Halide partial pressures

Polymerization of Ethylene by Zirconium Alkyl Halides in Toluene at 80°C. Concentration 3.00 X 10 3 mole liter-1 Ethylene Partial Pressure 10 atm.Hydrogen Partial Pressure 10 atm (9, 16)... 

The most important gaseous component is X2, as is the case in most oxides, halides, and sulfides. The stoichiometric variation will be linked to the partial pressure of the surrounding nonmetal atmosphere. The nonmetal component will be gained at high pressures and lost at low pressures. These options correspond to oxidation and reduction. 

Analyses of the defect chemistry and thermodynamics of non-stoichiometric phases that are predominately ionic in nature (i.e. halides and oxides) are most often made using quasi-chemical reactions. The concentrations of the point defects are considered to be low, and defect-defect interactions as such are most often disregarded, although defect clusters often are incorporated. The resulting mass action equations give the relationship between the concentrations of point defects and partial pressure or chemical activity of the species involved in the defect reactions. 

There are monomers, dimers and sometimes trimers in the vapors of alkali halides. It can be shown that Eq. (22) is valid not only for the total pressure but also for the partial pressures of each species. 

The four-coordinate alkyl complex, LNiI(C0)CH3, may coordinate with carbon monoxide to regenerate the five coordinate alkyl species, and this leads to insertion to form Ni-acyl complex. This complex, LNil (CO)(COCH3), can be cleaved either by water yielding acetic acid or by methanol to give methyl acetate. However, in the presence of high iodide concentration formation of acetyl iodide may predominate (29). This step is reversible and can lead to decarbonylation under low carbon monoxide partial pressure. Similar decarbonylations of acyl halides by nickel complexes are known (34). 

Reaction rates have first-order dependence on both metal and iodide concentrations. The rates increase linearly with increased iodide concentrations up to approximately an I/Pd ratio of 6 where they slope off. The reaction rate is also fractionally dependent on CO and hydrogen partial pressures. The oxidative addition of the alkyl iodide to the reduced metal complex is still likely to be the rate determining step (equation 8). Oxidative addition was also indicated as rate determining by studies of the similar reactions, methyl acetate carbonylation (13) and methanol carbonylation (14). The greater ease of oxidative addition for iodides contributes to the preference of their use rather than other halides. Also, a ratio of phosphorous promoter to palladium of 10 1 was found to provide maximal rates. No doubt, a complex equilibrium occurs with formation of the appropriate catalytic complex with possible coordination of phosphine, CO, iodide, and hydrogen. Such a pre-equilibrium would explain fractional rate dependencies. 

When the vapour of alkali metals is mixed at low pressures, of the order 10 3mm., with certain halogen compounds, a cold, highly diluted flame is produced. A deposit of alkali halide is formed on the wall of the tube in which the reaction takes place, and from the distribution of this deposit and the velocity of the gas stream the partial pressures of the reacting substances and the reaction velocity can be inferred. A number of investigations with various modifications of this method have been carried out by Polanyi and others, J and a careful analysis and interpretation of the results has yielded much interesting and valuable information about the speed of the chemical reactions involved. 

Binary Compounds and Related Systems.—Halides and Oxyhalides. At 1100—1450 °C TiCl4 reacts with metallic Ti to give lower Ti chlorides with a Cl Ti ratio in the gas phase of 2.00—2.50. An increase in temperature does not affect the degree of reaction of TiCl4. Reduction of the partial pressure of TiCl4 vapour in the original mixture with Ar reduces the Cl Ti ratio from 2.60 to 2.00.18 The fraction of Ti2+ ions in a NaCl melt at a concentration of Ti of 0.83—0.4 wt. % and at 950—1100°C is close to unity (0.80—0.97). The amount of Ti2+ increases with decreasing temperature. At... 

Even a minor amount of alkali vapor transport can be significant, as revealed by the turbine tolerance level of 0.02 ppm alkali needed for corrosion control in pressurized fluidized bed combustors (12). If we consider only the alkali halide content of the dolomite component, this tolerance level would require an alkali-scrubbing efficiency of better than 99.9999 percent for PFBC. Even if corrosion (alkali) resistant materials were available, uncontrolled alkali vapor transport would still lead to unmanageable deposits on cool downstream components. For instance, under typical coal gasifier conditions, a species partial pressure as low as 10 atm would lead to vapor transport and deposition in metric ton quantities on an annual basis. 

The experiments were performed at temperatures, partial pressures of the modifying agent and other parameters varying in broad ranges. The effect of chemical and thermal pre-tteatment of silica was also investigated. Generally, the halides MXn of both metals and nonmetals reacted with isolated silanol groups and with vicinal silanols. The concrete case of TiCU showed in Fig. 5.19 may serve to visualize the interactions. 

A fast and precise mass adjustment is possible by the use of a Hall probe and a mass programmer. This is very useful for the study of metal halides with their complex mass spectra [60] and the study of gas phase equilibria with very different partial pressures between the reacting species [80]. 

The experimental and theoretical studies on alkali halides are discussed and summarized in a book edited by Davidovits and McFadden [434]. Molecular parameters and thermodynamic properties including partial pressures are given for alkali halides and metal dihalides by Brewer and Brackett [43 S] as well as Brewer et al. [436], respectively. 

Murgulescu and Topor [488] obtained in an indirect way are comparatively small. The results of this work and those of Ref. 468 are based on a direct measurement of the Nal and (Nal)2 partial pressures. Work [489] as well as Mucklejohn and O Brien [490] used the equilibrium constant by Datz et al. [487] for the computation of partial pressures from the total vapor pressure and the vapor density over sodium iodide. The vaporization of sodium iodide and the thermochemistry of the vapor species is of particular importance for metal halide lamps [438]. The equilibrium constants obtained by Lelik et al. [469] and Emons et al. [470] result from investigations by Knudsen effusion mass spectrometry which in part deviate from well established data. 

No examples of catalysis of unimolecular elimination from halides or esters have been reported. Fades and Stimson (1962) have shown that t-butyl chloride undergoes elimination in the gas-phase at a rate independent of the partial pressure of added sulphur hexafluoride, a substance known to accelerate certain decompositions (Bose and Hinshelwood, 1959). However, the pyrolysis of alcohols, first studied by Kistiakowsky and Schultz (1934) is accelerated by the presence of hydrogen halides (Maccoll and Stimson, 1960). The former authors showed that t-butyl alcohol decomposed homogeneously to yield isobutene and water, at a rate given by... 

Studies of the process of hydroxide ion dissociation performed over a wide range of initial concentrations of oxide ions and partial pressures of H20 demonstrate that in molten alkali metal halides this process does not comply with the generally accepted equation (1.2.4) [232, 321], The dissociation process of OH-, both in the KCl-LiCl eutectic and in the molten KCl-NaCl equimolar mixture, was found to proceed according to the scheme ... 

Similarly, the spread of the calculated values of the equilibrium constant of the reaction described by the stoichiometry of equation (2.5.68) is very small at all initial molalities of the Lux base and all the partial pressures of water over the melt studied. Hence, the equilibrium (2.5.68) is more correct for the description of the dissociation process for hydroxide ions, at least, in the melts based on alkali metal halides than the generally accepted reaction (1.2.4). 

The partial hydrogenation seen in the preceding example (106) leads to the thought that catalytic reduction of the whole series seen below should be investigated in the presence of sufficient base to neutralize the resultant hydrogen halide. Low pressure conditions should be employed. 

In the "diffusion flame" method developed by von Hartel and Polanji (Z. physikal. Chem. B 1930,11, 97) sodium vapour is introduced throu a nozzle into an excess of organic halide and the extent of penetration before it is completely consumed by reaction is measured. In an experiment made by Cvetanovic and Le Roy (J. Chem. Phys. 1952, 20, 1016) at 532.7 K, a stream of sodium vapour at a partial pressure = 8.3 x 10" mm Hg in nitrogen carrier gas was passed through a nozzle of radius r = 0.125 cm into a stream of nitrogen and ethyl chloride vapour at a partial pressure p = 2.5 x 10" mm Hg. The radius R of the spherical zone of reaction made visible by illumination with sodium D-line resonance radiation was 1.55 cm. The partial pressure P of sodium at the visibility limit was estimated to be 7 X 10" mm Hg. The diffusion coef5cient D of sodium in the reaction mixture is 130 cm s. ... 

III. In this process a tungsten wire, which serves only as a substratum for the deposit, is heated to glowing in an atmosphere consisting of a volatile halide of the metal, a carbon compound and Hg. Moers recommends the use of hydrocarbons such as toluene, instead of CO the deposition of free carbon with the carbide is avoided if the partial pressure of the hydrocarbon in the system is low. The hydrogen atmosphere facilitates considerably the reaction at the glow wire by reducing the decomposition temperatures of the halides to a much greater extent than does reduced pressure or even vacuum. 

Binary Componnds and Related Systems.—Halides. The composition of niobium subchlorides prepared from Nb and NbClj by chemical transport reactions has been studied. When the disproportionation temperature of NbClj was maintained at 350°C, NbC, a mixture of NbC with NbCl3 13, NbCl3 13, and NbCl (2.75 x 3.02) were obtained, at partial pressures of NbClj of >4.0, 3.1—1.6, 1.2, and 1.0—0.6 atm., respectively. At a partial pressure of NbClj of 0.06 atm., the products obtained by disproportionation at 350 and 400—700°C were NbCl2.75 and NbCl2.67. respectively. The disproportionation behaviour of these halides and their X-ray diffraction characteristics have also been examined. ... 

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