Cyclohexane bromine reaction

Reaction with bromine. Unsaturated hydrocarbons react rapidly with bromine in a solution of carbon tetrachloride or cyclohexane. The reaction is the addition of the elements of bromine to the carbons of the multiple bonds. 

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... 

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... 

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. 

The rate of oxidation of cyclohexane by Co(III) acetate in acetic acid is enhanced in the presence of bromide ions.265 By analogy with alkylaromatic oxidations (see Section II.B.3.b), these reactions probably involve chain transfer by bromine atoms [cf. Eqs. (20l)-(204)]. 

All the hydrogen atoms in cyclohexane are equivalent, and free-radical chlorination gives a usable yield of chlorocyclohexane. Formation of dichlorides and trichlorides is possible, but these side reactions are controlled by using only a small amount of chlorine and an excess of cyclohexane. Free-radical bromination is highly selective (Section 4-14), and it gives good yields of products that have one type of hydrogen atom... 

When a solution of bromine (red-brown) is added to cyclohexene, the bromine color quickly disappears because bromine adds across the double bond. When bromine is added to cyclohexane (at right), the color persists because no reaction occurs. 

Reactions with Iodine and Bromine. All the reactions discussed above proceed at limiting rates that are independent of the concentration and nature of the reactant. However, reactions of iodine with Mn2(CO)j0 (6) and Re2(C0)1g (30) proceed by paths that are first order in [I2] as well as by the [I2]-independent homolytic fission paths. P-donor substituents increase the rates of reaction with I2 by several orders of magnitude (31) so that they proceed rapidly even at room temperature. Thus reaction of Mn2(C0)g P(C6Hu53)2 is estimated to occur over 108 times faster than Mn2(C0)jQ by a path first order in [I2] at 25°C in cyclohexane. In all cases the reactions proceed with fission of the metal-metal bonds to form the mononuclear iodo complexes. 

When bromine is added to cyclohexane, the bromine dissolves as it undergoes a substitution reaction and the product forms as a red-brown precipitate. 

In an earlier paper Barton and Onyon considered the unimolecular mechanism of dehydrochlorination to be of more universal application than the radical chain mechanism and postulated that a chloro-compound will decompose by a radical chain mechanism only so long as neither the compound itself nor the reaction products will be inhibitors for the chains . On the basis of this postulate the authors correctly predicted the mechanism of decomposition of a number of chlorine compounds. The postulate does not hold well for bromine compounds which show a greater tendency to decompose via radical chain mechanisms. However, from their early studies on 2-bromopropane 2-bromobutane, t-butyl bromide, and bromo-cyclohexane, Maccoll et a/.234,235,397,410,412 concluded that these compounds also decompose unimolecularly via a four-centre transition state similar to that proposed by Barton and Head. 

The dihalocyclopropane route is the method of choice for the synthesis of benzocyclopropenes and linearly fused cyclopropanaphthalenes, but is unsuccessful for angular cyclopropa[u]naph-thalene. Treatment of l,l-dichloro-la,2,3,7b-tetrahydro-l/f-cyclopropa[a]naphthalene(5) with potassium /ert-butoxide gave a mixture of 1-chloromethylnaphthalene, 1-terr-butoxymethyl-naphthalene and 2-terf-butoxy-l-chloromethylene-l,2,3,4-tetrahydronaphthalene, but none of the expected cyclopropa[n]naphthalene. The failure of the reaction has been attributed to difficulties in the aromatization. Isomerization of the initially produced cyclopropenyl double bond into the cyclohexane ring would require disruption of the aromatic character of the adjacent benzene nngT t-r>> 62 Similarly, attempted aromatization of l-chloro-l,2,3,7b-tetra-hydro-l//-cyclopropa[a]naphthalene (6) with 2,3-dichloro-5,6-dicyanobenzoquinone or via N-bromosuccinimide bromination followed by reaction with base afforded 4,5-benzotropone instead of cyclopropa[fl]naphthalenc. ... 

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