THE HYDROGENATION OF GLUCOSE WITH RANEY-NICKEL: AN EXAMINATION OF THE SIDE REACTIONS

The mechanism of gluconic acid formation in the glucose Raney-nickel hydrogenation system was investigated. The Cannizzaro reaction proposed by Jacot-Guillarmond (1963) has been shown to be incorrect. Evidence presented indicates the mechanism is a catalytic dehydrogenation of cyclic glucose to the lactone which opens to the free acid with alkali. The beta anomer is selectively dehydrogenated over the alpha anomer. In the absence of base the lactone can be hydrogenated back to glucose. Gluconic acid cannot be reduced under the conditions tested.; Initial pH was found to have no positive affect on the glucitol yield over the range of 6 to 11.6. Over the same initial pH range, mannitol and gluconic acid yields increased from 0 to 17 percent and from 1 to 3 percent, respectively. During a hydrogenation run the pH was found to decrease rapidly to ca. 5.0 regardless of the initial pH. This drop in pH results from the gluconic acid formed during the reaction.