Unsaturated fatty acids hydrogenation

Consider a cell membrane lipid derived from linoleic acid, which is an unsaturated fatty acid. Hydrogen atom abstraction of an allylic hydrogen by a hydroxyl radical leads to a resonance-stabilized free allylic radical in which the unpaired electron is delocalized over C-9, C-11, and C-13. 

Huges PE, Tove SB (1982) Biohydrogenation of unsaturated fatty adds. Purification and properties of cis-9, trans-11-octadecanoate reductase. J Biol Chem 257 3643-3649 Hunter WJ, Baker FC, Rosenfeld IS, Keyser JB, Tove SB (1976) Biohydrogenation of unsaturated fatty acids. Hydrogenation by cell-free preparations of Butyrivibrio fibrisolvens. J Biol Chem... 

Hydroxyl tion. Commercial lecithin can be hydroxylated at the unsaturated fatty acid chains by treatment with concentrated hydrogen peroxide and acids like lactic or acetic acid. 

The fatty acids obtained from the process can be used directly or further manipulated for improved or modified performance and stabiUty. Hardening is an operation in which some fraction of the unsaturated bonds present in the fatty acids are eliminated through hydrogenation or the addition of H2 across a carbon—carbon double bond. This process was initially intended to improve the odor and color stabiUty of fatty acids through elimination of the polyunsaturated species. However, with the growth in the use of specialty fatty acids, hydrogenation is a commercially important process to modify the physical properties of the fatty acids. 

Positionalisomeri tion occurs most often duting partial hydrogenation of unsaturated fatty acids it also occurs ia strongly basic or acidic solution and by catalysis with metal hydrides or organometaUic carbonyl complexes. Concentrated sulfuric or 70% perchloric acid treatment of oleic acid at 85°C produces y-stearolactone from a series of double-bond isomerizations, hydration, and dehydration steps (57). 

There are essentially four steps or unit operations in the manufacture of fatty acids from natural fats and oils (/) batch alkaline hydrolysis or continuous high pressure hydrolysis (2) separation of the fatty acids usually by a continuous solvent crystallisation process or by the hydrophilisation process (J) hydrogenation, which converts unsaturated fatty acids to saturated fatty acids and (4) distillation, which separates components by their boiling points or vapor pressures. A good review of the production of fatty acids has been given (1). 

Structure and Mechanism of Formation. Thermal dimerization of unsaturated fatty acids has been explaiaed both by a Diels-Alder mechanism and by a free-radical route involving hydrogen transfer. The Diels-Alder reaction appears to apply to starting materials high ia linoleic acid content satisfactorily, but oleic acid oligomerization seems better rationalized by a free-radical reaction (8—10). 

Clay-catalyzed dimerization of unsaturated fatty acids appears to be a carbonium ion reaction, based on the observed double bond isomerization, acid catalysis, chain branching, and hydrogen transfer (8,9,11). 

Addifion of oils and oilseeds to the diet is another method that has been used to reduce CH4 emissions (Beauchemin et ah, 2008 Eckard et ah, 2010). Lipid addition to the diet may reduce CH4 emissions by hydrogenation of unsaturated fatty acids, enhanced propionic acid production, and protozoal inhibition (Johnson and Johnson, 1995). Reductions in CH4 of >40% have been demonstrated with lipid supplementation... 

The daily output of fecal fat may be regarded as the simplest quantitative measure of the effect of gluten on these patients. The evidence available suggests that the extra fat is derived from dietary fat and mainly represents interference with absorption. There is usually a disproportionate increase of saturated as compared with unsaturated fats (W4). The reason for this is not clear. There may be selective rejection of longer chain and more saturated fats there may also be increased hydrogenation of unsaturated fatty acids (SI). The increase of fat output may occur within a day or 2, or it may be delayed for 10 days or more. There are many possible explanations for this delay. It may require many small insults to the mucous membrane... 

Additionally, it should be observed that the thermal oxidability and oxidative polymerization of the unsaturated fatty acids follows the trend linolenic > linoleic > oleic > > palmitoleic (Martinenghi, 1963). The oxidation involves, as first step, the abstraction of a hydrogen atom in allylic position to the double bonds. Certainly, this process is favoured in the case of fatty acids with two or more unconjugated double bonds where the formation of a free radical by allylic hydrogen abstraction leads quite necessarily to double bonds slippage with formation of conjugated double bonds ... 

The melting points of the pure saturated fatty acid-DETA derivatives were over 100°C and possessed low solubility in most organic solvents. The unsaturated fatty acid-diamides had much lower melting points. The industrial fatty-DETA derivatives with the exception of the product from hydrogenated tallow fatty acids melted at 60°C or below. 

The reactions studied were the catalytic formation of methane from carbon monoxide and hydrogen (according to Sabatier (34), normal pressure), the catalytic hydrogenation of unsaturated hydrocarbons and also of unsaturated fatty acids ( fat hardening according to Normann (35)). Here again, a certain analogy was established between... 

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