The kinetics of the reduction of mercuric salts by molecular hydrogen in aqueous solution

The kinetics of the homogeneous reduction of mercuric salts by-molecular hydrogen in aqueous solution have been examined over a wide range of solution composition, temperature and hydrogen partial pressure. In perchlorate solutions, where Hg⁺⁺and Hg₂⁺⁺ are uncomplexed the kinetic results can be expressed by the equation: -d[H₂]J/dt = k₁[H₂][Hg⁺⁺] + k₂[H₂][Hg₂⁺⁺] where k₁ = 4.2 x 10¹⁰ exp [-18100/RT] 1.mole⁻¹ sec.⁻¹ and k₂ = 1.2 x 10¹¹ exp [-20400/RT] 1.mole⁻¹ sec.⁻¹ It was concluded that the rate-determining process of the reaction involves the bimolecular interaction of one H₂ molecule with either Hg⁺⁺ or Hg₂⁺⁺ , i.e., Hg⁺⁺ + H₂ [symobal omitted] Hg + 2H⁺ Hg₂⁺⁺ + H₂ [symbol omitted] 2Hg + 2H⁺ The Hg atoms thus formed undergo further rapid reactions to yield the observed products (Hg₂⁺⁺ or metallic mercury) the nature of which is determined by •' thermodynamic considerations. Mercuric complexes also reacted homogeneously with hydrogen but in most cases more slowly than the simple Hg⁺⁺ ions. The order of decreasing reactivity of the complexes, HgAc₂ > HgCl₂ > HgBr₂ > Hg(ethylenediamine)₂⁺⁺, is the same as the order of their increasing stability. This is attributed to the reduction of the electron affinity of Hg⁺⁺ through electron donation from the complexing ligand. The reactivity of mercuric complexes such as HgAc₂ and Hg(ethylenediamine)₂⁺⁺ is increased by anions such as 0H⁻, CO₃⁼, Ac⁻, etc., the influence of which increases in the same order as their basicity. This is attributed to stabilization, by the anions, of the H⁺ ions which are released in the rate-determining step of the reaction. Some conclusions are drawn concerning the mechanism of heterogeneous activation of hydrogen by solid catalysts.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat

Topochemical reactions of boron nitride

An absorption complex or compound between boron nitride and chromyl chloride was discovered and studied in some detail. The method used to prepare the boron nitride had some effect on the composition of the complex but for a given sample of boron nitride the equilibrium composition for temperatures from 0°C to 160°C was constant. The kinetics of formation were studied at 24.1°C, 67.1°C, and 117.0°C. The reaction was interpreted as diffusion controlled with two diffusion coefficients--each for a certain concentration range. The corresponding two energies of activation were 5.0 and 6.1 kcal. These are of the same order of magnitude as for similar processes. X-ray studies of the complex showed a strong reflection line at the same place as for the main layer separation in boron nitride itself. There could have been a small amount of reflection due to a greater layer spacing, but it was not detected. Water hydrolyses the chromyl chloride in the complex, leaving the original boron nitride and a solution of dichromate and HCl. Carbon tetrachloride would not dissolve out the chromyl chloride from the complex. Similar complexes of chromyl chloride with disulfides of molybdenum, tungsten and uranium and of cupric and aluminum chlorides with boron nitride were discovered but the kinetics of their formation were not studied. The theory of formation of lamellar compounds is discussed.Science, Faculty ofChemistry, Department ofGraduat