And phenylhydrazone

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. 

Section IV, 135,5), but are unaflFected by the dimedone reagent (Section 111,70, 2). The general reactions are similar to those already given under Aliphatic Ketones (Section 111,74). Owing to their higher molecular weight, such derivatives as oximes and phenylhydrazones are frequently quite satisfactory. 

An example of the electrophilic reactivity of the C-4 atom is the easy formation of oxime and phenylhydrazone derivatives (422). It has been reported, however, that 2 pheny -A-2-thiazoline-4-one does not react with phenylhydrazine (397). 

The oxime and phenylhydrazone are liquid, and not suitable for identification purposes. 

Carbonyl compounds are also rapidly regenerated from the corresponding semicar-bazone and phenylhydrazone derivatives using ammonium persulfate impregnated... 

Reductions with aluminum are carried out almost exclusively with aluminum amalgam. This is prepared by immersing strips of a thin aluminum foil in a 2% aqueous solution of mercuric chloride for 15-60 seconds, decanting the solution, rinsing the strips with absolute ethanol, then with ether, and cutting them with scissors into pieces of approximately 1 cm [141,142]. In aqueous and non-polar solvents aluminum amalgam reduces cumulative double bonds [143], ketones to pinacols [144], halogen compounds [145], nitro compounds [146, 147], azo compounds [148], azides [149], oximes [150] and quinones [151], and cleaves sulfones [141, 152, 153] and phenylhydrazones [154] (Procedure 30, p. 212). 

Polarography of oximes and phenylhydrazones in aqueous buffers at pH 1.0. All give four-electron waves with half-wave potential dependent on pH. 

Allylic oxidation of a variety of cyclic alkenes with copper complexes of different pybox ligands (8) and with various peresters shows high enantioselectivity (80-96% ee). Use of phenylhydrazine as an additive and acetone as solvent accelerates the reaction. It has been suggested that the phenylhydrazone is responsible for the observed acceleration. Using EPR spectra, it has been shown that the Cu(II) species is reduced to Cu(I) by phenylhydrazine and phenylhydrazone. It has been found that the presence of a gem-diphenyl group at C(5) and a secondary or tertiary alkyl substituent at the chiral centre at C(4) of the oxazoline rings is crucial for high enantioselectivity. 

HTI was effective in converting phenylhydrazones and phenylhydrazones of a-keto esters into the parent ketones. The reaction proceeded through an azo intermediate, stable enough to be observable by H-NMR, and was essentially quantitative [50] ... 

CR(Q(262)1017>. The nucleophilic reactivity of the oxygen atom has been observed in the acetylation by acetic anhydride of 2-aryl- and 2-heteryl-A2-thiazolin-4-ones (Scheme 136). 2-Alkoxy and 2-methyl derivatives of A2-thiazolin-4-one (196) react with OPCl3 to yield thiazolylphosphoric esters (197) which have insecticidal uses (Scheme 137). An example of the electrophilic reactivity of the C-4 atom is the easy formation of oxime and phenylhydrazone derivatives. 5-Aryl-A2-thiazolin-4-one (198) gives the 1,3-dipolar cycloaddition product (199) with methyl fumarate and methyl maleate (Scheme 138). Under similar conditions, treatment of (198) with dimethyl acetylenedicarboxylate (DMAD) yields a thiophene derivative (202) when R = Ph and a pyridone derivative (203) when R = H (Scheme 139). The proposed mechanism involves the formation of a mesoionic intermediate (200) which reacts in a cycloaddition with a second molecule of DMAD, yielding (201), the decomposition of which depends on the R substituent. 

Isopropylamine is formed in the reduction of aeetoxime in sulphuric-acid solution at a lead cathode (Tafcl and Pfeffer-mann1). This process is a general one. The electrolytic reduction of ketoximes leads, like that of the aldoximes and phenylhydrazones, to the final formation of amines. About 66% of the theoretically possible quantity of isopropylamine is formed from aeetoxime acetonphenylhydrazone gives about the same yield. 

Tafel and Pfeffermann 5 have discovered a useful method for preparing amines. They electrolytically reduce oximes and phenylhydrazones in sulphuric-acid solution. Thus... 

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. 

Semicarbazones and phenylhydrazones of carbonyl compounds react analogously, but the reaction in this case requires 1- 5 min. for completion. 

Benzeneseleninic anhydride, C5HjSe(0)0(0)SeC5Hs, which is prepared in situ from diphenyldiselenide and tert-hniyX hydroperoxide, is used for the oxidation of alcohols to aldehydes or ketones [525]. This reagent is a suitable dehydrogenating agent for the introduction of double bonds a to carbonyl groups [526] and the regeneration of ketones from their oximes, semicarbazones, and phenylhydrazones [527]. 

The reaction of phenylhydrazine, and particularly substituted phenylhydrazines, with the carbonyl group of sugars is extensively utilized in their identification. The derivatives are called osazones if two molecules of phenylhydrazine add to one molecule of sugar, as in the case of glucose, and phenylhydrazones when one molecule... 

Further analysis indicated that porphyroxine contained one —OMe group, and that it was a tertiary base readily giving quaternary salts [7]. An acetyl-derivative was prepared showing the alkaloid to be an alcohol as the free hydroxy-compound was alkali-insoluble. The presence of a carbonyl group in the molecule was demonstrated by the preparation of an oxime, semicarbazone, and phenylhydrazone. Methylporphyroxine was obtained by treating the quaternary salts with alkali, and methyltetrahydroporphyroxine by sodium amalgam reduction of porphyroxine methomethylsulphate. These derivatives also yielded oximes [7]. 

Mg(HS04)2, wet Si02, rt, 72-96% yield. These conditions also cleave simple semicarbazones and phenylhydrazones. ... 

KMn04, CH3CN, H2O, rt, 25-96% yield. Alumina supported permanganate and KMn04-Mn02 are similarly effective. KMn04 also cleaves semicarbazones and phenylhydrazones. 

A. R. Hajipour, H. Adibi, and A. E. Ruoho, Wet silica-supported permanganate for cleavage of semicarbazones and phenylhydrazones under solvent free conditions, J. Org. Chem., 68 (2003) 4553-4555. 

Tropinone is a low melting tertiary base which readily forms a methio-dide. The decomposition of this methiodide in alkali, in contrast to that of tropine and tropidine, does not give the expected des-base. With potassium hydroxide resinification of the primary product occurs (129) however, with silver oxide (128) or sodium bicarbonate (129) a product thought to be A -dihydrobenzaldehyde (oxime and phenylhydrazone (117)) was isolated in good yield. (This sensitivity towards alkali is a general characteristic of -aminocarbonyl compounds.) Silver oxide oxidizes this aldehyde to a dihydrobenzoic acid, while at elevated temperatures benzoic acid is formed. 

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