Semicarbazone derivatives, formation

Use of nitrous acid to liberate a free keto-acid from its semicarbazone caused formation of hydrogen azide which was co-extracted into ether with the product. Addition of silver nitrate to precipitate the silver salt of the acid also precipitated silver azide, which later exploded on scraping from a sintered disc. The possibility of formation of free hydrogen azide from interaction of nitrous acid and hydrazine or hydroxylamine derivatives is stressed. 

The usual carbonyl reagents (hydrazines, semicarbazone, hydroxyl-amine) do not give the normal derivatives, but lead to ring contraction and formation of pyrazoles or isoxazoles. However, a semicarbazone and an oxime of 2,6-diphenylpyrone has been obtained by Arndt et al., indirectly, through the intermediacy of the more reactive 4-thiopyrone. 

It is of interest to mention that in the presence of small amounts of sodium phosphate or arsenate the formation of 69 becomes the dominant reaction at pH 6.0 and 50°C the ratio 69/68 is 90/10. The strong catalytic effect of the phosphate and arsenate anions on the rate of formation of the ethano derivative 69 bears some analogy to the semicarbazone formation between ketone and amine, which is also found to be effectively catalyzed by these anions (68JA4319). 

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... 

Ketones and aldehydes also condense with other ammonia derivatives, such as hydroxyl amine and substituted hydrazines, to give imine derivatives. The equilibrium constants for these reactions are usually more favorable than for reactions with simple amines. Hydroxylamine reacts with ketones and aldehydes to form oximes hydrazine and its derivatives react to form hydrazones and semicarbazide reacts to form semicarbazones. The mechanisms of these reactions are similar to the mechanism of imine formation. 

Examples adduced in Scheme 87 indicate the caution required when a nitrilimine intermediate favours the formation of a heterocycle other than triazole. The bromo derivative (179) of the semicarbazone (180) is formally analogous to (172) the nitrilimine (181) is formed even in the presence of such weak bases as sodium acetate or water and undergoes ring closure to the 1,3,4-oxadiazole (182), In anhydrous acetic acid the triazolinone (183 R = H) is formed (72JCS(P1)1918) a similar reaction occurs on treating the iV-methyl homologue of (180) with bromine in acetic acid to obtain (183 R = Me). 

Pyrolysis of certain compounds leads to heterocyclic rings, for example, when PhOM-Me2CH=CH2 is heated slowly to 320°C (M = Si) or 290°C (M = Ge), a 27/-l,2-benzoxasilin or a 27/-l,2-benzoxagermanin compound respectively results by Claisen rearrangement followed by intramolecular cycloaddition <81T2459>. Also, thermal decomposition of a chlorotriphenyltin benzil semicarbazone complex results in the formation of a 27/-l,3,2-benzoxazastannine derivative <89MI 627-05 >. 

Formation of semicarbazone and hydrazone derivatives. This can be used for electroinactive ketones and aldehydes. The... 

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