Hydrogenation of Fructose

Scheme 14 Hydrogenation of fructose to mannitol is catalyzed by hydrogenation catalysts such as Raney nickel and Ru/C.

Sorbitol is a hexahydric alcohol obtained from the hydrogenation of fructose-free glucose, usually obtained from com [8]. The reaction is ... 

Heinen, A.W., Papadogianakis, G., Sheldon, R.A., Peters, J.A., and van Bekkum, H. (1999) Factors effecting the hydrogenation of fructose with a water soluble Ru-TPPTS complex. A comparison between homogeneous and heterogeneous catalysis, J. Mol. Catal. A Chem. 142,17-26. 

Veksler, M.A., Petrov, Yu.I, Geling, N.G., and Klabunovskii, E.I. (1974) Study of stereospecific hydrogenation of fructose on skeletal Ni using the mathematic simulation, Izv. AN SSSR, Ser. khim. 53-57, Chem. Abstr. 1974,80, 108766v. 

Fructose (V) under similar conditions gives first the phenylhydrazonc (Va) by the direct condensation of the >C 0 group of carbon atom 2 with one molecule of phenylhydrazine. The second molecule of phenylhydrazine then oxidises the primary alcohol group of carbon atom 1 to the -CHO group by removal of two atoms of hydrogen, which as before serve to reduce the phenyl-hydrazine to aniline and ammonia. The compound (Vb) which is thus produced then undergoes direct condensation with the third molecule of phenylhydrazine, giving the osazone of fructose, or fructosazone (Vc). 

Figure 8.7 Reaction schemes for hydrogenation of d-fructose, d-xylose, and d-lactose.

Preliminary kinetic analysis revealed that the reactions mentioned for various sugars were close to first order with respect to the organic reactant, while the reaction order with respect to hydrogen varied between 0.5 and 2.2, being 0.7 for hydrogenation of lactose on sponge nickel and about 2 for fructose hydrogenation on CuO/ZnO. 

There are several examples of one-pot reactions with bifunctional catalysts. Thus, using a bifunctional Ru/HY catalyst, water solutions of corn starch (25 wt.%) have been hydrolyzed on acidic sites of the Y-type zeolite, and glucose formed transiently was hydrogenated on ruthenium to a mixture of sorbitol (96%), mannitol (1%), and xylitol (2%) [68]. Similarly a one-pot process for the hydrolysis and hydrogenation of inulin to sorbitol and mannitol has been achieved with Ru/C catalysts where the carbon support was preoxidized to generate acidic sites [69]. Ribeiro and Schuchardt [70] have succeeded in converting fructose into furan-2,5-dicarboxylic acid with 99% selectivity at 72% conversion in a one-pot reaction... 

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. 

Figure 6. Dependence of fructose hydrogenation activity on its concentration. Figure 7. The affect of FT on the concentration in which zero order stops.

Figure 10. Adsorption/desorption of fructose-catalyst species and its hydrogenation.

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