The separation of pinolenic acid from distilled tall oil fatty acid by the iodolactonization method was studied. The significance of prefractionation of tall oils and details of the iodolactonization procedure for the pinolenic acid purity achieved is discussed.
Pinolenic acid (5Z,9Z,12Z-octadecatrienoic acid, 1a), one of the most abundant trienoic fatty acids in nature, is very difficult to obtain in quantity in a pure state from the highly complex mixture of unsaturated tall oil fatty acids. For this reason its chemistry has been little studied when compared to linolenic or linoleic acids. A simple synthesis of esters of 1a and of 12Z,15Z-octadecadienoic acid 3 using the one pot double Wittig procedure is described here. The products of double Wittig reactions were purified by argentation chromatography, and their structural purity was established by 1 H-, 13 C-NMR and 2D-NMR spectroscopies.
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.
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