Benzalacetophenone

Place a solution of 10 -4 g. of benzalacetophenone, m.p. 57° (Section IV,130) in 75 ml. of pure ethyl acetate (Section 11,47,15) in the reaction bottle of the catalytic hydrogenation apparatus and add 0 2 g. of Adams platinum oxide catalyst (for full experimental details, see Section 111,150). Displace the air with hydrogen, and shake the mixture with hydrogen until 0 05 mol is absorbed (10-25 minutes). Filter oflF the platinum, and remove the ethyl acetate by distillation. RecrystaUise the residual benzylacetophenone from about 12 ml. of alcohol. The yield of pure product, m.p. 73°, is 9 g. 

Benzalacetophenone (Chalcone) [94-41 -7] M 208.3, m 56-58", b 208"/25mm, pK -5.73 (aq H2SO4). Crystd from EtOH wanned to 50° (about 5mL/g), iso-octane, or toluene/pet ether, or recrystd from MeOH, and then twice from hexane. SKIN IRRITANT. 

In a 3-I. round-bottomed, three-necked flask fltted with a liquid-sealed mechanical stirrer, a thermometer, and a 500-cc. separatory funnel are placed 1700 cc. of dry ben2ene and 160 g. (1.2 moles) of powdered, anhydrous aluminum chloride (Note i). The mixture is cooled to 10° by means of an ice-water bath and maintained at 10-20 during the addition of a solution of 120 g. (0.58 mole) of benzalacetophenone (Note 2) (Org. Syn. Coll. Vol. I, 71) in 300 cc. of dry benzene. This addition requires about thirty minutes. The cooling bath is then removed and stirring continued at room temperature until all the dense, yellow precipitate formed at first has gone into solution (Note 3). The reaction is complete after stirring for an additional hour. 

The benzalacetophenone must be quite pure (m.p. 55-56°) and, in particular, free from benzaldehyde. 

The addition of diazomethane to a,/l-unsaturated ketones, e.g., benzalace-tone and benzalacetophenone, results in A -pyrazolines (16) which decompose thermally to the conjugated ketones (17). Cyclopropane formation is not observed in this instance. 

Krohnke observed that phenacylpyridinium betaines could be compared to 3-diketones based on their structure and reactivity, in particular, their ability to undergo Michael additions. Since 3-dicarbonyls are important components in the Hantzsch pyridine synthesis, application of these 3-dicarbonyl surrogates in a synthetic route to pyridine was investigated. Krohnke found that glacial acetic acid and ammonium acetate were the ideal conditions to promote the desired Michael addition. For example, N-phenacylpyridinium bromide 50 cleanly participates in a Michael addition with benzalacetophenone 51 to afford 2,4,6-triphenylpyridine 52 in 90% yield. 

A solution of 20.8 g. (0.1 mole) of benzalacetophenone (Note 1) (Org. Syn. 2, 1) in 150 cc. of c.p. ethyl acetate (Note 2) is placed in the reaction bottle of the catalytic reduction apparatus (p. 10) and 0.2 g. of platinum oxide catalyst (p. 92) is added. The apparatus is evacuated, then filled with hydrogen, and the mixture shaken with hydrogen until 0.1 mole has been absorbed. The time required is usually about fifteen to twenty-five minutes (Note 3). The platinum is filtered off and the solvent removed from the filtrate by distillation. The benzylacetophenone is recrystallized from about 25 cc. of alcohol and melts at 72-730. The yield is 17-20 g. (81-95 per cent of the theoretical amount). 

The benzalacetophenone should be freshly recrystallized from alcohol just before using and should melt at 570. 

Owing to the comparatively slight solubility of benzalacetophenone in alcohol, ethyl acetate is used as a solvent during the reduction. 

Benzylacetophenone has been prepared by the reduction of benzalacetophenone with zinc and acetic acid1 and catalytic-ally with palladium and hydrogen 2 by the reduction of /3-duplo-benzylidene acetophenone monosulfide 3 by the oxidation of the corresponding car bind with chromic acid 4 by the hydrolysis of ethyl benzyl benzoylacetate 5 from acetophenone and benzyl chloride by the action of sodamide 6 and from benzoic and hydrocinnamic adds using as catalysts manganese oxide 7 and ferric oxide.8... 

Dibenzoylmcthane has been prepared by the hydrolysis of dibenzoyl acetic acid 1 by the slow spontaneous decomposition of acetyl dibenzoyl methane 2 by the action of metallic sodium,3 sodium ethylate,3 sodium methylate,4 alchoholic potash,4 or sodamide 5 on mixtures of acetophenone and ethyl benzoate and by the action of alcoholic potash,6 sodium methylate,7 or sodium ethylate 8 on benzalacetophenone dibromide. 

It is interesting to note that condensation of the N,N-bis(silylated) enamine 538 with a variety of chalcones such as benzalacetophenone 735 proceeds, via 539 and subsequent cyclization and oxidation, to pyridines such as 540 [106, 108] whereas persilylated co-amino ketones such as the 2-substituted pyridine 541 cyclize, via 542, in 29% yield, to the pyrrole 543 [109] (Scheme 5.36). 

Ordinary Grignard reagents react with a, -unsaturated carbonyl compounds and afford both 1,2-adduct and 1,4-adduct. However, methylsulfonyhnethylmagnesium bromide or p-tolylsulfonylmethylmagnesium bromide gave only 1,2-adducts in the reaction with conjugated carbonyl compounds such as crotonaldehyde, cinnamaldehyde, trans-4-phenyl-3-buten-2-one, benzalacetophenone and l,5-diphenyl-2,4-pentadien-l-one. 

An extensive paper by Burgada et l. reports the reactions of cyclic phosphites (75 ab) and cyclic phosphoramidites (76 ab) with trans-1,2-dibenzoylethene, methyl fumarate, benzalacetone (PhCH=CH COMe), methyl-4-keto-pent-2-enoate (MeCO.CH=CH.COgMe) and benzalacetophenone (PhCH=CHCOPh)95. These reactions lead to... 

Fig. 1.11 Dissociation ranges of colour indicators for determination of the acidity function H0 in H2S04-H20 mixtures (1) p-nitroaniline, (2) o-nitroaniline, (3) p-chloro-o-nitroaniline, (4) p-nitrodiphenylamine, (5) 2,4-dichloro-6-nitroaniline, (6) p-nitroazobenzene, (7) 2,6-dinitro-4-methylaniline, (8) benzalacetophenone, (9) 6-bromo-2,4-dinitroaniline, (10) anthraquinone, (11) 2,4,6-trinitroaniline. (According to L. P. Hammett and A. J. Deyrup)...

In view of the reaction behavior of l,2 i.5-oxaphosphetanes (22), treated above, it appears fitting to reconsider the mechanism of the hydroxylion induced fragmentation of p-bromophosphinic acid 6443). It was assumed that formation of the phosphinate 65 is followed by that of the four-membered heterocycle 66, which spontaneously decomposes to benzalacetophenone and phenyldioxophosphorane the latter then adds water to give the phosphonie acid 43 ... 

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