Question Video: Predicting the Product That Would Form from the Alkylation of Benzene Given the Reaction Equation Chemistry • Third Year of Secondary School

Video Transcript

Express the product that will be formed from the alkylation of benzene as shown in the reaction scheme.

Let’s begin by examining the given reaction scheme. The reactants are benzene and one equivalent of 2-chloro-2-methylpropane. 2-Chloro-2-methylpropane is a type of organic molecule known as a chloroalkane. Above the reaction arrow is the catalyst aluminum chloride. And we can see that one of the products is hydrogen chloride. When benzene reacts with a chloroalkane in the presence of the catalyst aluminum chloride, a type of reaction called Friedel–Crafts alkylation takes place. The Friedel–Crafts alkylation reaction belongs to a class of reactions known as alkyl substitution reactions. An alkyl substitution reaction is a type of reaction where parts of a molecule are removed and replaced with alkyl groups. In Friedel–Crafts alkylation, the substituted benzene produced is an alkylbenzene and the other product is hydrogen chloride.

Our job in this question is to determine the identity of the alkylbenzene formed. During the reaction, the aluminum chloride catalyst weakens the carbon-chlorine single bond of the chloroalkane, which accelerates the reaction with benzene. The alkyl portion of the chloroalkane replaces a hydrogen atom on the benzene ring. And the hydrogen atom that was removed combines with chlorine from the chloroalkane to form hydrogen chloride. Because we only have one equivalent of 2-chloro-2-methylpropane, only one hydrogen atom of benzene is replaced with an alkyl group. If we had more than one equivalent and the right reaction conditions, more hydrogen atoms on the benzene ring could be replaced with alkyl groups.

The name of the alkylbenzene formed is tert-butylbenzene, because the alkyl group bonded to the benzene ring is a tert-butyl group. This makes more sense once we see that the common name of the chloroalkane is tert-butyl chloride. In conclusion, the product formed from the alkylation of benzene shown in the reaction scheme is tert-butylbenzene and has the structure that we’ve drawn here.