A study on equilibrium and kinetics of carbocation-to-carbinol conversion for di- and tri- arylmethane dye cations in aqueous solutions: Relative stabilities of dye carbocations and mechanism of dye carbinol formation

Arylmethane dye cations form a-structurally interesting set of stable carbo cations. A detailed study on rate-equilibria of carbinol formation from two diarylmethane and nine triarylmethane dye carbocations in aqueous solution s has been carried out using spectrophotometric measurements. The conclusio ns reached are : (i) The stability order found (auramine O>crystal violet = methyl violet > victoria blue R> victoria pure blue BO = ethyl violet > pa rarosaniline > brilliant green > malachite green > carbocation form of Mich ler's hydrol > methyl green), seems to be determined by an interplay of dye carbocation / carbinol conformation and stereoelectronic effects of substi tuents; and (ii) carbinol formation is general base catalysed and occurs by the rate determining attack of a H2O molecule on the dye carbocation centr e via two kinetic pathways one mediated by another H2O molecule and the oth er by a OH- ion.