KINETICS OF ACID DECOMPOSITION OF HYDROXONICKEL(2) TETRAMER

The rate expression for the reaction of the hydroxonickel(II) tetramer with perchloric acid (10-3 to 10-1 M) is [formula omitted] where k1, the rate constant for a first-order, acid-independent reaction, is 690 sec-1 at 25° and μ = 1.5 M NaClO4. The value of ΔH1≠ is 17 kcal/mol and ΔS1≠ is 13 eu for this reaction, which is believed to be a distortion of the tetramer cluster in order to provide a site for H+ attack. The ratio of k-1/k2 is 0.099 M and the reaction approaches a first-order dependence in [H+] at pH 3. After the kinetically observable reaction with one proton, the tetramer reacts rapidly with additional acid to give the aquonickel ion. The decomposition reaction is general acid catalyzed. The rate is affected little by the strength of various acids, but electrostatic attraction enhances the rate as evidenced by the negatively charged HSO4- ion reacting five times faster than hydrogen ion. © 1969, American Chemical Society. All rights reserved.