Alcohols carbohydrates, primary groups

By the three preceding reactions and by the formation of carbohydrates by the oxidation of poly-hydroxy alcohols, carbohydrates are poly-hydroxy alcohols in which one alcohol group is oxidized to aldehyde (primary alcohol group at the end of the chain), or to ketone (secondary alcohol group). 

The irradiation of aqueous solutions of carbohydrates has the same effect as it does on alcohols. The hydroxyl groups are attacked to yield carbonyl compounds. Under anoxic conditions, dimer products and, ultimately, polymers are also formed. The primary alcohol... 

Pivaloyl-p-D-glucopyranuronic acid has been prepared in order to identify it as a metabolite of pivaloyloxyalkyl-containing prodrugs, the acid grouping being introduced by catalytic oxidation. i Electrochemical oxidation of some carbohydrate primary alcohols at a nickel hydroxide electrode in alkaline solution has been developed as a route to uronic acids. Examples... 

The reaction of aldoses with nitric acid leads to the formation of aldaric acids by oxidation of both the aldehyde and the terminal primary alcohol function to carboxylic acid groups Aldaric acids are also known as saccharic acids and are named by substi tutmg aric acid for the ose ending of the corresponding carbohydrate... 

One feature of this oxidation system is that it can selectively oxidize primary alcohols in preference to secondary alcohols, as illustrated by Entry 2 in Scheme 12.5. The reagent can also be used to oxidize primary alcohols to carboxylic acids by a subsequent oxidation with sodium chlorite.34 Entry 3 shows the selective oxidation of a primary alcohol in a carbohydrate to a carboxylic acid without affecting the secondary alcohol group. Entry 5 is a large-scale preparation that uses NaC102 in conjunction with bleach as the stoichiometric oxidant. 

Selectivity could be accomplished by this method in deoxygenation of primary and secondary alcohol groups,[2] as well as effective deoxygenation of hindered secondary hydroxyl groups, especially in the carbohydrate series. ... 

A double mediatory system consisting of modified TEMPO and halide ion or metal ion was also exploited for the oxidation of alcohols [53-55]. A number of carbohydrates have been chemoselectively oxidized at the primary hydroxyl group to uronic acids [56]. 

The oxidation of alcohols to aldehydes and ketones using catalytic amounts of TEMPO and controlled potential electrolysis has been reported, including the observation of a special selectivity for primary alcohols in the presence of secondary alcohols (equation 20) °. The oxidation of secondary alcohol is much slower than that of primary alcohols. This method is especially effective for oxidation of the primary alcohol group in carbohydrates (equations 21 and 22) . ... 

The first oxidations of alcohols by stoicheiometric RuO /H O were reported in 1958, of primary alcohols to aldehydes or carboxyhc acids and secondary alcohols to ketones [1]. The first Ru-catalysed oxidation of an alcohol was reported in 1965 when Parikh and Jones used RuO /aq. Na(IO )/CCl (Table 2.3) [2] to oxidise secondary alcohol groups in carbohydrates. 

Although these encompass primary and secondary alcohols they are considered here in a separate section since so much work has been done in the area, using RuO as the oxidant. In most cases it was used for oxidation of secondary alcohol groups in carbohydrates to ketones, but its first application, albeit stoicheiometrically as RuOy CCy was for the conversion of a secondary alcohol unit in l,2 5,6-di-0-isopropy-lidene-a-D-glucofuranose to the D-nfeo-hexofuranos-3-ulose (Fig. 2.13) [310]. There are early but illuminating reviews on carbohydrate oxidations by RuO [18, 311]. 

Primary Alcohol Groups in Carbohydrates to Carboxylic Acids... 

The secondary alcohol groups in PVA may be oxidized to ketones, and the primary alcohol groups in carbohydrates may be oxidized to carboxylic acids. Although these reactions do not reduce the degree of polymerization, they do increase the degree of water solubility of the polymers. 

The parent CDs are cyclic carbohydrates consisting of a variable number of glucopy-ranose units linked by 1,4-glycosidic bonds. The chemical structure of fi-CD (Fig. 1) shows the cyclic nature and the three hydroxyl groups on each glucopyranose unit. Two of the hydroxyls are secondary alcohols and are located at the C2 and C3 positions of the glucopyranose unit. The third hydroxyl is a primary alcohol at the C6 position. 

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