The benzene reacts with formaldehyde in the presence of HCl to give benzene methyl chloride. It is an electrophilic substitution reaction.

Benzene reacts with chlorine or bromine in the presence of a catalyst, replacing one of the hydrogen atoms on the ring by a chlorine or bromine atom. It reacts with some of the chlorine or bromine to form iron(III) chloride, FeCl3, or iron(III) bromide, FeBr3.

The six electrons in the π-system above and below the plane of the benzene ring are delocalised over the six carbon atoms, so the electron density is lower. The bromine cannot be polarised sufficiently to react, and the lower electron density does not attract the electrophile so strongly.

Bromobenzene

Bromobenzene is prepared by the action of bromine on benzene in the presence of Lewis acid catalysts such as aluminium chloride or ferric bromide. Bromobenzene is used to introduce a phenyl group into other compounds.

Bromobenzene is a clear, colorless liquid with a pleasant odor. It is used as a solvent and motor oil additive, and in making other chemicals.

Making iodobenzene Iodobenzene can be made from the reaction of benzene with iodine if they are heated under reflux in the presence of concentrated nitric acid, but it is normally made from benzenediazonium chloride solution.

Benzene reacts with concentrated nitric acid at 323-333k in the presence of concentrated sulphuric acid to form nitrobenzene. This reaction is known as nitration of benzene.

Substitution Reactions of Benzene and Other Aromatic Compounds

Benzene does undergo substitution reactions. If the reaction of benzene with bromine could produce phenyl bromide, the bromine water would be decolorized. Why is addition reaction of bromine to benzene difficult? Benzene is an aromatic compound, hence very stable. Upon addition ofbromine, it will lose its aromaticity. Hence, the addition reaction of bromine to benzene is difficult.

Bromine will combine with most other elements. Reaction with metallic elements leads to salts such as silver bromide ( AgBr ), in which the bromine atom has a −1 charge and oxidation number.

Bromine is intermediate in reactivity between chlorine and iodine, and is one of the most reactive elements. Bond energies to bromine tend to be lower than those to chlorine but higher than those to iodine, and bromine is a weaker oxidising agent than chlorine but a stronger one than iodine.

Cyclohexane has no pi-unsaturation and is therefore not nucleophilic. It does not react with bromine unless energy in the form of light or heat is applied. In such a case a free-radical substitution reaction occurs. Cyclohexene is a typical alkene, and benzene and anisole are aromatic compounds.