Fischer-Speier catalyst

Esterification with alicyclic alcohols proceeds best when the alcohol is saturated with hydrogen chloride and treated with an excess of the carboxylic acid (the Fischer-Speier method) a very impure ester results if sulphuric acid is used as the catalyst. 

Fischer-Speier esterification method. Esterification of acids by refluxing with excess alcohol in the presence of hydrochloric acid or other acid catalysts. 

Fischer-Speier esterification to give a salt of an amino acid ester (by refluxing an alkanol with anhydrous HC1 or hot benzyl alcohol with toluene-/>-sulphonic acid) is straightforward. The fact that the nearby amino group is protonated when the carboxy group reacts to give a-amino acid esters does not slow the reaction down unduly a nearby positive site might have been expected to reduce the electrophilic character of the carboxy carbon atom. Without an acid catalyst, Walkylation can accompany esterification (Equation 4.6). 

Many acid catalysts have been employed in the Fischer-Speier esterification process, such as dry HC1,3-5 H2SO46-8 and MeSChH.9 Adams4 reported that esterification of acetonedicarboxylic acid 12 with alcohol 13 (saturated with HC1) provided the diester 14 in about 40% yield. 

Methyl, ethyl, benzyl, benzhydryl, p-nitrobenzyl, p-methoxy-benzyl, 4-picolyl, j3j -trichloroethyl, j3-methylthioethyl, /J-p-toluenesulphonylethyl, and -p-nitrophenylthioethyl esters may be prepared directly from the acid and alcohol. TTie most usual method [4, 5] consists of heating the acid and an excess of the alcohol with an acid catalyst (e.g., Fischer-Speier, hydrochloric or sulphuric acid). The extent of reaction is improved if the water formed is removed by azeotropic distillation with an inert solvent (benzene, carbon tetrachloride, or chloroform). Considerable variation is possible in the natvire of the acid catalyst thus phosphoric acid [6], aryl sulphonic acids [7, 8, 9], alkyl sulphates [10], and acidic ion-exchange resins [11] may be employed. Removal of the water by azeotropic distillation during the formation of methyl esters is difficult and Brown and Lovette [12] introduced the novel reagent acetone dimethyl acetal (7) for the direct formation of methyl esters. In the presence of a trace of methanol and an acid catalyst the reagent acts as a scavenger of water formed by esterification and liberates further methanol for reaction. 

Esters can also be synthesized by a nucleophilic acyl substitution reaction of a carboxylic acid with an alcohol. Fischer and Speier discovered in 1895 that esters result simply from heating a carboxylic acid in alcohol solution containing a small amount of strong acid catalyst. Yields are good in this Fischer esterification reaction, but the need to use excess alcohol as solvent limits the method to the synthesis of methyl, ethyl, and propyl esters. 

In 1895, Fischer and Speier reported that carboxylic acids were esterified with alcohol in the presence of acid catalysts (i.e., HC1, H2S04) etc.)2... 

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