Nucleophilic catalysis by ClO₄ ⁻ anions during hydrolysis of o-nitroformanilide in concentrated aqueous perchloric acid solutions

Conclusions

• 1. The effective rate constants for the hydrolysis (k_eff) of o-nitroformanilide (ONFA) were measured at 25° in perchloric acid solutions in the range 44.86–71.39%.

• 2. In solutions containing 60% and more of HClO₄, hydrolysis is accomplished by the same route as is observed in dilute HClO₄, solution as well as by a route in which intermediate and activated complexes are formed from the nonionized ONFA molecule, the H₅O₂ ⁺ ion, and an anion that exhibits nucleophilic coaction. The ClO₄ ⁻ anions and hydrates$ClO_4 ^ - \cdot H_2 O$, not solvated by water, possess such properties in this reaction.

• 3. The ionization constants of ONFA were calculated from the dependence of k_eff on the acidity of the medium h_o and the activity of the hydroxonium ions$a_{H_3 O^ +}$. These constants are K_e, the equilibrium constant for the formation of the complexes at the carbonyl group with H₃O⁺, and K_BH+, the basicity constant. The obtained K_e and K_BH+ values differ somewhat from the values reported in [2], which is explained by the experimental errors and assumptions made in the calculations.