Hydrazones decomposition

Dinitrophenylhydra2ones usually separate in well-formed crystals. These can be filtered at the pump, washed with a diluted sample of the acid in the reagent used, then with water, and then (when the solubility allows) with a small quantity of ethanol the dried specimen is then usually pure. It should, however, be recrystallised from a suitable solvent, a process which can usually be carried out with the dinitrophenylhydrazones of the simpler aldehydes and ketones. Many other hydrazones have a very low solubility in most solvents, and a recrystallisation which involves prolonged boiling with a large volume of solvent may be accompanied by partial decomposition, and with the ultimate deposition of a sample less pure than the above washed, dried and unrecrystal-lised sample. 

Okfm Syntheses. Conversion of aldehydes and ketones to olefins by the base-catalyzed decomposition of -toluenesulfonic (Ts) acid hydrazones (10) is known as the Bamford-Stevens reaction (54,55). 

Carbenes of type (113), generated by thermal decomposition of the appropriate tosyl-hydrazone salts, undergo ring opening more readily when the ring heteroatom is oxygen rather than when it is sulfur (78JA7927). 

According to a detailed mechanistic study, the first step is the abstraction of the relatively acidic hydrazone proton (93- 97). This is followed by hydride attack on the trigonal carbon of the C=N bond, mainly from the a-side at C-3, together with the concomitant loss of the tosylate anion (97 -> 98). Expulsion of nitrogen from the resulting intermediate (98) yields a fairly insoluble anion-metal complex (99) which upon decomposition with water provides the methylene derivative (100). 

The classical procedure for the Wolff-Kishner reduction—i.e. the decomposition of the hydrazone in an autoclave at 200 °C—has been replaced almost completely by the modified procedure after Huang-Minlon The isolation of the intermediate is not necessary with this variant instead the aldehyde or ketone is heated with excess hydrazine hydrate in diethyleneglycol as solvent and in the presence of alkali hydroxide for several hours under reflux. A further improvement of the reaction conditions is the use of potassium tcrt-butoxide as base and dimethyl sulfoxide (DMSO) as solvent the reaction can then proceed already at room temperature. ... 

The Wolff-Kishner reaction175 is the reduction of carbonyl groups to methylene groups by base-catalyzed decomposition of the hydrazone of the carbonyl compound. It is thought that alkyldiimides are formed and then collapse with loss of nitrogen.276... 

The flask is then cooled to o°, and the hydrazone is filtered off and washed twice on the funnel with ioo-cc. portions of cold alcohol. The product melts at 149-1510 with decomposition. 

Most reactions with hydrazine are carried out with aldehydes and ketones in the presence of alkali. The reduction proper is preceded by formation of hydrazones that decompose in alkaline medium at elevated temperatures to nitrogen and compounds in which the carbonyl oxygen has been replaced by two hydrogens. The same results are obtained by alkaline-thermal decomposition of ready-made hydrazones of the carbonyl compounds. Both reactions are referred to as Wolff-Kizhner reduction [280]. 

Reduction of unsaturated aromatic aldehydes to unsaturated hydrocarbons poses a serious problem, especially if the double bond is conjugated with the benzene ring or the carbonyl or both. In Clemmensen reduction the a,)8-unsaturated double bond is usually reduced [160], and in Wolff-Kizhner reduction a cyclopropane derivative may be formed as a result of decomposition of pyrazolines formed by intramolecular addition of the intermediate hydrazones across the double bonds [280]. The only way of converting unsaturated aromatic aldehydes to unsaturated hydrocarbons is the reaction of... 

Reduction of the carhonyl group to methylene is carried out hy Clemmensen reduction [160, 758], hy Wolff-Kizhner reduction [280, 282], or hy its modifications decomposition of hydrazones with potassium /er/-butoxide in dimethyl sulfoxide at room temperature in yields of 60-90% [845], or hy reduction ofp-toluenesulfonylhydrazones with sodium borohydride (yields 65-80%) [811] (p. 134). 

Ketones are obtained from a-diketones by reduction with hydrogen sulfide in a pyridine-methanol solution [237], by refluxing with 47% hydriodic acid in acetic acid (yield 80%) [916], and by decomposition of monohydrazones with alkali [923]. Reduction of a-diketones to hydrocarbons is achieved by decomposition of bis-hydrazones by alkali [923]. 

The unconventional 3-diazoindoles were prepared by oxidative conversion of hydrazones and oximes. Thus, l-methyl-3-diazo-2-oxindole (21d) was prepared by mercuric oxide oxidation of l-methylisatin-3-hydrazone 297 (X = NNH2) in benzene at room temperature (1891JPR551) (Scheme 91). It can also be prepared by decomposition of l-methylisatin-3-tosyl-hydrazone 297 (X = NNHTs) with aqueous sodium hydroxide in a two-... 

The selective hthiation of 2-hexanone phenylaziridinyl-lEl-hydrazone 127 with LDA and subsequent alkylation with 8-(tert-butyldimethylsilyloxy)octyl bromide gave (Z)-hydrazone 128 in 65% yield. Its LDA-catalyzed selective decomposition followed by hydrolysis of the silyl ether yielded (Z)-9-tetradecen-l-ol, which was acetylated to afford the target compound 129 in 80% yield with a complete regioselectivity and a cisitrans ratio of 99.6/0.4. 

Other approaches to alkylidenecycloproparenes have been attempted without success. Aromatization of appropriate alkylidenecyclopropanes or their precursors could not be realized, and flash vacuum pyrolysis of methylene phthalide and 3-methylene-2-coumaranone afforded rearrangement products rather than alkylidenecycloproparenes via extrusion of 002. The photochemical or thermal decomposition of the sodium salt of benzocyclobutenone p-toluenesulfonyl hydrazone led to products derived from dimerization of the intermediate benzocy-clobutenylidene, or from its reaction with the solvent, but no ring-contracted products were observed. When the adduct of methylene-l,6-methano[10]annulene to dicyanoacetylene (249) was subjected to Alder-Rickert cleavage, phenylacety-lene (250) was formed, which derives reasonably from the parent 234. ... 

In search of a convenient procedure for preparing diazo substrates for the cycloaddition to Cgg, Wudl introduced the base-induced decomposition of tosyl-hydrazones [116]. This procedure allows the in situ generation of the diazo compoimd without the requirement of its purification prior to addition to Cgg. Since they are rapidly trapped by the fullerene, even unstable diazo compounds can be successfully used in the 1,3-dipolar cycloaddition. In a one-pot reaction the tosyUiydrazone is converted into its anion with bases such as sodium methoxide or butylHfhium, which after decomposition readily adds to Cgg (at about 70 °C). This method was first proven to be successful with substrate 142. Some more reactions that indicate the versatility of this procedure are shown in Table 4.4. Reaction of 142 with CgQ under the previously described conditions and subsequent deprotection of the tert-butyl ester leads to [6,6]-phenyl-C5j-butyric acid (PCBA) that can easily be functionalized by esterification or amide-formation [116]. PCBA was used to obtain the already described binaphthyl-dimer (obtained from 149 by twofold addition) in a DCC-coupling reaction [122]. 

The hydrazones derived from (133) and oxocarboxylic acids are thermally very sensitive and decompose immediately at 30 °C to give sulfur, nitrogen, and polymeric material. Decomposition also occurs on treatment with catalytic amounts of both acid and base. 

All hydrazones are purified by distillation or chromatography yielding colorless to pale yellow oils, which can be stored safely under argon at —20 C. Under the influence of light and air slow decomposition occurs and a brown color appears. 

Diazo compounds have previously been prepared by a variety of methods. Some of these methods Include hydrazone oxidations, the reaction of diazomethane with acid chlorides,4 the reaction of activated methylene compounds with tosyl azide, decomposition of N-nitroso compounds, ... 

---