Hydrogen in liquids

Removal of N -Benzyloxycarbonyl Groups from Sulfur-Containing Peptides BY Catalytic Hydrogenation in Liquid Ammonia O-tert-BurvL-L-SERYL-S-... 

REMOVAL OF N -BENZYLOXYCARBONYL GROUPS FROM SULFUR-CONTAINING PEPTIDES BY CATALYTIC HYDROGENATION IN LIQUID AMMONIA O-tcrf-BUTYL-L-SERYL-S-tert-BUTYL-L-CYSTEINE ferr-BUTYL ESTER... 

Gomez-Sainero et al. (11) reported X-ray photoelectron spectroscopy results on their Pd/C catalysts prepared by an incipient wetness method. XPS showed that Pd° (metallic) and Pdn+ (electron-deficient) species are present on the catalyst surface and the properties depend on the reduction temperature and nature of the palladium precursor. With this understanding of the dual sites nature of Pd, it is believed that organic species S and A are chemisorbed on to Pdn+ (SI) and H2 is chemisorbed dissociatively on to Pd°(S2) in a noncompetitive manner. In the catalytic cycle, quasi-equilibrium ( ) was assumed for adsorption of reactants, SM and hydrogen in liquid phase and the product A (12). Applying Horiuti s concept of rate determining step (13,14), the surface reaction between the adsorbed SM on site SI and adsorbed hydrogen on S2 is the key step in the rate equation. 

Storing of hydrogen in liquid form at cryogenic condition is attractive in that it offers low weight and volume per unit energy when compared to compressed hydrogen. 

Larpent and coworkers were interested in biphasic liquid-liquid hydrogenation catalysis [61], and studied catalytic systems based on aqueous suspensions of metallic rhodium particles stabilized by highly water-soluble trisulfonated molecules as protective agent. These colloidal rhodium suspensions catalyzed octene hydrogenation in liquid-liquid medium with TOF values up to 78 h-1. Moreover, it has been established that high activity and possible recycling of the catalyst could be achieved by control of the interfacial tension. 

Neutral hydrogen in the magnetic fields in interstellar space may have excited state life times that is measured in years—in contrast hydrogen in liquid water at room temperature display excited state lifetimes of 3 seconds. Why is this How come that the liquid water can lead to a more efficient relaxation of the proton... 

Fig. 1. Energy distribution of neutrons scattered by hydrogen in liquid argon at 100"K and 26.5 atm, as a function of time of flight for various scattering angles, 6. Solid curve, interpolation model. Dashed curve, Sears itinerant oscillator model. Jagged curve, Experiment. Abscissa is time of flight in usec/m and ordinate is cross section in mb sr-1 usee-1.

U. Stolz, R. Kirchheim, J.E. Sadoc, and M. Laridjani. Hydrogen in liquid-quenched and vapor-quenched amorphous PdgoSi20- J- Less-Common Mater., 103(1)r81—90, 1984. 

The gas species over solutions of hydrogen in liquid lithium were detected by mass spectrometric analysis of the saturated vapor effusing from a Knudsen cell. From the measurements of the gaseous equilibria... 

Ratsuta, H. Ishigai, T. Furukuwa, K. "Equilibrium Pressure and Solubility of Hydrogen in Liquid Lithium" Nucl. Tech. 1977, 32. 

New measurements of the solubility of hydrogen in liquid ammonia have been made. The values are close to those used in our previous work (7) and those used by Bar-Eli and Klein (1). 

At even lower temperatures, some unusual properties of matter are displayed. Consequently, new experimental and theoretical methods are being created to explore and describe chemistry in these regimes. In order to account for zero-point energy effects and tunneling in simulations, Voth and coworkers developed a quantum molecular dynamics method that they applied to dynamics in solid hydrogen. In liquid helium, superfluidity is displayed in He below its lambda point phase transition at 2.17 K. In the superfluid state, helium s thermal conductivity dramatically increases to 1000 times that of copper, and its bulk viscosity drops effectively to zero. Apkarian and coworkers have recently demonstrated the disappearance of viscosity in superfluid helium on a molecular scale by monitoring the damped oscillations of a 10 A bubble as a function of temperature. These unique properties make superfluid helium an interesting host for chemical dynamics. 

Hydrogenation in Liquid-Solid Systems with Hetert enized Metal Catalysts... 

Heldebrant and Jessop have investigated several hydrogenations in liquid polymers. The asymmetric hydrogenation of tiglic acid [Eq. (6)] proceeded in reasonable conversion and enantioselectivity (88% ee) in PEG-2000 dimethyl ether, but gave poor enantioselectivity in PPG-3500, PMPS-710 and PTHE-2900 [54]. In each case, the C02-expanded solvent was used, although afterward the product was extracted with hexane. 

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