We report here a kinetic study on the preparation reaction of monosubstituted 1-methylphtalazinium ylides carbanion. It is confirmed that ylides, both stable and unstable, are obtained through a simple unilateral successive reaction of the first order. Here, the inactivation process is a dimerization reaction of the second order. Calculated rate constants confirmed the increase in elimination of proton acidity and stabilization of the carbanion by electron attractive groups. In addition, electron repulsive groups were shown to increase carbanion nucleophility and promote the inactivation reaction.