Why is it preferable to produce chloroethane by the reaction of \(\mathrm{HCl}(g)\) with ethene than by the reaction of \(\mathrm{Cl}_{2}(g)\) with ethane? (See Exercise 62.)

Write the balanced chemical equations for the two reactions: 1. Reaction of \(\mathrm{HCl}(g)\) with ethene: \(\mathrm{C}_{2}\mathrm{H}_{4}(g) + \mathrm{HCl}(g) \rightarrow \mathrm{C}_{2}\mathrm{H}_{5}\mathrm{Cl}(g)\) 2. Reaction of \(\mathrm{Cl}_{2}(g)\) with ethane: \(\text{A. Initiation step: \( \mathrm{Cl}^{\cdot}_{2}(g) \longrightarrow 2\mathrm{Cl}^{\cdot}(g) \)\\ B. Propagation step: \) \( \mathrm{C}_{2}\mathrm{H}_{6}(g) + \mathrm{Cl}^{\cdot}(g) \rightarrow \mathrm{C}_{2}\mathrm{H}_{5}\mathrm{Cl}(g) + \mathrm{H}^{\cdot}(g)\)

The reaction of \(\mathrm{HCl}(g)\) with ethene is a faster reaction than the reaction of \(\mathrm{Cl}_{2}(g)\) with ethane because the second reaction requires the homolytic cleavage of the \(\mathrm{Cl}-\mathrm{Cl}\) bond, which is an energetically unfavorable process. Moreover, the reaction with ethane is a radical chain mechanism, which involves the formation and propagation of reactive radical intermediates, making the reaction slower and more complex.

The reaction of \(\mathrm{HCl}(g)\) with ethene is an electrophilic addition reaction, where the \(\mathrm{H}^{\delta+}\) atom from \(\mathrm{HCl}\) acts as an electrophile and forms a bond with the nucleophilic ethene double bond. This addition reaction is a relatively simple and direct mechanism. On the other hand, the reaction of \(\mathrm{Cl}_{2}(g)\) with ethane is a radical halogenation reaction, which proceeds via a more complex chain mechanism involving initiation, propagation, and termination steps. This complexity in the reaction mechanism can lead to side reactions and byproducts, reducing the overall yield of chloroethane.

While the reaction of \(\mathrm{HCl}(g)\) with ethene is highly selective for chloroethane, the reaction of \(\mathrm{Cl}_{2}(g)\) with ethane has several side reactions. These side reactions include the formation of more highly chlorinated products (e.g., 1,1-dichloroethane, 1,2-dichloroethane, etc.), as well as the reaction of \(\mathrm{Cl}_{2}(g)\) with both hydrogen and chlorine radicals. These side reactions reduce the overall yield of chloroethane and can cause environmental and safety concerns due to the generation of hazardous byproducts. In conclusion, it is preferable to produce chloroethane by the reaction of \(\mathrm{HCl}(g)\) with ethene rather than the reaction of \(\mathrm{Cl}_{2}(g)\) with ethane because of the faster reaction rate, simpler reaction mechanism, and fewer side reactions that reduce the yield and produce potentially harmful byproducts.