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Cis‐trans isomerization of octadecatrienoic acids during heating. Study of pinolenic ( cis ‐5, cis ‐9, cis ‐12 18∶3) acid geometrical isomers in heated pine seed oil
Author(s) -
Wolff Robert L.
Publication year - 1994
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/bf02675907
Subject(s) - isomerization , chemistry , cis–trans isomerism , linseed oil , double bond , structural isomer , stereochemistry , organic chemistry , catalysis
To understand the heat‐induced cis‐trans isomerization of ethylenic bonds in octadecatrienoic acids, pine seed oil, which contains the unusual nonmethylene‐interrupted pinolenic ( cis ‐5, cis ‐9, cis ‐12 18∶3) acid as a major component, was heated under vacuum at 240°C for 6 h together with linseed and borage oils. As a results, a small percentage of pinolenic acid undergoes cis‐trans isomerization. The main isomer that accumulates is the trans ‐5, cis ‐9, trans ‐12 18∶3 acid. Minor amounts of the three mono‐ trans isomers are also present. Identification of isomers was realized by combining gas‐liquid chromatography on a CP Sil 88 capillary column, argentation thin‐layer chromatography and comparing the equivalent chainlengths of artifacts to those of isomers present in NO 2 ‐isomerized pine seed oil. Hydrazine reduction was used to demonstrate that there was no positional shift of double bonds. Heat‐induced geometrical isomerization of pinolenic acid differs from that of α‐ and γ‐linolenic acids in at least two aspects. The reaction rate is slower (about one‐fourth), and mono‐ trans isomers are formed in low amounts.