- 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
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Arylmethane dye cations form a structurally interesting set of stable carbocations. A detailed study on rate-equilibria of carbinol formation from two diarylmethane and nine triarylmethane dye carbocations in aqueous solutions has been carried out using spectrophotometric measurements. The conclusions reached are : (i) The stability order found (auramine O>crystal violet = methyl violet > victoria blue R > victoria pure blue BO = ethyl violet > pararosaniline > brilliant green > malachite green > carbocation form of Michler's hydrol > methyl green), seems to be determined by an interplay of dye carbocation / carbinol conformation and stereoelectronic effects of substituents; and (ii) carbinol formation is general base catalysed and occurs by the rate determining attack of a H2O molecule on the dye carbocation centre via two kinetic pathways one mediated by another H2O molecule and the other by a OH ion.
- Sen Gupta,Mishra,Radha Rani
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p. 703 - 708
(2007/10/03)
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- Equilibrium and Kinetic Studies on the Formation of Triphenylmethanols from Triphenylmethane Dyes
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For five kinds of triphenylmethane dyes, the rate constants of hydration and dehydration reactions, and equilibrium constants in an aqueous solution were measured by a stopped-flow method.An increase in the number of dialkylamino groups caused a decrease in the rates and the equilibrium constants of the hydration, and the more the electron-donating effect of the dialkylamino groups, the slower the hydration rate became.The more protonated quinonoids were easily converted to the corresponding alcohols.On the basis of the equilibrium constants, Malachite Green was ascertained to be the best reagent of the five dyes for ion association with heteropolyacids in an aqueous medium.
- Hagiwara, Takuyuki,Motomizu, Shoji
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p. 390 - 397
(2007/10/02)
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