Cyclohexane bromination

A(-bromosuccinimide (NBS) is, however, one of the best known bromine donors. For exanq>le, it can brominate cyclohexane to give a 30% yield of the corresponding bromide. 7 NBS/dibenzoyl peroxide is not very selective, giving mixtures with methylcyclohexane, although decalin gives tetrabromides in a reasonably well-defined manner (equation 81). 

Within the cubane synthesis the initially produced cyclobutadiene moiety (see p. 329) is only stable as an iron(O) complex (M. Avram, 1964 G.F. Emerson, 1965 M.P. Cava, 1967). When this complex is destroyed by oxidation with cerium(lV) in the presence of a dienophilic quinone derivative, the cycloaddition takes place immediately. Irradiation leads to a further cyclobutane ring closure. The cubane synthesis also exemplifies another general approach to cyclobutane derivatives. This starts with cyclopentanone or cyclohexane-dione derivatives which are brominated and treated with strong base. A Favorskii rearrangement then leads to ring contraction (J.C. Barborak, 1966). 

Tetracyanoquinodimethane [1518-16-7] (5), 2,2 -(2,5-cyclohexadiene-l,4-diyhdene)bispropanedinitrile (TCNQ), is prepared by condensation of 1,4-cyclohexanedione with malononittile to give l,4-bis(dicyanomethylene)cyclohexane [1518-15-6] which is oxidized with bromine (31). 

Impurities can sometimes be removed by conversion to derivatives under conditions where the major component does not react or reacts much more slowly. For example, normal (straight-chain) paraffins can be freed from unsaturated and branched-chain components by taking advantage of the greater reactivity of the latter with chlorosulfonic acid or bromine. Similarly, the preferential nitration of aromatic hydrocarbons can be used to remove e.g. benzene or toluene from cyclohexane by shaking for several hours with a mixture of concentrated nitric acid (25%), sulfuric acid (58%), and water (17%). 

NBS can also be used to brominate alkanes. For example, cyclopropane, cyclopentane, and cyclohexane give the corresponding bromides when irradiated in a solution of NBS in dichloromethane. Under these conditions, the succinimidyl radical appears to be involved as the hydrogen-abstracting intermediate ... 

The benzylic position of an alkylbcnzene can be brominated by reaction with jV-bromosuccinimide, and the entire side chain can be degraded to a carboxyl group by oxidation with aqueous KMnCfy Although aromatic rings are less reactive than isolated alkene double bonds, they can be reduced to cyclohexanes by hydrogenation over a platinum or rhodium catalyst. In addition, aryl alkyl ketones are reduced to alkylbenzenes by hydrogenation over a platinum catalyst. 

Dipolar cycloadditkm reactions of nitrones to olefins, 46, 1,3-Dipolar cycloadditions with 3-phenylsydnone, 45, 98 Dispiro[5 1 5 l]tetradecane-7,14-dione, photolysis to cyclohexylidene-cyclohexane, 47, 34 preparation from cyclohexanecarbonyl chlonde and triethylamine, 47,34 Displacement of bromine from 1-bromo-2-fluoroheptane to give 2-fluoro-heptyl acetate, 46, 37... 

It is believed that equatorial substituents such as chlorine or bromine would increase the guest diameter beyond the allowed values (assuming that the guest molecules stack roughly parallel to the canal68)). Support for this comes from the study of fluorocyclohexane where the population of the axial conformer is not enhanced to any major extent70. Nitro-71) and cyano-cyclohexane, trans-l,2-dichloro-, trans-1,2-dibromo-, tram-1,4-dichloro-, trans-1,4-dibromo-, and trans-l-bromo-4-chloro-cyclohexane all pack most efficiently in the thiourea canals as the axial or diaxial conformer 68,72. Tram-2,3-dichloro-1,4-dioxane behaves similarly73. In contrast isocyanato-, tram-1,4-diiodo-, trans-1 -bromo-4-iodo-, and tram-1 -chloro-4-iodo-cyclohexane are present as mixtures of the axial/equatorial or diaxial/diequatorial conformations as appropriate 68,72). The reason for this anomalous behaviour of the iodosubstituted cyclohexanes is not clear. 

The parent hydrocarbon of this compound is cyclohexane. There are two bromine atoms attached at position numbers 1 and 3. Therefore, part of the prefix is 1,3-dibromo-. There is also a methyl group at position number 4. Because the groups are put in alphabetical order, the full prefix is l,3-dibromo-4-methyl-. (The ring is numbered so that the two bromine atoms have the lowest possible position numbers. See the Problem Tip on page 18.) The full name of the compound is l,3-dibromo-4-methylcyclohexane. 

Bromine (dry gas) Bromine (liquid) Bromobenzene Butanol Butyl acetate Butylamine Butylchloride Butyric acid Calcium chloride Carbon tetrachloride Castor oil Cellosolve Cellosolve acetate Chlorine (dry gas) Chlorine water Chloroacetic acid Chlorobenzene Chloroform Chlorosulfonic acid Chromic acid Citric acid Colza oil Copper sulfate Cyclohexane Cyclohexanol Cyclohexanone... 

A mixture consisting of the step 2 product (37 g) and 800 ml trimethyl phosphate were charged into a flask and treated with iodine (10.6 g) and the dropwise addition of bromine (19 g) dissolved in 70 ml trimethyl phosphate. After stirring for 4 hours additional bromine (9.5 g) dissolved in 35 ml of trimethyl phosphate was added and the mixture stirred overnight. The reaction liquid was then poured into water, extracted with chloroform, and washed with aqueous solutions of sodium thiosulfate and brine. The solution was then dried, concentrated, the residue purified by silica gel chromatography using cyclohexane/toluene, 20 1, respectively, and... 

Selective bromine-fluorine exchange of one bromine atom occurs in the reaction of tram-4,5-dibromo-m-cyclohexane-1.2-dicarboxylic anhydride (10) with sulfur tetrafluoride to give isomers of 5-bromo-l,l,3.3,7-pentafluoro-c/.v-octahydroisobenzofuran (11) and 4-bromo-5-fluoro-m-1.2-bis(trifluoromethyl)cyclohexane (12) in a 5 1 ratio and good total yield.11... 

Two stable compounds of formula C6H8 react with bromine and with KMn04. On hydrogenation with a platinum catalyst at 25°, both absorb two moles of hydrogen and form cyclohexane. Write possible structures for these substances and explain how electronic spectra may be used to tell which compound is which. 

The bromonium ion may be generated by other methods than direct bromination solvolytic reaction of trans-2-bromo-[(4-bromophenyl)sulphonyl]cyclohexane (36) (and cyclopentane) forms (reaction 7) the bromonium ion94 (37). If Br- is present in the reaction mixture, the generation of Br2 (and olefin) is observed (Scheme 14). This confirms the reversibility of the bromonium ion formation in the usual bromination pathway. When other olefin scavengers are present, a formal Br+ transfer is observed94. This may occur without the formation of Bit. 

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