Fatty acids and esters of monohydric alcohols

The physical properties of fatty acids and their simple esters will be discussed in considerable detail. Fatty acids are key components in most lipids and the present section should provide a basis for the understanding of physical effects due to variations in fatty acid structure such as chain length, presence of double bonds, branches, etc. 

The most complete investigation of the polymorphism of normal fatty acids in the interval C12-C29 was reported by Stenhagen and von Sydow (1953). Their results can be summarized by the following schematic phase relationships  

All three crystal forms can be obtained from solvent whereas only the C-form is obtained from the melt. The irreversible character of the transitions A to B and B to C shows that the C-form is the stable crystal form. It should be pointed out, however, that a transition in the solid state from the C-form to the crystal form A-super has been observed in lauric acid (see the next paragraph). 

The C -form is only stable in a small interval close to the melting point and the melt is supercooled so the C -form is not obtained on cooling. At other temperatures the B -form is the stable form. 

Carboxylic acids with shorter chains (Ci-Cio) have been examined by Baun (1961). The X-ray data indicate that their structures are related, and the long-spacing values can be described by the relation 2.22 n + 0.86, where n is the number of carbon atoms in the chain. The complete crystal structures have been determined for formic acid (Holzberg et aL, 1953) and acetic acid (Jones and Tempelton, 1958). The molecules are linked by hydrogen bonds forming infinite chains, not dimers which are most common in fatty acids. 

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Waxes are esters of fatty acids with alcohols other than glycerol. Most of them are derived from long-chain fatty acids and long-chain monohydric alcohols, both usually having an even number of carbon atoms. Therefore, a wax usually contains an even number of carbon atoms also. 

Waxes are solid or semi solid plastic substances consisting of mixtures of esters, fatty acids, hi gh molecular-weight alcohols and even hydrocarbons. Waxes differ from fats in that they are the esters of monohydric,... 

Furey, in U.S. Patent No. 3,273,981 (103), disclosed a lubricity additive as being a mixture of A + B, wherein A is a polybasic acid or a polybasic acid ester made by reacting the acid with Ci—C5 monohydric alcohols and B is a partial ester of a polyhydric alcohol and a fatty acid, for example, glyceryl monooleate, sorbitan monooleate, or pentaerythitol monooleate. The mixture finds application in jet fuels. 

Such interchanges include the molecular rearrangement of completely esteri-fied esters of glycerol and mixtures of fatty acids, such as vegetable and animal oils—e.g., cottonseed oil or tallow the ester-ester exchange between aromatic carboxylic acid esters of a monohydric alcohol, such as o-CeH (C02CH3)2, and aliphatic carboxylic acid esters of a polyhydric alcohol, such as triacetin or between monohydric alcohol esters of aliphatic carboxylic acids—e.g., ethyl stearate —and fatty acid esters of polyhydric alcohol—e.g., tributyrin or triolein. 

Waxes form natural coatings on fruits, leaves, furs, feathers and skin. These coatings have protective functions against physical damage as well as water-repellency functions (waterproofing of birds, control of water loss by transpiration in plants). Waxes derived from natural sources are used commercially in polishes, cosmetics, and ointments. Most waxes are mixtures of esters although some are hydrocarbons, alcohols, or ketones. The ester waxes are esters of a monohydric alcohol (an alcohol containing one OH) and a fatty acid. The alcohols and fatty acids are those of 16 to 36 carbons with unbranched structures and an even number of carbons. 

The term wax, however, is used for pure compounds and also for a variety of natural products of animal and vegetable origin, components of which are fatty acid esters with monohydric alcohols, but also other lipophilic compounds, such as higher hydrocarbons, free alcohols, ketones and fatty acid. These compounds, with the exception of fatty acids, are classified as Hpid accompanying substances (see Section 3.7). Esters of fatty acids with monohydric alcohols may even be minority constituents in these natural mixtures. It may therefore be more appropriate to use the term wax just for natural products rather than for pure compounds that are often called wax esters. 

The simple lipids include neutral lipids or glycerides, which are esters of glycerol and fatty acids, and the waxes, which are esters of long-chain monohydric alcohols and fatty acids. 

More hydrophobic additives such as free fatty acids and their esters and amides, long-chain monohydric alcohols, and nitriles may have an even more dramatic effect on the phase behavior of a surfactant due to solubilization phenomena. The general subject of solubilization in micellar systems is discussed in Chapter 6. For now, we will focus on the effects that the presence of solubilized materials may have on liquid crystal phases. 

Esterification is one of the most important reactions of fatty acids (25). Several types of esters are produced including those resulting from reaction with monohydric alcohols, polyhydric alcohols, ethylene or propylene oxide, and acetjiene or vinyl acetate. The principal monohydric alcohols used are methyl, ethyl, propyl, isopropyl, butyl, and isobutyl alcohols (26) (see Esterification Esters, organic). 

A drawback for the use of triglycerides and also of fatty acid esters of lower monohydric alcohols as a replacement for diesel fuel alone or in a mixture with diesel fuel has proven to be the flow... 

FATTY ESTER. A fatly acid with the active hydrogen replaced by the alkyl group of a monohydric alcohol. The esterification of a fatty acid. RCOOH. by and alcohol. R OH. yields the fatly ester RCOOR. The most common alcohol used is methanol, yielding the methyl ester RCOOCHj. The methyl esters of fatly acids have higher vapor pressures than the corresponding acids and are distilled more easily. 

Esters of fatty acids with monohydric alcohols find applications as emollients in cosmetics. They are prepared by acid- or base-catalyzed (trans)esterifications [200, 205]. As with biodiesel production, the use of enzymatic catalysis offers potential benefits but in the case of these specialty fatty acid esters there is a special advantage the products can be labelled as natural. Consequently, they command a higher price in personal care products where natural is an important customer-perceived advantage. Examples include the synthesis of isopropylmy-ristate by CaLB-catalyzed esterification [206] and n-hexyl laurate by Rhizomucor miehei lipase (Lipozyme IM-77)-catalyzed esterification [207] (see Fig. 8.38). 

Esters of fatty acids with glycerol and monohydric alcohols. 

Beeswax consists of 70-75% of a mixture of various esters of straight-chain monohydric alcohols with even-numbered carbon chains from C24 to C36 esterified with straight-chain acids. These straight-chain acids also have even numbers of carbon atoms up to 35 together with some Cig hydroxy acids. The chief ester is myricyl palmitate. Also present are free acids (about 14%) and carbohydrates (about 12%) as well as approximately 1 % free wax alcohols and stearic esters of fatty acids. 

Fatty alcohols and their derivatives are important in many industrial processes where thQ are used as raw materials for surfactants and lubricants. A fot alcohol is, in general defined as a monohydric aliphatic alcohol with six or more caibon atoms. The annual production of fotty alcohols is over 1 million metric tons. Commercially fotty alcohols are produced by one of three processes the Ziegler process, the Oxo process or ly a high pressure hydrogenation of fot acids or esters. The latter process is the only one process that uses renewable natural fots/oils whereas the two first processes utilize petrochemical... 

Alternately, oils found in plants may also be of the fatty acid (Table 3.10) or glyceride type or may even be esters of the higher monohydric alcohols and fatty acids. The acids most commonly found as glycerides, or esters in plants are... 

Esters of fatty acids with monohydric alcohols can also be produced by industry or in the laboratory. In this case, however, esters with lower alcohols, namely methanol, ethanol, propan-2-ol or butan-l-ol are produced. Esters of fatty acids with methanol are components of so-called biodiesel esters of fatty acids with ethanol and fusel oil alcohols are common components of alcoholic beverages. 

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