Half ester salts, carbonic acid

Keywords alcoholate, CO2, large scale, carboxylation, gas-solid reaction, carbonic acid half ester salts... 

An essentially neutral process for C-acylation relies on the reaction of imidazolides (542) with the magnesium salt (543) of a malonic acid half thiol ester (Scheme 119) (79AG(E)72>. The method requires slight modification when applied to an w-hydroxycarboxylic acid since a primary hydroxyl reacts with carbonyldiimidazole. The use of malonic acid half thiol esters in this fashion patterns the scheme proposed for carbon-carbon bond formation in the biosynthesis of fatty acids. 

The carbonates and thiocarbonates may be classified quite simply into the following types, (i) Mixed Esters. In these esters, the carbonic acid or thiocarbonic acid is esterified with both an alcohol and a carbohydrate, (ii) Acid Esters. Here, a metal salt of a half-ester of a carbohydrate has been formed, (iii) Intermolecular Esters. Here, an ester has been formed between one molecule of the acid and two molecules of carbohydrate, (iv) Cyclic or Intramolecular Esters. Here, one molecule of the acid is di-esterified with one molecule of carbohydrate. 

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