Carboxylic acids naturally occurring

Strictly speaking the term fatty add is restricted to those carboxylic acids that occur naturally in triacylglyc erols Many chemists and biochemists however refer to all unbranched carboxylic acids irrespective of their origin and chain length as fatty acids... 

With chemical treatment, the natural surfactants in crude oil can be activated [1384]. This method has been shown to be effective for highly viscous crude oil from the Orinoco Belt that has been traditionally transported either by heating or diluting. The precursors to the surfactants are preferably the carboxylic acids that occur in the crude oil. The activation occurs by adding an aqueous buffer solution [1382,1383]. The buffer additive is either sodium hydroxide in combination with sodium bicarbonate or sodium silicate. Water-soluble amines also have been found to be suitable [1506]. 

Stereochemistry of Amino Acids Naturally occurring amino acids belong to the T-family. That is, when the amino acid is drawn as a Fischer projection, with the carboxyl group at the top and the side chain at the bottom, the amino group is on the left, as shown in Figure 12.45. 

Although carboxylic acids do occur naturally, they most often are found as their ester or amide derivatives. Acetic acid is a major industrial chemical, produced in excess of 3 billion pounds annually. Some acids, such as acetyl salicylic acid (aspirin) and ibuprofen, have found considerable use in the medical field. 

The ease with which racemization of the carboxylic acid derivative occurs depends on the nature of the substrate. Carboxylic adds themselves are slow to racemize, since the carboxylic acid is initially deprotonated to form a carboxylate anion. 

The products of methanolysis and ethanolysis of a range of A-phosphino-thioyl-phosphazenes, X 2P(S) N=PX 2C1 (X and X include Cl and F), have since been shown to have analogous structures. The solvolysis of F2P(S) N=PF2C1 by carboxylic acids may occur in different ways, depending on the nature of the acid employed ... 

In nature, terpenoids are found to occur both in free and combined states. Most of the terpenoids that are not highly functionalized occur free. Carboxylic acids invariably occur in a free state, though occasional occurrence of methyl and other esters is known. Alcohols often occur both in the free state and as esters, in which the acid moiety is usually a simple aliphatic acid (e.g., acetic, tiglic, angelic, etc.) or less often an aromatic acid (e.g., benzoic, cinnamic), though esters... 

Many esters occur naturally Those of low molecular weight are fairly volatile and many have pleasing odors Esters often form a significant fraction of the fragrant oil of fruits and flowers The aroma of oranges for example contains 30 different esters along with 10 carboxylic acids 34 alcohols 34 aldehydes and ketones and 36 hydrocarbons... 

Fats and oils are naturally occurring mixtures of glycerol tnesters Fats are mixtures that are solids at room temperature oils are liquids The long chain carboxylic acids obtained from fats and oils by hydrolysis are known as fatty acids... 

Acetyl coenzyme A is the biosynthetic precursor to the fatty acids, which most often occur naturally as esters Fats and oils are glycerol esters of long chain carboxylic acids Typically these chains are unbranched and contain even numbers of carbon atoms... 

Icosanoids (Section 26 6) A group of naturally occurring com pounds derived from unsaturated C20 carboxylic acids Imide (Section 20 16) Compound of the type... 

Carboxylic Acid Esters. In the carboxyflc acid ester series of surfactants, the hydrophobe, a naturally occurring fatty acid, is solubilized with the hydroxyl groups of polyols or the ether and terminal hydroxyl groups of ethylene oxide chains. 

Phthalazinedione has been used in a similar manner for the synthesis of (35,55)-5-hydroxyhexahydropyridazine-3-carboxylic acid (171), a naturally occurring amino acid which is a constituent of the monamycin antibiotics (Scheme 93) (77H(7)119). 

The absolute configuration of naturally occurring 5(-)-azetidine-2-carboxylic acid has been established (73CL5), and the DL form has been resolved (69JHC993). ORD and CD curves have been determined for 2-methylazetidine and an octant rule has been proposed for the N-chloro- and N-cyano-2-methylazetidines (74T39). 

A number of 2-acylazetidines have been prepared by reaction of 1,3-dihaloacyl compounds with amino derivatives (Section 5.09.2.3.l(m)). This is illustrated for azetidine 2-carboxylic acid (56), the only known naturally occurring azetidine. Ring expansion of activated aziridines (43) and contraction of 4-oxazolines (55) has also found limited use (Section 5.09.2.3.2(f) and Hi)). 

According to Quinkert, photoexcited cyclic ketones may be transformed to open-chain unsaturated carboxylic acids in the presence of molecular oxygen. This reaction may compete efficiently with a-cleavage and secondary transformations thereof. Thus, both stereo iso meric 17-ketones (109) and (110) yield as much as 20% of the unsaturated acid (111) when irradiated in benzene under a stream of oxygen. This photolytic autoxidation has been used notably for partial syntheses of naturally occurring unsaturated 3,4-seco-acids from 3-oxo triterpenes (for references, see ref. 72). 

Similarly, permanganate oxidation of a number of naturally occurring canthin-6-one derivatives (295) leads to j8-carboline-l-carboxylic acid or its methyl ester.A j8-carboline-l-carboxylic acid... 

Decarboxylation of isoxazole-3-carboxylic acids is related to the nucleophilic cleavage of the isoxazole ring as far as the nature of the reaction products is concerned. It occurs at temperatures above 200°C and is accompanied by the cleavage of the nitrogen-oxygen bond of the heterocyclic ring to yield a j8-ketonitrile. It was first reported by Claisen with 5-methyl- and 5-phenyl-isoxazole-3-carboxylic acids (153- 154).Under the reaction conditions, j8-ketonitriles condense... 

Alcohols are among the most versatile of all organic compounds. They occur widely in nature, are important industrial 7, and have an unusually rich chemistry. The most widely used methods of alcohol synthesis start with carbonyl compounds. Aldehydes, ketones, esters, and carboxylic acids are reduced by reaction with LiAlH4. Aldehydes, esters, and carboxylic acids yield primary alcohols (RCH2OH) on reduction ketones yield secondary alcohols (R2CHOH). 

When the Woodward-Eschenmoser synthesis began, it was known from the work of Bernhauer et al.5 that cobyric acid (4), a naturally occurring substance, could be converted directly into vitamin B12. Thus, the synthetic problem was reduced to the preparation of cobyric acid, a molecule whose seventh side chain terminates in a carboxylic acid group and is different from the other side chains. Two strategically distinct and elegant syntheses of the cobyric acid molecule evolved from the combined efforts of the Woodward and Eschenmoser groups and both will be presented. Although there is naturally some overlap, the two variants differ principally in the way in which the corrin nucleus is assembled. 

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