Reaction times, pressure dependence

There is one important caveat to consider before one starts to interpret activation volumes in temis of changes of structure and solvation during the reaction the pressure dependence of the rate coefficient may also be caused by transport or dynamic effects, as solvent viscosity, diffiision coefficients and relaxation times may also change with pressure [2]. Examples will be given in subsequent sections. 

In the atomic resonance absorption spectrometric (ARAS) adaptation of the methods, atomic species are spectroscopically monitored as a function of time. H [7,9], D- [7,10], O- [7,11], N- [12], Cl- [13] and I-atom [14] reactions have been studied. Beer s law holds if absorbance, (ABS), is kept low, and then (ABS) s -ln(I/Io) (I and Iq are transmitted and incident intensities of the resonance light, respectively) is proportional to the atomic concentration. If the decay of atom A is controlled by a bimolecular reaction, A + R, where R is the stable reactant molecule, then the decay rate is pseudo-first-order provided [R] [A]. Because (ABS) is proportional to [A], observation of (ABS)t is sufficient to determine the decay constant. Values for kbini for each experiment are then determined by dividing the decay constant by [R]. The results from many experiments are usually displayed as Arrhenius plots. If a reaction is pressure dependent, experiments can also be carried by varying total density. Termolecular reactions can therefore be studied. In certain cases, chemical isolation is not possible, and numerical chemical simulations of the... 

For very fast reactions, as they are accessible to investigation by pico- and femtosecond laser spectroscopy, the separation of time scales into slow motion along the reaction path and fast relaxation of other degrees of freedom in most cases is no longer possible and it is necessary to consider dynamical models, which are not the topic of this section. But often the temperature, solvent or pressure dependence of reaction rate... 

Saturation of the oil with hydrogen is maintained by agitation. The rate of reaction depends on agitation and catalyst concentration. Beyond a certain agitation rate, resistance to mass transfer is eliminated and the rate oecomes independent of pressure. The effect of catalyst concentration also reaches hmiting values. The effects of pressure and temperature on the rate are indicated by Fig. 23-34 and of catalyst concentration by Fig. 23-35. Reaction time is related to temperature, catalyst concentration, and IV in Table 23-13. 

Vulcanisation being a chemical reaction, is time/temperature dependant. In factory operations, vulcanisation is usually carried out in an autoclave using steam under pressure at temperatures up to 160°C. If the lined unit is a vessel too large to fit in an autoclave and has an adequate pressure rating, all outlets can be sealed and it can itself be pressurised. If this technique is employed then care must be taken, as a failure of the steam supply with consequent condensation, can cause a vacuum and subsequent collapse of the vessel. 

Polyalphaolefin Hydraulic Fluids. Polyalphaolefms are made by oligomerizing alphaolefins such as 1-decene in the presence of a catalyst (Newton 1989 Shubkin 1993 Wills 1980). The crude reaction mixture is quenched with water, hydrogenated, and distilled. The number of monomer units present in the product polyalphaolefin oil depends on a number of reaction parameters including the type of catalyst, reaction temperature, reaction time, and pressure (Shubkin 1993). The exact combination of reaction parameters used by a manufacturer is tailored to fit the end-use of the resulting polyalphaolefin oil. A typical polyalphaolefin oil prepared from 1-decene and BF3- -C4H9OH catalyst at 30 °C contains predominantly trimer (C30 hydrocarbons) with much smaller amounts of dimer, tetramer, pentamer, and hexamer. While 1-decene is the most common starting material, other alphaolefins can be used, depending on the needs of the product oil. 

Calculation of kinetic parameters - In the experiments carried out in the single autoclave the H2 pressure was not maintained and the consumption of H2 controlled the conversion of AcOBu, which could be described by pseudo-first order rate constant. In the activity tests performed in SPR16 the conversion of AcOBu increased linearly up to ca. 50 % with reaction time. Initial reaction rates were calculated from AcOBu conversion vs. reaction time dependence, the initial concentration of substrate and the amount of catalyst or the amount of promoters in 1 g of catalyst. 

Figure 5.4 represents the dependence of CO conversion and C5+ selectivity on reaction time over the Ru/Mn/Al203 catalyst for FT synthesis under pressurized... 

Chiral nitrones derived from L-valine (62a-c) react with methyl acrylate to afford the corresponding diastereomeric 3,5-disubstituted isoxazolidines (565a-c) to (568a-c). The dibenzyl substituted nitrone (62a) also gave 3,4-disubstituted isoxazolidine (569) in 4% yield. The stereoselectivity was dependent on the steric hindrance of the nitrone and on reaction conditions. High pressure decreased the reaction time of the cycloadditions. The major products were found to have the C-3/C-6 erythro and C-3/C-5 Irons configuration (Scheme 2.262) (771). 

The use of a Type 1 mass spectrometer with a collision region may allow a reaction time on the order of milliseconds. Often the term single collision is used, which depends on the pressure of the reactant molecules, and in many studies the residence time in the reactant region is not specified. 

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