Reaction of Radical Cations of Tetramethylbenzidene with Colloidal Clays

Article abstract of DOI:10.1021/j150660a043

Pulsed laser photolysis studies have been used to investigate the nature of the interaction of the cation of tetramethylbenzidene, TMB⁺, with colloidal montmorillonite.TMB⁺ reacts rapidly at a diffusion-controlled rate with the clay particles with a rate constant k = 3E12 M^-1 s^-1.A further rapid reaction on the clay surface of TMB⁺ produces the dimer cation of the TMB.All events were identified by rapid spectrophotometry, which shows significant differences in the absorption spectra of the cations when adsorbed onto the clay particles.In homogeneous solution the TMB⁺ shows a spectrum with a pronounced maximum at λ = 470 nm.This maximum disappears when TMB⁺ is absorbed on clays, and the spectrum contains a maximum in the 400-nm region.The presence of the other anionic assemblies, e.g., micelles in the system, bind TMB⁺ and decrease the rate of cation exchange on the clay.The kinetics are identified by laser photolysis and discussed in terms of established reactions.