Showing papers on "Disproportionation published in 1983"
TL;DR: In this paper, a theoretical study of the 2 e, 2H+ reaction is presented for a surface reaction (adsorbed species, Langmuir isotherm or monolayer-modified electrode), or for a heterogeneous electrochemical reaction with protonations taking place in solution near the electrode.
163 citations
TL;DR: In this paper, a selective disproportionation of ethylbenzene, yielding benzene and diethylbenzenes in the ratio 1 : 1, was carried out in a micro flow reactor over various faujasite-type zeolites, hydrogen L zeolite and hydrogen ZSM-5.
93 citations
TL;DR: A series of water-soluble metalloporphyrins has been prepared and the redox chemistry investigated by electrochemical and pulse radiolytic techniques as mentioned in this paper, and cyclic voltammetry showed that the compounds undergo well defined reduction and oxidation steps, although the oxidation processes were not really reversible.
Abstract: A series of water-soluble metalloporphyrins has been prepared and the redox chemistry investigated by electrochemical and pulse radiolytic techniques. All of the metalloporphyrins exhibit reasonably intense absorption transitions (upsilon = ca. 2 x 10/sup 4/ dm/sup 3/ mol/sup -1/ cm/sup -1/) in the visible region and a strong absorption (upsilon = (2-7) x 10/sup 5/ dm/sup 3/ mol/sup -1/ cm/sup -1/) around 430 nm. Cyclic voltammetry showed that the compounds undergo well-defined reduction and oxidation steps, although the oxidation processes were not really reversible. For diamagnetic metalloporphyrins, the difference in E/sub 1/2/ between addition and removal of an electron for a particular compound was 2.05 +/- 0.20 V while the difference in E/sub 1/2/ between addition of one and two electrons was 0.28 +/- 0.12 V. Similarly, E/sub 1/2/ for the removal of a second electron from the porphyrin ..pi.. system was some 0.25 +/- 0.10 V higher than that for removal of the first electron. These findings are consistent with the central metal ion exerting only an inductive effect upon the porphyrin ..pi.. levels. The absorption spectra of the one-electron reduction and oxidation products were recorded by pulse radiolysis methods. Both products exhibit broad absorption transitions stretching across themore » entire visible and near-IR regions. The reduction products were identified as ..pi..-radical anions and, in many cases, these were unstable with respect to disproportionation. The oxidation products were identified as ..pi..-radical cations and these were also unstable in aqueous solution but the decay route remains obscure. 44 references, 6 figures, 3 tables.« less
92 citations
TL;DR: In this paper, the 2 e, 1H+ reaction was studied for a surface reaction (adsorbed species, Langmuir isotherm, or monolayer-modified electrodes) or for a heterogeneous electrochemical reaction with protonations occurring in solution near the electrode.
70 citations
TL;DR: In this article, the photochemistry of meso and d,l isomers of 2,4-diphenylpentan-3-one (DPP), of 1,3,4triphenylbutan-2-one, and of a-MeDBK has been investigated in homogeneous solvents and in "super-cage" environments that impose constraints on the diffusional displacements of the components of geminate radical pairs and thereby enhance the efficiency of cage reactions.
Abstract: The photochemistry of the meso and d,l isomers of 2,4-diphenylpentan-3-one (DPP), of 1,3,4-triphenylbutan-2-one (TPB), and of 1,3-diphenylbutan-2-one (a-MeDBK) has been investigated in homogeneous solvents and in "super-cage" environments that impose constraints on the diffusional displacements of the components of geminate radical pairs and thereby enhance the efficiency of cage reactions of geminate pairs. Solutions of ionic detergents containing micelles, porous glass, and porous silica provide examples of such super-cage environments. The major course of reaction in the photolysis of DPP in pentane or benzene is decarbonylation followed by coupling (-93%) or disproportionation ( N 3%) of PhCHCH3 radicals. In super-cage environments, the extent of disproportionation increases significantly, as does diastereomeric interconversion. Although temperature effects (in the range 25 to -77 "C) on the product of DPP are small for photolysis in homogeneous solution, substantial variations in product ratios with variation in temperature can be achieved when the photolyses are conducted in super-cage environments. Similarly, although magnetic field effects on the product distributions are negligibly small for photolysis in homogeneous solutions, significant variations are found for photolysis of DPP in super-cage environments. The general features of the results with DPP are analogous to those observed for photolysis of TPB and a-MeDBK. A scheme based on the established photochemistry of dibenzyl ketone is proposed which provides a working mechanism that is consistent with all of the observations of this investigation.
70 citations
67 citations
TL;DR: Reduction de diaryl 1,2 dibromo-1,2 ethanes en derives ethyleniques (le groupe aryl pouvant etre un groupe pyridyl) as mentioned in this paper.
Abstract: Reduction de diaryl-1,2 dibromo-1,2 ethanes en derives ethyleniques (le groupe aryl pouvant etre un groupe pyridyl)
58 citations
TL;DR: On H-mordenite, butane isomerizaton occurs through a disproportionation process, and the limiting step is the formation of a dimer species as mentioned in this paper, but hydrogen has no influence on the reaction mechanism but improves the stability of the catalyst by reducing coke formation.
Abstract: On H-mordenite, butane isomerizaton occurs through a disproportionation process. The limiting step is the formation of a dimer species. Hydrogen has no influence on the reaction mechanism but improves the stability of the catalyst by reducing coke formation.
57 citations
TL;DR: In this article, the authors reported the disproportionation of diphenylcarbinol over alumina to yield benzaldehyde, toluene, and water, in addition to the expected dehydration to the ether.
45 citations
TL;DR: In this article, the catalytic activity of mordenite zeolite for the disproportionation and transalkylation reaction of toluene was studied in a continuous fixed-bed reactor system.
42 citations
Patent•
10 Mar 1983TL;DR: In this paper, a method for treating modified ZSM-5 type zeolite catalysts with a vapor phase organophosphorus reagent such as trimethylphosphite or dimethylmethylphosphonate in order to improve the para-selective properties of such catalysts for the conversion of aromatic materials is provided.
Abstract: A method is provided for treating modified ZSM-5 type zeolite catalysts with a vapor phase organophosphorus reagent such as trimethylphosphite or dimethylmethylphosphonate in order to improve the para-selective properties of such catalysts for the conversion of aromatic materials. The modified zeolites so treated are those which contain a minor proportion of a difficultly reducible oxide such as magnesium oxide, calcium oxide and/or phosphorus oxide. Such catalyst compositions can be used in alkylation, transalkylation or disproportionation processes to provide alkylated aromatic product mixtures having exceptionally high concentrations of the para-dialkylbenzene isomer.
TL;DR: In this paper, the acidity of the bifunctional zeolite catalysts used for the disproportionation of ethylbenzene to benzene and diethylbenzenes is discussed.
TL;DR: In this paper, the acid strength distribution and catalytic behavior in the disproportionation of toluene of HZSM-5 zeolites with varying SiO2/Al2O3 ratios and calcined at different temperatures have been studied.
TL;DR: The rate constants predicted by the derived rate laws, as the concentrations of substrate and Cl– ion change, are in excellent agreement with the observed rate constants thus further verifying the rate laws and hence the proposed mechanisms.
Abstract: Available data on the kinetics of oxidations of amino-acids by sodium N-chloro toluene-p-sulphonamide (chloramine T) in acid and alkaline media have been critically examined. General mechanisms have been proposed for both acid and alkaline medium oxidations. The oxidation process in acid media has been shown to proceed via two paths, one involving the direct interaction of N-chlorotoluene-p-sulphonamide (RNHCl) with the neutral amino-acid in a slow step leading to the formation of the monochloroamino acid which subsequently interacts with another molecule of RNHCl, in a fast step, to give the NN-dichloroamino-acid which in turn undergoes molecular rearrangement and elimination to yield the products, and the other involving the interaction of Cl2 or H2OCl+, produced from the disproportionation of RNHCl in the presence or absence of Cl–, with the substrate to give the products. In the alkaline medium mechanisms involving the interaction of RNHCl, HOCl, RNCl–, and OCl– with the substrate are proposed. The mechanisms proposed and the derived rate laws are consistent with the observed kinetics. The rate constants predicted by the derived rate laws, as the concentrations of substrate and Cl– ion change, are in excellent agreement with the observed rate constants thus further verifying the rate laws and hence the proposed mechanisms.
TL;DR: In this article, a thermodynamic approach of the carbon-oxygen-iron cobalt alloy system predicts that a maximum expansion of the domain of stability of the metallic phase would be obtained with an alloy containing 50% cobalt, 50% iron.
TL;DR: In this paper, the rate of CO disproportionate catalysed by filings of an iron-cobalt alloy (49wt% Co, 49wt% Fe, 2wt% V) has been studied between 400°C and 650°C using C0 C0 2 mixtures ranging from 95% CO, 5% CO 2 to 35% CO.
TL;DR: In this article, the formation of metastable γ-Fe has also been conformed both by TEM and Mossbauer spectroscopy, and the mechanism of growth of the carbon filament is discussed.
TL;DR: In addition to dimerization and polymerization of samples as previously suggested, it appears that during FAB-MS, reactions in the sample matrix can occur to yield new compounds that are recombinations of molecular fragments.
TL;DR: In aprotic and aqueous media the proton-induced disproportionation of superoxide ion (O−2) yields a variety of reactive species (HO2·, H2O2, HO−2, and · OH) as mentioned in this paper.
Abstract: In aprotic and aqueous media the proton-induced disproportionation of superoxide ion (O−2) yields a variety of reactive species (HO2·, H2O2, HO−2, and · OH). In aprotic media O−2 rapidly degrades polychlorinated hydrocarbons (CCl4, HCCl3, and DDT) to oxygenated products (CCl4 Cl3COO·; HCCl3 Cl2C: and Cl2C=O). Alkyl halides react more slowly (BuCl BuOO· and BuOO−). Formation of O−2 in the presence of methyl viologen (MV2+), reduced flavins, esters, and low-valent transition metal complexes results in the formation of reactive oxygenating agents and reaction mimics for oxygenases [MV+-OO-, 4a-hydroperoxyflavins, RC(O)OO−, and Zn11(O2 ·)+]. Kinetic data for the proton-induced disproportionation of O−2 in water and the nucleophilic reactions of O−2 in aprotic solvents lead to the conclusion that the latter are probably of little significance for biological oxygenation reactions.
TL;DR: In this paper, the catalytic activities in CO disproportionate of iron-cobalt alloys of various composition have been compared to the activities of the pure metals at 600°C using a C 0 C 0 2 2 gas mixture (75% CO).
TL;DR: The species py 4 Cu 4 CI 4 O 2 is an active initiator for phenolic oxidative by dioxygen while its disproportionation product py 4Cu 4 CI 6 O is not as discussed by the authors.
TL;DR: The bis(triphenylphosphine)(η 3 -crotyl)nickel cation is a catalyst precursor for the oligomerisation of butadiene to cyclic or linear dimers.
TL;DR: In this article, the primary photochemical processes of magnesium tetraphenylporphyrin in micellar and microemulsion solutions were compared, and a disproportionation was observed between a triplet ground state reaction of two porphyrins.
TL;DR: In this paper, the sorption properties of a series of HZSM-5 catalysts prepared by varying the initial pH of the synthetic mixture were reported, and the variation in catalytic activity and selectivity was observed in reactions such as xylene isomerization, toluene disproportionation and toluenes alkylation with methanol and ethanol.
TL;DR: In this article, a deoxygenation mechanism was proposed on the basis of experimental evidence for 2-Melhyl-3-oxo-indolin-1-oxyl with trifluoroacetic acid.