Dissociation constants of aryl azopyrimidine compounds and the formation constants of their cobalt, nickel and copper complexes

The dissociation constants of uracil, thiouracil, 5-(substituted arylazo) u racil and 5-(substituted arylazo) thiouracil were evaluated at different te mperatures (25-45 degrees C) by potentiometric measurements in the presence of different percentages of ethanol-water and dioxane-water media (25%, 35 %, 50% and 75% v/v respectively). The compounds exhibit two pK's values cor responding to deprotonation of both the (4)-OH group (HN(3)) and (2)-OH gro up (H-N-(1)). The thermodynamic parameters of ionization were evaluated. Th e view of aquation and solvation is discussed. The formation constants of t he cobalt, nickel and copper complexes are evaluated and discussed.