Kinetic temperature effect

References to a number of other kinetic studies of the decomposition of Ni(HC02)2 have been given [375]. Erofe evet al. [1026] observed that doping altered the rate of reaction of this solid and, from conductivity data, concluded that the initial step involves electron transfer (HCOO- - HCOO +e-). Fox et al. [118], using particles of homogeneous size, showed that both the reaction rate and the shape of a time curves were sensitive to the mean particle diameter. However, since the reported measurements refer to reactions at different temperatures, it is at least possible that some part of the effects described could be temperature effects. Decomposition of nickel formate in oxygen [60] yielded NiO and C02 only the shapes of the a—time curves were comparable in some respects with those for reaction in vacuum and E = 160 15 kJ mole-1. Criado et al. [1031] used the Prout—Tompkins equation [eqn. (9)] in a non-isothermal kinetic analysis of nickel formate decomposition and obtained E = 100 4 kJ mole-1. 

Taft equation, 229-230 Temperature, effect on rate, 156-160 Temperature-jump method, 256 Termination reaction, 182 Thermodynamic products, 59 Three-halves-order kinetics, 29... 

Based on detailed kinetic investigations, a tentative mechanism for this asymmetric oxidation was proposed (Scheme 2) according to which optically active sulphoxides may be formed by two pathways external attack on the sulphur atom by the chiral titanium hydroperoxide (path A) or coordination of sulphur to titanium prior to the oxidation step (path B). Although paths A and B could not be distinguished experimentally, the temperature effect was tentatively ascribed to a change of the mechanism, path A being predominant above — 20 °C and path B becoming competitive at lower temperatures (or vice versa). 

I will assume that these kinetic models correctly account for temperature changes. More data are needed to verify this. The temperature effect in GASPP is practically the same as that claimed by Wisseroth in a recent letter (10). 

Table II summarizes the yields obtained from the CONGAS computer output variable study of the gas phase polymerization of propylene. The reactor is assumed to be a perfect backmix type. The base case for this comparison corresponds to the most active BASF TiC 3 operated at almost the same conditions used by Wisseroth, 80 C and 400 psig. Agitation speed is assumed to have no effect on yield provided there is sufficient mixing. The variable study is divided into two parts for discussion catalyst parameters and reactor conditions. The catalyst is characterized by kg , X, and d7. Percent solubles is not considered because there is presently so little kinetic data to describe this. The reactor conditions chosen for study are those that have some significant effect on the kinetics temperature, pressure, and gas composition.

A recent paper by Leffek and Matheson (1971) nicely complements this work, as it describes the results of a careful investigation of the temperature dependence of the kinetic isotope effect in the reaction studied by Kaplan and Thornton (1967). It is found that AAH = 134 + 30 cal mol and dd/S = 0-15 + 0-09 cal mol deg , demonstrating that the isotope effect is primarily due to an enthalpy difference, and providing support for the steric interpretation suggested by Kaplan and Thornton (1967). 

The differences between palytoxin and PDBu with respect to kinetics, temperature dependence, and effect on low affinity binding suggest that these two different types of tumor promoters may be acting through different mechanisms. Further, in contrast to PDBu, the effect of palytoxin is not readily reversible (33). To determine where the two pathways differ, we compared the relative ability of palytoxin and PDBu to inhibit EGF binding in protein kinase C depleted cells. Swiss 3T3 cells were depleted of protein kinase C to different extents by exposing confluent quiescent cells to 0, 20, 200, or 2000 nM PDBu for 72 hr. Previous results indicate that this treatment depletes cells of protein kinase C activity in a dose-dependent manner (31). 

Dangles, O and Brouillard, R., Polyphenol interactions. The copigmentation case — thermodynamic data from temperature-variation and relaxation kinetics. Medium effect. Can. J. Chem.-Rev. Can. Chim., 70, 2174, 1992. 

Temperature effect in the lipase-catalyzed kinetic resolution of solketal... 

The low-temperature method is effective not only in the kinetic resolution of alcohols but also in the enantioface-selective asymmetric protonation of enol acetate of 2-methylcyclohexanone (15) giving (f )-2-methylcyclohexanone (16). The reaction in H2O at 30°C gave 28% ee (98% conv.), which was improved up to 77% ee (82% conv.) by the reaction using hpase PS-C 11 in /-Pt20 and ethanol at 0°C. Acceleration of the reaction with lipase PS-C 11 made this reaction possible because this reaction required a long reaction time. The temperature effect is shown in Fig. 14. The regular temperature effect was not observed. The protons may be supplied from H2O, methanol, or ethanol, whose bulkiness is important. 

One-step hydroxylation of aromatic nucleus with nitrous oxide (N2O) is among recently discovered organic reactions. A high eflSciency of FeZSM-5 zeolites in this reaction relates to a pronounced biomimetic-type activity of iron complexes stabilized in ZSM-5 matrix. N2O decomposition on these complexes produces particular atomic oj gen form (a-oxygen), whose chemistry is similar to that performed by the active oxygen of enzyme monooxygenases. Room temperature oxidation reactions of a-oxygen as well as the data on the kinetic isotope effect and Moessbauer spectroscopy show FeZSM-5 zeolite to be a successfiil biomimetic model. 

Relatively detailed study has been done for the reaction pathways over Au/Ti02 catalysts mainly because of simplicity in catalytic material components. The rate of PO formation at temperatures around 323 K does not depend on the partial pressure of C3H6 up to 20vol% and then decreases with an increase, while it increases monotonously with the partial pressure of O2 and H2 [57]. A kinetic isotope effect of H2 and D2 was also observed [63]. These rate dependencies indicate that active oxygen species are formed by the reaction of O2 and H2 and that this reaction is rate-determining [57,63,64]. 

Based on C-H versus C-D zero point vibrational differences, the authors estimated maximum classical kinetic isotope effects of 17, 53, and 260 for h/ d at -30, -100, and -150°C, respectively. In contrast, ratios of 80,1400, and 13,000 were measured experimentally at those temperatures. Based on the temperature dependence of the atom transfers, the difference in activation energies for H- versus D-abstraction was found to be significantly greater than the theoretical difference of 1.3kcal/mol. These results clearly reflected the smaller tunneling probability of the heavier deuterium atom. 

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