Process for conjugating fatty acid esters

Details Process for conjugating fatty acid esters Process for conjugating fatty acid esters

2001-03-06

2002-11-12

Carr, Deborah (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Fatty compounds having an acid moiety which contains the...

C554S125000

Reexamination Certificate

active

06479683

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a process for producing conjugated fatty acid esters. More particularly, this invention relates to a process for producing conjugated fatty acid esters that comprises subjecting one or a mixture of unconjugated fatty acid esters to a base-catalyzed isomerization reaction in the presence of only small amounts of catalyst and solvent in a closed vessel at an elevated temperature and under the corresponding autogenic pressure.
BACKGROUND OF THE INVENTION
Fatty acids and fatty acid derivatives typically are derived from naturally occurring fats and oils. With few exceptions, such fatty acids or fatty acid derivatives are all straight-chain molecules having from three to eighteen carbon atoms. A significant fraction of these fatty acid molecules are polyunsaturated, meaning that they contain two or more double bonds. In most instances, the double bonds in naturally occurring polyunsaturated fatty acid molecules are separated from each other by two single bonds, with the structure —CH═CH—CH
2
—CH═CH—, and such molecules are generally referred to as unconjugated polyenes or methylene-interrupted polyenes. In more limited instances, naturally occurring polyunsaturated fatty acid molecules contain double bonds separated from each other by a lone single bond, having the structure —CH═CH—CH═CH—, and such molecules are generally referred to as conjugated polyenes. Among the naturally occurring conjugated polyenes, conjugated dienes and trienes are the most prevalent.
Upon exposure to oxygen, conjugated polyenes oxidize relatively quickly and can form cross-linked films. Accordingly, conjugated polyenes traditionally have been valued by the paint and varnish industries for use in drying oils. Drying oils have value because of their ability to polymerize or “dry” after they have been applied to a surface to form tough, adherent and abrasion-resistant films. “Drying” of a paint or varnish does not simply entail evaporation of solvent, but rather a chemical reaction that produces a durable organic film, formed upon oxygen-induced polymerization and cross-linking of polyenes, analagous to the sulfur-induced polymerization and cross-linking that produces vulcanized rubber. Unconjugated polyenes, such as those contained in linseed oil and tung oil, also cross-link to form such fihns; however, conjugated polyenes cross-link more rapidly. Hence, drying oil formulations incorporating conjugated polyenes have quicker drying times than those formulations that incorporate only unconjugated polyenes.
In the area of health and nutrition, researchers have shown that ingestion of conjugated polyenes may inhibit tumor growth, prevent heart disease, and reduce body fat. Indeed, there is presently a great deal of interest in the apparent health benefits imparted by certain conjugated linoleic acids, termed CLAs. CLAs, originally isolated from the fat and milk of ruminants, exhibit impressive physiological effects in animal studies. CLA is a loose term used to describe one or a mixture of conjugated octadecadienoic fatty acids. In a variety of chemical forms, including but not limited to free fatty acids (FFA) and fatty acid methyl esters (FAME), CLA reportedly has antidiabetic properties, leads to reduced carcinogenesis and atherosclerosis, and increases bone and muscle mass.
A factor hampering commercialization and research interests in CLA and other conjugated polyenes, however, is that such compounds are not naturally abundant. Conjugated polyenes typically are present in animal fats only at a level of about 0.5 percent. In plant sources, conjugated polyenes do not occur widely. Although a small number of conjugated C
18
trienes are found to a certain extent in some seed oils, such as tung oil (china wood oil,
Aleurites fordii
, Euphorbiaceae), and some conjugated C
18
dienes are present in tall oil, a product obtained from pine wood during sulfate pulping processes, there are few natural plant sources of conjugated polyenes. Thus, investigators continue to seek ways to obtain conjugated polyenes in quantity by partial or total synthesis.
Several methods exist for preparing conjugated polyenes, including (1) biosynthesis; (2) dehydration of hydroxy fatty acids; and (3) isomerization. Biosynthetic methods have been used to prepare a number of conjugated dienes. The use of bacterial enzymes in such syntheses came about when researchers discovered that bacteria found in the stomachs of ruminants convert dietary unsaturated fatty acids contained in plant food sources into conjugated isomers. For example, the enzyme linoleate isomerase, isolated from the rumen anaerobic bacterium
Butyrivibrio fibrisolvens
, isomerizes linoleic acid to mainly cis-9, trans-11-octadecadienoic acid (c9, t11-18:2), which is sometimes referred to as rumenic acid. However, biosynthetic methods are not preferred for several reasons, including generally low yields and the difficulty of isolating specific conjugated compounds from the mixture that results.
In preparing conjugated polyenes via dehydration of hydroxy fatty acids, various isomers can be obtained. For example, dehydration of ricinoleic acid (12-hydroxy-9-cis-octadecenoic acid, also termed 12-hydroxy oleic acid) at 235° C. with activated alumina catalyst leads to 9-cis,11-trans-18:2. Dehydration of ricinelaidic (12-hydroxy-9-trans-octadecenoic acid) at 200° C. under vacuum with potassium acid sulfate catalyst leads to 9-trans, 11-trans-18:2. Dehydration of methyl ricinoleate where the hydroxy group is first converted to its mesyl (methanesulfonate) or tosyl (toluene-p-sulfonate) ester also has been investigated. For example, heating the mesyl ester of methyl ricinoleate at 100° C. with NaOCH
3
/DMSO, DBU (1,5, -diazobicyclo(5.4.0)undec-5-ene), or DBN (1,5, -diazobicyclo(4.3.0)non-5-ene), leads to 9-cis,11-trans-18:2 conjugated ester. However, although these methods allow yields that are somewhat better than biosynthetic methods, yields seen in such dehydrogenation methods nevertheless are still less than about 70 percent. Moreover, dehydration of ricinoleates can produce conjugated compounds in which both double bonds have shifted relative to the starting compound. Due in part to these problems, these methods have not been widely utilized.
Synthesis of conjugated polyenes via isomerization typically proceeds from an unconjugated polyene fatty acid or fatty acid ester as precursor. Probably the most common unconjugated polyene precursor employed in such methods is linoleic acid. According to the delta (&Dgr;) nomenclature system, linoleic acid can be expressed as all-cis-9,12-octadecadienoic acid, or c9,c12-octadecadienoic acid, where c indicates the cis-configuration (the orientation that almost invariably occurs in linoleic acid derived from natural sources) and the numbers 9 and 12 indicate the position of the double bonds relative to the carboxyl carbon of the acyl chain (—COOH). This nomenclature can be abbreviated in several ways, including: 18:2 (&Dgr;9,12); 18:2-c9,c12; 9-cis,12-cis-18:2; and c9,c12-18:2, where c indicates the cis-configuration, 18 indicates the total number of carbon atoms, and 2 represents the number of double bonds in the molecule. Using alternative nomenclature, linoleic acid can be expressed in the (n-6) or omega (&ohgr;) system as 18:2 (n-6) or 18:2 &ohgr;6, where (n-6) or &ohgr;6 indicates the position of the first double bond beginning from the methyl end.
Isomerization produces various isomers that have the same atomic composition as the parent compound but that differ in chemical structure. The structural differences in isomers can be both positional and geometrical. Positional isomers result from the migration of double bonds. Geometric isomers result from the various combinations of cis and trans configurations such positional isomers can adopt. Thus, each positional isomer may occur as one or more of four possible geometric isomers. For example, isomerization of linoleic acid [18:2 (&Dgr;9,12)] could produce a total of at least eight isomers: two positiona

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