由直链不饱和脂肪酸异构制备支链脂肪酸的研究进展

介绍了直链不饱和脂肪酸制备支链脂肪酸的研究现状,综述了脂肪酸异构机理,异构催化剂如白土催化剂、沸石催化剂,催化剂的筛选原则,着重讨论了各种常用沸石对于脂肪酸异构反应不同的影响以及现有的合成工艺。分析了脂肪酸的分离技术,包括精馏分离法、溶剂结晶法、尿素包结法、超临界流体萃取法的优缺点,指出沸石催化生产支链饱和脂肪酸的关键问题是需要解决混合脂肪酸作为原料反应的选择性问题,其相关的基础性工作,如更明确的反应机理和催化剂结构参数对反应的影响,仍是将来的研究方向。     

Cis-Trans isomerization of unsaturated fatty acid methyl esters without double bond migration

Trans isomerization of monoenoic and dienoic fatty acid methyl esters has been carried out with thiols and diphenylphosphine in the presence of azobisisobutylnitrile. The equilibrium mixture contained 75–80%trans double bonds and there was no migration of the double bonds.     

Hydroformylation of unsaturated fatty acids

When hydroformylation of unsaturated fatty materials is done with rhodium-triphenyl phosphine (or phosphite) catalysts, a number of advantages become apparent compared to cobalt carbonyl-catalyzed reactions. With rhodium, the reaction can be carried out (a) at pressures as low as 200 psi, (b) at each double bond location in a polyunsaturated fatty acid, and (c) in high yield and conversion. Solubilized catalyst can be recovered from distillation residue and readsorbed on spent catalyst support by thermal treatment in a rotary kiln. The reconstituted catalyst is more active than the original catalyst and can be recycled indefinitely at a relatively low cost. Recently developed supports for “homogeneous” catalysis may make catalyst recovery even more effective. Acetalation, oxidation with air to polycarboxylic acids and catalytic hydrogenation to hydroxymethyl compounds can be done easily and in high yield on mono-, di- and triformyl derivatives alike. Other reactions investigated for monoformyl fatty esters include reductive amination to form aminomethyl derivatives and Tollen’s condensation with formaldehyde to form geminal,bis-hydroxymethyl compounds. although the Northern Center has carried out some basic investigations on the hydroformylation reaction and on the chemistry of the hydroformylated products, there is a great deal more that can be done with regard to synthesis of new compounds and development of new applications.     

Polymerization of unsaturated fatty acids

Summary A method is proposed for the preparation of polybasic fat acids or “dimer” acids directly from fatty acids which is readily adaptable to commercial use. The presence of moisture maintained in the reaction vessel by steam pressure substantially prevents decomposition and decarboxylation of the fatty acids. By this method a larger percentage of dibasic acids, as compared to tribasic acids, is produced than by the previously described methods. The method of high temperature polymerization of fatty acids in the presence of moisture is also used to remove polyunsaturated fatty acids from commercial oleic acid. Presented at 20th fall meeting, American Oil Chemists’ Society, Chicago, Ill., Oct. 30–Nov. 1, 1946.     

Homogeneously catalysed hydrogenation of unsaturated fatty acids to unsaturated fatty alcohols

The use of copper and cadmium oxides or soaps as catalysts for the hydrogenation of unsaturated fatty acids to unsaturated fatty alcohols has been investigated. It is shown that copper soaps homogeneously activate hydrogen. When copper and cadmium oxides are used as catalysts, they react with the acid under formation of a homogeneous soap solution. A continuous reaction system for the preparation of unsaturated fatty alcohols by hydrogenation under the influence of copper and cadmium soaps is described.     

Effect of oxygen and other factors in selenium catalyzed isomerization of unsaturated fatty acid esters

In thetrans-isomerization of ethyl linoleate using 1% selenium as catalyst under nitrogen, 200C was found to be the optimal temperature. Conjugation and polymerization were concurrent with the formation of thetrans esters. In the isomerization of ethyl oleate with selenium, the double bond did not migrate to any appreciable extent. Isomerization studies were performed on olive, safflower and linseed oils and ethyl esters of oleic, linoleic and linolenic acids. Time to reach maxi-maltrans isomer content was longest with linole-nate esters; glycerides reacted more rapidly than ethyl esters, and with lesser polymerization. Oxygen was found to be an important partici-pant in thetrans-isomerization reaction. Its ex-clusion resulted in sharply diminished reaction rates. Benzoyl peroxide and hydrogen peroxide accelerated while an antioxidant (BHT) retarded the reaction. Journal Paper No. 2046, Purdue University Agricultural Experi-ment Station Presented at the AOCS Meeting, New Orleans, 1962     

Oxidative decarboxylation of unsaturated fatty acids

Long‐chain internal olefins were prepared by silver(II)‐catalyzed oxidative decarboxylation of unsaturated fatty acids by sodium peroxydisulfate. Similar to saturated carboxylic acids, 1‐alkenes were the major decarboxylation product in the additional presence of copper(II), whereas in the absence of copper(II) alkanes were predominantly formed. In both cases, the internal unsaturation of the fatty acids remained largely intact, although the moderate yields indicated that side reactions occurred to a significant extent. The simple procedure makes this multistep one‐pot reaction useful for the synthesis of a variety of internally unsaturated hydrocarbons. The purified products, almost all of which are prepared for the first time, may serve as reference compounds for studies on the heterogeneously catalyzed decarboxylation of triglycerides and fatty acids in the absence of hydrogen. Practical applications: The products of the chemistry described in this contribution, i.e., unsaturated long‐chain hydrocarbons, provide bio‐based building blocks for further chemical modification toward products which may be applied as (bio)fuels, lubricants, solvents, and polymeric materials.     

Conversion of unsaturated fatty acids – cycloadditions with unsaturated fatty acids [1]

Diels-Alder reactions with methyl conjuenate ( 2 ) at room temperature, with methyl E-12-oxo-10-octadecenoate ( 11 ) as dienophile and radical cation catalyzed cycloadditions of 2 are described. 2 is prepared from methyl linoleate by base catalyzed isomerization with sodium dimethylsulfoxide in 90% yield. It undergoes readily Diels-Alder reactions at room temperature in the presence of 1–1.8 equivalents of a Lewis acid and catalytic amounts of iodine to form cycloadducts in 55–90% yield. At 140°C 2 reacts with dimethyl maleate and dimethyl acetylenedicarboxylate to cycloadducts in 86% and 73% yield, respectively. Methyl E-12-oxo-10-octadecenoate ( 11 ) can be combined in a Diels-Alder reaction with the dienes 2-(trimethylsilyloxy)-1,3-butadiene and 2,3-dimethylbutadiene in 69% and 86% yield, respectively. By way of radical cation catalysis 2 undergoes [4+2]-cycloadditions with dienes in high yield.     

Trans unsaturated fatty acids in bacteria

The occurrence oftrans unsaturated fatty acids as by-products of fatty acid transformations carried out by the obligate anaerobic ruminal microflora has been well known for a long time. In recent years, fatty acids withtrans configurations also have been detected in the membrane lipids of various aerobic bacteria. Besides several psychrophilic organisms, bacteria-degrading pollutants, such asPseudomonas putida, are able to synthesize these compoundsde novo. In contrast to thetrans fatty acids formed by rumen bacteria, the membrane constituents of aerobic bacteria are synthesized by a direct isomerization of the complementarycis configuration of the double bond without a shift of the position. This system of isomerization is located in the cytoplasmic membrane. The conversion ofcis unsaturated fatty acids totrans changes the membrane fluidity in response to environmental stimuli, particularly where growth is inhibited due to the presence of high concentrations of toxic substances. Under these conditions, lipid synthesis also stops so that the cells are not able to modify their membrane fluidity by any other mechanism.     

Geometric isomerization of fatty acids with nickel catalyst

Cis-trans isomerization studies were performed on commercial oleic acid and refined sunflower oil. Reactions were carried out at constant temperature, under inert atmosphere (without hydrogen), using an industrial nickelcontaining hydrogenation catalyst. With sunflower oil, hydrogen transfer and polymerization were concurrent with the formation ofrans isomers. Based on work done in partial fulfillment of requirements for completion of the doctoral dissertation of Maria A. Grompone.     

Double bond oxidation of unsaturated fatty acids

Different oxidizing agents for performing the cleavage oxidation of the double bond of the unsaturated fatty acids are presented, and their economic performance is analyzed. Ozone and sodium hypochlorite are the most commercially efficient oxidants. Laboratory work for the oxidation of oleic acid to azelaic and pelargonic acids using hypochlorite as oxidant is described. The advantages of working in an emulsion system and using RuCl₃ as a catalyst are discussed, and a possible mechanism of the reaction is presented. A flow sheet for an industrial process based on this concept is proposed. A simulation of a plant using this technology is made by a computerized model, and the economic parameters obtained permit us to conclude that the sodium hypochlorite can be an interesting reagent for industrial oxidations of double bonds in fatty acids.     

Liquid-phase catalytic oxidation of unsaturated fatty acids

Liquid-phase catalytic oxidation of oleic acid with hydrogen peroxide in the presence of various transition metal/metal oxide catalysts was studied in a batch autoclave reactor. Azelaic and pelargonic acids are the major reaction products. Tungsten and tantalum and their oxides in supported and unsupported forms were used as catalysts. Alumina pellets and Kieselguhr powder were used as supports for the catalysts. Tungsten, tantalum, molybdenum, zirconium, and niobium were also examined as catalysts. Tertiary butanol was used as solvent. Experimental results concluded that tungsten and tungstic oxide are more suitable catalysts in terms of their activity and selectivity. The rate of reaction observed in the case of supported catalysts appears to be comparable or superior to that of unsupported catalysts. In pure form, tungsten, tantalum, and molybdenum showed strong catalytic activity in the oxidation reaction; however, except for tantalum the other two were determined to be economically unfeasible. Zirconium and niobium showed very little catalytic activity. Based on the experimental observations, tungstic oxide supported on silica is the most suitable catalyst for the oxidation of oleic acid with 85% of the starting oleic acid converted to the oxidation products in 60 min of reaction with high selectivity for azelaic acid.     

Reaction of oxygen and unsaturated fatty acids

Oxygen reacts readily with unsaturated fatty acids so that every time these compounds are handled there is a danger they will become contaminated with oxidation products. The products formed first are allylic hydroperoxides which are labile molecules that change rapidly to other compounds, some of which are highly flavorous. Sometimes these changes are desirable and may be promoted: frequently they are not and have to be inhibited. Instrumental procedures recently introduced—especially separation by high performance liquid chromatography and identification by¹H and¹³C nuclear magnetic resonance spectroscopy—have led to a renewed interest in this subject. For the nonenzymic processes of autoxidation and photooxygenation we now have a better understanding of the routes leading to the first-formed allylic hydroperoxides and an improved appreciation of the structure of further oxidation products including dihydroperoxides and hydroperoxides which also contain one or more cyclic peroxide units. Direct chemical routes to several of these compounds have also been developed. Oxidation of linoleic acid by plant-derived lipoxygenases gives diene hydroperoxides similar to those produced by autoxidation, except that the former are optically active and the latter racemic. Enzymic oxidation of arachidonic acid and certain related C₂₀ acids in animal systems produces a wide variety of prostaglandins, physiological properties. These compounds have been described as “tomorrow’s drugs”.     

Separation of saturated/unsaturated fatty acids

Fatty acid mixtures can be separated into one fraction rich in saturated fatty acids and the other rich in unsaturated acids. Since saturated fatty acids have a higher melting point than unsaturated, liquid mixture to be fractionated is cooled to a temperature at which the larger part of the saturated acids crystallize, while the greater part of unsaturated acids remain in liquid form. Different industrial methods to separate the two phases are described. The oldest and simplest method is slowly to cool and crystallize the mixture in shallow pans to form cakes which then are pressed in presses of different design. By applying high pressure, the liquid olein is thus squeezed out from the cake, leaving the stearin fraction behind. A new process to separate the phases is to mix an aqueous solution, containing a wetting agent, with the crystallized fatty acid mixture. The stearin crystals are thus wetted and transferred into the aqueous phase, which then can be separated from the olein phase in a centrifuge. The stearin/aqueous suspension is heated to melt the stearin, which can then be separated in a second centrifuge. Other methods to improve phase separation use organic solvents, among which are methanol, acetone, methyl formate and propane. In the solvent fraction process, the miscella has to be cooled to a lower temperature than in the aforementioned methods, due to the solubility effect of the solvents. The solvents are removed by distillation from the fraction. Typical operation results with different types of raw materials are given. The advantages and disadvantages of the different methods are discussed.     

Alkaline cleavage of hydroxy unsaturated fatty acids. I. Ricinoleic acid and lesquerolic acid

The effects of temperature and media on the fusion of ricinoleic and lesquerolic acid derivatives with concentrated aqueous alkali were examined. Improved yields ofω-hydroxy acids were obtained by use of excess 2-octanol. The effect of excess 2-octanol is discussed in relation to a recently proposed reaction mechanism. A laboratory of the W. Utiliz. Res. Devel. Div., ARS, USDA.     

Biochemistry of unsaturated fatty acid isomers

Recognition that catalytic hydrogenation changes the configuration and position of double bonds and alters the physical properties of unsaturated fats prompted numerous early investigations on the bio-chemical effects of ldtrans isomers.” Recent research has provided data on positional isomer metabolism. Some aspects of fatty acid isomer metabolism are now reasonably well understood, but other issues are not resolved. Human and animal data have provided good evidence that isomers in partially hydrogenated oils are well adsorbed and incorporated into all organs and tissues. Analyses of human tissues also indicate that hydrogenated oils are the major source of fatty acid isomers in the US diet. Tissue composition data combined with isolated enzyme studies and isotope tracer experiments with whole organisms show unquestionably that structural differences between various fatty acid isomers influence specific biochemical transformations. Examples are differences in the reaction rates and/ or specificities of acyl transferase, lipase, desaturase and cholesteryl esterase/hydrolase for various positional fatty acid isomers. Isolated microsomes and mitochondria also have been used to identify dif-ferences in acyl CoA activation, oxidation, and elongation of posi-tional isomers. In addition, isotope tracer experiments show that preferential metabolism of individual positional isomers occurs in vivo. In vivo studies with hydrogenated vegetable oil diets containing adequate levels of linoleic acid produced no obvious physiological changes. Experiments with specific polyunsaturated isomers have produced changes in blood cell properties, pulmonary weight, lino-leic acid requirements and tissue lipid composition. These changes may be related to a number of factors such as membrane fluidity and permeability, cell function, synthesis of arachidonic acid, homo-gamma-linoleic acid or prostaglandins. Whether differences in the biochemistry of fatty acid isomers are desirable or undesirable and whether these differences contribute to long-term or subtle effects important to the etiology of atherosclerosis and cancer are not resolved. Presented at the 73rd AOCS annual meeting, Toronto, 1982.     

cis/trans isomerization of unsaturated fatty acids as possible control mechanism of membrane fluidity inPseudomonas putida P8

Exponentially growing cells ofPseudomonas putida had an increased ratio of saturated to unsaturated fatty acids in response to increased growth temperatures. Resting cells in which fatty acid biosynthesis was stopped reacted to a thermal increase by convertingcis-monounsaturated fatty acids totrans isomers.cis/trans isomerization of up to 60% of the unsaturated fatty acids was also activated by alcohols of different chain length. Their effective concentrations apparently depended on the lipophilic character of the alcohols. Also, a salt shock caused by the addition of NaCl resulted in the production oftrans fatty acids. However, cells that were adapted to growth media of high osmolarity synthesized cyclopropane fatty acids instead oftrans fatty acids. Activity ofcis/trans-isomerase was dependent on the growth phase and was significantly higher during logarithmic growth than during the stationary phase. The results of this study agree with the hypothesis that the isomerization ofcis intotrans unsaturated fatty acids is an emergency action of cells ofP. putida to adapt membrane fluidity to drastic changes of environmental conditions.