Carbohydrates esterification reactions

It has been demonstrated that organotin-mediated multiple carbohydrate esterifications can be controlled by the acytaring reagent and the solvent polarity. When acetyl chloride is used, the reactions are under thermodynamic control, whereas when acetic anhydride is employed, kinetic control takes place. Very good selectivity can furthermore be obtained in more polar solvents. These results can be used in the efficient preparation of prototype carbohydrate structures. 

Fatty acids of sugars are potentially useful and fully green nonionic surfactants, but the lipase-mediated esterification of carbohydrates is hampered by the low solubility of carbohydrates in reaction media that support lipase catalysis in general. Because the monoacylated product (Figure 10.8) is more soluble in traditional solvents than is the starting compound, the former tends to undergo further acylation into a diester. In contrast, the CaLB-catalyzed esterification of glucose with vinyl acetate in the ionic liquid [EMIm][BF4] was completely selective. The reaction became much faster and somewhat less selective when conducted in... 

The 2-(trimethylsilyl)ethyl thioethers are stable towards trifluoroacetic acid under conditions typically used to cleave acetals. The standard acylation and trans-esterification reactions are also fully compatible. Many Lewis acids are tolerated but halogenating agents react. Mild conditions for the cleavage of 2-(trimethyl-sily )ethyl sulfides, which are compatible with many of the standard transformations in carbohydrate chemistry, entails treatment of the thioether in dichloro-... 

Oxidative esterification, Japanese chemists have reported a novel oxidation discovered in the carbohydrate field. Reaction of the tri-n-butylstannyl alkoxide (D with 1 equiv. of NBS in CCU at 20° gives the ester (2) and succinimide (3) in high yield. The reaction involves oxidation of (1) to an aldehyde, which then reacts with (1) to form the ester (2). 

Jones RA, Davidson R, Tran AT, Smith N, Galan MC (2010) Iodine-catalyzed one-pot acetalation-esterification reaction for the preparation of orthogonally protected glycosides. Carbohydr Res 345 1842-1845... 

Esterification. The hydroxyl groups of sugars can react with organic and inorganic acids just as other alcohols do. Both natural and synthetic carbohydrate esters are important in various apphcations (1,13). Phosphate monoesters of sugars are important in metabohc reactions. An example is the enzyme-catalyzed, reversible aldol addition between dibydroxyacetone phosphate [57-04-51 and D-ylyceraldehyde 3-phosphate [591-57-1 / to form D-fmctose 1,6-bisphosphate [488-69-7],... 

Selective esterification, particularly p-toluenesulfonylation and methanesulfonylation, of one, or two, of several hydroxyl groups in carbohydrate molecules is an important reaction for constitutional and configurational alterations. 

One of the consequences of forming a cyclic hemi-acetal or hemiketal is that the nucleophilic hydroxyl adds to the carbonyl group and forms a new hydroxyl. This new group is susceptible to many normal chemical reactions of hydroxyls, e.g. esterification, and this type of reaction effectively freezes the carbohydrate into one anomeric form, since the ringopening and equilibration can now no longer take place. Consider esterification of glucose with acetic anhydride (see Section 7.9.1). P-o-Glucose will be... 

Abstract Polyfunctionality of carbohydrates and their low solubility in conventional organic solvents make rather complex their conversion to higher value added chemicals. Therefore, innovative processes are now strongly needed in order to increase the selectivity of these reactions. Here, we report an overview of the different heterogeneously-catalyzed processes described in the literature. In particular, hydrolysis, dehydration, oxidation, esterification, and etherification of carbohydrates are presented. We shall discuss the main structural parameters that need to be controlled and that permit the conversion of carbohydrates to bioproducts with good selectivity. The conversion of monosaccharides and disaccharides over solid catalysts, as well as recent advances in the heterogeneously-catalyzed conversion of cellulose, will be presented. 

Here we report an overview of the different heterogeneously-catalyzed pathways designed for the selective conversion of carbohydrates. On the basis of these results, we shall try to determine the key parameters allowing a better control of the reaction selectivity. Water being commonly used as solvent in carbohydrate chemistry, we will also discuss the stability of solid catalysts in the aqueous phase. In this review, heterogeneously-catalyzed hydrolysis, dehydration, oxidation, esterification, and etherification of monosaccharides and polysaccharides are reported. 

Esterification of carbohydrates with fatty esters is an important reaction that provides an important class of safer non-ionic surfactants. These biodegradable surfactants are widely used in the detergent, cosmetic, pharmaceutical, and food industries [124-127]. 

N. R. Pedersen, R. Wimmer, J. Emmersen, P. Degn, and L. H. Pedersen, Effect of fatty acid chain length on initial reaction rates and regioselectivity of lipase-catalysed esterification of disaccharides, Carbohydr. Res., 337 (2002) 1179-1184. 

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