Cyclohexyl bromide preparation

A 3-I. three-necked, round-bottom flask is fitted with a mechanical stirrer through a mercury seal, a reflux condenser and a i-l. separatory funnel. A mixture of 200 g. (r mole) of 2,3-dibromopropene (Org. Syn. 5, 49) and 200 cc. of dry ether is added. The flask is now cooled in an ice bath, the stirrer is started, and one molecular equivalent of cyclohexylmagnesium bromide, prepared from 31 g. of magnesium, 204 g. of cyclohexyl bromide and 400 cc. of dry ether (Note i) is added at such a rate that the mixture refluxes gently (Note 2). The addition takes about one-half to three-quarters of an hour. Two layers are formed and magnesium bromide may or may not separate. 

The preparation of cyclohexylmagnesium bromide is described on p. 22. The solution may be standardized by titrating against 0.5 N hydrochloric acid, and exactly one mole equivalent is used in the preparation. Five cubic centimeters of cyclohexylmagnesium bromide solution is slowly added to 20 cc. of water, an excess of the standard acid is added, and the excess acid titrated with sodium hydroxide. If 85 g. (3.5 moles) of magnesium, one liter of dry ether, and 571 g. of cyclohexyl bromide (3.5 moles) are used, a solution results which is about 2 molar. 

Cyclohexyl bromide, for exfflnple, is converted to cyclohexene by sodium ethoxide in ethanol over 60 times faster than cyclohexyl chloride. Iodide is the best leaving group in a dehydrohalogenation reaction, fluoride the poorest. Fluoride is such a poor leaving group that alkyl fluorides are rarely used as starting materials in the preparation of alkenes. 

In an attempt to clarify the situation the rotating cryostat has been used to prepare cyclohexyl radicals in a variety of matrices by the reaction of cyclohexyl bromide with sodium. The radicals were allowed... 

The synthetic equivalent for the cyclohexyl carbocation is cyclohexyl bromide. Thus, cyclohexanol can be prepared by the reaction of cyclohexyl bromide with hydroxide ion. 

Prepared from cyclohexyl bromide and excess sodium azide in DMF see A. J. Parker. 

The phosphine is prepared according to the above procedure starting with 24.1 g (0.99 mole) of magnesium turnings in 350 mL of dry diethyl ether and 162 g (122 mL, 0.99 mole) of cyclohexyl bromide (bromocyclohexane) in 130 mL of dry diethyl ether. The resulting Grignard reagent is cooled in an ice-salt bath and treated dropwise (2 hr) with 81 g (61.4 mL, 0.45... 

Mercury dicyclohexyl.—This compound proved more difficult to isolate than the phenyl derivative, but has been obtained by the action of mercuric bromide on a large excess of magnesium cyclohexyl bromide. It is much less stable than mercury diphenyl, decomposing even in a few hours to a black oil when kept over phosphorus pentoxide in the dark in a vacuum desiccator. Mercury dicyciohexyl forms white, hard granules, M.pt. 78° to 79° C., which are more soluble than mercury diphenyl, and combines directly with mercuric halides or cyanide in any solvent to form cyclohexylmercuric salts. It has also been prepared by the sodium amalgam method, when it is said to form white needles, M.pt. 189° C., -which can be sublimed in small quantities in vacuo ... 

Lead diphenyl dicyclohexyl may be prepared either by the interaction of magnesium cyclohexyl bromide and lead diphenyl dibromide or magnesium phenyl bromide and lead dicyclohexyl dibromide. It forms pale yellow needles, Mq t. 178° to 180° C., the yellow liquid soon depositing metallic lead. The compound is soluble in alcohol, benzene, carbon tetrachloride, or ethyl acetate. ... 

ROM—>RBr. In the cyclohexane series reaction of diols with PBr is attended with rearrangements. Thus treatment of the 1,3- and 1,4-cyclohexanediols with PBrj affords mixtures of cis- and trans-1,3- and l,4-dibromides. Eliel and Haber found that cu-d-i-butylcyclohexanol reacts with PBr to give trani-4-/-butylcyclo-hexyl bromide, together with a small amount of olefin and a mixture of dibromides. Thus PBr, is evidently superior to PBr, for conversion of secondary alcohols into bromides. However, the Hunsdiecker reaction seems to be the method of choice for preparation of cyclohexyl bromides. ... 

Related bromide salts with other primary and secondary alkyl ligands (R) can be obtained similarly and in comparable yields. Thus, the complexes with R = Me, Bu, i-Pr and cyclohexyl are prepared starting from the corresponding alkyl bromides. In the case of R = Me, gaseous methyl bromide is passed through... 

A solution of sodamide in liquid ammonia (essentially the amide NHg ion) is a very powerful alkylation catalyst, enabling condensations to be carried out with ease and in good yield which are otherwise either impossible or pro oeed with difficulty and are accompanied by considerable by-products. Thus 3-alkylp3 ridines, otherwise inaccessible, are easily prepared from 3-picoline (see 3-n-amylpyridine in Section V,20). Also benzyl cyanide (I) and cyclohexyl bromide give a- r/ohexylphenylacetonitrile (II) ... 

The use of threo and erythro alkyl isomers can be extended and in some cases the preparative aspects improved by the use of other groups on the a-carbon besides H and D. For example, RR, SS) and RS, SR)-C6H5(CHF)(CHD)Br have been used in studies of oxidative addition. Although a secondary carbon is introduced, 5/ )-Ph(CHF)-(CHBrC02Et) has also been used successfully. Both of these systems, however, have the potential of interpretational problems arising if apparent retention is observed. Cis- and trans-substituted cyclohexyl groups provide an opportunity to utilize well-known coupling patterns for the study of stereochemistry.Thus, the oxidative addition of cyclohexyl bromides to [ py) dmg)2Co l)] proceeds with inversion. ... 

INSTRUCTOR PREPARATION. For each chromatograph used, a mixture of cyclohexene and cyclohexyl bromide (approximately 80 30 by volume) should be injected once the parameters of the column are set. This is to establish the retention times of the components in the mixture. 

An ethereal soln. of 3,3-pentamethylenediazirine added with ice-cooling to a Grignard soln. prepared from cyclohexyl bromide and Mg in ether, then allowed to stand 1 hr. without cooling l-cyclohexyl-3,3-pentamethylenediaziridine. Y F. e. s. E. Schmitz and R. Ohme, B. 94, 2166 (1961). 

The problem then becomes choosing a synthetic equivalent for the carbocation. A synthetic equivalent for a positively charged synthon needs an electron-withdrawing group at just the right place. Cyclohexyl bromide, with an electron-withdrawing bromine, is a synthetic equivalent for the cyclohexyl carbocation. Cyclohexanol, therefore, can be prepared by treating cyclohexyl bromide with hydroxide ion. This method, however, is... 

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