Aldehyde phenylhydrazones

Nitranions originated by the deprotonation of aldehyde phenylhydrazones can be seen as diazaallylic anions jr-charge delocalization has also been investigated using the NMR approach in these systems112. 

The reaction of aroylhydrazines with DMAD gives rise to the hydrazones of oxaloacetic ester, which undergo thermal transformation to the corresponding diaroylhydrazines. b. Hydrazones. Ethyl l,3,5-triphenylpyrazole-4-carboxylate has been reported to be formed in the reaction of benzaldehyde phenylhydrazone with ethyl phenylpropiolate. In a detailed investigation, George and co-workers have shown that aldehyde phenylhydrazones react with DMAD, yielding a mixture of pyrazoles and pyrazolines. Thus, in the reaction of benzaldehyde phenylhydrazone with DMAD, products such as dimethyl l,3-diphenylpyrazoline-4,5-dicarboxylate (129), dimethyl... 

Benzaldehydepherrylbydrazone (called Benzyliden -phenylhydrazin Benzal-phenyl-hydraZin or Benz-aldehyd-phenylhydrazon in Ger), C6H6.NH.N CH.C6Hs, mw 196.24, N 14.28%, is described in Beil 15,134,(31) St [57]... 

One instance of visual observation of a luminescence has been reported by Gallagher (164). He noted a glow from an irradiated sample of benz-aldehyde phenylhydrazone when heated to 100°C. on a watch glass. Unfortunately, Zanella (166) was unable to reproduce this experiment. 

The one-pot three-component reaction of polyethylene glycol-supported acrylate 623 with aldehydes 621 and hydrazines 622 in the presence of chloramine-T followed by methanolysis afforded pyrazolines 624 in good yields and high purities (Scheme 77) <2003SL1467>. 1,3-Dipolar cycloaddition of resin-supported acrylic acid 625 with the nitrilimines generated in situ by oxidation of the aldehyde phenylhydrazones with (diacetoxy)iodobenzene under microwave irradiation gave 626, which was converted into l-phenyl-3-substituted-2-pyrazolinyl-5-carboxylates 627 (Scheme 78) <2004SC3521>. 

Cj HgBrFX Os 4 71uor-5>brom-3 nltro Balloyb aldehyd-phenylhydrazon 15 II79. 

C2sHaBrlNs03 5-Brom>4 Jod>3 nitro 8alioyl aldehyd-phenylhydrazon 15 II 79. 

CaHaIl(0j Verbindung CaHaN,0, aus Benz< aldehyd-phenylhydrazon 15 1 32. 

Nitto.3-metho . 4-b(aizaylozy-beiiz< aldehyd-phenylhydrazon 1 205. 

The reaction of aliphatic aldehyde phenylhydrazones with electron-deficient alkenes gives phenylazoalkanes via an ene reaction (Scheme 37). ° With more electron-deficient alkenes such as /S-nitrostyrene, however, Michael reaction at nitrogen occurs followed by cyclization to give pyrazolidines. 

Benzaldehyde m-nitrophenylhydrazone Benzaldehyde phenylhydrazone Benzaldehyde semicarbazone Benzaldehyde thiosemicarbazone Benzyl ethyl ketone isonicotinoylhydrazone p-Bromophenylacetone semicarbazone p-Chloroacetophenone semicarbazone Cumyl aldehyde phenylhydrazone p-Dimethylaminobenzaldehyde m-nitro-phenylhydrazone... 

The photochemical ,Z-isomerization of phenylhydrazones has also been investigated." " The introduction of a nitro group to the N-aryl group of pyridine-2-aldehyde phenylhydrazone enhances the quantum yield of the photoisomerization of the E-isomer to the Z-isomer in benzene, but decreases the quantum yield to zero for the reverse process. - Thus, a direct irradiation of the E-isomer of pyridine-2-aldehyde 4-nitrophenylhydrazone in benzene resulted in a complete one-way isomerization to the Z-form, the stability of which apparently arises from an intramolecular hydrogen bond between the nitrogen of the pyridine ring and NH (Scheme 26). ... 

Aldehydes and ketones may frequently be identified by their semicarbazones, obtained by direct condensation with semicarbazide (or amino-urea), NH,NHCONH a compound which is a monacidic base and usually available as its monohydrochloride, NHjCONHNH, HCl. Semicarbazones are particularly useful for identification of con jounds (such as acetophenone) of which the oxime is too soluble to be readily isolated and the phenylhydrazone is unstable moreover, the high nitrogen content of semicarbazones enables very small quantities to be accurately analysed and so identified. The general conditions for the formation of semicarbazones are very similar to those for oximes and phenylhydrazones (pp. 93, 229) the free base must of course be liberated from its salts by the addition of sodium acetate. 

The Fischer Indolisation Reaction occurs when the phenylhydrazone of a suitable aldehyde or ketone undergoes cyclisation with loss of ammonia, under the influence of various reagents, such as zinc chloride, ethnnolic hydrogen chloride, or acetic acid. For example, the phenylhydrazone of acetophenone (p. 257) when heated with zinc chloride gives 2 phenylindole. ... 

Experimental details for the preparation of oximes, phenylhydrazones and p-nitrophenylhydrazones will be found under Aromatic Aldehydes, Section IV,135,4-6. 

Phenylhydrazones (compare Section III,74,C). Dissolve 0-5 g, of colourless phenylhydrazine hydrochloride and 0 8 g. of sodium acetate in 5 ml. of water, and add a solution of 0-2-0-4 g. of the aldehyde (or ketone) in a little alcohol (free from aldehydes and ketones). Shake the mixture until a clear solution is obtained and add a little more alcohol, if necessary. Warm on a water bath for 10-15 minutes and cool. Filter ofiF the crystalline derivative, and recrystalhse it from dilute alcohol or water sometimes benzene or light petroleum (b.p. 60-80°) may be used. 

An important general method of preparing indoles, known as the Fischer Indole synthesis, consists in heating the phenylhydrazone of an aldehyde, ketone or keto-acld in the presence of a catalyst such as zinc chloride, hydrochloric acid or glacial acetic acid. Thus acrtophenone phenylhydrazone (I) gives 2-phenyllndole (I V). The synthesis involves an intramolecular condensation with the elimination of ammonia. The following is a plausible mechanism of the reaction ... 

Both aldehydes and ketones contain the carbonyl group, hence a general test for carbonyl compounds will Immediately characterise both classes of compounds. The preferred reagent is 2 4-dinilrophenylhydrazine, which gives sparingly soluble phenylhydrazones with carbonyl compounds ... 

Phenylhydrazones.—Nearly all aldehydes form condensation products with phenylhydrazine, known as phenylhydrazones, according to the following equation —... 

Butyric Aldehyde.—This body, C3H7COH, has been found in the oils of Eucalyptus globulus and Cajuput. It boils at 75° and forms a para-nitro-phenylhydrazone, melting at 91° to 92°. 

Analog erhalt man z. B. die 2,4-Dinitro-phenylhydrazone der folgenden Aldehyde ... 

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