Photobehavior of aqueous uranyl ion and photo-oxygenation of isobutane using light from the visible region

2003 ◽  
Vol 81 (3) ◽  
pp. 219-229 ◽  
Author(s):  
Trevor M Bergfeldt ◽  
William L Waltz ◽  
Xiangrong Xu ◽  
Petr Sedlák ◽  
Uwe Dreyer ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Perchloric Acid ◽  
Rate Constants ◽  
Butyl Alcohol ◽  
Uranyl Ion ◽  
Quantum Yields ◽  
Tert Butyl ◽  
Tert Butyl Alcohol ◽  
Butyl Radical ◽  
Electronically Excited

The photochemical and photophysical behavior of the aqueous uranyl ion [UO2(H2O)5]2+ has been studied under the influence of visible light and with added perchloric acid over the range of 0.01–4 M. In the presence of 2-methylpropane (isobutane), photo-oxygenation of isobutane occurs to yield, as the major product, 2-methyl-2-propanol (tert-butyl alcohol) along with lesser amounts of 2-methyl-2-propene (isobutene) and other C1–C8 products. The quantum yield for formation of tert-butyl alcohol is independent of light intensity at the irradiation wavelength of 415 nm and of uranyl concentration, but it increases from 0.016 ± 0.001 at 0.01 M HClO4 (pH 2) to 0.13 ± 0.01 at 4 M HClO4. The emission spectrum from the electronically excited uranyl ion and the associated quantum yields have been measured in the presence and absence of isobutane, as a function of added perchloric acid. While in both cases the shape of the spectrum remains invariant, the quantum yields increase with increasing perchloric acid concentration. The strong dependence on added perchloric acid is interpreted within the context of the presence and interconversion of two electronically excited species, an acid form, *[UO2(H2O)5]2+, and a base form, *[UO2(H2O)n(OH)]+. It is proposed that both forms react with isobutane to give a tert-butyl radical, and that oxidation of coordinated aqua ligands occur, the latter generating a hydroxyl radical whose reaction with isobutane rapidly leads also to a tert-butyl radical. The reaction of this alkyl radical with ground-state [UO2(H2O)5]2+ then gives rise to the stable tert-butyl alcohol product and reduced forms of uranyl ion. Based upon the values of the quantum yields and of excited-state lifetime measurements reported in the literature, a comprehensive mechanism has been developed in a quantitative manner to provide calculated values of the rate constants for the individual mechanistic steps. The calculated rate constants provide a basis to calculate the values of quantum yields for emission and chemical reaction, as well as for lifetimes, that agree very satisfactorily with the experimental values over a 400-fold concentration change in added perchloric acid.Key words: photo-oxidation, photo-oxygenation, uranyl ion, isobutane, tert-butyl alcohol, lifetime, quantum yield, acid–base dissociation.

The Charge Transfer Photochemistry of the Hexaaquoiron(III) Ion, the Chloropentaaquoiron(III) Ion, and the µ-Dihydroxo Dimer Explored with tert-Butyl Alcohol Scavenging

1975 ◽  
Vol 53 (16) ◽  
pp. 2430-2435 ◽  
Author(s):  
Cooper H. Langford ◽  
John H. Carey
Keyword(s):  
Charge Transfer ◽  
Quantum Yield ◽  
Butyl Alcohol ◽  
Extinction Coefficients ◽  
Photochemical Processes ◽  
Tert Butyl ◽  
Tert Butyl Alcohol ◽  
Radical Yield

There have been several studies of the charge transfer photochemistry of aqueous Fe3+ but the complexity of hydrolytic equilibria and the requirement for scavengers to render the primary photochemical processes observable has left several issues moot as recent reports show. Using tert-butyl alcohol as a scavenger, it is shown that (at 35 °C), charge transfer irradiation at 254 nm of Fe(OH2)63+ gives free •OH with a quantum yield of 0.065, charge transfer irradiation of Fe(OH2)5Cl2+ at 350 nm gives free Cl• with a quantum yield of 0.093, and that as a result of the combined patterns of extinction coefficients and hydrolytic equilibria it is difficult to make Fe(OH2)5OH + the main absorbing species at either wavelength. The dihydroxo-bridged dimer gives only a small radical yield. The scavenger, tert-butyl alcohol, appears to react with •OH or Cl• to give •CH2—C(CH3)2OH which, on reaction with a second Fe(OH2)63+ gives HOCH2C(CH3)2OH.

The reactivity of allyl and propargyl alcohols with solvated electrons: temperature and solvent effects

1979 ◽  
Vol 57 (8) ◽  
pp. 839-845 ◽  
Author(s):  
Alexei M. Afanassiev ◽  
Kiyoshi Okazaki ◽  
Gordon R. Freeman
Keyword(s):  
Activation Energy ◽  
Ethylene Glycol ◽  
Rate Constants ◽  
Allyl Alcohol ◽  
Trap Depth ◽  
Activation Energies ◽  
Butyl Alcohol ◽  
Solvated Electrons ◽  
Tert Butyl ◽  
Tert Butyl Alcohol

The rate constants k1 for the reaction of solvated electrons with allyl alcohol in a number of hydroxylic solvents differ by up to two orders of magnitude and decrease in the order tert-butyl alcohol > 2-propanol > 1-propanol ≈ ethanol > methanol ≈ ethylene glycol > water. In methanol and ethylene glycol the rate constants (7 × 107 M−1 s−1 at 298 K) and activation energies (16 kJ/mol) are equal, in spite of a 32-fold difference in solvent viscosity (0.54 and 17.3 cP, respectively) and 3-fold difference in its activation energy (11 and 32 kJ/mol, respectively). The reaction in tert-butyl alcohol is nearly diffusion controlled and has a high activation energy that is characteristic of transport in that liquid (E1 = 31 kJ/mol, Eη = 39 kJ/mol). The activation energies in the other alcohols are all 16 kJ/mol, and it is 14 kJ/mol in water. They do not correlate with transport properties. The solvent effect is connected primarily with the entropy of activation. The rate constants correlate with the solvated electron trap depth. When the electron affinity of the scavenger is small, a favorable configuration of solvent molecules about the electron/scavenger encounter pair is required for the electron jump to take place. The behavior of the rate parameters for propargyl alcohol is similar to that for allyl alcohol, but k1, A1, and E1 are larger for the former. The ratio k(propargyl)/k(allyl) at 298 K equals 10.5 in water and decreases through the series, reaching 1.3 in tert-butyl alcohol. Rate parameters for several other scavengers are also reported.

Solvolysis of 2-substituted-9-(otrho-substituted phenylmethyl)fluoren-9-yltrimethylammonium ions in various solvents. The effect of steric crowding on alkene formation

1986 ◽  
Vol 64 (6) ◽  
pp. 1060-1071 ◽  
Author(s):  
Peter James Smith ◽  
Jyotsna Pradhan
Keyword(s):  
Rate Constants ◽  
Isotope Effects ◽  
Butyl Alcohol ◽  
Reaction Proceeding ◽  
Tert Butyl ◽  
Tert Butyl Alcohol ◽  
Leaving Group ◽  
Steric Crowding ◽  
Hydrogen Deuterium ◽  
Deuterium Isotope Effects

The solvolytic reaction of several 9-(ortho-substituted phenylmethyl)fluoren-9-yltrimethylammonium salts has been investigated in several different solvents. Substitution and elimination products were found for the reactions in all the solvents studied, with the exceptions that reaction in both tert-butyl alcohol and chloroform led exclusively to the alkene product. The observed rate constants for alkene formation and the percent alkene were measured and it was found that the di-ortho compounds reacted at a faster rate but produced less alkene than the reaction of the corresponding mono-ortho salts. Hydrogen–deuterium isotope effects were also determined for the various reactions. The results are discussed in terms of the reaction proceeding by way of the E1 mechanism, where steric acceleration promotes the loss of the bulky ammonium leaving group to give the carbocation intermediate.

scholarly journals Mechanism of protection of adenosine from tert-butoxyl radicals and repair of adenosine radicals by α-tocopherol in aqueous solution

2014 ◽  
Vol 7 (1) ◽  
Author(s):  
G. Vijayalakshmmi ◽  
M. Adinarayanna ◽  
P. Jayaprrakash Rao
Keyword(s):  
Aqueous Solution ◽  
Rate Constant ◽  
Butyl Alcohol ◽  
Quantum Yields ◽  
Oh Radicals ◽  
Butyl Hydroperoxide ◽  
Tert Butyl ◽  
Tert Butyl Hydroperoxide ◽  
Tert Butyl Alcohol

The rates of oxidation of adenosine and α-tocopherol by tert-butoxyl radicals (t-BuO•) were studied spectrophotometrically. Radicals (t-BuO•) were generated by the photolysis of tert-butyl hydroperoxide (t-BuOOH) in presence of tert-butyl alcohol to scavenge •OH radicals. The rates and the quantum yields () of oxidation of α-tocopherol by t-BuO• radicals were determined in the absence and presence of varying concentrations of adenosine. An increase in the concentration of adenosine was found to decrease the rate of oxidation of α-tocopherol, suggesting that adenosine and α-tocopherol competed for t-BuO• radicals. From competition kinetics, the rate constant of α-tocopherol reaction with t-BuO• was calculated to be 7.29 x 108 dm3 mol-1 s-1. The quantum yields expt and cal values suggested that α-tocopherol not only protected adenosine from t-BuO• radicals, but also repaired adenosine radicals, formed by the reaction of adenosine with t-BuO• radicals.

The photoreduction of hexaaquoiron(III) perchlorate in the presence of tertiary aliphatic alcohols. The effect of added copper

1977 ◽  
Vol 55 (7) ◽  
pp. 1207-1212 ◽  
Author(s):  
John H. Carey ◽  
Barry G. Oliver ◽  
Cooper H. Langford
Keyword(s):  
Quantum Yield ◽  
Outer Sphere ◽  
Butyl Alcohol ◽  
Amyl Alcohol ◽  
Quantum Yields ◽  
Direct Reaction ◽  
Tertiary Butyl ◽  
Tert Butyl Alcohol ◽  
Hydroxyalkyl Radicals ◽  
Good Agreement

The irradiation of ferric perchlorate in the presence of tert-amyl alcohol produces Fe(II) with a quantum yield of 0.110 ± 0.002, 12% lower than the yield obtained when tert-butyl alcohol was used as scavenger. Other tertiary alcohols studied, 3-methyl-2-pentanol and 3-ethyl-3-pentanol, exhibited similar lower yields. It is shown that this reduction is due to the formation of γ-hydroxyalkyl radicals which do not reduce ferric ion to ferrous. The addition of copper causes these radicals to be oxidized. The Fe(II) quantum yield for the irradiation with tertiary amyl alcohol as scavenger in the presence of copper is in good agreement with the tertiary butyl alcohol results in the absence of copper (0.124 ± 0.003).Quantum yields are observed which are independent of scavenger concentration indicating outer sphere photooxidations are not taking place. This result supports the suggestion that an H on the carbon bearing oxygen is necessary for direct reaction between scavenger and the ferric charge transfer excited state.

Thermodynamic and Kinetic Investigation of the Solvent Effect on the Oxidation of [Co(en)2SCH2COO]+ with S2O82- In Water-Methanol and Water-tert-Butyl Alcohol Mixtures

1993 ◽  
Vol 58 (5) ◽  
pp. 1001-1006 ◽  
Author(s):  
Oľga Vollárová ◽  
Ján Benko
Keyword(s):  
Transfer Functions ◽  
Activation Parameters ◽  
Butyl Alcohol ◽  
Oxidation Of Co ◽  
Kinetics Of Oxidation ◽  
Tert Butyl ◽  
Tert Butyl Alcohol ◽  
Alcohol Mixtures ◽  
Kinetics Of

The kinetics of oxidation of [Co(en)2SCH2COO]+ with S2O82- was studied in water-methanol and water-tert-butyl alcohol mixtures. Changes in the reaction activation parameters ∆H≠ and ∆S≠ with varying concentration of the co-solvent depend on the kind of the latter, which points to a significant role of salvation effects. The solvation effect on the reaction is discussed based on a comparison of the transfer functions ∆Ht0, ∆St0 and ∆Gt0 for the initial and transition states with the changes in the activation parameters accompanying changes in the CO-solvent concentration. The transfer enthalpies of the reactant were obtained from calorimetric measurements.

scholarly journals Impacts of Sn(II) doping on the Keggin heteropolyacid-catalyzed etherification of glycerol with tert-butyl alcohol

2021 ◽  
pp. 116913
Author(s):  
Márcio José da Silva ◽  
Diego Morais Chaves ◽  
Sukarno Olavo ferreira ◽  
Rene Chagas da Silva ◽  
Jose Balena Gabriel Filho ◽  
...  
Keyword(s):  
Butyl Alcohol ◽  
Tert Butyl ◽  
Tert Butyl Alcohol

Selective synthesis of 2,5-dimethyl-2,4-hexadiene by condensation of iso-butyl aldehyde with tert-butyl alcohol over molecular sieve catalysts

2004 ◽  
Vol 5 (1) ◽  
pp. 41-43 ◽  
Author(s):  
Hua Wang ◽  
Zhongmin Liu ◽  
Chenglin Sun ◽  
Gongwei Wang
Keyword(s):  
Molecular Sieve ◽  
Butyl Alcohol ◽  
Selective Synthesis ◽  
Tert Butyl ◽  
Tert Butyl Alcohol
Sign in / Sign up

Export Citation Format

Share Document