hydrophobic interactions and urea-hydrocarbons, water-mediated, interactions. One, shown by the n-butylurea, is similar to that of diluted or moderately concentrated solutions of alkanols in water. Another is shown by the tert-butylurea and tetramethylurea. The kind of aliphatic substituents (linear or branched) and their position determine probably large differences in the cooperativity and effectiveness of the interactions. © 1983.