Polyalcohol aldehydes

Treatment of an aldose or ketose with NaBH4 reduces it to a polyalcohol called an alditol. The reduction occurs by reaction of the open-chain form present in the aldehyde/ketone hemiacetal equilibrium. Although only a small amount of the open-chain form is present at any given time, that small amount is reduced, more is produced by opening of the pyranose form, that additional amount is reduced, and so on, until the entire sample has undergone reaction. 

The free aldehyde form of glucose (Problem 19.72) is reduced in the same manner described in the text for other aldehydes to produce the polyalcohol sorbitol. 

Polyether. A polymer in which the repeating unit includes a carbon-oxygen bond derived from, aldehydes, epoxides, polyalcohols or similar materials (Refs 1 4a). 

The aldehyde or ketone group of a sugar can be reduced to a hydroxyl group, forming a polyol (polyalcohol). 

From studies on numerous compounds in aqueous alkaline solutions, Johnson concluded that all aldehydes, alcohols, polyalcohols, and carbohydrates are electrochemi-cally detected by the pulsed amperometric scheme described above [61-63] these compounds include the oligosaccharides [64, 65]. Detection limits are typically less than 0.1 ppm for early eluting peaks when the sample volume is approximately 50 pL. 

It is well known that the condensation of aldehydes with polyalcohols may produce diastereoisomeric 1,3-dioxolane derivatives, as the difference in energy between the endo and exo isomers is small. 

Hence carbohydrates may be defined as polyalcohols of aldehydes and ketones. In large carbohydrate molecules, ketone and aldehyde groups are not directly seen, but when they are hydrolyzed, the aldehyde or ketone groups become apparent. 

Aldehydes readily react with alcohols into hemiacetals and acetals. The first reaction involves simple addition, whereas water is liberated in the second reaction. The reactions are acid-catalyzed and reversible. Acid catalysis is, however, not a necessary condition for the reaction to proceed. Frequently, particularly in the case of aliphatic aldehydes, the reaction proceeds without a catalyst. If both alcohol and aldehyde are bifunctional reagents, it is possible that cyclic structures may form or that polymerization may occur. Whether or not one or the other of these reactions occur depends on the energy factors, steric accessibility of the reaction sites, and finally, as in all reversible reactions, on the position of the equilibrium according to the concentration of reagents and products in the solution. Starch, being a polyalcohol, also reacts with aldehydes. This subject was formerly reviewed by Roberts.1274... 

A cationic starch can be prepared by blending a condensate of formaldehyde plus an inorganic ammonium salt with starch and heating at 80 °C for up to 1 h.1316 A great interest was developed with urea-formaldehyde resins that were made to react with such polyalcohols as starch.1317-1319 It was reported that the reaction of starch with urea-formaldehyde resin required an acidic catalyst592,1320-1325 and the use of such dispersants as polyphosphates.1326 Ammonium metaphosphate catalyzed the reaction without the addition of any other acid catalyst.1327 A product that formed a paste was produced by controlling the proportion of starch to aldehyde (either up to 20% of formaldehyde or up to 30% of acetaldehyde) and urea (up to 15%) at pH 2 1.1328... 

Sugars differ from the polyalcohols from which they are theoretically derived in that one of the alcohol groups is oxidized to a carbonyl group. Thus removal of two H atoms from glycerol results in either an aldehyde or a ketone according to the position of the carbonyl group formed as shown below ... 

This activity refers to the oxidation of primary alcohols to aldehydes and of secondary alcohols to ketones, as well as to the corresponding reverse reductions. Besides simple aliphatic mono and polyalcohols, such as ethanol and ethylene glycol, some steroids, such as 3-keto and 3-beta-hydroxysteroids have also been found to... 

Anodic detection of the aldehyde and alcohol functionalities in carbohydrates occurs in a potential region where there is only a very small background signal for the concurrent formation of surface oxide. Mode 1. The development of positive peaks for carbohydrates and polyalcohols by Mode 1 in LC-PAD is illustrated in Figure 10.3A by the chronoamperometiic (i—t) response curves generated following the potential step from E ed to det in the PAD waveform. The residual current (curve a)... 

Carbohydrates are polyhydroxy aldehydes or ketones. Therefore, one of their primary chemical properties is that of a polyalcohol. It is natural then that one of the first types of derivatives to be formed was esters. The formation of a completely acetylated carbohydrate can be obtained by the reaction with acetic anhydride in the presence of either a basic or an acidic catalyst. When reducing carbohydrates react with acetic anhydride in the presence of sodium acetate at 4°C, the (3-anomer is favored (reactions 4.1 and 4.2). 

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