Acetates, sugar

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). 

Molecular ion Chemical ionization using ammonia as reagent gas establishes the molecular weights of sugar acetates. 

Loss of C(0)0CH3 from methyl esters Loss of OC3H7 from propyl esters Methyl esters of 2-hydroxycarboxylic acids Loss of CH3C(0)0 from sugar acetates... 

Loss of acetic anhydride from sugar acetates... 

P. M. Bhaskar, M. Mathiselvam, and D. Loganathan, Zeolite-catalyzed selective deprotection of di- and tri-O-isopropylidene sugar acetals, Carbohydr. Res., 343 (2008) 1801-1807. 

T. roseopersicina is a phototrophic purple sulphur bacterium the strain marked BBS has been isolated from the cold water of the North Sea. Its anaerobic photosynthesis uses reduced sulphur compounds (sulphide, thiosulfide, or elementary sulphur), but it can also grow on organic compounds (sugar, acetate) in the dark. The bacterium contains a nitrogenase enzyme complex, thus it is capable of fixing atmospheric N2, a process accompanied by H2 production [Vignais et al., 1995],... 

Surfactant Long-chain fatty Sugar acetals None 50-90 27... 

The Hines64 showed that, as acids, ethanol, isopropyl alcohol, and tert-butyl alcohol are weaker than water, whereas methanol is stronger. The influence of the solvent could thus be interpreted in terms of equation 1. In methanol, the equilibrium would be more displaced to the right, and the rate of simple ammonolysis and transesterification would be enhanced, with concomitant decrease in the yields of amido sugars. In water (for the ammonolysis of sugar acetates) and in alcohols other than methanol, the equilibrium would be displaced to the left and this would allow operation of the orthoester mechanism a better chance. The isolation, from the reaction in isopropyl alcohol, of mono-O-benzoylated bis(benzamido)alditols, could also be explained on this basis. 

A typical representative of the class, D-arabinose diethyl dithioacetal tetraacetate, will be considered. The molecular ion of this compound decomposes along several pathways. As with the sugar acetates, the first series of fragments is that represented by ions differing from each other in 60 (acetic acid) or 42 (ketene) mass units. The first fragment of the series (Ui) has m/e 364 and is formed by fission of acetic acid from the molecular ion. 

Anomerization through the agency of a Lewis acid (electron acceptor) has found numerous applications for the preparation of the more stable form of a sugar acetate—usually a member of the a-D-series. Several of these applications are listed in Table III. Acetic anhydride, and mixtures of acetic anhydride and acetic acid, are the most commonly used solvents. Painter96 has shown that the rate of reaction is increased by addition of an inert solvent, carbon tetrachloride. Zinc chloride and sulfuric acid have been most frequently used as catalysts. Although these transformations have found frequent application, few theoretical studies have been made. 

The D-mannopyranose pentaacetates were treated with stannic trichloride acetate (labeled with carbon14 in the carboxyl group) in chloroform solution, in the presence of stannic chloride. The rate at which radioactivity was introduced into the sugar acetate was followed. The exchange had been shown to be specific for the Cl-acetoxy group of the D-glucopyranose pentaacetates,33 and this was assumed in the present... 

It has been pointed out, with reference to Table II, that the strongly acidic conditions which are ordinarily employed to replace the Cl-acetoxy group of a sugar acetate by halogen have yielded only one of the two anomeric O-acetylglycosyl halides. In 1901, Fischer and Armstrong106 described diastereoisomers for the acetochloro and acetobromo derivatives of... 

The Cl-acetoxy group of a sugar acetate is replaced by a phenoxy group on heating the acetate with a phenol in the presence of an acid catalyst.124 The steric result depends on the reaction conditions. By proper choice of the kind and amount of catalyst, the reaction time, and the tem-... 

In the early 1920 s, while attempting to obtain the sodium salt of n-glu-cose, with the cooperation of Alfons Kunz, he discovered a new process for the catalytic saponification of sugar acetates, using sodium methoxide, a method which has now become a standard procedure. The process was modified and somewhat improved later, with the assistance of Eugen Pacsu and Arpad Gerecs. 

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