Semicarbazones cyanohydrins

The carbonyl group forms a number of other very stable derivatives. They are less used as protective groups because of the greater difficulty involved in their removal. Such derivatives include cyanohydrins, hydrazones, imines, oximes, and semicarbazones. Enol ethers are used to protect one carbonyl group in a 1,2- or 1,3-dicarbonyl compound. 

Semicarbazones can be prepared from 17-ketones by the conventional procedure. The formation of 17-cyanohydrins by exchange with acetone cyanohydrin and the use of this protective group has been already discussed (see section II-A-2). ... 

The other reactions of the aldehydes, which are extraordinarily reactive substances, need only he mentioned here. Such reactions are reduction to alcohols, formation of hydrazones, oximes, semicarbazones, bisulphite compounds, acetals and cyanohydrins (by addition of hydrogen cyanide). 

Ferrocene carboxaldehyde [12093-10-6] M 214.1, m 117-120°, 118-120°, 121°, 124.5°. The aldehyde forms red crystals from heptane/CH2Cl2, EtOH or petroleum ether and sublimes at 70°/lmm. The cyanohydrin has m 104° (from C6Hg/EtOH). The semicarbazone has m 217-219°(dec) after recrystallisation from aqueous EtOH. The oxime provides two isomers from petroleum ether viz m 96-99° and m 155°. The 0-acetyloxime has m 80-81° after recrystallisation from hexane [Lindsay Hauser J Org Chem 22 355 1957]. The 2,4-dinitrophenylhydrazone has m 248°(dec). Beilstein 16 IV 1798, Graham et al. JAm Chem Soc 79 3416 1957, Broadhead st al. J Chem Soc 650 7P58.]... 

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