2229-07-4Relevant academic research and scientific papers
Photolysis of Acetyl Benzoyl Peroxide Isolated in an Argon Matrix: The Stability of the Benzoyloxy and Acetoxy Radicals toward Decarboxylation
Pacansky, J.,Brown, D. W.
, p. 1553 - 1559 (1983)
Exposure of matrix-isolated acetyl benzoyl peroxide to UV light (λ > 2800 angstroem) produces methyl benzoate, the methyl-phenyl radical pair, and carbon dioxide.The results of the low-temperature irradiation reveal that methyl benzoate is formed by recombination of the benzoyloxy-methyl radical pair.Since phenyl acetate was not detected during the low-temperature irradiation, it was concluded that the lifetime of the acetoxy-phenyl radical pair is too short to allow concentrations that could be detected by infrared spectroscopy.Ab initio calculations are used to provide an explanation for the dramatic lifetime differences between the benzoyloxy and acetoxy radicals.In addition, it was shown that electronic excitation of the phenyl radical does not induce a chemical reaction with carbon dioxide.Arguments based on experiment and theory are presented to explain this unexpected result.
2′-deoxyguanosine (DG) oxidation and strand-break formation in DNA by the radicals released in the photolysis of N-tert-butoxy-2-pyridone. Are tert-butoxyl or methyl radicals responsible for the photooxidative damage in aqueous media?
Adam, Waldemar,Marquardt, Stefan,Kemmer, Diana,Saha-Moller, Chantu R.,Schreier, Peter
, p. 225 - 228 (2002)
Chemical equation presented The photolysis of pyridone 3b (photo-Fenton reagent) in benzene releases tert-butoxyl radicals, which have been trapped by DMPO and EPR-spectrally identified. In aqueous solution, however, the fragmentation of the tert-butoxyl into methyl radicals prevails and the former radicals are of no direct consequence in the photooxidation of 2′-deoxyguanosine (dG) and pBR 322 DNA. The photooxidative damage of nucleic acids is caused by the oxyl radical species generated from the methyl radicals with oxygen.
Photoinduced reactions of methyl radical in solid parahydrogen
Fushitani, Mizuho,Sogoshi, Norihito,Wakabayashi, Tomonari,Momose, Takamasa,Shida, Tadamasa
, p. 6346 - 6350 (1998)
Photolysis of methyl iodide in solid parahydrogen (p-H2) at about 5 K is studied with ultraviolet light at 253.7 and 184.9 nm. It is found that the light at 253.7 nm produces only methyl radical, whereas the light at 184.9 nm yields both methyl radical and methane. The mechanism of the formation of the photoproducts is elucidated by analyzing the temporal behavior of the observed vibrational absorption. It is concluded that methyl radical in the ground state does not react with p-H2 molecules appreciably but that the radical in the electronic excited state of B(2A1′), accessible by reabsorption of 184.9 nm photons by the radical, decomposes to a singlet methylene CH2 a(1A1) and a hydrogen atom (2S) and that the singlet methylene reacts with a p-H2 molecule to give methane.
Microwave kinetic spectroscopy of reaction intermediates: O + ethylene reaction at low pressure
Endo, Yasuki,Tsuchiya, Soji,Yamada, Chikashi,Hirota, Eizi,Koda, Seiichiro
, p. 4446 - 4452 (1986)
A microwave spectroscopic method has been developed to study elementary reactions in real time through in situ observation of rotational spectra of reaction intermediates such as free radicals with lifetime as short as 1 ms.This method was applied to the O(3P) + ethylene reaction in order to assess the roles of (a) vinoxy + H and (b) CH3 + CHO channels in the initial process.The reaction was initiated by irradiating an N2O/C2H4 mixture containing a trace amount of mercury with the 253.7 nm mercury resonance line, and the time evolution of vinoxy, HCO, and H2CO was followed by measuring their microwave absorption intensities as functions of time.The branching ratio was thus determined to be 0.4 +/- 0.1 and 0.5 +/- 0.1 for (a) and (b), respectively, at the sample pressure of 30 mTorr.The present result agrees with those obtained by Hunziker et al. using much higher pressures of samples, but is not compatible with the observation of Buss et al. that (a) is dominant in collision-free conditions.
The gaseous reaction of vinyl radical with oxygen
Wang,Wang,He,Kong
, p. 1742 - 1746 (2001)
Time-resolved Fourier transform infrared (TR-FTIR) emission spectroscopy was used to explore the gaseous reaction of C2H3 vinyl radical. As a result, several new primary and secondary products of the C2H3+O
Rate parameters for the reaction of atomic hydrogen with dimethyl ether and dimethyl sulfide
Lee, J. H.,Machen, R. C.,Nava, D. F.,Stief, L. J.
, p. 2839 - 2844 (1981)
Absolute rate constants for the reaction of atomic hydrogen with dimethyl ether (DME) and dimethyl sulfide (DMS) were obtained using the flash photolysis-resonance fluorescence technique.Under conditions where secondary reactions are avoided, rate constants for the H + DME reaction over the temperature range 273-426 K are well represented by the Arrhenius expression k1 = (4.38 +/- 0.59) * 10-12 exp( - 1956 +/- 43/T) cm3 molecule-1 s-1.The corresponding Arrhenius expression for the H + DMS reaction over the temperature range 212-500 K is k2 = (1.30 +/- 0.43) * 10-11 exp( -1118 +/- 81/T) cm3 molecule-1 s-1.The Arrhenius plot for k2 shows signs of curvature, however, and separate Arrhenius expressions are derived for the data above and below room temperature.These results are discussed and comparisons are made with previous determinations which employed flow discharge and product analysis techniques.
Photosensitized Dissociation of Di-tert-butyl Peroxide. Energy Transfer to a Repulsive Excited State
Scaiano, J. C.,Wubbels, Gene G.
, p. 640 - 645 (1981)
Energy transfer from a variety of aromatic hydrocarbons and ketones to di-tert-butyl peroxide has been examined by using nanosecond laser flash photolysis techniques.Triplet energy transfer to the peroxide leads to its efficient cleavage into two tert-butoxy radicals.Representative rate constants for triplet quenching in benzene at 25 deg C are 7.9*1E6, 3.4*1E6, and 7.0*1E4 M-1 s-1 for p-methoxypropiophenone, benzophenone, and benzanthracene, respectively.The rate of transfer for p-methoxypropiophenone (ET ca. 72.5 kcal/mol) is approximately temperature independent; for lower energy sensitizers ca. 0.17 kcal/mol activation energy is required for each kilocalorie per mole decrease in triplet energy.No evidence indicating exciplex intermediacy was found.A model for energy transfer to a repulsive state of peroxide is proposed in which no activation energy is required if the sensitiser meets the energy requirements at the O-O equilibrium distance.For sensitizers of lower triplet energy, energy transfer to a repulsive state is proposed to occur from a thermally activated ground state having a greater than equilibrium oxygen-oxygen bond lenght.The same mechanism may apply in other systems where the acceptor lacks low-lying excited states.A few rate constants for the quenching of singlet sensitizers have also been determined by using fluorescence techniques.
Time-Resolved Observation of Sequential Bond Cleavage in a Gas-Phase Azoalkane
Adams, J. Stephen,Burton, Katherine A.,Andrews, B. Kim,Weisman, R. Bruce,Engel, Paul S.
, p. 7935 - 7938 (1986)
The gas-phase photodissociation of an unsymmetrical azoalkane, 3-(methylazo)-3-methyl-1-butene, was studied with time-resolved coherent anti-Stokes Raman spectroscopy (CARS) to probe for product formation.Appearance kinetics were measured for all three primary photoproducts.The results indicate a two-step dissociation mechanism in which the 1,1-dimethylallyl fragment is formed within 2 ns of excitation, whereas the methyl radical and N2 are formed through decay of reaction intermediate having a lifetime of 12 +/- 2 ns.These findings mark the first direct demonstration of a stepwise homolysis mechanism for an azoalkane.
Experimental and theoretical studies of gas phase NO3 and OH radical reactions with formaldehyde, acetaldehyde and their isotopomers
D'Anna, Barbara,Bakken, Vebjorn,Beukes, Jon Are,Nielsen, Claus J.,Brudnik, Katarzyna,Jodkowski, Jerzy T.
, p. 1790 - 1805 (2003)
Formaldehyde and acetaldehyde are among the most abundant carbonyls in the atmosphere. The vapor phase reactions of formaldehyde, formaldehyde-d2, 13C-formaldehyde, acetaldehyde, acetaldehyde-1-d1, acetaldehyde-2,2,2-d3, and acetaldehyde-d4 with NO3 and OH radicals were studied at 298 K and 1013 mbar using long-path FTIR detection. The OH and NO3 radicals reacted with formaldehyde and acetaldehyde entirely through Hald-abstraction. The acetaldehyde with OH proceeded via two pathways - CH3CHO + OH → CH3CO + H2O and CH3CHO + OH → CH3 + CO + H2O - with a branching ratio of ≈ 9:1 at 298 K. In the acetaldehyde reaction with NO3, the latter reaction path was not important in atmospheric conditions. Theoretical calculations results apparently reproduced all essential features of the experimental kinetic data for the parent compounds. Theoretical analysis of the kinetics of CH3CHO + OH indicated a complex and a temperature dependent reaction mechanism with significant dominance of the formation of the adduct at low temperatures. However, the observed kinetic isotope effects for reactions of NO3 were much smaller than those calculated by conventional transition state theory. This was also attributed to the formation of pre-reactions adducts.
Absolute rate constants and Arrhenius parameters for the addition of the methyl radical to unsaturated compounds: The methyl affinities revisited
Zytowski, Torsten,Fischer, Hanns
, p. 12869 - 12878 (1997)
Absolute rate constants and their Arrhenius parameters are reported for the addition of the methyl radical to 21 monosubstituted and 1,1- disubstituted alkenes and to 6 benzenes in 1,1,2-trifluoro-1,2,2- trichloroethane solution. They are used to convert relative reaction rates known as methyl affinities from the work of M. Szwarc and others for about 250 additional unsaturated compounds to the absolute scale. An analysis shows that the addition rates depend on the reaction enthalpy but also indicates a moderate nucleophilic polar effect for the liquid-phase reactions. It is pointed out that this polar effect may be smaller in the gas phase.
