- Fischer found that if one molecule of phenylhydrazine acted upon one molecule of an aldose or ketose a hydrazone resulted which in most cases was very soluble in water, but if three molecules of the hydrazine reacted (one of which is reduced to ammonia and aniline) insoluble crystalline substances resulted, termed osazones, which readily characterized the sugar from which it was obtained.
A ketose may also be obtained by reducing the osazone with zinc and acetic to an osamine, which with nitrous acid gives the ketose: R R R C :N NHPh.
These reactions permit the transformation of an aldose into a ketose; the reverse change can only be brought about by reducing the ketose to an alcohol, and oxidizing this compound to an aldehyde.
The osazone prepared from a-acrose resembled most closely the glucosazone yielded by glucose, mannose, and fructose, but it was optically inactive; also the ketose which it gave after treatment with hydrochloric acid and reduction of the osone was like ordinary fructose except that it was inactive.
D-Erythrulose is a ketose of this series.