2 - Simple Nucleophilic Exchange Reactions and Aromatic Substitution Reactions

Abstract

This chapter discusses the synthesis of haloalkanes by halogen-halogen exchange and related reactions. Liquid:liquid conditions are not usually successful for the conversion of chloroalkanes into the corresponding bromo derivatives, as the reaction is reversible and, consequently, requires high concentrations of the inorganic bromide salt. Kinetic data indicate that the conversion of bromoalkanes into the corresponding chloro compounds is 150 times faster than the reverse process. Solid:liquid conditions are more successful. It is also established that the position of equilibrium in the exchange process depends on the inorganic cation, for example, lithium or calcium bromide is superior to sodium or potassium bromide. In an alternative procedure, the chloroalkane is treated with a volatile brominating agent and either the bromoalkane or the volatile chloride by-product is removed continuously during the reaction. It is noteworthy that the conversion of chloroalkanes into iodoalkanes is accomplished under liquid:liquid conditions, whereas the reverse reaction occurs when iodoalkanes are heated with tetra n- butylammonium chloride with the chloroalkane distilling as it is formed.