1-Methyl-4-ethynylpridinum triflate: Reaction with Thiophenol Giving Rise to Chromophoric (E)-1-methyl-4-[2-(phenylsulfanyl)-1-ethenyl]pyridinium triflate. An Example of Nucleophilic Reaction on Triple Bond
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1-Methyl-4-ethynylpridinum triflate 6 was prepared by treatment of 4-ethynylpyridine 5 with methyl triflate in dichloromethane. Thiophenol added to the triple bond to give regioselectively (E)-1-methyl-4-[2-(phenylsulfanyl)-1-ethenyl]pyridinium triflate 7. The addition of glutathione to 1-methyl-4-ethynylpridinum triflate 6 with in TES buffer at pH 7 was a second order reaction (k = 4200 M-1 s(-1) at 25 degrees C). The addition products showed an intense long wavelength absorption band (lambda(max) = 360 nm, epsilon = 27500 M-1 cm(-1)). The reaction rate and the spectroscopic properties show the usefulness of 4-ethynyl-1-methylpridinium triflate 6 as reagent for the determination of thiol.