p<i>K</i>_aValues of Some Piperazines at (298, 303, 313, and 323) K

Abstract

The dissociation constants of the conjugate acids of six cyclic diamines [piperazine, 1-methylpiperazine, 2-methylpiperazine, 1-ethylpiperazine, 1-(2-hydroxyethyl)piperazine, and 1,4-dimethylpiperazine] were calculated using the potentiometric titration method at (298, 303, 313, and 323) K. The p K a values of piperazine were compared with published data to validate the procedure used. The thermodynamic quantities (Δ H ° and Δ S °) for the dissociation processes were determined using the van’t Hoff equation. A trend is proposed related to the variation of the p K a with the addition of different radical groups to the base piperazine molecule.