Semicarbazone formation preparation

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). ... 

Experiments.—Being a primary hydrazide (of carbamic acid), semicarbazide reduces ammoniacal silver solutions and Fehling s solution. It reacts readily with aldehydes and ketones with the elimination of water and formation of semicarbazones, which, since they are more easily hydrolysed than are phenylhydrazones and oximes, are to be preferred to the latter for purposes of separation and purification of carbonyl compounds. Shake an aqueous solution of the hydrochloride (prepared as described above) with a few drops of benzaldehyde, isolate the semicarbazone and purify it by recrystallisation from alcohol. Melting point 214° decomp. Benzaldehyde semicarbazone is decomposed into its constituents by gentle warming with concentrated hydrochloric acid. 

One of the most characteristic reactions of the aminochromes is the ready formation of mono-derivatives with typical ketone reagents, e.g. semicarbazide, phenylhydrazine, etc. A relatively large number of derivatives of this nature have been prepared because of then-reported hemostatic activity (cf. refs. 2 and 3). Compounds of this type that had been described in the literature prior to December 1959 are listed in a previous review (Heacock3). Some further examples of this class of compounds have been described recently. They are N-ethylnoradrenochrome semicarbazone (84) (orange-red needles, m.p.180 215°)65 7-iodoadrenochrome methyl ether semicarbazone... 

The syntheses of the monoxime [mono- or di-hydrate, m.p. 178° (decomp.)] and monosemicarbazone [m.p. 223° (decomp.)] of DL-adrenochrome have recently been described by Remizov.191 The majority of previous publications referring to these compounds have dealt with derivatives of adrenochrome prepared initially from L-adrenaline. The picrates obtained from the DL-oxime and dl-semicarbazone of adrenochrome were described as yellow powders, decomposing at 124 and 150°, respectively.191 Remizov also described the formation of highly colored complexes from the interaction of the DL-oxime and DL-semicarbazone with certain metal ions (e.g. Co++, Ni++, Cr+++ Fe++ and Fe+++).191... 

The preparation and reactions of the azine, phenylhydrazone, and phenyl-semicarbazone of 4-amino-5-formyl-2-methyltriazole proceeded normally. One acetal has been prepared as follows. 4-Amino-3-benzyl-5-formyltriazole and boron trifluoride (as diethyl ether complex), stirred in methanol, gave 4-amino-3-benzyl-5-dimethoxymethyltriazole (20°C, 6 hr, 53%) and a dimeric by-product, 4-amino-3-benzyl-5-(3-benzyl-5-dimethoxytriazol-4-ylimino-methyl)triazole [73JCS(P1)2037]. The amino group in 4-aminotriazole-5-carbaldehydes lends itself readily to the formation of amidines and imidates (Section III,B,1), but it resists acylation. 

Removal of the acetaldehyde by distillation shifts the equilibrium to the right The formation of semicarbazones (III) is a reaction common to all aldehydes. For preparative reasons we have only described reactions involving aromatic aldehydes, since these afford semicarbazones which crystallise very readily (eqn. 2) ... 

It is also possible to characterize 9-fluorenone by preparation of an oxime or semicarbazone. Formulate equations showing clearly the formation of fhese fwo derivatives and name each reagent used in the preparation. 

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