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Preparation and phase behavior of positionally isomeric propylene glycol monoesters
Author(s) -
Martin J. B.,
Lutton E. S.
Publication year - 1965
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/bf02540095
Subject(s) - melting point , stearic acid , crystallization , chemistry , metastability , stearate , polyvinyl alcohol , phase (matter) , acyl group , crystallography , organic chemistry , group (periodic table)
Primary even‐chain‐length monoesters of propylene glycol (1,2‐propanediol), myristate through behenate, have been prepared, and also the secondary monostearate. Phase behavior of the pure compounds and of the binary system of isomeric stearates has been studied. This behavior is one of considerable complexity. The highest‐melting stable form of the primary stearate is a single‐chain‐length (SCL) perpendicular form (Form II) of very weak long‐spacing intensities. A metastable perpendicular double‐chain‐length (DCL) a form occurs at the (metastable) melting point after chilling the primary esters; it transforms to a perpendicular DCL Form III on cooling. Low temp crystallization from dilute hexane gives a titled DCL Form I, the typical room temp form in crude preparations of primary ester. The secondary stearate exhibits a single similar DCL Form I at 25C and a perpendicular SCL a form just under the melting point of the chilled melt. Polymorphism is modified by mol wt and purity. Primary arachidate and behenate do not show Form II, hence show stable a at their (stable) melting points. Repeated crystallization of the 80% primary ester obtained on direct esterification with stearic acid yields pure primary ester. Special synthesis via 1‐tetrahydropyranyl propylene glycol is necessary to prepare pure secondary ester. The pure primary monobehenate could be obtained only by acylation of 2‐tetrahydropyranyl propylene glycol obtained by reduction of tetrahydropyranyl ethyl lactate. Removal of the tetrahydropyranyl blocking groups was accomplished without acyl migration by using boric acid as a cleaving agent.