Acetal linkages hydrolysis

Naturally occurring compounds called cyanogenic glycosides, such as lotau-stralin, release hydrogen cyanide, HCN, when treated with aqueous acid. The reaction occurs by hydrolysis of the acetal linkage to form a cyanohydrin, which then expels HCN and gives a carbonyl compound-fa) Show the mechanism of the acetal hydrolysis and the structure of the cyanohydrin that results. 

The polymerized system gives similar results. The IR spectrum of the polymerized lipid shows two absorption peaks at 1805 cm-1 and 1735 cm"1 which correspond to the lactone carbonyl and ester groups, respectively. After the polymerized vesicle had been allowed to stand in an aqueous system for 2 weeks, the lactone carbonyl absorption peak at 1805 cm"1 disappeared as seen in Figure 3, which indicates the hydrolysis of the connecting acetal linkages has been completed. 

The main cyanogenic glycoside in laurel is prunasin, the P-o-glucoside of benzaldehyde cyanohydrin. The enzymic hydrolysis of prunasin may be visualized as an acid-catalysed process, first of all hydrolysing the acetal linkage to produce glucose and the cyanohydrin. Further hydrolysis results in reversal of cyanohydrin formation, giving HCN and benzaldehyde. 

Cellulose differs from amylose principally in the stereochemistry of the acetal linkages, which are a in amylose but P in cellulose. a-Amylase is specific for al 4 bonds and is not able to hydrolyse pi 4 bonds. An alternative enzyme, termed cellulase, is required. Animals do not possess cellulase enzymes, and thus cannot digest wood and vegetable fibres that are predominantly composed of cellulose. Ruminants, such as cattle, are equipped to carry out cellulose hydrolysis, though this is dependent upon cellulase-producing bacteria in their digestive tracts. 

Gums are tasteless, odorless, colorless, and nontoxic. None, except the starches and starch derivatives, are broken down by human digestive enzymes. All are subject to microbiological attack. All can be depolymerized by acid- and enzyme-catalyzed hydrolysis of the glycosidic (acetal) linkages joining the monomeric (saccharide) units. 

The remaining four hydroxyl groups can be methylated in basic solution by dimethyl sulfate or by methyl iodide and silver oxide in N,N-dimethyl-methanamide, HCON(CH3)2, solution. Hydrolysis of either of these penta-methyl glucose derivatives with aqueous acid affects only the acetal linkage and leads to a tetramethylated glucose, 20, as shown in Figure 20-4. 

Hydrolysis of the acetal linkage between the pyranose and the furanose gives the following products ... 

Figure III-16 Acid-catalyzed hydrolysis of acetal linkages in a-methyl-D-lactoside.

Heller et al.201,202) showed that the polyacetals prepared by the condensation of a divinyl ether and a diol are only marginally useful for the release of norethindrone because hydrolysis of the acetal linkage at pH 7.4 is too slow. On the other hand the... 

Carbohydrates. The two functional groups subject to hydrolysis in wood polysaccharides are the ester and acetal linkages, of which the acetals are more important because of their greater abundance and their role in connecting the monosaccharides in the polymers. Hydrolysis may take place under both acidic and alkaline conditions. The extent and consequences of acid hydrolysis are greater. 

Under acidic conditions, however, the liberation of free acetic acid during hydrolysis of the esters can increase the acidity and enhance further hydrolysis of not only additional ester groups, but acetal linkages and lignin bonds as well. A prime example is the so-called autohydrolysis reaction (2) in which acetic acid liberated by steam can cause complete hydrolysis of the hemicelluloses and convert the lignin into soluble fragments. 

Acid hydrolysis of the acetal linkages in wood polysaccharides follows the normal hydrolysis of glycopyranosides with fission of the... 

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