Acid anhydrides with carbohydrates

Although the reaction of acetic anhydride in the presence of an acid catalyst with carbohydrates of all classes, and their derivatives, has been studied for some ninety years, no survey on the topic has been written in this Series. The present brief article does not attempt to give a full historical development of the subject (particularly for polysaccharides), but it attempts to bring together in one place an account of the reactions possible with the reagents. Thus, the uses of reactions are stressed, rather than the mechanistic interpretations of them. Some aspects of this topic have been discussed in other articles in this Series, and mention of them will be made where appropriate. 

The alcohol groups of carbohydrates undergo chemical reactions typical of hydroxyl functions They are converted to esters by reaction with acyl chlorides and carboxylic acid anhydrides... 

Esterification is normally carried out by treating the carbohydrate with an acid chloride or acid anhydride in the presence of a base (Sections 21.4 and 21.5). All the —OH groups react, including the anomeric one. For example, /3-o-glucopyranose is converted into its pentaacetate by treatment with acetic anhydride in pyridine solution. 

G. J. F. Chittenden, Oxidation of some derivatives of D-galactose with methyl sulphoxide-acid anhydride mixture a route to derivatives of D-gulose and D-talose, Carbohydr. Res., 15 (1970) 101-109. 

Weber [61,62] has developed in the context of prebiotic chemistry an original pathway for a-aminothioester synthesis [180], which can start from hydroxyaldehydes 30 intermediates in the formose reaction (a likely prebiotic pathway to carbohydrates). Obviously, thioesters themselves are not observed as products because of their fast hydrolysis in the medium, but they could be converted into peptide bonds in the presence of amino acids or peptide free amino groups, and into mixed anhydride with phosphoric acid in the presence of inorganic phosphate. The reaction involves two key-steps the condensation of ammonia and of the mercaptan on a-keto aldehyde 31... 

Following the observation that benzyl ethers are cleaved by acetic anhydride in the presence of sulfuric acid or perchloric acid, Allerton and Fletcher S extended the work to carbohydrate systems. 2,5-Di-O-benzyl-l,3 4,6-di-0-methylene-D-mannitol (12) gave 1,3,4,6-tetra-0-acetyl-2, 5-di-O-benzyl-D-mannitol in the presence of 0.09% of sulfuric acid, but, with 2.4% of the acid, the hexaacetate was formed. With 1,6-di-O-benzyl-2,4 3,5-di-0-methylene-L-iditol (13), brief acetolysis gave the di-0-acetyl-di-O-methylene derivative longer treatment gave the hexaacetate. 

Succinic acid has been produced in 90% yield by the anaerobic fermentation of carbohydrates.28 It was heated to form succinic anhydride, which was then oxidized to maleic anhydride with oxygen, using an iron phosphate catalyst (12.8) in more than 95% selectivity at up to 58% conversion. 

Itaconic Acid. Methylenesuccinlc acid propylene-dicarboxylic acid. CsH404 mol wt [30.10. C 46.16%, H 4.65%, O 49.19%. Obtained by dry distillation nf citric acid and subsequent treatment of the anhydride with water- Produced on a large scale by submerged aerobic fermentation using Aspergillus terreus and low cost carbohydrates from beet or cane Kane et al. U.S. pat. 2,385,283 (1945 to Pfi-... 

Acylation of the hydroxyl groups of carbohydrates with acyl chlorides or acid anhydrides in pyridine as the solvent yields esters. The configuration at each chirality center, including the anomeric carbon, is retained. Thus, a-D-glucopyranose is converted to the pentaacetate shown. 

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