Exercise 9: - Radical reactions

1. tert-Butyl peroxide is a source of free radicals:

A mixture of methylpropane and CCl₄ is stable at 130°C. If a small amount of tert-butyl peroxide is added, a reaction occurs that yields 2-chloro-2-methylpropane and chloroform. A small amount of 2-methyl-2-propanol, (CH₃)₃COH, equivalent to the peroxide used, is also formed. Propose a mechanism which explains the formation of these products.

2. A mixture of H₂ and Cl₂ does not react at room temperature. At high temperature or under the influence of light (of wavelength absorbed by chlorine) a violent reaction takes place and HCl is formed. The photochemical reaction yields as many as a million molecules of HCl for each photon absorbed. The presence of a trace of oxygen slows down the reaction. Propose a possible mechanism for this reaction.

3. When a mixture of methane and chlorine is irradiated, reaction begins at once. However, when irradiation is stopped, the reaction gradually slows down; it does not stop immediately. Why?

4. Bromination of methane is slowed down by the addition of fairly large amounts of HBr. Suggest an explanation.