The phases of saturated 1‐monoglycerides C14‐C22

Abstract Phase behavior of a homologous series of saturated even 1‐monoglycerides, starting with monomyristin, has been reviewed and their study extended to monoarachidin and monobehenin. The occurrence of sub α, α, β′ and β polymorphs was confirmed for all compounds, except in the case of β′ for monomyristin. It has been firmly established that there is a reversible sub α 2 ⇄ sub α 1 transition, (indicated by Malkin for monostearin) below the reversible sub α (sub α 1 )⇄α transition, for C 18 through C 22 compounds; it occurs at about 50 C and is apparently almost independent of chain length. The sub α 2 to sub α 1 transformation is particularly sensitive to impurity and disappears for 1‐monobehenin at about 10% 2‐monobehenin as produced by heating at 96 C. Heats of transformation are, for β′ and β crystal melting, about 50 cal/g; for α melting, about 35; for sub α → α transition, about 15 and for sub α 2 to sub α 1 transition about 3, which is several times as large as typical heats of melting of mesomorphic states. Diffraction data confirm the essential identity of all long spacing values and the occurrence of tilted chains for all polymorphs of a given compound. Much similarity is encountered between sub α and β′ patterns. Sub α 2 and sub α 1 are difficult to distinguish by diffraction pattern.