INFLUENCE OF VITAMIN C ON THE RATE OF H$_2$O$_2$ DECOMPOSITION CATALYZED BY Fe (II) CATIONS

Abstract

By gasometric method the influence of vitamin C on the catalized by Fe(II) cations rate of H₂O₂ decomposition has been studied at 298 K. In the range pH=2–4 and n = [H₂O₂ ]₀ / [Fe(II)]₀ $\gg$1 the reaction rate ( $R^0_{\mathrm {O}_2}$ ) does not depend on the medium’s acidity. But at pH>4 the increase of pH value results in $R^0_{O_2}$ decrease, which is due to the catalyzing hydrolysis. The rate law is $R^0_{\mathrm {O}_2} = k\dfrac{[\mathrm{H}_2\mathrm{O}_2 ]_0 [\mathrm{Fe(II)}]_0}{a+[\mathrm{H}_2\mathrm{O}_2 ]_0}$. This law is discussed. In the presence of low quantities of vitamin C, e.g. 1.25· 10^-3 M, the rate diminishes 3 times. When TEMPO is present with vitamin C (~10^-4 M) the O₂ evolution rate somewhat increases. Both phenomenas are explained. On the ground of analysis of obtained kinetic data it is assumed that the studied reaction probably occurs parallel by radical and nonradical mechanisms.