Palmitic acid glycerol esters

Solids. —It may Idc a hydrocM bon (c .g., paraffin wa, naphthalene) highei alcohol eg., cetyl alcohol) aldehyde e.g., z5-hydroxybenzaldehyde) ketone and qiiinonc e.g., benzo-phenone, camphor) acid (higher fatty, e.g., palmitic acid or aromatic acid) ester (of glycerol, phenols or aromatic alcohols) phenol e.g., thymol),... 

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 acid CH3(CH,),4COOH, stearic acid CH,(CH,),4C00H and oleic acid CH,(CH,),CH=CH(CH,),COOH. Upon hydrolysis, fats yield glycerol and the alkali salts of these acids (soaps) ... 

Soybean oil is a statistical mixture of glycerol esters of palmitic acid (10%), stearic acid (3%), oleic acid (23%), linoleic acid (55%), and linolenic acid (9%). 

Figure 1-5. Separation of selected representatives of different lipid classes. (1) Paraffin, (2) K-hexadecyl palmitate (3) cholesterol palmitate (4) stearic acid methyl ester (5) glycerol tripalmitate (6) hexadecyl alchohol (7) stearic acid (8) cholesterol (9) glycerol-1,3-dipalmitate (10) glycerol-l,2-dipalmitate (11) glycerol monopalmitate (12) erucylamide. Column LiChrosphere Diol (125 x 3mm) 5- xm particles. Gradient from isooctane (A) to 60% methyl tritbutyl ether (MTBE) in 34min -t lOmin isocratic hold. (Reprinted from reference 14, with permission.)...

The natural fats and oils are also esters, principally of the trihydroxy alcohol glycerol. Animal fats consist mainly of the glyceryl esters of palmitic acid and stearic acid. Glyceryl oleate, the glyceryl ester of oleic acid, is found in olive oil, whale oil, and the fats of coldblooded animals these fats tend to remain liquid at ordinary tempera-lures, whereas glyceryl palmitate and glyceryl stearate form the solid hits. 

Lard, with an unusually high level of palmitic acid in the p-position, crystallizes naturally in the p form. When randomized, the content of 2-pahnito-glycerol esters is reduced from around 64% to 24% and the interesterified product crystallizes in the p form with consequent improvement in shortening properties. 

Constitution of Fats and Oils.—These acids which have all been previously discussed (pp. 136 and 170) embrace the more common ones that are found as esters in most oils and fats. The tri-acid ester of glycerol and palmitic acid may be taken as an example of a typical fat. It is exactly analogous to the ester of glycerol and acetic acid which we have just considered, and its formula is ... 

Saponification.—With a fat, which is a glycerol ester of a higher fatty acid, typified by glyceryl tri-palmitate, the reaction yields glycerol and the salt of the acid or acids, present, as follows ... 

The sodium or potassium salt of palmitic acid, or of stearic acid or the mixed salts of several acids obtained from ordinary fats, is the common substance known as soap. This particular reaction of hydrolysis, is, therefore, known, also, as a reaction of saponification (soap formation). Strictly speaking the reaction of saponification applies only to the alkaline hydrolysis of fats, i,e., of glycerol esters, but, as the hydrolysis of other esters is a reaction of exactly the same character, the term is used to apply equally to the hydrolysis of any ester in presence of an alkali. In the case of the lower alcohol and lower acid esters, e.g., ethyl acetate, the salt formed is not a soap but is a crystalline salt, sodium acetate. 

As commercially made by the saponification of fats, soaps are not pure chemical individuals but consist of a mixture of the alkali-metal salts of the several fatty acids contained as esters in the original fat or oil. The composition of soap, therefore, depends upon the composition of the fat from which it is made. As the common fats and oils which are used for this purpose contain, mostly the glycerol esters of palmitic, stearic and oleic acids, the common soaps are mixtures of sodium, or potassium, palmitate, stearate and oleate. We shall consider now,... 

FIGURE 1.9 Tripalmitate. Tnpalmitate is a Iriglycetide consisting of a glycerol backbone that is linked, via ester bonds, to three molecules of palmitic acid, a 16-carbon carboxylic acid-... 

As previously mentioned, the triglycerides found in biomass are esters of the triol, glycerol, and fatty acids (Fig. 3.6). These water-insoluble, oil-soluble esters are common in many biomass species, especially the oilseed crops, but the concentrations are small compared to those of the polysaccharides and lignins. Many saturated fatty acids have been identified as constituents of the lipids. Surprisingly, almost all the fatty acids that have been found in natural lipids are straight-chain acids containing an even number of carbon atoms. Most lipids in biomass are esters of two or three fatty acids, the most common of which are lauric (Cn), myristic (Cu), palmitic (Cia), oleic (Cis), and linoleic (Cis) acids. Palmitic acid is of widest occurrence and is the major constituent (35 to 45%) of the fatty acids of palm oil. Lauric acid is the most abundant fatty acid of palm-kemel oil (52%), coconut oil (48%), and babassu nut oil (46%). The monounsaturated oleic acid and polyunsaturated linoleic acid comprise about 90% of sunflower oil fatty acids. Linoleic acid is the dominant fatty acid in com oil (55%), soybean oil (53%), and safflower oil (75%). Saturated fatty acids of 18 or more carbon atoms are widely distributed, but are usually present in biomass only in trace amounts, except in waxes. 

A membrane cell recycle reactor with continuous ethanol extraction by dibutyl phthalate increased the productivity fourfold with increased conversion of glucose from 45 to 91%.249 The ethanol was then removed from the dibutyl phthalate with water. It would be better to do this second step with a membrane. In another process, microencapsulated yeast converted glucose to ethanol, which was removed by an oleic acid phase containing a lipase that formed ethyl oleate.250 This could be used as biodiesel fuel. Continuous ultrafiltration has been used to separate the propionic acid produced from glycerol by a Propionibacterium.251 Whey proteins have been hydrolyzed enzymatically and continuously in an ultrafiltration reactor, with improved yields, productivity, and elimination of peptide coproducts.252 Continuous hydrolysis of a starch slurry has been carried out with a-amylase immobilized in a hollow fiber reactor.253 Oils have been hydrolyzed by a lipase immobilized on an aromatic polyamide ultrafiltration membrane with continuous separation of one product through the membrane to shift the equilibrium toward the desired products.254 Such a process could supplant the current energy-intensive industrial one that takes 3-24 h at 150-260X. Lipases have also been used to prepare esters. A lipase-surfactant complex in hexane was used to prepare a wax ester found in whale oil, by the esterification of 1 hexadecanol with palmitic acid in a membrane reactor.255 After 1 h, the yield was 96%. The current industrial process runs at 250°C for up to 20 h. 

The oil consists mainly of glycerol esters of stearic acid (and some palmitic acid) at this point. 

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