Phenylhydrazone, 269 Table

Baker has also reported the reaction of butadiene with phenylhydra-zones leading to azoalkenes (example 14, Table IV). This is also a Grig-nard-type reaction which is catalytic. Analogous results were obtained with methylhydrazones (136). A wider scope was recently attained by causing allylic esters to react with phenylhydrazones in the presence of zero-valent nickel complexes having trialkyl phosphites (example 15, Table IV). 

Alkyl- and aryl-hydrazones of aldehydes and ketones readily peroxidise in solution and rearrange to azo hydroperoxides [1], some of which are explosively unstable [2], Dry samples of the p-bromo- and p-fluoro-hydroperoxybenzylazobenzenes, prepared by oxygenation of benzene solutions of the phenylhydrazones, exploded while on filter paper in the dark, initiated by vibration of the table or tapping the paper. Samples were later stored moist with benzene at —60°C to prevent explosion [3], A series of a-phenylazo hydroperoxides derived from the phenyl-or p-bromophcnyl-hydrazones of acetone, acetophenone or cyclohexanone, and useful for epoxidation of alkenes, are all explosive [4], The stability of several substituted phenylazo hydroperoxides was found to be strongly controlled by novel substituent effects [5],... 

The phenylhydrazone (0.02 mol) and the haloalkane (0.03 mol) are added with stirring to TBA-Cl (0.3 g, l.l mmol) in aqueous NaOH (50%, 20 ml). The mixture is stirred for 0.5-3 h at 30-60°C (Table 5.7) and then poured into H20 (100 ml). The alkylated product generally precipitates from the mixture and can be recrystallized. Liquid products are extracted from the mixture with CHCI3 (3 x 25 ml). The extracts are washed with H20 (4 x 25 ml), dried (MgS04), and evaporated under reduced pressure. 

Table 4. N—H stretching frequencies (cm 1) of benzaidehyde phenylhydrazones, 0 05 M in 0 4 mm cells...

Table I. Free Radicals from Sugar Phenylhydrazones and Osazones in Methyl Sulfoxide-1 % Potassium ferf-butoxide at 25 zt 3°C...

You should already be familiar with approximately half of the reactions listed in Table 9.2 from your introductory class. Moreover, you have probably tried to prepare an oxime, a phenylhydrazone, a 2,4-dinitrophenylhydrazone, or a semicarbazone. These compounds serve as crystalline derivatives with sharp and characteristic melting points for identifying aldehydes and ketones and for distinguishing them. When spectroscopic methods for structure elucidation were not available, such a means of identification was very important. 

The 15N CP/MAS NMR spectra of 15N doubly-labelled (Na from (15N) aniline, Nb from Na15N02), 3-methyl-l-phenylpyrazole-4,5-dione 4-phenylhydrazone (40), l-phenylazo-2-naphthol (35, R = H), 2-hydroxy-5- erf-butylazobenzene (29) and 4-hydroxyazobenzene (32) have been recorded and the temperature dependence of <5(15N) (Table 20) was followed105. For compound 35 (R = H), representing a mixture of the azo and hydrazone forms, the hydrazone content was calculated from the 15N chemical shifts of both nitrogen atoms at various temperatures (Table 21). The dependence of In K (K = [hydrazone form]/[azo... 

These derivatives are useful both as starting materials for further reactions (see Section 19-18) and for characterization and identification of the original carbonyl compounds. Oximes, semicarbazones, and phenylhydrazones are often solid compounds with characteristic melting points. Standard tables give the melting points of these derivatives for thousands of different ketones and aldehydes. 

If an unknown compound forms one of these derivatives, the melting point can be compared with that in the table. If the compound s physical properties match those of a known compound and the melting point of its oxime, semicarbazide, or phenylhydrazone matches as well, we can be fairly certain of a correct identification. 

The Fischer indole synthesis is commonly recognized as one of the most powerful and versatile tools for construction of indoles, as reflected by the amount of recent publications in which it has been used successfully. The usual approach involves initial preparation of a phenylhydrazone 323 from a suitable phenylhydrazine and an enolizable carbonyl compound, followed by an acid-induced cyclization to the target indole 324, featuring a [3,3]-sigmatropic rearrangement as the key step (Scheme 38). Some selected new examples of indoles prepared using standard Fischer conditions are collected in Table 2. 

TABLE 5-IX Rates of Phenylhydrazone and Oxime Formation of Aldehydes as Related to Internal H Bonding... 

Triphenylhydrazine reacts in a similar way with enol ethers to cinnoline derivatives (Table 12, number 5). The electrooxidation of A -alkylhydrazines leads to an iminium ion, which can react with olefins to five-membered rings [Eq. (28)] [254]. The anodic oxidation of phenylhydrazones of benzaldehyde affords diphenylnitrilimines, which add to dipolarophilic compounds [255]. 

These compounds are listed in Table XLVIII. 4-Amino-3,5-pyrazolidinediones have been prepared by reduction of the corresponding 4-oximino compounds.981 1048,1339 The preparation of 4-arylazo-3,5-pyrazolidinediones by direct introduction of this substituent has already been mentioned in Section 2 of this chapter.976,1048 Billow and Bozenhardt257 have prepared 4-phenylazo-3,5-pyrazolidinedione by cyclization of the phenylhydrazone of mesoxalic acid hydrazide in acetic acid (eq. 259). Stepanov and Kuzin1340 have suggested that the... 

Fairly good yields of 2-methylindole and tetrahydrocarbazole were formed from the cyclization of the phenylhydrazones of acetone and cyclohexanone, respectively, over CaX or REX catalysts as shown in Table XXVI. 

Experiments were first conducted with acetic and polyphosphoric acids, and with several concentrations of H2SO4. As expected for a methyl ketone, with 1-phenyl-2-propanone phenylhydrazone use of PPA catalyst resulted in a large variation in isomer ratio (see Table 1). With 3-heptanone the variations resulting from use of different acids were much smaller. Of several active zeolite catalysts tested, H-beta was found to be the most selective heterogeneous catalyst for the synthesis of the linear isomer from 3-heptanone and l-phenyl-2-butanone phenylhydrazones whereas, in contrast, H-Na-Y gave about equal amounts of both isomers. 

Although adsorption experiments with H-beta gave results in accordance with the preference for the linear product from 3-heptanone phenylhydrazone, with a bulky/linear adsorption ratio of 28/72 being found [23], and similar results were obtained for the indole isomers from 1-phenyl-2-butanone [22], total adsorption was small. Furthermore, when a sample of beta, the external surface of which had been passivated by silylation [24], was employed, no activity was found. This strongly suggests that it is the external surface, rather than the internal pore walls, which is responsible for the activity observed, thus variations in isomer distribution cannot be ascribed to pore-induced shape selectivity. Comparison of the calculated relative stabilities of the isomeric enehydrazines and indoles with the selectivity data of Table 1 indicate that the reactions are kinetically controlled, so that factors such as solvent effects are probably instrumental in establishing the observed product ratios. 

An attempt has been made to assign the structures of geometric isomers (54 and 55) of rifeohexoside-3-ulose phenylhydrazone. The relevant parameters are listed in Table VII. 

---