Replacement, aldehyde group by hydroxyl

Oxidation. Oxidation of hydroxybenzaldehydes can result in the formation of a variety of compounds, depending on the reagents and conditions used. Replacement of the aldehyde function by a hydroxyl group results when 2- or 4-hydroxybenzaldehydes are treated with hydrogen peroxide in acidic (42) or basic (43) media pyrocatechol or hydroquinone are obtained, respectively. 

The non-aqueous oxidation of various ketones and aldehydes to hydroxyaldehydes and hydroxy ketones has been carried out in two steps the first step is a bromination and the second a hydrolysis, or replacement of the bromine atoms by hydroxyl groups. Fischer and Landsteiner " brominated acetal in the presence of calcium carbonate (reaction 20). The bromoaldehyde Avas then treated with cold barium hydroxide solution (reaction 21) the resulting glycolic aldehyde was identified by conversion to glyoxal phenylosazone (reaction 22) and by the formation of calcium glycolate, after oxidation with bromine (reaction 23). 

Dakin reaction. Replacement of the aldehyde or acetyl groups in phenolic aldehydes or ketones by a hydroxyl group by means of hydrogen peroxide. 

A carboxyl group at C-1 gives rise to high activity. Aldehydes, alcohols and simple acetals can be active, but they may be converted to a carboxyl in vivo. Replacement of the carboxyl hydroxyl with an azido group reduces activity by 90% [22]. 

With increasing molar ratio between EpCl and HA cross-linked pol5mer is got that precipitates. By sodium periodate oxidation vicinal hydroxyl groups of HA are replaced with two aldehyde groups. 

Xylitol is a sugar alcohol. The aldehyde group (C = O) of the pentose sugar—5-carbon sugar—xylose is replaced by a hydroxyl group (OH). It can be made from birchwood chips, berries, leaves and mushrooms. Xylitol is commercially produced in Finland from birchwood chips hydrolyzed by acid to xylose. In the body, xylitol is formed as an intermediate during the formation of xylulose. Ingested xylitol is also converted to xylulose. Xylulose then enters the pentose-phosphate cycle of carbohydrate metabolism. 

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