Solvolysis of Organic Phosphates. IV. 3-Pyridyl and 8-Quinoly Phosphates as Effected by the Presence of Metal Ions

Publisher Website
Google Scholar
Abstract
Influence of nickel(II), copper(II), and thorium(IV) ions on the hydrolysis of 3-pyridyl and 8-quinolyl phosphates was investigated at μ=0.10 in a lower pH region. The reaction in the presence of the bivalent metal ions followed apparent first-order kinetics with respect to the phosphates in homogeneous phase. The copper ion showed a positive catalytic effect only on the hydrolysis of 8-quinolyl phosphate, and such effect increased markedly as pH was raised. The nickel ion, however, did not show any significant effect on the hydrolysis of both phosphates. The requisites for effective catalysis of bivalent metals have been postulated previously: (1) preliminary chelate formation, and (2) transitional chelate formation. Accordingly, complex formation of the present phosphates with copper(II) and nickel(II) was studied by means of potentiometric measurements. The results strongly suggest the importance of (1) for yielding catalytic efficiency. The presence of the thorium ion resulted in a profound acceleration of hydrolysis of both phosphates in a relatively lower temperature range. The reaction rate did not follow the simple kinetic law although the reaction system was kept homogeneous under the present experimental conditions. The complex formation with the phosphate moiety, which would provide effective charge neutralization for the substrate, is most likely the necessary cause for the thorium-catalysis. Plausible reaction mechanisms and the corresponding potential energy correlations were postulated for the present catalysis.