The ‘dimer mechanism’ in aromatic nucleophilic substitution by amines in aprotic solvents

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Abstract
The mechanism of aromatic nucleophilic substitutions by amines in protic solvents is well established; on the contrary the mechanism/s of the reactions in aprotic solvents is/are still subject of controversy. The present paper describes several systems for which fourth‐order kinetics (third‐order in amine) were observed. A mechanism is proposed to account for this as well as other observation such as: overall negative energies of activation, quadratic dependence of kA with non‐nucleophilic tertiary bases, spectacular effects of hydrogen‐bond donor (HBD) and hydrogen‐bond acceptor (HBA) catalysts, etc. Other alternative mechanisms are also discussed.