Carboxylic acids salts, reaction with bases

Similar to inorganic acids, the reaction of carboxylic acids and bases produces carboxylic acid salts. Several of these salts are commonly used in foods and beverages as preservatives. The most common are salts from benzoic, propionic, and sorbic acids. The salts of these acids have names ending with ate, and can often be found in the list of ingredients of baked goods and fruit drinks. Several common preservatives are shown in Figure 15.11. 

Fig. 13.10. Formation of carboxylate enolates ("carboxylic acid dianions") by reaction of carboxylic acid salts with strong bases.

Review. New synthetic reactions based on the onium salts of aza-arenes have been reviewed (75 references). The reactions discussed involve activation of carboxylic acids or alcohols with 2-haIopyridinium, benzoxazolium, benzothiazolium, and pyridinium salts to afford 2-acyloxy or 2-alkoxy intermediates, which can be transformed into esters, amides, thiol esters, (macrocyclic) lactones, acid fluorides, olefins, allenes, carbodiimides, isocyanates, isothiocyanates, and nitriles under appropriate conditions. 

Acetic acid shows all the characteristic properties of carboxylic acids. Hydrogen gas and acetate salts are formed upon reaction with metals and it undergoes neutralization reactions with bases and basic salts. 

Many examples of the usual route to /S-lactams via imines and acid chlorides, ketens, or keten equivalents have appeared.These include syntheses of 3-[bis(alkylthio)methylenamino]-2-azetidinones, ° of spiro-azetidinones and bis-azetidinones, and the use of l-methyl-2-halogenopyridinium salts to activate carboxylic acids towards coupling with imines. A non-hazardous alternative route to 3-amido-2-azetidinones, avoiding the use of azidoacetyl chloride, involves the reaction of Schiff bases with salts of [(a-methyl-/3-methoxycar-bonyl)vinylamino]acetic acid, e.g. (20), in the presence of ethyl chloroformate, as shown in Scheme 5. Formaldimines can be generated from their trimers by treatment with Lewis acids immediately prior to reaction with acid chlorides, so allowing the formation of the nocardicin nucleus which is unsubstituted at C-4. ... 

Although they are weak, carboxylic acids react readily with strong bases such as sodium hydroxide or potassium hydroxide to form salts. Reaction 5.4 gives the general reaction, and Reactions 5.5 and 5.6 are two specific examples ... 

All acid derivatives react with water in the presence of an acid catalyst to generate the parent carboxylic acid used to prepare that derivative. In other words, the product is the carboxylic acid used to generate the acid derivative. This reaction is known as acid hydrolysis. The reaction of an acid derivative with aqueous hydroxide also generates the parent carboxylic acid, but the basic conditions convert the acid to its carboxylate salt, as described before. Therefore, a second reaction with aqueous acid is required to convert the carboxylate salt to the carboxylic acid. This reaction is known as base hydrolysis. Both reactions are discussed in this section. 

The pedigree of the synthetic surfactant industry is reasonably well documented, unlike that of the more ancient natural alkali soaps. However, it is not an easy task to pinpoint the exact time when the industry came into being. In a strictly chemical sense, a soap is a compound formed by the reaction of an essentially water-insoluble fatty acid with an alkali metal or organic base to produce a carboxylic acid salt with enhanced water solubility, sufficient to produce useful surface activity. Since the soaps require some form of chemical modification to be useful as surfactants, they could be considered to be synthetic however, custom dictates that they not be classified in the same category as the materials prepared by more elegant synthetic routes. 

The intramolecular reaction oF allcenes with various O and N functional groups offers useful synthetic methods for heterocycles[13,14,166]. The reaction of unsaturated carboxylic acids affords lactones by either exo- or endo-cyclization depending on the positions of the double bond. The reaction of sodium salts of the 3-alkenoic acid 143 and 4-alkenoic acid 144 with Li2PdCl4 affords mostly five-membcrcd lactones in 30-40% yields[167]. Both 5-hexe-noic acid (145) and 4-hexenoic acid (146) are converted to five- or six-mem-bered lactones depending on the solvents and bases[168]. Conjugated 2,4-pentadienoic acid (147) is cyclized with Li2PdCl4 to give 2-pyrone (148) in water[i69]. 

Hydrolysis (Section 20 4) Acyl chlorides react with water to yield carboxylic acids In base the acid is converted to its carbox ylate salt The reaction has little prepara tive value because the acyl chloride is nearly always prepared from the carboxyl ic acid rather than vice versa... 

The anti-inflammatory agent Oxapro2in, 2-(4,5-diphenyl-2-oxa2ole)propionic acid mono aluminum and dihydroxyalurninum salts, is made by reaction of the sodium salt with aluminum sulfate under controlled conditions (96). Again, the aluminum salts of many carboxylic acid based dmgs are less irritating, ulcerous, and/or toxic, and have a more pleasant taste than their parent acids. 

Reaction of anthranilic acid (o-aminobenzoic acid) with HN02 and H2SO4 yields a diazonium salt that can be treated with base to yield a neutral diazonium carboxylate. 

Treatment of a carboxylic acid with the strong base NaOH harms the sodium salt of the acid. With acetic acid, the acid-base reaction is... 

Carboxylic acids can be alkylated in the a position by conversion of their salts to dianions [which actually have the enolate structures RCH=C(0")2 ] by treatment with a strong base such as LDA. The use of Li as the counterion is important, because it increases the solubility of the dianionic salt. The reaction has been applied to primary alkyl, allylic, and benzylic halides, and to carboxylic acids of the form RCH2COOH and RR"CHCOOH. This method, which is an example of the alkylation of a dianion at its more nucleophilic position (see p. 458),... 

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