Cyclopinolenic acids: Synthesis, derivatives and thermal properties

Abstract

The two isomeric cyclopinolenic acids (CP‐1 and CP‐2), components of distilled tall oil, have been synthesized by means of an intramolecular Diels‐Alder reaction of isomers of 5,10,12‐octadecatrienoic esters, themselves synthesized in a stereocontrolled manner. The 5cis,10‐trans,12trans isomer cyclizes at 200°C to a 1:3 mixture of esters of CP‐1 and CP‐2. At 200°C, the 5cis,10trans,12cis isomer is unreactive, but at 240°C it gives the same CP‐1 + CP‐2 ester mixture, presumably by way of prior isomerization to the 5cis,10trans,12trans isomer. A subambient thermal study of CP‐1 and CP‐2 and their derivatives shows that the compounds, excluding CP‐1, lack crystalline structures or melting points, and display glass transitions only, below −80°C for esters and below −50°C for the carboxylic acids.

Elucidation of cyclic fatty acid monomer structures. Cyclic and bicyclic ring sizes and double bond position and configuration

“…The two proposed structures (13,34) differ in the length of the ring substituent, ethyl or methyl; both were also observed (GC peaks 14 and 15, respectively). It was demonstrated that similar monounsaturated bicyclic fatty acid structures, originating from octadecatrienoic acids, are formed during tall oil distillation (35). These tentative structures are also consistent with the IR data.…”