Henry Taube

The Exchange of Water Between Hydrated Cations and Solvent

The rate of exchange of water between the hydrated forms of Al+++, Cr+++, Fe+++, Ga+++, and Th+4 and the solvent water has been measured in solutions of varying acidity. With the exception of chromic ion, and of ferric ion at low acidity, the exchange is complete in ca 3 min at 25°. For chromic ion, the half‐time for exchange is independent of acidity over a wide range and is ca 40 hr at 1 M salt concentration. The coordination number of chromic ion for water over the entire acidity range is 6.0. The initial hold‐back of oxygen by ferric ion at low acid is slight and is attributed to the presence of polynuclear hydrolyzed species. For all the cations, the distribution of oxygen isotopes in the final solution is noticeably different from random, the cations showing a greater affinity for H2O18 over H2O16.The rates of exchange are correlated with the electronic structure, which influences the energy required to form the transition state.

Some Photochemical Reactions of O3 in the Gas Phase

When a gaseous mixture containing O3 and CO2 of different isotopic composition is illuminated by uv light, the oxygen that is formed has undergone some exchange with CO2. The extent of this exchange has been studied as a function of initial O3 and CO2 pressure, and the influence of foreign gases on it was also studied. It is concluded that O1D is the intermediate which undergoes rapid exchange with CO2, and further that the reaction O1D+CO2⇌CO+O2 does not provide the dominant mechanism for this exchange. The results suggest that at low total pressures exchange takes place by O*+CO2⇌O+CO2* and that at high total pressures, CO3 is formed as an intermediate.

The Exchange of Water between Co(NH3)5H2O+++ and Solvent

The rate of exchange of water between Co(NH3)5H2O+++ and solvent has been measured by a method involving isotopic assay of the bound water. The half‐time for the exchange is independent of salt concentration and of acidity over a range of these variables and is 24.5 hr at 27°. The half‐time is increased by SO4=, indicating that complex ion formation competes with the exchange process and thus supporting an SN1 mechanism as a reaction path. The equilibrium quotient [Co(NH3)5H2O18+++](H2O)/(Co(NH3)5H2O+++)×(H2O18) was measured as 1.019±0.001.

FLOW ADAPTATION OF THE ISOTOPIC DILUTION METHOD FOR THE STUDY OF IONIC HYDRATION

A method is described for rapid mixing and sampling in the application of the isotopic dilution technique to the study of ionic hydration. The behavior of solutions of various salts has been compared with that of solutions containing a hydrated cation of known formula, namely Cr(H2O)6+ + +. The holdback of water per ion of Al+ + + is the same (within 0.4 molecules of H2O as that of Cr+ + +, and t½ for the exchange of Al(H2O)6+ + + with H2O is >0.02 sec. at 25°·t½ for the exchange of water between Ni+ + (aq) or Fe+ + + (aq) and solvent is less than 0.02 sec.

Exchange of Methanol between Solvated Cations and Solvent. I

The exchange of methanol between solvated Li+, Cd++, and Mg++, and the solvent has been studied by the isotope dilution technique at —82.5° and —96.9°C. Even at —96.9°C the exchange is complete for Li+ and Cd++ within the time of sampling, 0.5 min. However, the exchange for solvated Mg++ is observable. At —82.5° and —96.9°C the half‐lives for the isotopic exchange are 3.7 and 64 min, respectively. The activation energy ΔH‡ is 12.5±2.0 kcal/mole and the entropy of activation ΔS‡ is +(4±4) eu. The ``kinetic solvation number of Mg++ with respect to methanol as determined by the isotope dilution technique is less than six, where six is the coordination number of Mg++ in these solutions. The defect is caused by residual water which both displaces methanol from the coordination sphere and labilizes it for exchange.

Tracer Experiments on the Reaction of UH3 with Aqueous Acid

The reaction of UH/sub 3/ with DC1 in D/sub 2/O was studied at DC1 concentrations of 16 and 11 M. The results were: (1) In 16 M DCl, there was an initial violent reaction with the productin of much gas and a red solution, presumedly U/sup 3+/, followed by a much slower reaction which formed gas of approximately 20% of the total evolved gas and a solution with a green color characteristic of U/sup 4+/. (2) In 11 M DCl, a slow reaction continued over a period of weeks with the production of some gas and a solution contaiing U/sup 4+/ and a residue with a composition approximating U/sub 3/O/sub 4/. The evolved gas was collected for both reactions (1) and (2) and analyzed for H/sub 2/, HD, and D/sub 2/. The relative ratio of H/sub 2/: HD: D/sub 2/ for reaction (1) was 0.11: 1: 0.20 for the initial phase and 0.26: 1: 0.44 for the last phase; the ratio for reaction (2) was 9.6: 1: 9.0 for the first 5 days and 3.6: 1: 2.6 for the time interval of 8 to 21 days. The difference between the H/sub 2/: HD: D/ sub 2/ ratios in (1) andmorexa0» (2) is ascribed to the formation of an oxide film which prevents direct attach of D/sup +/ on UH/sub 3/ in 11 M DC1 and hence prevents formation of HD. In 16 M DC1, the oxide film is not formed, but the fact that all the hydride H is given off as gas (either as HD or H/sub 2/) in (1) as well as in (2) iadicatee that D/sup +/ must attach the hydride at H sites on the surface. (D.L.C.)«xa0less