Phenylethyl esters of fatty acids for the analytical resolution of petroselinate and oleate

Liu, Linsen; Hammond, Earl G.

doi:10.1007/bf02635667

Cited by 13 publications

(9 citation statements)

References 5 publications

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“…Good separation of the ∆6 and ∆9 isomers has been reported using phenylethyl (6), isopropyl (7), and butyl (8)(9)(10) esters. The phenylethyl ester gives near baseline resolution on a 15-m polar phase (DB-23) column when the esterification reaction conditions are mild using acid or base catalysis.…”

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confidence: 93%

Improvement in the gas chromatographic resolution of petroselinate from oleate

Isbell

Green

DeKeyser

et al. 2006

J Americ Oil Chem Soc

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In the extraction of oils from seeds of the genus Coriandrum, GC separations of petroselinate from oleate often gave poor resolution of these two isomers. Oleic and petroselinic acids were esterified with a series of alcohols (methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-1-propanol, 1-butanol, 3-methyl-1-butanol, and 2-ethyl-1-hexanol). GC resolution of the ∆6 from the ∆9 and ∆11 octadecenoates was examined for all ester derivatives on a polar phase column. The ∆6 and ∆9 isomers were unresolved as methyl esters; however, the 2-ethyl-1-hexyl esters gave baseline separation of all three isomers under temperature programming conditions. When isothermal conditions were optimized for each ester, separation of these isomers was possible with good resolution values (>89%) for all the alcohols except methanol, which had a partial resolution of 51%. The rates of esterification of all the alcohols were determined for reactions with both oleic acid and triolein using potassium hydroxide as the esterification catalyst. Methanol gave the largest rate constant in both acid and oil esterification reactions with a rate constant 10-fold better than all of the other alcohols. Based on rates of reaction, resolution of petroselinate from oleate, and removal of residual alcohol, the ethyl ester derivative appears to be the best choice for seed oils containing petroselinic acid.Petroselinic acid is present in a number of seed oils but is most commonly found in the Umbelliferae family. One interest in this acid is that it could serve as a useful raw material for producing adipic and lauric acids via oxidative cleavage of the ∆6 double bond in petroselinic acid. Adipic acid is commonly used as a monomer for nylon synthesis, and lauric acid is used in detergent applications. Analysis of petroselinic acid in natural oils by GC is typically confounded by the presence of oleic acid. When methyl esters of petroselinic and oleic acids are synthesized, the GC separation of these two isomers is incomplete (1,2). Separation of petroselinate from oleate was reported to have only a 0.04 equivalent chain length (ECL) unit resolution, which made quantification of the individual isomers difficult.In an effort to overcome these quantification problems, several tedious chromatographic separation or derivatization techniques have been devised. Kleiman (3) used a combination of silver ion chromatography to isolate the monoene fraction of Umbelliflorae seed oils followed by ozonolysis and GC quantification of the cleavage products. Santinelli (4) epoxidized the olefins and then converted the epoxides to chlorohydrins via a hydrochloric acid-mediated ring opening. The resulting chlorohydrins were converted to their trimethylsilyl ethers, which were partially resolved by GC. Thies (5) treated the FA with dimethyldisulfide to make the bis-methylthio derivatives, which gave only partial separation by GC.Good separation of the ∆6 and ∆9 isomers has been reported using phenylethyl (6), isopropyl (7), and butyl (8-10) esters. The phenylethyl ester gives n...

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confidence: 93%

Improvement in the gas chromatographic resolution of petroselinate from oleate

Isbell

Green

DeKeyser

et al. 2006

J Americ Oil Chem Soc

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“…GC (9). The esters were analyzed by a Hewlett-Packard (Wilmington, DE) model 5890 gas chromatograph fitted with an FID and a 15 m × 0.244 mm Alltech (Deerfield, IL) DB-23 capillary column.…”

Section: Methodsmentioning

confidence: 99%

How is chemical interesterification initiated: Nucleophilic substitution or α‐proton abstraction?

Liu

2004

J Americ Oil Chem Soc

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Esters of carboxylic acids including 2-methylhexanoic, 2-methylbutyric, 2,2-dimethyl-4-pentenoic, palmitic, and oleic acids were tested as substrates in methoxide-catalyzed interesterification and transesterification. The aliphatic acid esters participated in the ester-ester interchange upon addition of catalytic sodium methoxide. Their isopropyl esters also produced methyl esters on heating with sodium methoxide. The esters of α-methyl-substituted acids did not participate in the ester-ester interchange. Their isopropyl esters did not react with methoxide to produce methyl esters. However, upon addition of methanol with sodium methoxide, their methyl esters were produced. These results indicate that the first step in interesterification is possibly that methoxide abstracts the α-hydrogen of an ester to form a carbanion. Interesterification is then likely completed via a Claisen condensation mechanism involving the β-keto ester anion as the active intermediate. The β-keto ester anion contains positively charged ketone and acyl carbons that are active sites for nucleophilic attack by anions such as methoxide and glycerinate, which would produce a methyl ester or rearrange acyls randomly. On the other hand, transesterification is a nucleophilic substitution by methoxide at the acyl carbon in the presence of methanol.Chemical interesterification rearranges the distribution of FA in TG. This rearrangement changes the TG composition, and therefore the physical properties of the oils, and does not lead to the formation of trans FA.Interesterification can occur without catalysts at very high temperatures, such as 250°C, or catalytically under milder conditions, such as 60°C. Many compounds have been patented as interesterification catalysts including metal salts, alkali hydroxide, alkoxide (alkylates), and alkali metals (1-3). Sodium methoxide is the most commonly used catalyst for chemical interesterification. The reaction is commonly divided into three periods: induction, interchange, and completion. During the induction period (ranging from seconds to minutes), sodium methoxide reacts with glycerides to produce an intermediate commonly referred to as the "real catalyst" (1); no interchange of acyl groups takes place during this period. Although the existence of this real catalyst is not doubted by those skilled in the art, experimental evidence revealing the identity or structure of the catalytic species is still lacking. Once the real catalyst is formed, the interchange period of the reaction begins. Acyl groups continue to interchange until thermodynamic equilibrium is reached and no further net change in the distribution of FA occurs. At this point, the reaction reaches the third period, completion, which is usually terminated out by quenching with water to destroy the real catalyst.Two reaction mechanisms have been proposed for interesterification. Weiss et al. (4) suggested that interesterification was initiated when methoxide abstracted the α-hydrogen of an ester to form an enolate anion (α-carbanion ester) tha...

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“…The resolution of the named fatty acids as methylthioderivates [10] on a 25 m FFAP capillary column is insufficient for quantification. The phenylethyl ester [11] of petroselinic and oleic acid allow baseline separation, but the derivatization procedure is laborious.…”

Section: Introductionmentioning

confidence: 99%