Hydrolysis, acetal sugar

The concept that a catalyst provides an alternate mechanism for accomplishing a reaction, and that this alternate path is a more rapid one, has been developed in many individual cases. The basis of this idea is that the catalyst and one or more of the reactants form an intermediate complex, a loosely bound compound which is unstable, and that this complex then takes part in subsequent reactions which result in the final products and. the regenerated catalyst. Homogeneous catalysis can frequently be explained in terms of this concept. For example, consider catalysis by acids and bases.. In aqueous solutions acids and bases can increase the rate of hydrolysis of sugars, starches, and esters. The kinetics of the hydrolysis of ethyl acetate catalyzed by hydrochloric acid can be explained by the following mechanism ... 

Other methods of production iaclude hydrolysis of glycolonittile [107-16 ] with an acid (eg, H PO or H2SO2) having a piC of about 1.5—2.5 at temperatures between 100—150°C glycolonittile produced by reaction of formaldehyde with hydrogen cyanide recovery from sugar juices and hydrolysis of monohalogenated acetic acid. None of these has been commercially and economically attractive. 

Cellobiose was prepared first by Skraup and Konig by the saponification of the octaacetate with alcoholic potassium hydroxide, and the method was improved by Pringsheim and Merkatz.3 Aqueous barium hydroxide also has been employed for the purpose, and methyl alcoholic ammonia has been used extensively for the hydrolysis of carbohydrate acetates. The method of catalytic hydrolysis with a small quantity of sodium methylate was introduced by Zemplen,i who considered the action to be due to the addition of the reagent to the ester-carbonyl groups of the sugar acetate and the decomposition of the addition compound by reaction with alcohol. The present procedure, reported by Zemplen, Gerecs, and Hadacsy, is a considerable improvement over the original method (see Note 2). 

Glycosides are named by first citing the alkyl group and then replacing the -ose ending of the sugar with -oside. Like all acetals, glycosides are stable to neutral water. They aren t in equilibrium with an open-chain form, and they don t show mutarotation. They can, however, be converted back to the free monosaccharide by hydrolysis with aqueous acid (Section 19.10). 

Digestion (Section 29.1) The first stage of catabolism, in which food is broken down by hydrolysis of ester, glycoside (acetal), and peptide (amide) bonds to yield fatty acids, simple sugars, and amino acids. 

When 35 was heated in acetic acid containing hydrogen bromide, the tribromide 46 was obtained as a single product in 74% yield. Debromina-tion of 46 with zinc dust in acetic acid furnished the cyclohexene derivative 47, which was converted into compound 48 by osmium tetraoxide hydroxyl-ation and acetylation. The substitution reaction of 48 with acetate ions provided carba-a-DL-glucopyranose pentaacetate (49), which gave the carba-sugar 50 on hydrolysis. ... 

Starting from 149, novel carba-sugar pentaacetates of the P-L-allo (168) and a-u-manno (171) configuration have been synthesized. Reduction of 149 with diisobutylaluminum hydride (DIBAL-H) and acetylation gave a mixture of acetates 162 and 163. Hydroxylation of the mixture with osmium tetraoxide and hydrogen peroxide provided compounds 164 and 165 in the ratio of 9 1. Hydrolysis of 164 gave compound 166, which was transformed into 168 by a reaction analogous to that employed in the preparation of 157 from 153. 

Cellulase and all chemicals used in this work were obtained from Sigma. Hydrolysis experiments were conducted by adding a fixed amount of 2 x 2 mm oflSce paper to flasks containing cellulase in 0.05 M acetate buffer (pH = 4.8). The flasks were placed in an incubator-shaker maintained at 50 °C and 100 rpm. A Box-Behnken design was used to assess the influence of four factors on the extent of sugar production. The four factors examined were (i) reaction time (h), (ii) enzyme to paper mass ratio (%), (iii) amount of surfactant added (Tween 80, g/L), and (iv) paper pretreatment condition (phosphoric add concentration, g/L), as shown in Table 1. Each factor is coded according to the equation... 

Neutral sugars were quantified by trifluoroacetic acid hydrolysis (3) and gas chormatography of alditol acetates (4). Uronic acids were determined by Blumenkrantz method... 

Chromatographic characterisation of hydrolysis products Hydrolysis products from sodium polypectate were analysed by thin-layer chromatography on silica gel G-60, using ethyl acetate / acetic acid / formic acid / water (9 3 1 4, by volume) as the mobile phase system. Sugars were detected with 0,2% orcinol in sulphuric add-methanol (10 90ml) [14]. 

Fresh plant material is mixed with two volumes of methanol containing 0.3% concentrated HCl. If particularly labile compounds are known or found to be present, methanol containing 5% acetic acid may be used to advantage because this prevents hydrolysis of the acyl groups sometimes present on the sugar moieties while maintaining the low pH required to retain the pigments in the flavinium ion form. 

The unusual formation of an anhydro sugar by the hydrolysis of a trityl derivative has been described.76 The treatment of 5-trityl-D-ribofuranose triacetate with hydrogen bromide in acetic acid gives a ribosan diacetate which is presumed to be 1,5-anhydro-D-ribofuranose diacetate. 

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