Showing papers on "Disproportionation published in 1973"

Kinetics and mechanism of the oxidation of thiosulphate ions by copper(II) ions in aqueous ammonia solution

Abstract: Copper(II) ions in aqueous ammonia solution oxidize thiosulphate ions initially to tetrathionate ions; the latter then undergo a subsequent disproportionation reaction to yield trithionate and thiosulphate ions. The detailed kinetics of the reaction suggest a mechanism which involves substitution of thiosulphate ion into the co-ordination sphere of a triamminecopper(II) complex in the rate-determining step. A one-equivalent electron transfer from the thiosulphate to the copper(II) ion, occurring in the intermediate triamminecopper(II)–thiosulphate complex, gives rise to copper(I) and S2O3– ions, the latter dimerizing to tetrathionate ions.

Chemically Induced Dynamic Nuclear Polarization XI. Intermediary vinyl alcohol during photochemical reactions of acetaldehyde and of acetoin

Abstract: Vinylalcohol, formed by disproportionation of α-hydroxyethyl radicals, is detected by NMR. spectroscopy during photoreactions of acetaldehyde and acetoin in solution and slowly tautomerizes to acetaldehyde.

Olefin disproportionation catalyst

Abstract: A catalyst for the olefin disproportionation of unsaturated hydrocarbons is provided comprising a physical mixture of a solid disproportionation catalyst and a double bond isomerization catalyst wherein the double bond isomerization catalyst is further treated with a base.

The Enol of Acetone during Photochemical Reactions of 3‐Hydroxy‐3‐methyl‐2‐butanone and of Acetone

Abstract: The enol of acetone, formed by disproportionation reactions of 1-hydroxy-1-methylethyl radicals, is detected by NMR, spectroscopy during photoreactions of 3-hydroxy-3-methyl-2-butanone in acetonitrile and of acetone in 2-propanol and slowly tautomerizes to acetone. The photolysis of 3-hydroxy-3-methyl-2-butanone is shown to proceed via Type I cleavage, predominantly from an excited triplet state.

Direct and sensitized photolysis of dimethyl sulphoxide in solution

Abstract: Excitation (2537 A 112 kcal/mole) of dimethyl suiphoxide (DMSO) in solution leads to singlet excited DMSO (E5 = 105 kcal/mole) that undergoes three primary reactions: fragmentation to methyl and methanesuiphinyl radicals, a bimolecular disproportionation reaction to dimethyl sulphone and dimethyl sulphide by a reaction with a ground state DMSO molecule at higher DMSO concentrations, and deactivation to DMSO ground state molecules. The triplet state of DMSO (ET = 83 ± 3 kcal/mole), if formed at all, appears to be chemically inert. At relatively dilute DMSO solutions, the fragmentation (D = 53 kcal/mole) occurs with a quantum yield of 0.14 which is independent of the nature of the solvent (acetonitrile, alcohols, water), of the viscosity of the solvents as well as of the pH of the solvents. No H/D and 160/180 exchanges take place thermally or photochemically under the reaction conditions applied. In acetonitrile, the radicals formed in the primary reactions abstract hydrogen atoms from the solvent; in water, electron transfer from methanesulphinyl radical to methyl radical proceeds thereby producing solvated ions, whereas both these reactions occur in alcohols depending upon the alcohols' ability to stabilize such ions. Methanesulphinyl radicals are able to undergo various reactions: they abstract hydrogen from acetonitrile and alcohols, they dimerize in neat DMSO, they transfer an electron to methyl radicals in water, and they add to an aromatic system such as benzene. Methyl radicals, however, were found to undergo exclusively hydrogen abstraction except in water where they accept an electron from the methanesulphinyl radical. DMSO proved itself as a very poor hydrogen donor. Only during photolysis of neat DMSO was the appearance of 'dimsyl' radicals, CH3SOCH2, apparent; their major reaction under these conditions is fragmentation to formaldehyde and methanesuiphenyl radicals. A qualitative as well as a quantitative analysis of all the products formed in neat DMSO and in various solvents has been made; the reaction sequences that ar assumed to follow the primary processes can quantitatively account for all the products observed such as methane, methanesulphonic acid, dimethyl disuiphide, dimethyl suiphide, and methyl methanethiolsuiphonate. Photolysis of DMSO can be sensitized by benzene and toluene whereas p-cymene, tetralin, mesitylene, acetone, and benzophenone are incapable of doing so. Fluorescence quenching of benzene by DMSO and the inefficiency of cyclohexene to quench the benzene-sensitized photolysis of DMSO show that singlet—singlet energy transfer and decomposition of the singlet excited DMSO take place. The kinetics of the methane formation (methanesuiphinyl Present address: Institut fur Organische Chemie der Universitat Munchen, 8000 Munchen 2, Karlstrasse 23, Germany.

Electron paramagnetic resonance study of catalysts derived from molybdenum hexacarbonyl

Abstract: E.p.r. spectroscopy has been used to study supported molybdenum hexacarbonyl olefin dispproportionation catalysts. Activation of silica and alumina supported catalysts causes the appearance of a signal attributed to molybdenum(V) in square pyramidal co-ordination. Exposure of activated catalysts to oxygen gives a signal due to O–2, probably formed by electron transfer from tetrahedrally co-ordinated molybdenum(V). A second strongly adsorbed O–2 species obtained on alumina supported catalysts is associated with exposed aluminium ions in the support. The square pyramidal molybdenum(V) species cannot be correlated with the activity of the catalysts for propene disproportionation, and it is suggested that the active species is a precursor of the tetrahedral molybdenum(V), possibly molybdenum(IV).

A kinetic model of persulfate–bisulfite‐initiated acrylonitrile polymerization

Abstract: The molecular weight distribution has been derived for a homopolymer polymerized in a continuous-feed reactor under homogeneous conditions. The derived equations are then compared with data obtained on polymers of acrylonitrile–co(vinyl acetate) prepared under heterogeneous conditions with the potassium peroxydisulfate–sodium bisulfite–iron redox system. The termination reaction is assumed to be effected completely by recombination of active radicals with no disproportionation. The only transfer reaction considered is the transfer-to-activator reaction The transfer and termination reactions produce polymers with different acid groups as endgroups. Each molecule, on the average, contains one sulfonate group, whereas the concentration of sulfate groups depends upon the extent of the transfer-to-activator reaction. The basic dye acceptance of the polymer depends on the number of acid groups in the polymer and hence on the activator and catalyst concentrations. Analysis of the basic dye acceptance and conversion data at a variety of catalyst and activator concentrations yields the following parameters at 50°C: kp/k = 1.01 (1./mole sec)1/2, ktr/kp = 0.2063, and k1 [see eq. (1)] = 50.7 l./mole sec. Owing to the heterogeneous nature of the polymerization, the weight-average molecular weight of the polymer depends only on the activator concentration and the conversion and not directly on the catalyst concentration as predicted.

Flash photolysis studies in a time‐of‐flight mass spectrometer. I. Divinyl ether and reactions of the vinyl and vinoxy radicals

Abstract: The lower pressure flash photolysis of divinyl ether has been monitored by time‐of‐flight mass spectrometry. The primary photodecomposition process is restricted essentially to the formation of vinyl and vinoxy radials: C2H3OC2H3→C2H3+C2H3O. The vinyl radical (m/e=27) has been observed directly and its 2nd order decay constant measured. The decay is primarily by disproportionation 2C2H3→C2H4+C2H2 and k10 has an average value of 5.3± 0.5× 10−12cc molecule−1·sec−1 over the pressure range studied (65–200 mtorr). The vinoxy radical has not been observed directly in this work. Our results favor a rapid isomerization, followed by decomposition C2H3O⇄CH3CO→CH3+CO. A mass balance is achieved within 400 μsec of the photolysis flash and a mechanism proposed to account for the major (C2H4, C2H2, CO) and the minor products (CH4, C2H6, 2‐butenal, acetaldehyde, and ketene).

Disproportionation of saturated hydrocarbons employing a catalyst that comprises platinum and tungsten

Abstract: A process for disproportionation of saturated hydrocarbons which comprises contacting the saturated hydrocarbons in a disproportionation reaction zone and in the presence of no more than 5 weight percent olefins with a catalyst mass comprising a platinum component and a tungsten component, wherein the volumetric ratio of the platinum component to the tungsten component is greater than 2:7 and less than 7:2. Preferably the volumetric ratio of the platinum component to the tungsten component is between 3:7 and 10:7, and the reaction is preferably carried out at a temperature between 400* to 800*F.