Kinetic studies on the metallation of low acidity acetylenic hydrocarbons by the UV method

1-Phenyl-1-butyne and 1-phenyl-1-propyne have been metallated at the propargylic position with an excess of n-butyllithium in diethyl ether at 25°C. The formation of mono- and di-lithio derivatives has been followed by the UV-Visible method and the pseudo-first order rate coefficients for consecutive irreversible reactions have been calculated. Monolithio derivatives have been prepared by metallation with methyllithium in ether/tetrahydrofuran. The pseudo-first order rate constant of the metallation of the previously prepared monoanion of 1-phenyl-1-butyne to its dianion has been calculated, and found to be about ten times smaller than that obtained from the consecutive reactions.