Esters to Carboxylic Acids

Two methods for converting carboxylic acids to esters fall into the mechanistic group under discussion the reaction of carboxylic acids with diazo compounds, especially diazomethane and alkylation of carboxylate anions by halides or sulfonates. The esterification of carboxylic acids with diazomethane is a very fast and clean reaction.41 The alkylating agent is the extremely reactive methyldiazonium ion, which is generated by proton transfer from the carboxylic acid to diazomethane. The collapse of the resulting ion pair with loss of nitrogen is extremely rapid. 

Esterification and transesterification using TiIV compounds are useful methods for functionalization of ester moieties under mild conditions. In the transformation of carboxylic acids to esters, a catalytic amount of TiCl(OTf)3 is effective (Scheme 30).110 Titanium alkoxides, such as Ti(OEt)4 or Ti(0 Pr)4, easily promote transesterification of alkoxy groups to other ones—even to more hindered groups.111 Anomerization of glycosides to Q-isomers using a Tilv-bascd Lewis acid is an important method for controlling the product structure.112... 

Scheme 24 Cathodic alkylation of carboxylic acids to esters R alkyl, aryl, R alkyl, yields 24-96%.

The conversion of carboxylic acids to esters is a fundamental transformation in the synthetic chemists toolbox, as such Wiles et al. (2003) investigated the ability to efficiently synthesize a series of methyl, ethyl,... 

Figure 8.2 Transformations of carboxylic acids to esters and amides.

Additionally, transformation of carboxylic acids to esters and amides are illustrated in Figure 8.2. The related conversions of esters to acids and amides are shown in Figure 8.3. Finally, transformations of aldehydes and ketones to imines, oximes, and enamines are summarized in Figure 8.4. 

Fischer Esterification— Acid-Catalyzed Conversion of Carboxylic Acids to Esters 849... 

Loss of water from the tetrahedral intermediate is reversible too just as ROH will attack a protonated carboxylic acid, H2O will attack a protonated ester. In fact, every step in the sequence from carboxylic acid to ester is an equilibrium, and the overall equilibrium constant is about 1. In order for this reaction to be useful, it is therefore necessary to ensiue that the equilibrium is pushed towards the ester side by using an excess of alcohol or carboxylic acid (usually the reactions are done in a solution of the alcohol or the carboxylic acid). In this reaction, for example, using less than three equivalents of ethanol gave lower yields of ester. 

Two of the general procedures for conversion of carboxylic acids to esters involve nucleophilic substitution reactions. A very common method for formation of methyl esters involves the reaction of the acid with diazomethane in an inert solvent such as ether or chloroform. This reaction involves formation of the transient methyldiazonium ion, presumably in an ion pair that immediately breaks down to give the ester and nitrogen ... 

If our assumptions are correct, a plot of 1 / (1 - p) vs. time should be linear, and indeed this is empirically observed for step-growth polymerizations. To determine p you need a method that can follow the conversion of all functional groups in the monomers to all the associated functional groups in the polymer, such as carboxylic acids to esters in the formation of polyester. 

Fischer Esterification—Acid-Catalyzed Conversion of Carboxylic Acids to Esters 848 Conversion of Carboxylic Acids to Amides with DCC 850 Acid-Catalyzed Hydrolysis of an Ester to a Carboxyhc Acid 851 Base-Promoted Hydrolysis of an Ester to a Carboxyhc Acid 852 Amide Hydrolysis in Base 856 Hydrolysis of a Nitrile in Base 864 Reduction of a Nitrile with LiAlH4 865 Reduction of a Nitrile with DIBAL-H 866... 

Trifluoroacetic anhydride (TFAA) and A,A -dicyclohexylcarbodii-mide (DCCD) are modern reagents for the synthesis of depsides (see Scheme 19). A mild conversion of carboxylic acids to esters using... 

Other new derivatization methods are also being developed [13,14]. For example, the use of alkylchloroformates as derivatizing agents allows conversion of certain amines to carbamates and carboxylic acids to esters. 

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