Catalysed reactions static

In a static reactor the rate changes with time as the reactants are consumed, and the initial rate is often used. In a dynamic reactor under steady state conditions the rate is independent of time, and with a known flow of reactant into the reactor the observed fractional conversion is readily changed into a rate. What is of great interest in understanding a catalysed reaction is the response of the rate to variations in operating conditions, especially the concentrations or pressures of the reactants, and temperature. It is frequently observed that, at least over some limited range of temperature, the Arrhenius equation in the form... 

The concept of acid site is based on the idea that protons are fixed at definite position. Thus, the measures of the acid strength, which are described so far, are basically based on the static properties of OH groups. However, the solid acid catalysed reactions are often carried out at higher temperatures than room temperature. In general, the catalysts undergo structural and chemical change under reaction conditions. Therefore, the characterization of properties of zeolites at high temperatures is more desirable. 

The conversion of (298) into (300) upon gas-phase thermolysis occurs by a Cope rearrangement and not by a [1,3] carbon shift or a bisallyl radical mechanism. Thus, similar treatment of (299) affords only (301). Rearrangement of 3-oxobicyclo-[3,2,l]oct-6-ene to 3-oxobicyclo[3,3,0]oct-6-ene occurs only at much higher temperature and presumably by way of a non-concerted mechanism. The nickel-catalysed reaction of norbornene with butadiene affords the 1 2 cxo-adduct (302) which upon thermolysis is converted into the valence isomer (303). Concerted and non-concerted Claisen-type rearrangements have been observed in the A, -phosphorin series. Tricyclo[7,3,0,0 ]dodeca-2,5,7,10-tetraene (304), which is available in six steps starting from bicyclo[3,3,0]octa-3,7-dien-2,6-dione, appears to be an essentially static structure (as assessed by n.m.r. spectroscopy) up to 141 The slow... 

In direct nitroso aldol reactions of a-branched aldehydes, an L-prolinamide (50) catalyses to give a-hydroxyamino carbonyl compounds which are otherwise dis- favoured ees up to 64% were found.149 Another prolinamide derivative gives similar results in a nitrosobenzene reaction.150 For proline-catalysed cases involving highly substituted cyclohexanones, DFT calculations have highlighted the roles of electro- static and dipole-dipole interactions in the level of de achieved.151 (g)... 

Neopentyl chloride to HC1+ 1,1 -dimethylcy clopropane -fmethylbutenes+isobutene-t-CH +CHjCI+chlorinated isobutenes gas phase, static (410-496) unimolecular-I-radical chain (3/2 order). HCl catalysed. For chain reaction A = 3.5xl0 E = 56.3 567... 

The scheme was verified usii chronopotentiometric and potentio-static methods (Alberts and Shain, 1963). A similar scheme was considered for the reduction of o- and p-nitrophenols and nitroanilines but the theoretical treatment is more involved owing to the irreversibility of the first four-electron reduction step. Similarly also a chemical reaction is interposed between the first and second electrode process in the reductions of a-substituted ketones of the type RCO.CHg—X (for X=NR2, NR, SR, SRf, OR, PRJ and halogen) and in the reductions of a,)9-unsaturated ketones. In both these systems enolate is a primary electro-inactive reduction product that must be first transformed into the electro-active keto-form. The rate of this transformation, which is acid-base catalysed, limits the wave-height of the more negative wave of the saturated ketone. Similarly it was explained why the more negative wave observed on curves of benzil is smaller than expected for the given concentration of benzoin. 

Due to the fact that the difference between a sensitised and a catalysed photoreaction is somewhat arbitrary, due to the different and complex mechanisms involved (static and dynamic sensitisation, interaction with a photoproduct, photoinduced reactions,...), the term, photocatalysis has therefore been defined as broad as possible without the specific implication of any special mechanism, and refers then to the action of a substance whose function is activated by the absorption of a photon. A photocatalyst can be described as one involved in the quantum yield expression for a photochemical reaction without its stoichiometric involvement or more precisely, it appears in the quantum yield expression for reaction from a particular excited state to a power greater than its coefficient in the stoichiometric equation [14]. 

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