Determination of ionization constants of primaquine and study of its coordination ratio with vitamin C
Yang, X.C.; Li, Y.G.; Xiao, Z.F.; Liu, H.J.; Liu, P.X.
Yao Xue Xue Bao 26(7): 531-536
1991
ISSN/ISBN: 0513-4870 PMID: 1805512 Document Number: 382235
Primaquine (P) has long been used as an antimalarial drug. The following formulas are derived for determination of the ionization constants of PH33+ by pH-titration method: Ka1=[aH + (3-a)Cp]/[(a-2)Cp/aH-1], Ka3=[(1-a)Cp aH-Kw]/(a Cp + Kw/aH)=(1/Ka2)[(2-a)CpaH2-Kw aH]/(Kw/aH+aCp) + [(1-a) Cp aH - Kw]/(Kw/aH + a Cp) in which Kw is the ionic product of water, a is the mole ratio of HClO4 to primaquine and Cp is the total concentration of primaquine. The ionization constants of primaquine in 50% (v/v) ethanol in water determined at 25.degree.C in the ionic strength range of 5 .times. 10-3 .apprx. 5 .times. 10-2 mol/L are: Ka1 = (3.84 .+-. 2.35) .times. 10-2 (attributed to the secondary ammonium group of primaquine); Ka2=(1.50 .+-. 1.17) .times. 10-8 (attributed to the tertiary ammonium group); Ka3 = (2.07 .+-. 0.27) .times. 10-10 (attributed to the primary ammonium group). The coordination ratio of primaquine to vitamin C in the above solvent is determined by continuous variation and mole ratio methods based on pH and conductance measurements to be 1:1, indicating that the coordination compound formed in the solution is mainly a 1:1 compound.