Bromo acetophenone

Pipera2ine-N,AT-dithioacetamide (44) condensed with [Pg.197]

Desyl bromide (a-bromo-desoxybenzoin, m-bromo-co-phenyl acetophenone) [484-50-0] M 275.2, m 57.1-57.5 . Crystd from 95% EtOH. 

Bromine (128 g., 0.80 mole) is added dropwise to the well-stirred mixture over a period of 40 minutes (Note 4). After all the bromine has been added, the molten mixture is stirred at 80-85° on a steam bath for 1 hour, or until it solidifies if that happens first (Note 5). The complex is added in portions to a well-stirred mixture of 1.3 1. of cracked ice and 100 ml. of concentrated hydrochloric acid in a 2-1. beaker (Note 6). Part of the cold aqueous layer is added to the reaction flask to decompose whatever part of the reaction mixture remains there, and the resulting mixture is added to the beaker. The dark oil that settles out is extracted from the mixture with four 150-ml. portions of ether. The extracts are combined, washed consecutively with 100 ml. of water and 100 ml. of 5% aqueous sodium bicarbonate solution, dried with anhydrous sodium sulfate, and transferred to a short-necked distillation flask. The ether is removed by distillation at atmospheric pressure, and crude 3-bromo-acetophenone is stripped from a few grams of heavy dark residue by distillation at reduced pressure. The colorless distillate is carefully fractionated in a column 20 cm. long and 1.5 cm. in diameter that is filled with Carborundum or Heli-Pak filling. 4 hc combined middle fractions of constant refractive index are taken as 3-l)romoaccto])lu iu)nc weight, 94 -100 g. (70-75%) l).p. 75 76°/0.5 mm. tif 1.57,38 1.5742 m.]). 7 8° (Notes 7 and 8). 

Nuclear halogenation of acetophenone depends on formation of the aluminum chloride complex. If less than one equivalent of aluminum chloride is used, side-chain halogenation occurs. 3-Bromoacetophenone has been prepared from 3-aminoaceto-phenone by the Sandmeyer reaction. The synthesis described here has been taken from work of the submitters, who have used it to prepare many 3-bromo- and 3-chloroacetophenones and benzaldehydes, as well as more highly halogenated ones (Notes 7 and 8). 

A solution of N-(2-aminobenzvl)-1-phenyl-2-metKylaminoethanol-1 was prepared by the reaction of a-bromo-acetophenone and (2-nitrobenzyl)methylamine, followed by hydrogenation of the nitro group by means of nickei on diatomaceous earth at room temperature and reduction of the CO group by means of sodium borohydride. The intermediate thus produced was dissolved in 100 ml of methylene chloride and introduced dropwise into 125 ml of sulfuric acid at 10° to 15°C. After a short standing, the reaction mixture was poured onto ice and rendered alkaline by means of a sodium hydroxide solution. Dy extraction with ether, there was obtained 1,2,3,4-tetrahydro-2-methyl-4-phenyl-8-amino-iso-quinoline. The base is reacted with maleic acid to give the maleate melting point of the maleate 199° to 201°C (from ethanol). 

YVe saw in Section 17.4 that keLones react with NaBH4 to yield alcohols. We ll also see in Section 22.3 that ketones react writh Br2 to yield a-bromo ketones. Perhaps surprisingly, treatment with NaBH4 of the a-bromo ketone from acetophenone yields an epoxide rather than a bromo alcohol. Show the structure of the epoxide, and explain its formation. 

Acetophenone bromination to 3 bromo acetophenone, 40,9 chlorination to 3 chloroacetophenone 40,9... 

Our recent studies on effective bromination and oxidation using benzyltrimethylammonium tribromide (BTMA Br3), stable solid, are described. Those involve electrophilic bromination of aromatic compounds such as phenols, aromatic amines, aromatic ethers, acetanilides, arenes, and thiophene, a-bromination of arenes and acetophenones, and also bromo-addition to alkenes by the use of BTMA Br3. Furthermore, oxidation of alcohols, ethers, 1,4-benzenediols, hindered phenols, primary amines, hydrazo compounds, sulfides, and thiols, haloform reaction of methylketones, N-bromination of amides, Hofmann degradation of amides, and preparation of acylureas and carbamates by the use of BTMA Br3 are also presented. 

These reaction conditions also permit the chemoselective quantitative reduction of benzaldehyde to benzyl alcohol without any concomitant reduction of either acetophenone or 3,3-dimethylbutan-2-one present in the same reaction mixture.83 Additionally, this useful method permits the reduction of aldehyde functions in polyfunctional compounds without affecting amide, anhydride, eth-ylenic, bromo, chloro, or nitro groups.79,80,319... 

Asymmetric reduction of 2-bromo-(3-nitro-4-benzyloxy) acetophenone. . 157... 

ASYMMETRIC REDUCTION OF 2-BROMO-(3-NITRO-4-BENZYLOXY)ACETOPHENONE[161... 

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 higher yields of the coupled products from the reaction of the a-bromo-acetophenones have been attributed to the differences in the two-phase distribution of the ions, compared with the other systems. The 1,4-diketone was isolated, as the major product, from the reductive debromination of a-bromocamphor. 

Barba and coworkers [84-91] have published a number of papers dealing with novel syntheses based on the reduction of phenacyl bromides. Electrolysis of phenacyl bromide at a mercury cathode leads to an intermediate, which reacts to give 2,4-diphenylfuran [84]. However, when a proton donor (CH3OH) is present, the reduction of phenacyl bromide yields acetophenone and 2-bromo-l,3-diphenyl-3,4-epoxy-butan-l-one. Interestingly, if phenacyl bromide is slowly introduced into an electrolysis cell so that the unreduced starting material is maintained at a low concentration, the products are different [85] (Scheme 7). 

Uses Intermediate in production of styrene, acetophenone, ethylcyclohexane, benzoic acid, 1-bromo-l-phenylethane, 1-chloro-l-phenylethane, 2-chloro-l-phenylethane, p-chloroethylbenz-ene, p-chlorostyrene, and many other compounds solvent in organic synthesis. 

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