Esters by Fischer esterification

Following are equations for the synthesis of each ester by Fischer esterification. 

First convert 3-methylbenzoic acid to its ethyl ester by Fischer esterification, and then treat the ester with diethylamine to give Deet. 

RCOH + R OH RCOR Preparation of esters by Fischer esterification. The equilibrium... 

Benzyl esters. Preparation of benzyl esters by Fischer esterification proceeds with difficulty. An alternative method involves decomposition of benzyldimethylanilinium salts of carboxylic acids in a refluxing inert solvent. 

Each amide can be prepared by treating the carboxylic acid with SOCI2 to form the acid chloride (Section 13.7) and then treating the acid chloride with an amine (Section 14.5A). Alternatively, the carboxylic acid can be converted to an ester by Fischer esterification (Section 13.6) and the ester treated with an amine to give the amide. Solution (a) uses the acid chloride route, solution (b) the ester route ... 

A carboxylic acid can be converted to an ester by Fischer esterification. Show how to synthesize each... 

What alcohol and acid are required to form each of the following esters by Fischer esterification ... 

Carboxyl groups of ammo acids and peptides are normally protected as esters Methyl and ethyl esters are prepared by Fischer esterification Deprotection of methyl and ethyl esters is accomplished by hydrolysis m base Benzyl esters are a popular choice because they can also be removed by hydrogenolysis Thus a synthetic peptide protected at both... 

Section 20.7 Esters occur naturally or are prepared from alcohols by Fischer esterification or by acylation with acyl chlorides or acid anhydrides (see Table 20.3). 

Esters are usually prepared from carboxylic acids by the methods already discussed. Thus, carboxylic acids are converted directly into esters by SK2 reaction of a carboxyfate ion with a primary alkyl halide or by Fischer esterification of a carboxylic acid with an alcohol in the presence of a mineral acid catalyst. In addition, acid chlorides are converted into esters by treatment with an alcohol in the presence of base (Section 21.4). 

Because the acidic hydrogen is the usual cause of undesired reactivity, carboxylic acids are commonly protected as esters. Most often, simple methyl esters are used. The ester can be prepared via the acyl chloride or by Fischer esterification (see Section 19.4). The ester group can be converted back to the carboxylic acid by hydrolysis under acidic or basic (saponification) conditions (see Section 19.5). 

Cycloserine has been synthesized by several workers including Stammer and Evans. The method of Evans will be briefly described. Evans reported cycloserine can be synthesized by converting DL-Serine to its methyl ester hydrochloride by Fischer esterification. 

Prepare methyl ester (a) by Fischer esterification (Section 13.6) of phenylacetic acid with methanol.Then treat this ester with ammonia to prepare amide (b). Alternatively, treat phenylacetic acid with thionyl chloride (Section 13.7) to give an acid chloride, and then treat the acid chloride with two equivalents of ammonia to give amide (b). Reduction of amide (b) by LiAIH4 gives the 1 ° amine (c). Similar reduction of either phenylacetic acid or ester (a) gives 1 ° alcohol (d) ... 

Carboxyl groups are most often protected by conversion to methyl, ethyl, or benzyl esters. Methyl and ethyl esters are prepared by Fischer esterification (Section 17.7A) and are removed by hydrolysis in aqueous base (Section 18.4C) under mild conditions. Benzyl esters are conveniently removed by hydrogenolysis with over a palladium or platinum catalyst (Section 21.5C). Benzyl groups can also be removed by treatment with HBr in acetic acid. 

Figure 11.3 Biotransformations of p-hydroxy nitriles and analogs by nitrile hydratase and amidase in whole cells of Rhodococcus rhodochrous ATCC BAA-870 [15]. To determine the enantiomeric excess, both p-hydroxy amides and p-hydroxy acids were separately converted into the corresponding methyl ester using Fischer esterification.

Esters cannot be prepared from tertiary alcohols using the Fischer esterification method because these alcohols tend to dehydrate under acid conditions. Esters of phenols also cannot be prepared by Fischer esterification because the equihbrium constant for the reaction is about 10". ... 

We recall that esters of alcohols can be prepared by Fischer esterification (Section 20.12). Esters of phenols cannot be prepared by this method because the equilibrium constant is not favorable. However, acid chlorides react with of both alcohols and phenols to give esters. The reaction produces HCl, and pyridine is added to the reaction mixture to neutralize the HCl. 

Hydrolysis (Sections 20 10 and 20 11) Ester hydrolysis may be catalyzed either by acids or by bases Acid catalyzed hydrolysis is an equilibrium controlled process the reverse of the Fischer esterification Hydrolysis in base IS irreversible and is the method usual ly chosen for preparative purposes... 

Section 2010 Ester hydrolysis can be catalyzed by acids and its mechanism (Figure 20 4) is the reverse of the mechanism for Fischer esterification The reaction proceeds via a tetrahedral intermediate... 

Although the term ester, used without a modifier, is normally taken to mean an ester of a car boxylic acid, alcohols can react with inorganic acids in a process similar- to the Fischer esterification. The products are esters of inorganic acids. For example, alkyl nitrates are esters formed by the reaction of alcohols with nitric acid. 

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