Bases gas-phase

Design issues for membrane-based, gas phase microchemical systems, Chem. Eng. 

QuiramJI.J.HsingJ.-M.Pranz, A.J.JensenJC.F.SchmidtM.A., Designissuesformembrane-based,gas phase microchemical systems, Chem.Eng. Sd. 55 ( 2000)3065-3075. 

The availability of the electron pair in the isolated ligand can be directly measmed by photoelectron spectroscopy. The comparative ionization potentials show a reverse of the proton aftrnities in aqueous systems. For example, the gas-phase basicity of PPhs (lower ionization energy) is greater than that of PMc3 a selection of values is given in Table 6. These differences between solution based gas-phase basicities are ascribed to solvation effects. 

Fig. 3.4. The SV plot at 23°C of a PdOEP-based gas-phase sensor excited by a rubrene-doped Alqs OLED [17]. The sensing film was prepared by drop casting. The SV plot is linear up to 40% O2. Copyright 2006, with permission from Elsevier...

Ube has also developed Pd/MeONO-based gas-phase processes for the production of dimethyl oxalate and dimethyl carbonate (Eqs. (8.9) and (8.10)) using... 

The most extensive efforts to develop the OLED-based sensor platform have focused on PE-based gas-phase and dissolved O2 (DO) sensors. Such sensors, which have been studied for many years, are based on the efficient quenching of the PL of dyes such as Ru complexes and Pt or Pd porphyrins by collisions with O2 molecules the sensitivity to O2 is due to the nearly unique triplet nature of the ground state of O2. In an ideal homogeneous matrix, the O2 concentration [O2I is related to the steady-state PL intensity I and the PL decay time x by the Stern-Volmer (SV) equation ... 

Figure 5.6. Adsorption isotherms of water vapor on BPL carbon (bituminous coai-based, gas-phase carbon, from Caigon Corp.) at 25°C. Untreated BPL ( ) and BPL oxidized by 6 M HNO3 at time lengths in hours HNO3-O.5 ( ) HNO3-KA) HN03-2(o) HN03-4(H) HNO3 - 7(T). Data taken from Barton et ai., 1984.

Quesada, J. Grossmann, D. Fernandez, E. Romero, J. Sanhueza, E. Moortgat, G. Cmtzen, P.J., 2001 Ground Based Gas Phase Measurements in Surinam during the LBA-Claire 98 Experiment , in Journal of Atmospheric Chemistry, 39 15-36. 

A. (The gas phase estimate is about 100 picoseconds for A at 1 atm pressure.) This suggests tliat tire great majority of fast bimolecular processes, e.g., ionic associations, acid-base reactions, metal complexations and ligand-enzyme binding reactions, as well as many slower reactions that are rate limited by a transition state barrier can be conveniently studied with fast transient metliods. 

The Empirical Conformational Energy Program for Peptides, ECEPP [63, 64], is one of the first empirical interatomic potentials whose derivation is based both on gas-phase and X-ray crystal data [65], It was developed in 1975 and updated in 1983 and 1992. The actual distribution (dated May, 2000) can be downloaded without charge for academic use. 

Several alternative attempts have been made to quantify Lewis-acid Lewis-base interaction. In view of the HSAB theory, the applicability of a scale which describes Lewis acidity with only one parameter will be unavoidably restricted to a narrow range of struchirally related Lewis bases. The use of more than one parameter results in relationships with a more general validity ". However, a quantitative prediction of the gas-phase stabilities of Lewis-acid Lewis-base complexes is still difficult. Hence the interpretation, not to mention the prediction, of solvent effects on Lewis-add Lewis-base interactions remains largely speculative. 

Finally, the solvent also interacts with sites of the Lewis acid and the Lewis base that are not directly involved in mutual coordination, thereby altering the electronic properties of the complex. For example, delocalisation of charges into the surrounding solvent molecules causes ions in solution to be softer than in the gas phase . Again, water is particularly effective since it can act as an efficient electron pair acceptor as well as a donor. 

For the evaporation process we mentioned above, the thermodynamic probability of the gas phase is given by the number of places a molecule can occupy in the vapor. This, in turn, is proportional to the volume of the gas (subscript g) 12- oc V In the last chapter we discussed the free volume in a liquid. The total free volume in a liquid is a measure of places for molecules to occupy in the liquid. The thermodynamic probability of a liquid (subscript 1) is thus V, oc V, frgg. Based on these ideas, the entropy of the evaporation process can be written as... 

The Beckstead-Derr-Price model (Fig. 1) considers both the gas-phase and condensed-phase reactions. It assumes heat release from the condensed phase, an oxidizer flame, a primary diffusion flame between the fuel and oxidizer decomposition products, and a final diffusion flame between the fuel decomposition products and the products of the oxidizer flame. Examination of the physical phenomena reveals an irregular surface on top of the unheated bulk of the propellant that consists of the binder undergoing pyrolysis, decomposing oxidizer particles, and an agglomeration of metallic particles. The oxidizer and fuel decomposition products mix and react exothermically in the three-dimensional zone above the surface for a distance that depends on the propellant composition, its microstmcture, and the ambient pressure and gas velocity. If aluminum is present, additional heat is subsequently produced at a comparatively large distance from the surface. Only small aluminum particles ignite and bum close enough to the surface to influence the propellant bum rate. The temperature of the surface is ca 500 to 1000°C compared to ca 300°C for double-base propellants. 

Diborane [19287-45-7] the first hydroborating agent studied, reacts sluggishly with olefins in the gas phase (14,15). In the presence of weak Lewis bases, eg, ethers and sulfides, it undergoes rapid reaction at room temperature or even below 0°C (16—18). The catalytic effect of these compounds on the hydroboration reaction is attributed to the formation of monomeric borane complexes from the borane dimer, eg, borane-tetrahydrofuran [14044-65-6] (1) or borane—dimethyl sulfide [13292-87-0] (2) (19—21). Stronger complexes formed by amines react with olefins at elevated temperatures (22—24). 

Chemiluminescent analyzers are based on the light (chemiluminescence) emitted in the gas-phase reaction of ozone with ethylene, which is measured with a photomultipHer tube. The resulting current is proportional to the ozone concentration (see Luminescent materials, chemiluminescence). 

Most commercial processes produce polypropylene by a Hquid-phase slurry process. Hexane or heptane are the most commonly used diluents. However, there are a few examples in which Hquid propylene is used as the diluent. The leading companies involved in propylene processes are Amoco Chemicals (Standard OH, Indiana), El Paso (formerly Dart Industries), Exxon Chemical, Hercules, Hoechst, ICl, Mitsubishi Chemical Industries, Mitsubishi Petrochemical, Mitsui Petrochemical, Mitsui Toatsu, Montedison, Phillips Petroleum, SheU, Solvay, and Sumimoto Chemical. Eastman Kodak has developed and commercialized a Hquid-phase solution process. BASE has developed and commercialized a gas-phase process, and Amoco has developed a vapor-phase polymerization process that has been in commercial operation since early 1980. 

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