Catalytic relative reactivity

Eurosuper gasoline Engine speed 1500 rpm Equivalence ratio 1,00 Sample point upstream of catalytic converter Relative reactivity factor Total teactivity 2.66 g O lg HC... 

Transition metal complexes that are easy to handle and store are usually used for the reaction. The catalytically active species such as Pd(0) and Ni(0) can be generated in situ to enter the reaction cycle. The oxidative addition of aryl-alkenyl halides can occur to these species to generate Pd(II) or Ni(II) complexes. The relative reactivity for aryl-alkenyl halides is RI > ROTf > RBr > RC1 (R = aryl-alkenyl group). Electron-deficient substrates undergo oxidative addition more readily than those electron-rich ones because this step involves the oxidation of the metal and reduction of the organic aryl-alkenyl halides. Usually... 

The above process involves the acylation of a relatively reactive aromatic substrate. In order to be widely applicable, catalytic methodologies must be effective with less reactive... 

Asymmetric diarylmethanes, hydrogenolytic behaviors, 29 229-270, 247-252 catalytic hydrogenolysis, 29 243-258 kinetics and scheme, 29 252-258 M0O3-AI2O3 catalyst, 29 259-269 relative reactivity, 29 255-257 schematic model, 29 254 Asymmetric hydrogenations, 42 490-491 Asymmetric synthesis, 25 82, 83 examples of, 25 82 Asymmetry factor, 42 123-124 Atom-by-species matrix, 32 302-303, 318-319 Atomic absorption, 27 317 Atomic catalytic activities of sites, 34 183 Atomic displacements, induced by adsorption, 21 212, 213 Atomic rate or reaction definition, 36 72-73 structure sensitivity and, 36 86-87 Atomic species, see also specific elements adsorbed... 

Catalytic hydrogenolysis (continued) M0O3-AI2O3 catalyst, 29 258-269 relative reactivity, 29 255-257 schematic model, 29 254 diphenylmethane kinetics, 29 241-243 reaction mechanism, 29 267 Catalytic oxidation,... 

Experiments on the bromination of equilibrated ketone-acetal systems in methanol were also recently performed for substituted acetophenones (El-Alaoui, 1979 Toullec and El-Alaoui, 1979). Lyonium catalytic constants fit (57), but for most of the substituents the (fcA)m term is negligible and cannot be obtained with accuracy. However, the relative partial rates for the bromination of equilibrated ketone-acetal systems can be estimated. For a given water concentration, it was observed that the enol path is more important for 3-nitroacetophenone than for 4-methoxyacetophenone. In fact, the smaller the proportion of free ketone at equilibrium, the more the enol path is followed. From these results, it can be seen that the enol-ether path is predominant even if the acetal form is of minor importance. The proportions of the two competing routes must only depend on (i) the relative stabilities of the hydroxy-and alkyoxycarbenium ions, (ii) the relative reactivities of these two ions yielding enol and enol ether, respectively, and (iii) the ratio of alcohol and water concentrations which determines the relative concentrations of the ions at equilibrium. Since acetal formation is a dead-end in the mechanism, the amount of acetal has no bearing on the relative rates. Bromination, isotope exchange or another reaction can occur via the enol ether even in secondary and tertiary alcohols, i.e. when the acetal is not stable at all because of steric hindrance. 

Systematic examination of the catalytic properties of dimeric complexes was initiated shortly after the identification of dinuclear iron sites in metalloenzymes. The first report of a reactive dimeric system came from Tabushi et al. in 1980, who examined the catalytic chemistry of [Fe3+(salen)]20, 1 (salen is N,N -(salicylaldehydo)-l,2-ethylenediamine) (12). They reported interesting stereoselectivity in the oxidation of unsaturated hydrocarbons with molecular oxygen in the presence of mercaptoethanol or ascorbic acid and pyridine as a solvent ([l]<<[alkane]<<[2-mercaptoethanol]). With adamantane as substrate, they observed the formation of a mixture of (1- and 2-) adamantols and adamantanone (Table I) (12). Both the relative reactivity between tertiary and secondary carbons (maximum value is 1.05) and final yield ( 12 turnovers per 12 hr) were dependent on the quantity of added 2-mercaptoethanol. Because autoxidation of adamantane gave a ratio of 3°/2° carbon oxidation of 0.18-0.42, the authors proposed two coexisting processes autooxidation and alkane activation. 

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