Esters from carboxylate salts

Phenacyl esters, easily prepared from carboxylic salts and phenacyl bromide nnder phase transfer catalysis, regenerate the original carboxylic acid by treatment with sodinm hydrogen telluride in DMF. ... 

You can t make esters from carboxylic acids and alcohols under basic conditions because the base deprotonates the carboxylic acid (see p. 288). However, you can reverse that reaction and hydrolyse an ester to a carboxylic acid (more accurately, a carboxylate salt) and an alcohol. 

Formation of the 3j8-acetoxyeti-5-enic esters has been used to obtain optically pure samples of (+)- and (—)-tran5-verbenoP and to resolve an alcohol intermediate in the synthesis of the witchweed seed germination stimulant (+)-strigol. A general synthesis of thiol esters from carboxylic acids, exemplified by the formation of the n-propylthio-, isopropylthio-, and t-butylthio-esters of cholic acid, comprises reaction with diethyl chlorophosphate-triethylamine, followed by the thallium(i) salt of the appropriate thiol. 

The formation of esters from carboxylic acids by using Ar-alkyl-2-halopyridinium salts, such as 2-chloro-l-methylpyridine iodide (1) and alcohols, was first reported by Mukaiyama and, thus, the reaction is defined as the Mukaiyama esterification. The active ester (2) forms esters in good yield under mild conditions when subjected to alcohols. 

Olofsson and coworkers have developed a general and high-yielding synthesis of various diaryl ethers 681 using the reaction of diaryliodonium salts with phenols under basic conditions (Scheme 3.273) [874]. The scope of products includes bulky orf/io-substituted diaryl ethers, which are difficult to obtain by metal-catalyzed protocols. A similar procedure has been used for the metal-free synthesis of aryl esters from carboxylic acids and diaryliodonium salts [875]. 

Carboxylic acid trityl esters from carboxylic acids via tbeir salts... 

A-Acyl-4-pyridones can serve as useful acyl group transfer reagents for the esterification of alcohols in >80% yields.Two notable points about these reagents are their effectiveness in the preparation of formate esters (c/. ref. 157), and their much greater rate of reaction with primary alcohols, (c/. ref. 147). Thioesters and amides can also be prepared from such pyridones by reaction with thiols or amines, respectively. Other useful reagents for the direct formation of esters from carboxylic acids and alcohols are 2-fluoropyridinium salts in the presence of caesium fluorideand certain benzoisothiazole derivatives. Primary alcohols can be esterified with 2,2 -bipyridyl-6-yl carboxylates and CsF. Selective esterification of a primary alcohol in the presence of a secondary alcohol can be achieved in acceptable yields with this reagent (c/. ref. 144). 

Halogenopyridine methiodideJtri-n-butylamine o-Halogenocyclimmonium salts as condensing agents Carboxylic acid esters from carboxylic acids and alcohols... 

Carbanions Derived from Esters and Carboxylate Salts... 

Synthesis of Esters from Carboxylic Acids, Esterification (eq 1) proceeds by activation of the carboxyl component using a 2-halopyridinium salt (2 X = Cl, Y = I or X = F, Y = OTs) and (1) (2,4 equiv) in the presence of an alcohol. The best solvents for this process are CH2CI2 or MeCN, but a range of other solvents may also be used. 

Saponification (Section 20 11) Hydrolysis of esters in basic solution The products are an alcohol and a carboxylate salt The term means soap making and denves from the process whereby animal fats were converted to soap by heating with wood ashes... 

Reactant and product structures. Because the transition state stmcture is normally different from but intermediate to those of the initial and final states, it is evident that the stmctures of the reactants and products should be known. One should, however, be aware of a possible source of misinterpretation. Suppose the products generated in the reaction of kinetic interest undergo conversion, on a time scale fast relative to the experimental manipulations, to thermodynamically more stable substances then the observed products will not be the actual products of the reaction. In this case the products are said to be under thermodynamic control rather than kinetic control. A possible example has been given in the earlier description of the reaction of hydroxide ion with ester, when it seems likely that the products are the carboxylic acid and the alkoxide ion, which, however, are transformed in accordance with the relative acidities of carboxylic acids and alcohols into the isolated products of carboxylate salt and alcohol. 

Attempts to prepare fluorothiophenes from diazonium salts (the fluoro-borate and hexafluorophosphate salts) have met only variable success. Methyl 3-fluorothiophene-2-carboxylate (32) was obtained in 89% yield by this method (Scheme 12), but the 3-diazonium salt of the corresponding 4-ester could not be isolated. Furthermore, the methyl ester of 2-diazothiophene-3-carboxylic acid coupled before decomposition could be attempted [85H(23) 1431]. 

Sodium salts of carboxylic acids, including hindered acids such as mesitoic, rapidly react with primary and secondary bromides and iodides at room temperature in dipolar aprotic solvents, especially HMPA, to give high yields of carboxylic esters.679 The mechanism is Sn2. Another method uses phase transfer catalysis.680 With this method good yields of esters have been obtained from primary, secondary, benzylic, allylic, and phenacyl halides.681 In another procedure, which is applicable to long-chain primary halides, the dry carboxylate salt and the halide, impregnated on alumina as a solid support, are subjected to irradiation by microwaves in a commercial microwave oven.682 In still another method, carboxylic acids... 

Acyl cations are now well-established chemical species. They can be prepared in quantity in solution, and several have been isolated as their crystalline salts. Recent papers have described their formation from carboxylic acids and esters under strongly acidic conditions81214, but they are most conveniently available from the reactions of acyl halides with L.ewis acids21 well-defined Lewis acid-base complexes are formed, which decompose in a second stage to the acyl cations21-23, viz. 

The apparent abnormal formation of ethyl pyrrole-2-carboxylate from the reaction of ethyl chloroformate and alkali metal salts of pyrrole could be accounted for by a thermal rearrangement during the isolation of the products. However, whilst this may be partly correct, an analysis of the reaction products prior to their isolation has established (77CJC4103) the formation of the thermodynamically more stable 2-carboxylic ester from the 1-isomer by a reaction sequence shown in Scheme 36. 

A significant portion of the neutral ethyl ether extract from the salts of carboxylated methyl linoleate consists of ,/3-unsaturated cyclic ketones. This material is produced in small but significant amounts (4-10%) (Table I) from the carboxylation of polyunsaturates but not from the corresponding monounsaturated fatty acids and esters (19). These ,/ -unsaturated cyclic ketones were identified spectroscopically (IR, UV, and NMR) as 4. This structural assignment was firmly established by mass spectral analyses before and after hydrogenation of the carbon-carbon double bond. 

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