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'Oxyl Radicals' in keywords Facet   section ZfN Section B  [X]
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1985 (1)
1984 (2)
1983 (1)
1Author    Eberhard Bothe, Nien Man, Dietrich Schuchmann, Schulte-Frohlinde, Clemens Von SonntagRequires cookie*
 Title    Hydroxyl Radical-Induced Oxidation of Ethanol in Oxygenated Aqueous Solutions. A Pulse Radiolysis and Product Study  
 Abstract    y-Radiolysis of N20-saturated water or photolysis of aqueous H2O2 provided a source of OH radicals. These radicals react with ethanol by preferentially abstracting an H atom at C-l. In the presence of oxygen these radicals are converted into the corresponding peroxyl radicals. The a-hydroxyethylperoxyl radicals decay by first order kinetics (k = ki + k2 [OH -]) acetaldehyde and H02/H+ + 01 being the products (ki (20 °C) = 50 ± 10 s" 1 , Ea = 66 ± 7 kJ-mol -1 , k2= (4± 1) X 10 9 M -1 s -1). In competition (favoured by low pH, low tem-perature and high dose rate) they also decay by second order kinetics (2k3 = (7 ^ 2) x 10 8 M~ 1 s _1). The most important route in the bimolecular decay leads to acetaldehyde, acetic acid and oxygen (ca. 75%). This route might largely be concerted (Russell mech-anism), but there might also be a contribution from the disproportionation of oxyl radicals within the solvent cage. There is also a concerted route that leads to two molecules of acetic acid and to hydrogen peroxide (ca. 10%). Another pathway (ca. 15%) yields two oxyl radicals and oxygen. The former may either decompose into formic acid and methyl radicals (ca. 5%) or rearrange into 1,1-dihydroxyethyl radicals (ca. 10%). These radicals add oxygen and the resulting peroxyl radicals rapidly decompose into acetic acid and HO2. The reaction of a-hydroxyethylperoxyl radicals with H02/02 radicals appears to be slow (k» 10 7 M-is-i). 
  Reference    Z. Naturforsch. 38b, 212—219 (1983); received September 28 1982 
  Published    1983 
  Keywords    Pulse Conductometry, Peroxyl Radicals, Oxyl Radicals, Radical Rearrangements, Radiation Chemistry 
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 TEI-XML for    default:Reihe_B/38/ZNB-1983-38b-0212.pdf 
 Identifier    ZNB-1983-38b-0212 
 Volume    38 
2Author    Heinz-Peter Schuchmann, Clemens Von SonntagRequires cookie*
 Title    Methylperoxyl Radicals: A Study of the y-Radiolysis of Methane in Oxygenated Aqueous Solutions  
 Abstract    A product study has been made of the y-radiolysis of aqueous methane solutions that also contained nitrous oxide and oxygen. Formaldehyde (G = 2.8), hydrogen peroxide (G = 2.1), methanol (G = 1.5), methylhydroperoxide (G = 0.8), formic acid (G = 0.3), and dimethylper-oxide (G = 0.1) were found. In alkaline solutions (pH 8, 10-3 M phosphate buffer), the formal­ dehyde yield rises to G = 3.2, while the formic acid yield falls to almost zero (G = 0.05). The initial precursor of the carbon-containing products is the methylperoxyl radical. The methyl­ peroxyl radicals decay through a short-lived tetroxide along various pathways. The most promi­ nent one leads to formaldehyde, methanol and oxygen. Methoxyl radicals (and oxygen) are also formed and, after rearrangement into hydroxymethyl radicals and their conversion into hy-droxymethylperoxyl radicals, eventually yield formic acid and probably further formaldehyde. A route to formaldehyd and hydrogen peroxide is also envisaged. Methylhydroperoxide is formed in the reaction of methylperoxyl radicals with H 0 2 / 0 27 radicals (from radiolytic H atoms and the unimolecular decay of the hydroxymethylperoxyl radical). 
  Reference    Z. Naturforsch. 39b, 217 (1984); received September 19 1983 
  Published    1984 
  Keywords    Autoxidation, Peroxyl Radicals, Oxyl Radicals, Radical Rearrangements, Radiation Chemistry 
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 TEI-XML for    default:Reihe_B/39/ZNB-1984-39b-0217.pdf 
 Identifier    ZNB-1984-39b-0217 
 Volume    39 
3Author    Alicja Piesiak, M. An, Nien Schuchmann, Henryk Zegota, Clemens Von SonntagRequires cookie*
 Title    ß-Hydroxyethylperoxyl Radicals: A Study of the y-Radiolysis and Pulse Radiolysis of Ethylene in Oxygenated Aqueous Solutions  
 Abstract    Hydroxyl radicals (and H atom s) generated in the radiolysis of N20-co n tain in g w ater add to ethylene forming /3-hydroxyethyl radicals (and ethyl radicals). In the presence of oxygen these are converted into the corresponding peroxyl radicals which decay bim olecularly (2 k — 2 x 108 M ~'s-1) as m easured by pulse radiolysis. The m ajor products (G values in brackets) are glycolaldehyde (3.3), form aldehyde (1.6), ethylene glycol (0.8), acetaldehyde (0.5), organic peroxidic m aterial (0.5), and hydrogen peroxide (2.4) (dose rate 0.26 Gy s-1, pH 5.6). A m aterial balance has been obtained with respect to the primary w ater radicals (6.0) and oxygen uptake (4.8). The products and their yields can be accounted for if in the rate determ ining step atetro x id e is form ed which decomposes via three m ajor pathways leading to; (i) H 20 2 and two m olecules of glycolaldehyde (ca. 45%), (ii) 0 2, glycolaldehyde and ethylene glycol (ca. 30%), and (iii) 0 2, two molecules of form aldehyde and two C H 2OH radicals (ca. 15%). A 1,2-H shift of interm ediate oxyl radicals is unim portant in this system. 
  Reference    Z. Naturforsch. 39b, 1262—1267 (1984); received March 5 1984 
  Published    1984 
  Keywords    Peroxyl Radicals, Oxyl Radicals, Pulse Radiolysis, Ethylene, Reaction Kinetics 
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 TEI-XML for    default:Reihe_B/39/ZNB-1984-39b-1262.pdf 
 Identifier    ZNB-1984-39b-1262 
 Volume    39 
4Author    Nien Man, Henryk Schuchmann, Zegota, Clemens Von SonntagRequires cookie*
 Title    Acetate Peroxyl Radicals, 0 2 CH 2 C0;: A Study on the y-Radiolysis and Pulse Radiolysis of Acetate in Oxygenated Aqueous Solutions  
 Abstract    Hydroxyl radicals from the radiolysis of N 2 0/0 2 (4:1 v/v)-saturated aqueous solutions have been reacted with acetate ions (1CT 2 M). As measured by pulse radiolysis, the resulting "CH 2 C0 2 radicals react with oxygen yielding the corresponding peroxyl radicals, 0 2 CH 2 C0 2 (k = 1.7 x 10 9 M-V 1). These peroxyl radicals decay bimolecularly (2k = 1.5 x 10 8 M _1 s _1) giving rise to the products (G values in brackets) glyoxylic acid (2.7), glycolic acid (0.7), formaldehyde (1.4), carbon dioxide (1.4), organic hydroperoxide (0.7) and hydrogen peroxide (2.5). Oxygen is consumed with a G value of 5.3. Aided by data from pulse radiolysis it is concluded that the intermediate tetroxide formed upon the bimolecular decay breaks down by various routes to yield: (i) hydrogen peroxide and two molecules of glyoxylic acid (ca. 27%); (ii) oxygen, glycolic acid and glyoxylic acid (ca. 25%); (iii) hydrogen peroxide and two molecules of formaldehyde, carbon dioxide and OH~ (25%). These reactions do not involve free radicals as intermediates; (iv) There is some 0 2 (G = 0.5) formed in the decay of the peroxyl radicals, which is attributed to the decay of intermediate oxyl radicals (tetroxide —* • 0 2 + 2 0CH 2 C0 2) by 1,2-H shift, oxygen addition and H0 2 elimination, a reaction sequence which gives rise to glyoxylic acid (10%); (v) The reaction of 0 2 with the organic peroxyl radical yields the hydroperoxide (13%). Reaction (iii) is a novel peroxyl radical reaction. 
  Reference    Z. Naturforsch. 40b, 215—221 (1985); received October 24 1984 
  Published    1985 
  Keywords    Acetic Acid, Peroxyl Radicals, Oxyl Radicals, Superoxide Radicals, Pulse Radiolysis 
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 TEI-XML for    default:Reihe_B/40/ZNB-1985-40b-0215.pdf 
 Identifier    ZNB-1985-40b-0215 
 Volume    40