Ester linkage/esterification

Esterification. The esterification of rosin provides important commercial products for the adhesive industry. Rosin esters are formed by the reaction of rosins with alcohols at elevated temperatures. Because the carboxyl group of the resin acids is hindered by attachment to a tertiary carbon, esterification with an alcohol can only be accomplished at elevated temperatures. This hindrance is in turn responsible for the high resistance of the resin acid ester linkage to cleavage by water, acid and alkali. 

The synthesis of the macrocycle is outlined in Scheme 17. Union of the polyol segment 86 and polyene segment 107 proved difficult, presumably due to steric hindrance about the ester linkage. After a series of standard esterification protocols failed, it was found that this coupling could be accomplished in 70 % yield... 

Hi) Enzymatic Esterifications. A major alternative to the classical basic catalysis is the use of enzymes for esterification, in particular with proteases and lipases.110 112 To make these enzymes, which normally hydrolyze amide or ester linkages, work in the reverse direction of esterification, the reactions have to be performed in organic media, with only the small amount of water necessary to preserve their active conformation. In such reactions, the difficulty is to find those conditions of solvent and temperature compatible with both the solubility of the substrates and the stability and the activity of the enzyme.113,114 In the case of sucrose (Scheme 9), most proteases lead selectively to monoesters at position p nl-ii5,ii6 Ypggg reactions are often performed in DMF, but examples in Me2SO, which is much less toxic, have also been reported, despite the ability... 

The effect of the degree d xrlarization of the ester linkages in low-motecular-weight esters on their reactivity has been examined by studying the reaction of alcoholysis, with ceUulose, of methyl esters of benzoic, p-chloro-, p-hydroxy, p-hydroxy-, p- and o-nitrobenzoic acids, and those of phenyl-, phenoxy-, 2,4-dichlorophenoxy- and monodiloro-acetic adds. The trans-esterification reaction was carried out in non-aqueous dinrethylformamide in the presence of catalysts (sodium methylate, cadmium acetate, p-toluenesulphonic add) at 110-140° C. 

To avoid any possible a — 7 conversion promoted by the anhydrous conditions during esterification Franzblau (1962) and Franzblau el al. (1963) developed a method by which the hydroxamic acids could be formed directly from the unmodified proteins in an aqueous system. This was achieved using a water-soluble carbodiimide, 1-cyclohexyl-3[2-morpholinyl-(4)-ethyl]-carbodiimide metho-p-toluene sulfonate (Fig. 5). The reaction conditions (pH 4, 25°C, in aqueous medium) eliminated any possibility of a —> 8 conversion. These conditions also precduded the possibility of hydroxyaminolysis of the natural ester linkages of collagen which will be discussed in Section V. This method, in common with all the others used to study 7-glutamyl links, was not quantitative. After subsecpient dini-... 

The esterification of a 1,3-ketoaldehyde enol with a diethoxyphosphinylalkanoic acid, forming the ester linkage of the final molecule first, allows ring closure via an intramolecular Horner-Emmons reaction. ... 

As before, R indicates that the two R groups can be the same or different. The process of ester formation is called esterification, and the carbonyl carbon-oxygen single bond of the ester group is called the ester linkage ... 

Ester hydrolysis is the reaction of an ester with water to break an ester linkage and produce an alcohol and a carboxylic acid. This process is simply the reverse of the esterification reaction (Reaction 5.8). Strong acids are frequently used as catalysts to hydrolyze esters ... 

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