Competitive process

The reason for the constancy and sharpness of the melting j)oint of a pure crystalline solid can be appreciated upon reference to Fig. 7,10, 1, in which (a) is the vapour pressure curve of the solid and (6) that of the liquid form of the substance. Let us imagine a vessel, maintained at constant temperature, completely filled with a mixture of the above liquid and solid. The molecules of the solid can only pass into the liquid and the molecules of the liquid only into the solid. We may visualise two competitive processes taking place (i) the solid attempting to evaporate but it can only pass into the liquid, and (ii) the liquid attempting to distil but it can only pass into the solid. If process (i) is faster, the solid will melt, whereas if process (ii) proceeds with greater speed the... 

The methylation of benzylamine (1) and of ammonia (2) are competitive processes by increasing the proportion of hexamine, the source of ammonia, the yield of benzaldehyde is increased and that of metliylbenzylamine is decreased. 

Combination and disproportionation are competitive processes and do not occur to the same extent for all polymers. For example, at 60°C termination is virtually 100% by combination for polyacrylonitrile and 100% by disproportionation for poly (vinyl acetate). For polystyrene and poly (methyl methacrylate), both reactions contribute to termination, although each in different proportions. Each of the rate constants for termination individually follows the Arrhenius equation, so the relative amounts of termination by the two modes is given by... 

Figure 8.21 The competitive processes of X-ray fluorescence (XRF) and Auger electron emission...

Although there are no new methane VPO competitive processes, current technology may be usehil for the production of impure methanol in remote areas for use as a hydrate inhibitor in natural gas pipelines (119,120). 

Centrifugation is a well-established liquid-solid separation process popular in commercial and municipal waste treatment facilities. It is usually used to reduce slurry and sludge volumes and to increase the solids concentration in these waste streams. It is a technically and economically competitive process and is commonly used on waste sludges produced from water pollution control systems and on biological sludges produced in industry and municipal treatment facilities. 

Flocculation and sedimentation arc two processes used to separate waste streams that contain both a liquid and a solid phase. Both are well-developed, highly competitive processes, which arc oflcii used in the complete treatment of waste streams. They may also be used instead of, or in addition to, filtration. Some applications include the removal of suspended solid particles and soluble heavy metals from aqueous streams. Many industries use both processes in the rcmowal of pollutants from their wastewaters. These processes work best when the waste stream contains a low concentration of the contaminating solids. Although they are applicable to a wide variety of aqueous waste streams, these processes arc not generally used to treat nonaqueous or semisolid waste streams such as sludges and slurries. 

Table 8-2 Examples of competitive processes vs. different products... 

Intramolecular isotope effect studies on the systems HD+ + He, HD+ + Ne, Ar+ + HD, and Kr + + HD (12) suggest that the E l dependence of reaction cross-section at higher reactant ion kinetic energy may be fortuitous. In these experiments the velocity dependence of the ratio of XH f /XD + cross-sections was determined. The experimental results are presented in summary in Figures 5 and 6. The G-S model makes no predictions concerning these competitive processes. The masses of the respective ions and reduced masses of the respective complex reacting systems are identical for both H and D product ions. Consequently, the intramolecular isotope effect study illuminates those... 

Normally, the radical anion could be the starting point for a competitive process leading also to the same arylated nucleophile but the presence of radical scavengers, such as dinitrobenzene or ditertiobutylphenol would inhibit this secondary way of arylation, increasing the overall yield of arylation. 

For 4-alkynylamines, IH in the presence of PdCl2(MeCN)2 proceeds by two competitive processes a major 5-Exo-Dig cyclization and a minor 6-Endo-Dig one (Eq. 4.70) [278]. 

Another competitive process is associated with the cell effect in the adsorption layer... 

In a competitive process, the excess energy can be dissipated by emission of a second or Auger electron from an outer shell of the atom, leaving it in a doubly ionised excited state. The relative importance of AES and XRF depends upon the atomic number (Z) of the element involved. High Z values favour fluorescence, whereas low Z favours AES. This fact, taken together with X-ray absorbance in air, makes XRF into a method which is not very sensitive for elements with atomic numbers below Z 10. Measurements of solid samples are normally made under vacuum, as the absorption of air renders analysis of elements lighter than Ti impossible. 

Data used for the design of adsorption processes are normally derived from experimental measurements. The capacity of an adsorbent to adsorb an adsorbate depends on the compound being adsorbed, the type and preparation of the adsorbate, inlet concentration, temperature and pressure. In addition, adsorption can be a competitive process in which different molecules can compete for the adsorption sites. For example, if a mixture of toluene and acetone vapor is being adsorbed from a gas stream onto activated carbon, then toluene will adsorbed preferentially, relative to acetone and will displace the acetone that has already been adsorbed. 

Although the half-life of "Tc in steller interiors is remarkably decreased, a substantial amount of the isotope ean survive the s-process. Observations have revealed that more than 50 stars contain technetium in their outer envelope. According to other calculations, the production of neutrons in the competitive processes of neutron capture and / -decay is even more enhanced at such high temperatures, and this fact almost compensates for the depletion of "Tc [41]. 

If k3 k4 + k5, the is determined by three pairs of competitive processes. The first is the formation of X from Ru3(CO)i2 in competition with decay to Ru3(CO) 2 an< occurs with an efficiency The second is the competition between decay of X back... 

Of course, in determining the various competitive processes relating S0, , ... 

Chemat and his collaborators [92] reported the UV- and MW-induced rearrangement of 2-benzoyloxyacetophenone, in the presence of bentonite, into l-(o-hydroxy-phenyl)-3-phenylpropane-l,3-dione in methanol at atmospheric pressure (Sch. 14.2). The reaction, performed in the reactor shown in Fig. 14.7, was subject to a significant activation effect under simultaneous UV and MW irradiation this corresponded at least to the sum of the individual effects (Fig. 14.11). The rearrangement, however, was not studied in further detail. Such competitive processes can be described by the diagram in Fig. 14.9, because the product obtained from both types of activation was the same. 

The reactions of azofurazans have been used to obtain the hydrazine and the amino derivatives. For example, reactions of azofurazans, including macrocyclic azofurazan 196, with BunLi and the lithium derivatives of methylfur-azans were studied. Several competitive processes were found to occur (1) the addition of a Li reagent at the N=N bond (2) the redox reaction giving rise to hydrazofurazans and (3) the reaction of the side chain of azofurazan (Scheme 44) <2004RCB615>. 

The chemical structure of the CL precursor, not only the central portion containing the electronically excited group, but also the side chain The nature and concentration of other substrates affecting the CL pathway and favoring other nonradiative competition processes The selected catalyst... 

Several processes may compete with fluorescence for deactivation of the lowest excited singlet state. As a result only a fraction of the molecules formed in the lowest excited singlet state, < )/, actually fluoresce. <()/ is called the quantum yield or fluorescence efficiency. It is usually a fraction but may be unity in some exceptional cases and is related to the probabilities (rate constants) of fluorescence (kf) and competitive processes (kd) by... 

The preparation of optically active analogues of the natural amino acids has proven reasonable using the reaction of tris(trimethylsilyl) phosphite with chiral aldimines prepared from optically active amines.225 The asymmetric induction has been observed to be as high as 80%, a significant competitive process compared to the multistep approaches available.226227 An alternative one-step approach involving asymmetric induction upon addition to an aldimine derived from a chiral N-substituted urea provided a product with less desirable optical purity.228... 

The catalyst can be treated with a solvent to extract hydrocarbon deposits. The most straightforward solvent to use is isobutane, which has been shown to restore catalytic activity only partially. Supercritical solvents have been tested, but they also lead to only partial restoration of the activity. Supercritical alkylation to remove the deposits in situ has been shown in Section III.D.l to be less effective. It is unlikely that this method of operation will lead to a competitive process. 

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