1,721,136 research outputs found
Metal catalysis in oxidation by peroxides. Part 191 1 Part 18: O. Bortolini, V. Conte, F. Di Furia and G. Modena, J. Mol. Catal., 19 (1983) 331.. On the mechanism of rhodium-catalyzed oxidation of terminal olefins to methyl ketones by dioxygen
No full textThe mechanism of the rhodium-catalyzed oxidation of oct-1-ene to octan-2-one by dioxygen in ethanol has been investigated by deuterium labelling studies, employing ethanol-d1 and [2-2H]oct-1-ene respectively. In both sets of experiments, substantial label exchange with the solvent has been observed, suggesting a decomposition pathway for the peroxometallocycle intermediate which does not involve a β-hydride shift. © 1984
Metal Catalysis in Oxidation by Peroxides. Part 17. On the Mechanism of the Vanadium and Molybdenum Catalyzed Oxidation of Sulphides and Olefins Bearing Neighbor Hydroxo Groups by tert-Butyl Hydroperoxide and Hydrogen Peroxide
No full textThe rates of oxidation of 4-chlorophenylmethyl suphide, 1, 2-[(4-chlorophenyl) thio]ethanol, 2, 1-methylcyclohexene, 3, and geraniol, 4, by t-butylhydroperoxide and hydrogen peroxide in the presence of V(V) and Mo(IV) catalysts have been measured at various temperatures. The kinetic data and the Arrhenius parameters obtained allow a comparison among the substrates and the oxidizing systems. On the basis of such a comparison, the effect of the hydroxo group on the behaviour of 2 and 4 may be estimated. The suggestion is made that the enhanced reactivity of such substrates, in some cases, is related to the specific interaction of the OH group in the transition state with the peroxide oxygen rather than to the formation of a ground-state alkoxo-peroxo complex. © 1983
Metal Catalysis in Oxidation by Peroxides. Part 16. Kinetics and Mechanism of Titanium-Catalyzed Oxidation of Sulphides with Hydrogen Peroxide
No full textThe oxidation to the corresponding sulphoxides of two dialkyl sulphides, Bun-S-Bun and Bun-S-But, and three aryl alkyl sulphides, p-methyl-phenyl sulphide, p-chlorophenyl methyl sulphide and phenyl t-butyl sulphide, with hydrogen peroxide in the presence of catalytic amounts of TiO-(acac)2 has been studied in aqueous ethanol, at 25 °C. Kinetic experiments show that the oxidation rate is first-order in the catalyst and almost zero-order in hydrogen peroxide. This latter feature is interpreted as arising from a large value of the association constant H2O2-Ti(IV) to form a side-bonded peroxotitanium(IV) species. A non-linear dependence of rates on substrate concentration is observed for sulphides which are not sterically hindered, whereas for the two t-butyl derivatives, a kinetic first order is found. This behaviour suggests that non-bulky sulphides coordinate to Ti(IV) in solution. The consenquences of such a process on the efficiency of the oxidizing system are discussed and, in partic..
Metal Catalysis in Oxidation by Peroxides. Part 15. Steric Effects in the Oxidation of Organic Sulphides with V(V) and Mo(VI) Peroxo Complexes
No full textThe rates of oxidation to the corresponding sulphoxides of two dialkyl sulphides, Bun-S-Bun and Bun-S-But, and two arylalkyl sulphides, Ph-S-CH3 and Ph-S-But, with t-butylhydroperoxide and hydrogen peroxide in the presence of catalytic amounts of vanadium (VO(acac)2) and molybdenum (MoO2(acac)2), have been measured in ethanol. The steric retardations observed are compared with those previously found in the acid-catalyzed oxidation of the same substrates, with hydrogen peroxide in ethanol, a typical 'electrophilic' oxidation. This comparison indicates very similar behaviour of the various oxidizing systems, thus confirming the generality of the external 'electrophilic' oxidation by metalperoxo species. © 1982
Metal Catalysis in Oxidation by Peroxides. Part 13. The Electrophilic Character of Oxygen Transfer from Peroxomolybdenum (VI) to Sulphides
No full textThe effect of the addition of HMPT on the oxidation rates of p-chlorophenylmethyl sulphide and of a series of phenyl-substituted arylmethyl sulphides with hydrogen peroxide in the presence of catalytic amounts of MoO2(acac)2 in ethanol at 25 °C was studied. HMPT added at relatively low concentration inhibits the oxidation of p-ClC6H4SCH3, whereas at higher HMPT the oxidation rates become independent of its concentration. Under these conditions the substituent effect on the oxidation rates of the set of arylmethyl sulphides follows the Hammett free-energy relationship (p = -0.7) contrary to the complex behaviour observed previously. These findings, while ruling out the possibility that the oxidation occurs at the complexed sulphide, strongly support the electrophilic mechanism for these oxidation reactions. © 1982
Oxo-Peroxo Oxygen Exchange in Peroxovanadium(V) and Peroxomolybdenum(VI) Compounds
No full textAbstrac
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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