L-bromo-2-chlorobenzene

The present method of preparation of 4,4 -dimethyl-l,l -biphenyl is that described by McKillop, Elsom, and Taylor 15 It has the particular advantages of high yield and manipulative simplicity and is, moreover, applicable to the synthesis of a variety of symmetrically substituted biaryls 3,3 - and 4,4 -Disubstituted and 3,3, 4,4 -tetrasubstituted 1,1 -biphenyls are readily piepared, but the reaction fails when applied to the synthesis of 2,2 -disubstituted-l,T biphenyls The submitters have effected the following conversions by the above procedure (starting aromatic bromide, product biphenyl, % yield) bromobenzene, biphenyl, 85,1 -bromo-4-methoxybenzene, 4,4 -dimethoxy-l, 1 -biphenyl, 99, 1 bromo 3 methylbenzene, 3,3 dimethyl-1,l -biphenyl, 85 4-bromo-l,2-dimethylbenzene, 3,3, 4,4 -tetramethyl-l,l -biphenyl, 76, l-bromo-4-chlorobenzene, 4,4 -dichloro-l,l -biphenyl, 73, l-bromo-4-fluorobenzene, 4,4 -difluoro-l,l -biphenyl, 73... 

As discussed in Section 15.5.2, the separation of two or more sublimable substances by fractional sublimation is theoretically possible if the substances form true solid solutions. Gillot and Goldberger(10°) have reported the development of a laboratory-scale process known as thin-hlm fractional sublimation which has been applied successfully to the separation of volatile solid mixtures such as hafnium and zirconium tetrachlorides, 1,4-dibromobenzene and l-bromo-4-chlorobenzene, and anthracene and carbazole. A stream of inert, non-volatile solids fed to the top of a vertical fractionation column falls counter-currently to the rising supersaturated vapour which is mixed with an entrainer gas. The temperature of the incoming solids is maintained well below the snow-point temperature of the vapour, and thus the solids become coated with a thin film (10. im) of sublimate which acts as a reflux for the enriching section of the column above the feed entry point. 

Similarly, interphase catalysis permits carbonylation of haloaryls and halovinyls by NaCo(CO)4 with CO in water. The reaction proceeds according to S l mechanism and leads to high enough yields of carboxylic acids. Because C r-Cl bond is inert in these conditions, the direct and selective synthesis of chlorocarboxylic acids becomes possible. Thus, l-bromo-4-chlorobenzene gives 4-chlorobenzoic acid only (Brunet et al. 1983 Scheme 7.67). 

Because of the different rates of hydrogenolysis, aryl halides containing different halogens can be reduced selectively. 1 -Bromo-2-chlorobenzene is reduced to chlorobenzene in 96% yield on treatment for 2 h at room temperature with a complex reducing agent prepared from nickel(II) chloride, sodium hydride and t-pentyl alcohol. l-Bromo-4-chlorobenzene is converted to chlorobenzene on treatment with... 

Reducing action. The reagent reduces organic halides and amines to the corresponding hydrocarbons. The ease of replacement of halogen is 1 > Br > CE. l-Bromo-4-chlorobenzene is reduced to chlorobenzene in 75% yield. Other papers. " ... 

This results in a characteristic pattern of four lines in the aromatic region, as seen in Fig. 3.31. The same four-line splitting pattern would be expected for para-disubstituted aromatic compounds, such as l-bromo-4-chlorobenzene, because such a molecule has a similar plane of symmetry as shown ... 

A soln. of l-bromo-4-chlorobenzene and triphenyltin hydride heated 3.3 hrs. 

Some years later, ligandless conditions were tilso used by Prashad and coworkers [25]. An efficient large-scale synthesis of l-(4-chlorophenyl)-3,3-dimethyl-2-butanone by arylation of pinacolone with l-bromo-4-chlorobenzene in the presence of Pd(OAc)2 and NaOfBu in toluene was described. An increase in the concentration of NaOfBu to 2.5-3.0 equiv suppressed the formation of over-arylated products. The yield of the l-(4-chlorophenyl)-3,3-dimethyl-2-butanone was very similar when ligandless conditions were applied [25]. 

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