Addition reactions, with bromine

As in the case of the steroids, introduction of additional nuclear substituents yields morphine analogs of increased potency. The more important of these are derived from one of the minor alkaloids that occur in opium. Thebaine (14), present in crude opium in about one-tenth the amount of morphine, exhibits a reactive internal diene system that is well known to undergo various addition reactions in a 1,4 manner (e.g., bromination). Thus, reaction with hydrogen peroxide in acid may be visualized to afford first the 14-hydroxy-6-hemiketal (15). Hydrolysis yields the isolated unsaturated ketone (16). Catalytic reduction... 

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. 

Addition reactions with bromine, chlorine, hydrogen bromide or hydrogen chloride are very vigorous and may be explosive if uncontrolled. 

According to K. H. Meyer, this surprising reactivity—which is also encountered amongst the enols—is explained by the fact that the OH-group activates the double bond adjacent to it and the two neighbouring double bonds of the conjugated system (Thiele s theory) are also involved in this activation. Phenol, therefore, can yield 1 2- and 1 4-substitution products with bromine, addition reactions first taking place ... 

Acetylene undergoes electrophilic addition reaction with bromine in the dark. Bromine adds successively to each of the two n bonds of the aUcyne. In the first stage of the reaction, acetylene is converted to an alkene, 1,2-dibromoethene. In the final stage, another molecule of bromine is added to the n bond of this alkene, and produces 1,1,2,2-tetrabromoethane. 

Although aromatic hydrocarbons are unsaturated, they have very different chemical properties to alkenes and allies. For example, benzene doesn t undergo an addition reaction with bromine despite having a double bond. 

BusSnH. Internal addition of amine to allylic acetates, catalyzed by Pd(PPh3)4, leads to cyclic products via a 8 2 reaction.Three-membered cychc amines (aziridines) can be prepared from chiral conjugated amides via bromination and reaction with an amine. Four-membered cychc amines (azetidines) have been prepared in a different way ... 

Bromine addition to cyclopropanes is slow in the absence of light unless the ring is heavily substituted . In the presence of light, reaction is rapid since halogen radical attack on substituted cyclopropanes is fast even at — 78°C. In the presence of light, HBr is produced and cyclopropane reacts more competitively with proton acids than with bromine. Addition reactions to cyclopropane are generally slow in the absence of acid catalysts and therefore the conjugate acid is probably involved in reaction. The more facile reaction of cyclopropane with HBr compared with bromine is in contrast with alkene chemistry where bromine addition is the more rapid ... 

Bromine is an electrophile which will undergo an addition reaction with alkenes in the dark. The lack of a reaction in the dark with Br2 indicates that the molecule is not an alkene. In the presence of light, bromine will undergo a substitution reaction with alkanes. Therefore, the molecule is most likely an alkane and the only alkane with the molecular formula C3H6 is cyclopropane. 

Fig. 7 A sequence of free-radical bromination, hydrolysis, reaction with PCI5 and addition of Cl, to double bonds yields 1,2,4,5,6,910-heptachlorodecane [8]...

Addition Reactions with Bromine. Bromine in aqueous solution forms... 

Acetylene reacts with fluorine with explosive violence. Reactions with other halogens, chlorine, bromine, and iodine are violent, too. Acetylene chloride, which is formed from addition reaction with chlorine, explodes spontaneously. It forms unstable acetylides with metals such as copper,... 

Chlorine also reacts readily with tropolone by substitution, entering the 5-position more readily than does bromine [291,293]. Trichlorotropolones undergo addition reactions with more chlorine to give adducts which rearrange with formation of a six-membered ring [294]... 

Annulene undergoes addition reactions with bromine or with maleic anhydride thus its simple chemistry differs markedly from that of benzene [16]. Under special conditions it gives reactions which provide products typical of electrophilic substitution, but these reactions may not proceed by straightforward electrophilic substitution mechanisms. Thus it may be acetylated with acetic anhydride - boron trifluoride [52], and nitrated with copper(ll) nitrate in acetic anhydride, giving a mixture of dinitro-isomers [52,53]. Pyridinium bromide perbromide provided either monobromo-... 

The mechanism in Figure 9.5 also provides a rationalization for some observations of solvent effects in bromine addition reactions. The major product of the reaction of bromine with cyclohexene in methanol is trans-2-bromo-l-methoxycyclohexane. traMS-l,2-Dibromocyclohexane is observed if Br is added to the solution, but the yield of the dibromo adduct approaches 0% as [Br ] approaches 0 M. This result stands in contrast to the 27% of 1,2-dibromo adduct obtained from the corresponding reaction in acetic acid. It appears that the greater polarity of methanol accelerates the dissociation of IIP to DI, and the greater nucleophiliciW of methanol enhances the reaction of solvent with IIP, SSIP, DI, and SSIP. ... 

Alkynes show the same kind of addition reactions with chlorine and bromine that alkenes do. 

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