Hydrogenation of glucose

In general, metal-based (Ni, Pt, Ru) catalysts are used for hydrogenation of glucose. For example, a new process has been recently developed in a 1.5 m3 gas-liquid-solid three-phase Airlift Loop Reactor over Raney nickel catalysts.[53] As compared with a Stirred Tank Reactor process, some improvements have been obtained, namely, shorter reaction time, higher yield in sorbitol and less than 1 % yield of mannitol. 

However, when acidic zeolites are used as supports in the hydrogenation of aqueous solutions of disaccharides, such as sucrose, and polysaccharides, such as starch, a cooperative hydrolysis effect is observed.156 The simultaneous hydrolysis of sucrose and hydrogenation of the two liberated monosaccharides, i.e. glucose and fructose, leads to a mixture of glucitol and mannitol in the expected ratio 3 1. For starch, consisting only of glucose units, sorbitol is the major product obtained after simultaneous hydrolysis and hydrogenation. 

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Sorbitol is a sweetener often substituted for cane sugar because it is better tolerated by dia betics It IS also an intermediate in the commercial synthesis of vitamin C Sorbitol is prepared by high pressure hydrogenation of glucose over a nickel catalyst What is the structure (including stereochemistry) of sorbitoP... 

An example for a non-structure-sensitive reaction is provided by Davis et al. [102], who investigated the liquid-phase hydrogenation of glucose over carbon and silica based ruthenium catalysts with particle sizes between 1.1 and 2.4 run. Depending on catalyst loading which was between 0.56 wt.% and 5 wt.%, dispersion decreased from 91% to 43%. At the same time, TOFs varied only insignificantly in a range between 0.21 1/s and 0.32 1/s. 

B. Kusserow, S. Schimpf and P. Claus, Hydrogenation of Glucose to Sorbitol over Nickel and Ruthenium Catalysts, Adv. Synth. Catal. 345 (2003) 289. 

Sorbitol is produced by high-pressure catalytic hydrogenation of glucose derived from cornstarch. It can also be produced as a co-product with mannitol if invert sugar (50% glucose, 50% fructose) is used as raw material. 

Normally, however, the reaction involving the formation of hydroxy-methylfurfural proceeds less readily than does the hydrogenation of glucose and fructose to mannitol and sorbitol, but its occurrence is detected by the fact that tetrahydrofuran derivatives have been isolated from the hydrogenation products. Thus, we have isolated tetrahydrofuran 2,5-dicarbinol (identified as its ditosyl derivative), 5-methyltetra-hydrofurfuryl alcohol and 2,5-dimethyltetrahydrofuran (VII) together with hydrogenolysis products of these compounds. 

Scheme 12 Various catalysts have been applied to facilitate the catalytic hydrogenation of glucose to sorbitol, notably Pt supported on activated carbon cloth using which 99.5% yield of sorbitol can be obtained.

A detailed investigation was carried out to study the deactivation of a Ru-alumina industrial catalyst326 used in the hydrogenation of glucose. This and numerous other patent applications327-332 testify to the importance of industrial applications of the hydrogenation of aliphatic aldehydes. 

As cystine, there is no free thiol available to react with the catalyst metal and, therefore, no mechanism for catalyst deactivation. As seen in Table 1, the addition of cystine had no effect on the hydrogenation of glucose. 

HOCH2(CHOH). CHjOH, being required during WWll for the prepn of ascorbic acid (Vitamin C), a method was developed by Tettamanzi St Atnaldi (Ref) for the prepn of sorbitol by the hydrogenation of glucose. Their method required smaller amts of catalyst, lower temperatures, lower pressures and shorter time than previously described methods... 

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