Relative Reactivities of Amide, Diphenylphosphide, and Diphenylarsenide Ions toward Aryl Radicals

Article abstract of DOI:10.1021/jo00193a025

Competition experiments have been carried out in liquid ammonia at reflux temperature to determine the relative rate constants for the coupling reactions of amide (NH2^-), diphenylphosphide (Ph2P^-), and diphenylarsenide (Ph2As^-) toward aryl radicals.It is proposed that these nucleophiles react under photostimulation with halo aromatic substrates through an S_RN1 mechanism of aromatic substitution.Relative rate constants of NH2^- vs.Ph2P^- ions toward 2,4,6-trimethylphenyl radicals and Ph2P^- vs.Ph2As^- ios toward 2-quinolyl radicals have been determined.The results here reported indicate that NH2^- (1.00) < Ph2P^- (6.4) = Ph2As^- (6.4).The fact that there is not a difference in the rate constants of Ph2P^- vs.Ph2As^- suggests that both nucleophiles react at diffusion-controlled rate.In competition experiments of Ph2P^- vs.Ph2As^- ions toward phenyl radicals, it was found that Ph2P^- (1.00) > Ph2As^- (0.44).The decrease of the Ph2As^- ion reactivity is attributed to the reversible coupling of this nucleophile with phenyl radicals.