Benzil monohydrazone

Phenylbenzoyldiazomethane may be prepared by the oxidation of benzil-monohydrazone with mercuric oxide in the presence of dry etber as a solvent Tbe addition of a little alcoholic potassium hydroxide serves to catalyse the reaction ... 

Benzil monohydrazone. Method 1. Boil a mixture of 26 g. of hydrazine sulphate, 55 g. of crystallised sodium acetate and 125 ml. of water for 5 minutes, cool to about 50°, and add 115 ml. of methyl alcohol. Filter off the precipitated sodium sulphate and wash with a little alcohol. Dissolve 25 g. of benzil (Section IV,126) in 40 ml. of hot methyl alcohol and add the above hydrazine solution, heated to 60°. Most of the benzil hydrazone separates immediately, but reflux for 30 minutes in order to increase the yield. Allow to cool, filter the hydrazone and wash it with a httle ether to remove the yellow colour. The yield is 25 g., m.p. 149-151° (decomp.). 

Method 2. Drop 10 g. of hydrazine hydrate (85 per cent, aqueous solution see Section 11,49,Id) into a hot solution of 35 g. of benzil (Section IV,126) in 70 ml. of alcohol with stirring. When about three-fourths of the hydrazine hydrate has been introduced, the product begins to separate. After all the reagent has been added, heat the solution under reflux for 5 minutes, cool to 0°, filter at the pump, and wash twice with 20 ml. portions of alcohol. The yield of benzil monohydrazone, m.p. 149-151° (decomp.), is almost quantitative. 

The condensation of dihydrazones of aryl-substituted 1,2-diketones with aryl-substituted 1,2-diketones has also been described, albeit with rather low yields (up to 15 %).20 Subsequently, it was explicitly shown that this reaction leads to the same products as the dimerization of benzil monohydrazones, i.e. the 1,2,5,6-tetrazocine system, is not produced, rather the bicyclic tetraazapentalene system is obtained,21... 

This ring system could be prepared by thionation of benzil monohydrazone 172 with Lawesson s reagent (LR) followed by cyclization. The reaction gives 2,3-diphenyl-7,8,9,9a-tetrahydro-27/,677-pyrido[2,TA][l,3,4]thiadiazine 173 in a diastereoselective way, with the hydrogens at 2- and 9a-position in trans orientation. Benzil monohydrazone 172 was obtained by condensation of benzil 170 with 1 equiv of iV-aminopiperidine 171 (Scheme 23) <1998TA1531>. 

The treatment of aliphatic monoamines, benzil monooxime, benzil monohydrazone, and alkyl, monohaloalkyl arylketoximes bearing two or three a-hydrogens with tetrasulfur tetranitride to afford 1,2,5-thiadiazoles was presented in CHEC(1984) and CHEC-II(1996). 

Fifty-six grams (0.25 mole) of benzil monohydrazone (Org. Syn. 15, 62) (Note 1) is mixed in a mortar with 81 g. (0.38 mole) of yellow mercuric oxide and 35 g. of anhydrous calcium sulfate (Note 2). The mixture is introduced into a i-l. three-necked... 

A convenient route to pyridazine derivatives is found in the reaction of monohydrazones of 1,2-diketones with DMAD. The reaction of benzil monohydrazone with DMAD, for example, gives a mixture of products consisting of dimethyl 5,6-diphenylpyridazine-3,4-dicarboxylate (135), benzil dimethyl oxaloacetate ketazine (136) and benzil bisketazine (137). A similar reaction of acenaphthenequinone... 

Benzil monohydrazone can also be obtained in practically quantitative yield using hydrazine hydrate, a method first suggested by Curtius and Thun.1 Hydrazine hydrate (45 g., 0.75 mole, of an 85 per cent solution of hydrazine hydrate in water) is slowly dropped into a hot solution of benzil (158 g., 0.75 mole) in alcohol (300 cc.) with stirring. The product begins to separate from the hot solution after three-fourths of the hydrazine hydrate has been added. The solution is heated under reflux for a period of five minutes after all the hydrazine hydrate has been added. 

Benzil monohydrazone (610) and urea are reported to form 5,6-diphenyl-l,2,4-triazin-3-one (611) (71MI21903), and a-hydrazonocarboxylic acids (612) can be cyclized with imidates to l,2,4-triazin-5-ones (613) (74T3171). Both these reactions can also be treated as [2+2 + 2] syntheses, since the hydrazones (610) and (612) are prepared from the appropriate ketones and hydrazine. 

The Ugi four-component condensation allowed straightforward access to pyridazine derivatives when benzil monohydrazones and active methylene acids were employed as the amino and the acid component, respectively. The Ugi products 105 spontaneously cyclized to 2,3-dihydro-3-oxopyridazines 106 in fair to good yields (Scheme 2.38) [69]. 

Benzoylphenyldiazomethane was hydrogenated to 1,2-diphenylaminoethanol in ethyl acetate, but with uptake of 1 mol of hydrogen the intermediate benzil monohydrazone could be isolated in good yield (eq. 9.89). Hydrogenation of the hydrazone under the same conditions gave 1,2-diphenylaminoethanol in 60% yield. 

Although this method has had limited application, it represents the most convenient synthesis for the important diphenylketene. This consists in converting benzil monohydrazone to the diazo compound by the action of mercuric oxide suspended in benzene. The presence of anhydrous calcium sulfate is needed to remove the water formed in the oxidation. The benzene solution is then dropped slowly into a distilling flask maintained at 100-110°, whereby the benzene distils and the diazo... 

Dihydrazones of a-diketones, when treated with mercuric oxide at higher temperatures, yield acetylenes [393, 394, 395, 396], Diphenylacet-ylene is obtained by refluxing benzil dihydrazone with mercuric oxide [396] in benzene or by refluxing benzil monohydrazone with mercurous trifluo-roacetate in ether for 2 h (yield 43%) [405], The oxidation of dihydrazones... 

Jiphcnylacetyl chloride (2) with tripropylamine or with quinoline,- but later expressed preference for a method introduced by Schroeter.- The Schroeter method is described in Organic Syntheses.- benzil monohydrazone is oxidized in benzene... 

Cope et aU"). Benzil monohydrazone, required for the preparation of phenylbenzoyldiazomethane, is prepared by slowly adding hydrazine hydrate to a hot solution of benzil in ethanol refluxing for 5 min. completes the reaction. To prepare the dihydrazone, the Cope group refluxed benzil with 2 equivalents of hydrazine hydrate in n-propanol (b.p. 97°) for 60 hrs. 

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