Binary freezing‐point diagrams for alpha‐ and beta‐eleostearic acids with each other and with acetamide

Abstract

Summary Complete binary freezing‐point data have been obtained for each of the polymorphic modifications of acetamide with alpha‐eleostearic acid and beta‐eleostearic acid and for alpha‐eleostearic acid with beta‐eleostearic acid. In the light of previously published data the fact that all of these systems are of the simple eutectic type suggests that the tendency of the long‐chain fatty acids to form 1∶1 molecular compounds with acetamide and with each other decreases as the degree of unsaturation increases. The fact that the heat of fusion of beta‐eleostearic acid, 13.2 kcal. per mole, calculated from the freezing‐point data is greater than that for the alpha acid, 10.5 kcal. per mole, corroborates the conclusion that the beta acid is the trans‐trans‐trans modification. Calculations of heats of fusion have been made, based upon all the available freezing‐point data in the literature for binary systems between pairs of C 18 fatty acids of different degrees of unsaturation, and certain trends have been dsicussed.