Separation and purification of pinolenic acid by the iodolactonization method

Abstract

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.

Synthesis of Ethyl 5Z,9Z,12Z‐octadecatrienoate (ethyl pinolenate) and Methyl 12Z,15Z‐octadecadienoate

“…The combined ether phases were dried on Na 2 SO 4 and the solvent evaporated to give 4-(tetrahydropyran-2-yloxy)butanol 4 (23.5 g, 19%). 1 …”

“…The eluate was monitored by TLC (CH 2 Cl 2 /EtOAc 5:1) and the fractions containing the product collected to give 10.2 g (50%) of 5 as an oil. 1 Flash chromatography of the concentrate in a silica gel column (elution with 5% ethyl acetate in CH 2 Cl 2 ) yielded 14.8 g of crude 9-(tetrahydropyran-2-yloxy)-5Z-nonenoic acid ethyl ester 8 containing ca. 15% of the 5E-isomer (by 1 H-integrals).…”

“…Flash chromatography (silica gel, elution with 5% ethyl acetate in CH 2 Cl 2 ) yielded 1.88 g (overall 16.5% from 5) of 6 containing ca 15% of the 5E-isomer. 1 Propylene-1,3-bis(triphenylphosphonium dibromide) (2) 1,3-Dibromopropane (16.0 g, 0.080 mol), triphenylphosphine (40.5 g, 0.15 mol) and 1.0 g of K 2 CO 3 were refluxed in acetonitrile (200 mL) for 2 days under Ar to give 31.5 g (54%) of white crystals of 2.…”

“…The yield of pure 1b (99% by GC and 1 H NMR) was 12.0 mg (9.3%). 1 12-Oxododecanoic Acid Methyl Ester (9) 12-Hydroxydodecanoic acid was prepared by reduction [12] of commercial (Fluka) dodecadienoic acid. 12-Hydroxydodecanoic acid was then oxidized with NACAA [(as above for 4-(tetrahydropyran-2-yloxy)butanal 5)] to give the aldehyde ester 9 in 38% yield.…”

“…Owing to the difficulties in obtaining pinolenic acid in quantity in a pure state, its chemistry has been little studied when compared to linolenic or linoleic acids. We reported [1] earlier the isolation of 1a from tall oil by an iodo-lactonization method, its alkali isomerization and the synthesis of many of the isomers [2] and their intramolecular Diels-Alder cyclization reactions [3,4].…”