γ Radiolysis of Liquids at High Pressures. VI. Hydrogen-Atom Reactions in Aqueous 0.8N H2SO4 Solutions

Abstract

The competition between Reactions [1] and [2], $$\mathrm{H}\mathrm{\hspace{0.17em}+\hspace{0.17em}}\mathrm{S}\to {\mathrm{no\; H}}_2$$ , $$\mathrm{H}\mathrm{\hspace{0.17em}+\hspace{0.17em}}\mathrm{RH}\to {\mathrm{H}}_2\mathrm{\hspace{0.17em}+\hspace{0.17em}}\mathrm{R}$$ , in aqueous $\text{0.8N}$ H₂SO₄ solutions was studied at 20° over the applied pressure range of 0–6.34 kbar by measurement of $\mathrm{G(}{\mathrm{H}}_2)$ from the gamma‐irradiated solutions. With O₂ as S, in aerated solutions, relative specific rates $k_1^0{\mathrm{\hspace{0.17em}/\hspace{0.17em}k}}_2^0$ were determined at atmospheric pressure for methanol, glucose, glycerol, ethanol, and isopropanol as RH. From the pressure dependence of $k_1{\mathrm{\hspace{0.17em}/\hspace{0.17em}k}}_2$ and an estimated ${\mathrm{\Delta V}}_1^{‡}\text{\hspace{0.17em}=\hspace{0.17em}1.6}{\mathrm{ml\; mole}}^{\text{−1}}$ for S ≡ O₂, values of ${\mathrm{\Delta V}}_2^{‡}$ in the range −5.5 to −6.7 ml mole⁻¹ are obtained for the five H donors. The average value ${\mathrm{\Delta V}}_2^{‡}\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}5.9}{\mathrm{ml\; mole}}^{\text{−1}}$ is taken as characteristic for Reaction [2]. Values of $k_1^0{\mathrm{\hspace{0.17em}/\hspace{0.17em}k}}_2^0$ at atmospheric pressure also were determined for four deaerated $\text{0.8N}$ H₂SO₄ solutions: (1) RH ≡ glucose and S ≡ benzyl alcohol; (2) RH ≡ glucose and S ≡ BrCH₂COOH; (3) RH ≡ S ≡ acetone; (4) RH ≡ S ≡ ClCH₂COOH. Because little or no pressure dependence of ${\mathrm{G(H}}_2)$ and, therefore, of $k_1{\mathrm{\hspace{0.17em}/\hspace{0.17em}k}}_2$ was observed with these four solutions, ${\mathrm{\Delta V}}_1^{‡}{\mathrm{\hspace{0.17em}\approx \hspace{0.17em}\Delta V}}_2^{‡}\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}5.9}{\mathrm{ml\; mole}}^{\text{−1}}$ . Thus, for a variety of H‐atom reactions, which are not diffusion controlled, the value of ${\mathrm{\Delta V}}^{‡}$ is approximately constant. From this result a value of $\mathrm{V̄(}\mathrm{H})$ in the range 5.9–10.3 ml mole⁻¹ is estimated. It also is concluded that abstraction of Br or Cl by H occurs, rather than electron transfer, in Reaction [1] with BrCH₂COOH or ClCH₂COOH as S, respectively. Anomalous results obtained in a deaerated $\text{0.8N}$ H₂SO₄ solution of glucose and allyl alcohol are discussed.