SOME IMPORTANT CARBOXYLIC ACIDS

Some important carboxylic acids, such as oxalic acid and adipic acid, have two or more carboxyl groups. An acid with two carboxyl groups is called a dicarboxylic acid. Others have additional functional groups such as hydroxyl groups, as shown in Figure 23-12. Typically, these acids are more soluble in water and often more acidic than acids with only a carboxyl group. 

Carboxylic Acids Carboxylic acids, R—C—OH, are named by dropping the -e from the alkane name and adding -oic acid however, many common names are used. For example, the four-C acid is butanoic acid (the carboxyl C is counted when choosing the root) its common name is butyric acid. Figure 15.15 shows some important carboxylic acids. The carboxyl C already has three bonds, so it forms only one other. In formic acid (methanoic acid), the carboxyl C bonds to an H, but in all other carboxylic acids it bonds to a chain or ring. 

Structure and Physical Properties Nomenclature Some Important Carboxylic Acids Reactions Involving Carboxylic Acids An Environmental Perspective Garbage Bags from Potato Peels... 

Some aromatic carboxylic acids are also commercially important. Benzoic acid is used as an ingredient in medications, a preservative in foods, and a starting material for synthesis. Benzoic acid can be produced by the oxidation of toluene with potassium permanganate, nitric acid, or other strong oxidants. 

The presence of hydrogen bonding has important effects on the solid state structures of many compounds, as we have already discussed for ice (Section 7.2) and carboxylic acids (Box 10.4). The solid state structures of some simple carboxylic acids are more complex than one might at first imagine. Figure 10.5c shows part of the solid state packing... 

It is mainly the lower carboxylic acids and some aromatic carboxylic acids that are active as odour- or taste-active compounds. Taste-active substances are predominantly polyhydric carboxylic acids and some aliphatic carboxylic acids such as acetic and lactic acids, which are major carriers of the sour taste in food raw materials and foods. Short chain fatty acids also have some importance as flavour-active substances (C and Cg) and medium chain fatty acids (Cg-Ci2). A number of carboxylic acids can become precursors of important flavour-active derivatives, such as, for example, esters and lactones. 

Activation of Carboxyiic Acids Synthesis of Acyi Imida-zoies. iV.iV -Carbonyldiimidazole (1) converts carboxylic acids into the corresponding acylimidazoles (2) (eq 1). The method can be applied to a wide range of aliphatic, aromatic, and heterocyclic carboxylic acids, including some examples (such as formic acid and vitamin A acid) where acid chloride formation is difficult. The reactivity of (2) is similar to that of acid chlorides, but the former have the advantage that they are generally crystalline and easily handled. Isolation of (2) is simple, but often unnecessary further reaction with nucleophiles is usually performed in the same reaction vessel. Conversion of (2) into acid chlorides (via reaction with HCl), hydrazides, hydroxamic acids, and peroxy esters have all been described. Preparation of the more important carboxylic acid derivatives is described below. 

This difference in behavior for acetic acid in pure water versus water buffered at pH = 7 0 has some important practical consequences Biochemists usually do not talk about acetic acid (or lactic acid or salicylic acid etc) They talk about acetate (and lac tate and salicylate) Why Its because biochemists are concerned with carboxylic acids as they exist in di lute aqueous solution at what is called biological pH Biological fluids are naturally buffered The pH of blood for example is maintained at 7 2 and at this pH carboxylic acids are almost entirely converted to their carboxylate anions... 

Naphthenic acid is a collective name for organic acids present in some but not all crude oils. In addition to true naphthenic acids (naphthenic carboxylic acids represented by the formula X-COOH in which X is a cycloparaffin radical), the total acidity of a crude may include various amounts of other organic acids and sometimes mineral acids. Thus the total neutralization number of a stock, which is a measure of its total acidity, includes (but does not necessaiily represent) the level of naphthenic acids present. The neutralization number is the number of milligrams of potassium hydroxide required to neutralize one gram of stock as determined by titration using phenolphthalein as an indicator, or as determined by potentiometric titration. It may be as high as 10 mg KOH/gr. for some crudes. The neutralization number does not usually become important as a corrosion factor, however, unless it is at least 0.5 mg KOH/gm. 

Plasticizers can be classified according to their chemical nature. The most important classes of plasticizers used in rubber adhesives are phthalates, polymeric plasticizers, and esters. The group phthalate plasticizers constitutes the biggest and most widely used plasticizers. The linear alkyl phthalates impart improved low-temperature performance and have reduced volatility. Most of the polymeric plasticizers are saturated polyesters obtained by reaction of a diol with a dicarboxylic acid. The most common diols are propanediol, 1,3- and 1,4-butanediol, and 1,6-hexanediol. Adipic, phthalic and sebacic acids are common carboxylic acids used in the manufacture of polymeric plasticizers. Some poly-hydroxybutyrates are used in rubber adhesive formulations. Both the molecular weight and the chemical nature determine the performance of the polymeric plasticizers. Increasing the molecular weight reduces the volatility of the plasticizer but reduces the plasticizing efficiency and low-temperature properties. Typical esters used as plasticizers are n-butyl acetate and cellulose acetobutyrate. 

During electrochemical fluorination retention of important functional groups or atoms in molecules is essential. Acyl fluorides and chlorides, but not carboxylic acids and anhydrides (which decarboxylate), survive perfluorination to the perfluorinated acid fluorides, albeit with some cyclization in longer chain (>C4) species [73]. Electrochemical fluorination of acetyl fluoride produces perfluoro-acetyl fluoride in 36-45% yields [85]. Electrochemical fluorination of octanoyl chloride results in perfluorinated cyclic ethers as well as perfluorinated octanoyl fluonde. Cyclization decreases as initial substrate concentration increases and has been linked to hydrogen-bonded onium polycations [73]. Cyclization is a common phenomenon involving longer (>C4) and branched chains. a-Alkyl-substituted carboxylic acid chlorides, fluorides, and methyl esters produce both the perfluorinated cyclic five- and six-membered ring ethers as well as the perfluorinated acid... 

The chemistry of carboxylic acids is the central theme of this chapter. The importance of carboxylic acids is magnified when we realize that they are the parent compounds of a large group of derivatives that includes acyl chlorides, acid anhydrides, esters, and amides. Those classes of compounds will be discussed in Chapter 20. Together, this chapter and the next tell the story of some of the most fundamental structural types and functional group transfonnations in organic and biological chemistry. 

Nitriles are similar in some respects to carboxylic acids and are prepared either by SN2 reaction of an alkyl halide with cyanide ion or by dehydration of an amide. Nitriles undergo nucleophilic addition to the polar C=N bond in the same way that carbonyl compounds do. The most important reactions of nitriles are their hydrolysis to carboxylic acids, reduction to primary amines, and reaction with organometallic reagents to yield ketones. 

Carboxylic acids can be prepared by oxidizing primary alcohols and aldehydes with a strong oxidizing agent, such as acidified aqueous potassium permanganate solution. In some cases, an alkyl group can be oxidized directly to a carboxyl group. This process is very important industrially. 

Although, the enzymatic reaction of esters with amines or ammonia have been well documented, the corresponding aminolysis with carboxylic acids are rarer, because of the tendency of the reactants to form unreactive salts. For this reason some different strategies have been used to avoid this problem. Normally, this reaction has been used for the preparation of amides of industrial interest, for instance, one of the most important amides used in the polymer industry like oleamide has been produced by enzymatic amidation of oleic acid with ammonia and CALB in different organic solvents [10]. 

It is obvious that many carboxylic acids of the formulas RCH2COOH and RR CHCOOH can be synthesized by this method (for some other ways of preparing such acids, see 10-106, 10-108, and 10-109). Another important example is the acetoacetic ester synthesis, in which Z is COOEt and Z is COCH3. In this case the product can be decarboxylated with acid or dilute base (12-38) to give a ketone or cleaved with concentrated base (12-41) to give a carboxylic ester and a salt of acetic acid ... 

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