Glyceride

Glycerides.— There have been no radical developments in the area of glyceride syntheses but standard methods have been reviewed (see ref. 155a) and continue to be used and improved, particularly for enantiomeric glycerides of known configuration. 

Symmetrical 1,3-diacylglycerols have been made by acylation and reduction of dihydroxyacetone. One French report describes several ways of making triacylglycerols having three different acyl groups and another is concerned with the mono- and di-oleatesof 2-methyl-and2,2-dimethyl-butane-l,4-diol.  

2- and 2,3-Diacyl-5 -glycerols with mixed acyl groups have been prepared from D-mannitol via the appropriate glycerol carbonates with the help of 

Derbesy, M. Chicheportiche, and M. Naudet, Bull. Soc. chim. France, 1971,1789 

2-trichloroethyl chloroformate. Certain advantages are claimed for the trichloroethoxycarbonyl protecting group. 

Glycerol can be esterified commercially with one, two, or three fatty acids to produce mono-, di-, or triglycerides. Fats and oils are naturally occurring triglycerides, the distribution of which varies in different plants and animals. 

The properties of triglycerides depend on the fatty acid composition and on the relative location of fatty acids on the glycerol. As accurate methods for determining the composition are available, several conventions have been developed to specify arrangements of fatty acids on the glycerol molecule. Natural fats and oils are designated as the triglyceride type in terms of saturated and unsaturated acids and isomeric forms. 

A stereospecific numbering system (Sn) is used to indicate the location of specific fatty acids in triglyceride molecules such as in 1-stearoyl-2-oleoyl-3-myristoyl-Sn-glycerol the respective fatty acids are indicated in the 1, 2, and 3 positions. This kind of information is very valuable in relating properties of certain fats to compositional data. Table 4.4 

TABLE 4.3 Triglyceride Types and Isomeric Forms of Natural Fats 

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Liquid or solid films which reduce or prevent adhesion between surfaces solid-solid, solid-paste, solid-liquid. Waxes, metallic soaps, glycerides (particularly stearates), polyvinyl alcohol, polyethene, silicones, and fluorocarbons are all used as abherents in metal, rubber, food, polymer, paper and glass processing. 

CH3-[CH2],8-C00H. M.p. 75 C. A fatty acid occurring as glycerides in peanut and other vegetable oils. 

CH3 [CHJb-COOH. M.p. 31 5"C, b.p. 268-270 C. A fatty acid, occurring in wool as the potassium salt, as esters in fusel oil, and as glycerides in cows and goats milk and coconut and palm oils. 

The fatty acids occur in nature chiefly as glycerides see fats), which constitute the most important part of the fats and oils, and as esters of other alcohols, the waxes. The naturally occurring fatty acids are mostly the normal straight-chain acids with an even number of carbon atoms. 

CH20H-CH(0H)-CH,0H, C3HHO3. Normally obtained as a colourless, odourless, viscous liquid with a very sweet taste. M.p. 20 C, b.p. 182 C/20mm. It absorbs up to 50% of its weight of water vapour. It occurs (glycerides) in combination with various fatly acids in all animal and vegetable fats and oils. 

C12H24O, CH3 [CH,]io COOH. Needles, m.p. 44 C, b.p. 225"C/I00mm. A fatty acid occurring as glycerides in milk, spermaceti, laurel oil, coconut oil, palm oil and other vegetable oils. The metal salts are widely used. 

Commercial lecithin is a mixture of phos-phatides and glycerides obtained in the manufacture of soya bean oil. It gives a thick yellow emulsion with water, and is widely used in the food and other industries. 

CifiHjjOi. A fatly acid which is easily oxidized in air.-It occurs widely, in the form of glycerides, in vegetable oils and in mammalian lipids. Cholesieryl linoleale is an important constituent of blood. The add also occurs in lecithins. Together with arachidonic acid it is the most important essential fatty acid of human diet. 

Colourless liquid. B.p. 286 C/100 mm., insoluble in water. Oleic acid occurs naturally in larger quantities than any other fatty acid, being present as glycerides in most fats and oils. It forms one third of the total fatty acids of cow s milk. A crude grade from inedible tallow is used in the production of lubricants, detergents, resins and other products. 

Lipoproteins. The lipid moiety of lipoproteins is quite variable both qualitatively and quantitatively. The a-lipoprotein of serum contains glyceride, phosphatide and cholesterol to about 30 -40% of the total complex. The -lipoprotein of serum contains some glyceride but the phosphatide and cholesterol account for nearly 75% of the total. 

M.p. SS C, b.p. 2I0 C. Important fatty alcohol obtained from naturally occurring glycerides. Used in the pharmaceutical and cosmetics industries and as a gel stabilizer for greases. 

If the original ester is a fat or oil and produces an odour of acrolein when heated, it may be a glyceride. Esters of ethylene glycol and of glycol with simple fatty acids are viscous and of high b.p. They are hydrolysed (method I) and the ethyl alcohol distilled ofl. The residue is diluted (a soap may be formed) and acidified with hydrochloric acid (Congo red paper). The acid is filtered or... 

The term fat is applied to solid esters of fatty acids with glycerol (glycerides) if the fat is liquid at the ordinary temperature, it is conventionally called a fatty oil, vegetable oil or animal oil. The acids which occur most abundantly are palmitic ticid CH3(CHj),4COOH, stearic acid CH3(CH2)isCOOH and oleic acid CH3(CH2),CH=CH(CH2),C00H. Upon hydrolysis, fats yield glycerol and the alkali salts of these acids (soaps) ... 

The free acids are obtained upon acidification. Fata usually consist of mixtures of glycerides. The term wax is usually applied to esters of fatty acids with other alcohols such as cetyl alcohol CH3(CH2),4CHjOH and oleyl alcohol CH3(CHj),CH=CH(CHj),CH30H. 

Both FI and FD provide good molecular mass information, but few if any fragment ions, and allow thermally labile substances such as peptides, nucleosides, and glycerides to be examined, as well as inorganic salts. 

Residual monomers in the latex are avoided either by effectively reacting the monomers to polymer or by physical or chemical removal. The use of tert-huty peroxypivalate as a second initiator toward the end of the polymeri2ation or the use of mixed initiator systems of K2S20g and tert-huty peroxyben2oate (56) effectively increases final conversion and decreases residual monomer levels. Spray devolatili2ation of hot latex under reduced pressure has been claimed to be effective (56). Residual acrylonitrile also can be reduced by postreaction with a number of agents such as monoamines (57) and dialkylamines (58), ammonium—alkali metal sulfites (59), unsaturated fatty acids or their glycerides (60,61), their aldehydes, esters of olefinic alcohols, cyanuric acid (62,63), andmyrcene (64). 

Phospholipids. Glycerides esterified by fatty acids at the 1,2 positions and a phosphoric acid residue at the 3 position constitute the class called phosphoHpids (3). In older Hterature and in commercial practice, these materials are described as phosphatides. 

Historically, many attempts have been made to systematize the arrangement of fatty acids in the glyceride molecule. The even (34), random (35), restricted random (36), and 1,3-random (37) hypotheses were developed to explain the methods nature utilized to arrange fatty acids in fats. Invariably, exceptions to these theories were encountered. Plants and animals were found to biosynthesize fats and oils very differently. This realization has led to closer examination of biosynthetic pathways, such as chain elongation and desaturation, in individual genera and species. 

The crystal stmcture of glycerides may be unambiguously determined by x-ray diffraction of powdered samples. However, the dynamic crystallization may also be readily studied by differential scanning calorimetry (dsc). Crystallization, remelting, and recrystallization to a more stable form may be observed when Hquid fat is solidified at a carefully controlled rate ia the iastmment. Enthalpy values and melting poiats for the various crystal forms are shown ia Table 3 (52). 

Partial glycerides tend to melt higher than thek triglyceride counterparts, as shown in Figure 6. This observation is consistent with the presence of free hydroxyl groups which can participate in increased intermolecular hydrogen bonding. 

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