Kinetics of the Acid-Catalyzed Hydrolysis of Amine Disulfonate Ion. The Third Ionization Constant of Amine Disulfonic Acid

Year: 1948 DOI: 10.7907/bdxy-bd03
The rate of the acid-catalyzed hydrolysis of amine disulfonate ion, HN(SO₃)⁼₂, in water solution has been thoroughly studied over the temperature range 25-45° C. The effect of varying the concentration of reactants, the effect of ionic strength (neutral salt effect), and the effect of temperature have been studied. All results at constant ionic strength confirm the rate equation

- d(HN(SO₃)⁼₂)/dt = k(H⁺)(SO₃)⁼₂)

if the equilibrium between sulfate ion and hydrogen ion is taken into account. The uncatalyzed hydrolysis was found to have an undetectable rate compared to the rate of the catalyzed reaction.

The variation of the rate constant with ionic strength implies that the charge product of the ions involved in the rate determining reaction is -2.

The internal energy of activation, ΔE≠, was found to be 23.5 ± 1 Kcal., and the entropy of activation, ΔS≠, was found to be +7.2 ± 1.5 e.u. for the reaction at zero ionic strength.

A mechanism involving an activated complex of amine disulfonate ion and hydronium ion may be invoked to explain these results.

In addition, the ionization function (classical ionization constant) for the equilibrium

HN(SO₃)⁼₂) = H⁺ + N(SO₃)⁼₂)

was measured in a sodium chloride solution at an ionic strength of 1.00 at 25° C. It was found that

(H⁺)N(SO₃)⁼₂)/HN(SO₃)⁼₂) = 3.2 x 10⁻⁹.