Platinum cyanohydrins

L-Mannitol has been prepared by the reduction of L-mannosaccharo-dilactone or L-mannose. By far the most convenient procedure is that used by Baer and Fischer for their preparation of L-glyceraldehyde by the oxidative cleavage of l,2 5,6-diisopropylidene-L-mannitol with lead tetraacetate. L-Arabinose was converted to L-mannonolactone by the cyanohydrin synthesis and this was hydrogenated over platinum oxide to the desired L-mannitol. High hydrogen pressures, rather than low as usually employed with this catalyst, were used. 

With tropinone cyanohydrin (eq. 7.55)104 and steroid cyanohydrins (eq. 7.56),105 however, hydrogenation over platinum oxide in acetic acid in the absence of hydrochloric acid gave satisfactory results. 

The nitrile group can be selectively hydrogenated in the presence of aldehydes, ketones but not in the presence of olefins, acetylenes, and nitro groups. Cyanohydrins are reduced to amino alcohol mostly over platinum oxide in acetic acid . 

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