Selective monomethylations, dicarboxylic acids, diazomethane

Monoesterification of dicarboxylic acids. Chemiabsorption of a dicarboxylic acid on alumina or silica can be used to effect selective esterification of one acid group with diazomethane. The method was demonstrated by conversion of terephthalic acid, C6H4-l,4-(COOH)2) into the monomethyl ester in quantitative yield. 

Mono esters of dicarboxylic acids.1 Aliphatic straight-chain dicarboxylic acids when adsorbed on alumina react with diazomethane to form monomethyl esters in quantitative yield. Terephthalic acid, isophthalic acid, and 1,4-cyclohexanedi-carboxylic acid are also converted selectively to the monomethyl esters. However, phthalic acid does not show any enhanced selectivity under these conditions. Evidently selectivity for monoesterification results from adsorption of one of the acid groups on alumina. 

Selective monomethylation of dicarboxylic acids has been reported using A/ /wi a as an additive (eq 9) " It is thought that one of the two carboxylic acid groups is bound to the surface of the alumina and is therefore not available for reaction. Carboxylic acids that are engaged as lactols will also undergo methylation with diazomethane to provide the methyl ester and aldehyde (eq 10). ... 

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