The rearrangement of fatty cyclopropenoids in the presence of boron trifluoride

Gilkison, Ian S.; Shone, G. G.

doi:10.1007/bf02545328

Cited by 2 publications

(1 citation statement)

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“…A blanket condemnation of the use of BF 3 with fish oils seemed unwarranted because of our extensive and successful experience with BF 3 -methanol alone, although some adverse effects from BF 3 esterification of sensitive fatty acids are known (21)(22)(23)(24). Cyclopropene fatty acids rearrange in the presence of BF 3 (25) as do cyclopropane fatty acids (26), and squalene is destroyed by BF 3 -MeOH (27). Hydroxylated and conjugated dienoic fatty acids are dehydrated to produce conjugated trienes (7), and care is recommended in conjugated linoleic acid (CLA) analyses (28).…”

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Remarks on official methods employing boron trifluoride in the preparation of methyl esters of the fatty acids of fish oils

Ackman

1998

J Americ Oil Chem Soc

118

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Some "official methods" for preparing methyl esters of the fatty acids from oils or fats may be referred to by users as the boron trifluoride (BF 3 ) method and invariably have two stages. The first stage, brief treatment with alkali [commonly NaOH in methanol (MeOH), sometimes NaOCH 3 ] and heat has been popularly described as a saponification step for over 30 yr. In fact, the disappearance of visible fat or oil is mostly transesterification, which can be accomplished in a few minutes under mild conditions. Free fatty acids (FFA) originally present, or produced by saponification, are not converted to methyl esters at this stage. The second stage, heating in BF 3 -MeOH, has in practice been as short as 2 min. It can convert all FFA to methyl esters, but this step requires at least 30 min. Examples from the recent literature illustrate the necessity of extending the time for BF 3 -MeOH transesterification of lipids or oils and methylation of FFA. No alkali transesterification is needed. JAOCS 75, 541-545 (1998). KEY WORDS:Boron trifluoride-methanol, free fatty acids, methyl esters, transesterification.The use of boron trifluoride-methanol (BF 3 -MeOH) was originally developed by industrial chemists when gas-liquid chromatography (GLC) was in its infancy and was applied to familiar and common oils. We are now in an era when more delicate biochemical analyses, often with fatty acids of diverse structures or from very small samples, are in common use. The objective of "determining fatty acid composition" has recently been defined in INFORM (1). A flow schematic of the process to achieve that objective by GLC included seven steps, and each step had a factor or factors that could affect the accuracy of the results. The confidence of many North American research workers in their use of the popular BF 3 -MeOH reagent for preparation of methyl esters may well have been shaken if they became aware of one of two papers published in sequence in the Journal of the Japanese Oil Chemists' Society in 1996. The first paper (2) reported an interlaboratory collaborative study and method standardization that was carried out by six laboratories in Japan. Three refined fish oils were analyzed for eicosapentaenoic (20:5n-3, EPA) and docosahexaenoic (22:6n-3, DHA) acids. Methylation was carried out by transesterification with 2 M KOH in methanol. These six laboratories accessed pure EPA and DHA methyl esters, and with reference to the internal standard of tricosanoic acid (23:0), determined experimental flame-ionization detector (FID) correction factors of 1.01 for EPA and 1.06 for DHA to yield accurate results for these fatty acids, expressed in mg/g of sample. The corresponding values calculated from the theoretical FID response data of Craske and Bannon (3) are 1.02 and 1.03. In all respects, this paper (2) stands alone and satisfies one of the problems identified in the INFORM article, that of the availability of an appropriate reference standard. This paper (2) and its conclusions seem to be entirely acceptable. Regrettably, the al...

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