The Rate-Constant of the Reaction of Hydroxyl Radicals With Methanol, Ethanol and (D3)Methanol

1986 ◽  
Vol 39 (11) ◽  
pp. 1775 ◽  
Author(s):  
PG Greenhill ◽  
BV Ogrady
Keyword(s):  
Hydroxyl Radicals ◽  
Rate Constant ◽  
Flash Photolysis ◽  
Hydrogen Abstraction ◽  
Reaction Scheme ◽  
Resonance Absorption ◽  
Rate Coefficients ◽  
Secondary Reactions ◽  
Temperature Ranges ◽  
Predominant Process

The rate coefficients for hydrogen abstraction by hydroxyl radicals from methanol and ethanol have been determined in the temperature ranges 260-803 K and 255-459 K respectively. Flash photolysis combined with resonance absorption detection of OH was used to obtain results which may be described by the Arrhenius expressions:   Methanol ��� k(T) = (8.0�1.9)×10-12 exp[-(664�88)K/T]cm3 s-1 ������� (1)   Ethanol ���� k(T) = (1.25�0.24)×10-11 exp[-(360�52)K/T]cm3 s-1 (2)  The results obtained for methanol are in excellent agreement with results obtained by other workers, but the Arrhenius parameters for ethanol are markedly different to those obtained in the only other study of the temperature dependence of this reaction. The rate constant for reaction with (D3)methanolhas been determined at 293 K: (D3)Methanol ����� k(293) = 5.0�0.2×10-13 cm3 s-1 (3) The presence of an isotope effect confirms that the predominant process is abstraction of hydrogen from the carbon rather than the oxygen. The results obtained for the reaction with ethanol were analysed by using a 21 reaction scheme to determine the effect of [OH]O and secondary reactions on k(T). The simulations indicate that secondary reactions involving OH are relatively unimportant in determining the bimolecular rate coefficients found in this study.

Rates of OH Radical Reactions. I. Reactions with H2, CH4, C2H6, and C3H8 at 295 K

1975 ◽  
Vol 53 (22) ◽  
pp. 3374-3382 ◽  
Author(s):  
R. P. Overend ◽  
G. Paraskevopoulos ◽  
R. J. Cvetanović
Keyword(s):  
Gas Phase ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Hydrogen Abstraction ◽  
Resonance Absorption ◽  
Oh Radicals ◽  
Oh Radical ◽  
Absolute Rate ◽  
Absorption Spectrophotometry ◽  
Secondary Reactions

A fast flash photolysis kinetic spectrophotometer capable of measuring rates of up to 105 s−1 is described. The rates of hydrogen abstraction from H2, CH4, C2H6, and C3H8 by OH radicals at 295 ± 2 K, have been measured in the gas phase by hydroxyl resonance absorption spectrophotometry. The influence of secondary reactions on the measured rates and the derivation of the absolute rate constants is discussed in detail.The absolute rate constants in units of cm3 mol−1 s−1 were found to be: [Formula: see text][Formula: see text][Formula: see text] and [Formula: see text]

The production of vibrationally excited hydroxyl radicals under isothermal conditions by flash photolysis

1961 ◽  
Vol 260 (1302) ◽  
pp. 293-303 ◽  
Keyword(s):  
Oxygen Atom ◽  
Hydroxyl Radicals ◽  
Flash Photolysis ◽  
Vibrational Energy ◽  
Hydrogen Abstraction ◽  
Electronic Energy ◽  
Vibrationally Excited ◽  
Isothermal Conditions ◽  
Abstraction Reaction ◽  
Hydrogen Abstraction Reaction

The flash photolysis of ozone in the presence of ammonia, hydrogen, hydrogen chloride, methane and water has been investigated under isothermal conditions. In each case the presence of vibrationally excited hydroxyl radicals has been shown spectroscopically. The concentration of these species is highest at the shortest time (i.e. during the photolysis flash) and decreases rapidly to below detectable limits within about 20 μs. The hydroxyl radical is produced by the reaction O( 1 D ) + HR -> OH + R + 29 to 46 kcal rotationally cold but with up to at least two quanta of vibrational energy, the energy for which is supplied by the electronic energy of the oxygen atom. Under some conditions, the spectrum of oxygen molecules with up to 16 quanta of vibrational energy is also seen and shows that the reaction competes successfully with the hydrogen abstraction reaction. O( 1 D ) + O 2 -> O 2 * + O 2 competes successfully with the hydrogen abstraction reaction.

Mechanistic studies of aromatic ketone-sensitized photoreduction of bis(acetylacetonato)copper(II)

1983 ◽  
Vol 61 (5) ◽  
pp. 801-808 ◽  
Author(s):  
Yuan L. Chow ◽  
Gonzalo E. Buono-Core ◽  
Bronislaw Marciniak ◽  
Carol Beddard
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Decay Rates ◽  
Polynuclear Aromatic Hydrocarbons ◽  
Aromatic Ketone ◽  
Quantum Yields ◽  
Triplet States ◽  
Quenching Rate ◽  
Triplet Energy

Bis(acetylacetonato)copper(II), Cu(acac)2, quenches triplet excited states of ketones and polynuclear aromatic hydrocarbons efficiently, but only aromatic ketones with high triplet energy successfully sensitize photoreduction of Cu(acac)2 in alcohols under nitrogen to give derivatives of aeetylacetonatocopper(I), Cu(acac). For the triplet state benzophenone-sensitized photoreduction of Cu(acac)2, the quantum yields of photoreduction (ΦC) and those of benzophenone disappearance (ΦB) were determined in methanol with various concentrations of Cu(acac)2. The values of the quenching rate constant, kq, determined from these two types of monitors on the basis of the proposed mechanism were in good agreement (6.89 ~ 7.35 × 109 M−1 s−1). This value was higher, by a factor of about two, than that obtained from the monitor of the benzophenone triplet decay rates generated by flash photolysis in the presence of Cu(acac)2. The quenching rate constants of various aromatic ketone and hydrocarbon triplet states by Cu(acac)2 were determined by flash photolysis to be in the order of the diffusion rate constant and the quantum yields of these photoreductions were found to be far from unity. Paramagnetic quenching, with contributions of electron exchange and charge transfer, was proposed as a possible quenching mechanism. For a series of aromatic ketone sensitizers with higher triplet energy, this mechanism was used to rationalize the observed high quenching rate constants in contrast to the low quantum yields of photoreduction.

scholarly journals Photochemical Degradation of Sulfadiazine

2013 ◽  
Vol 39 (3) ◽  
pp. 79-91 ◽  
Author(s):  
Natalia Lemańska-Malinowska ◽  
Ewa Felis ◽  
Joanna Surmacz-Górska
Keyword(s):  
Hydrogen Peroxide ◽  
Uv Radiation ◽  
Hydroxyl Radicals ◽  
Rate Constant ◽  
Photochemical Degradation ◽  
Photochemical Processes

Abstract The photochemical degradation of the sulfadiazine (SDZ) was studied. The photochemical processes used in degradation of SDZ were UV and UV/H2O2. In the experiments hydrogen peroxide was applied at different concentrations: 10 mg/dm3 (2.94*10-4 M), 100 mg/dm3 (2.94*10-3 M), 1 g/dm3 (2.94*10-2 M) and 10 g/dm3 (2.94*10-1 M). The concentrations of SDZ during the experiment were controlled by means of HPLC. The best results of sulfadiazine degradation, the 100% removal of the compound, were achieved by photolysis using UV radiation in the presence of 100 mg H2O2/dm3 (2.94*10-3 M). The determined rate constant of sulfadiazine reaction with hydroxyl radicals kOH was equal 1.98*109 M-1s-1.

Direct rate constant measurements for atomic hydrogen + methane .fwdarw. methyl + hydrogen, 897-1729 K, using the flash photolysis-shock tube technique

1991 ◽  
Vol 95 (2) ◽  
pp. 674-681 ◽  
Author(s):  
M. J. Rabinowitz ◽  
J. W. Sutherland ◽  
P. M. Patterson ◽  
R. B. Klemm
Keyword(s):  
Shock Tube ◽  
Rate Constant ◽  
Atomic Hydrogen ◽  
Flash Photolysis

On the Mechanism of Radical Polymerization of Methyl Methacrylate with Dithiobenzoic Acid as Mediator

2006 ◽  
Vol 59 (8) ◽  
pp. 549 ◽  
Author(s):  
Duc Hung Nguyen ◽  
Philipp Vana
Keyword(s):  
Methyl Methacrylate ◽  
Induction Period ◽  
Hydrogen Abstraction ◽  
Ester Group ◽  
Reaction Scheme ◽  
Ionization Mass ◽  
Controlled Polymerization ◽  
Induction Periods ◽  
Methyl Methacrylate Polymerization ◽  
Raft Agent

Dithiobenzoic acid (DTBA) induces controlled polymerization behaviour in methyl methacrylate polymerization at 60°C, accompanied by a pronounced induction period of several hours. DTBA is partially transformed during this induction period into a dithioester with a tertiary ester group moiety, which constitutes an efficient reversible addition–fragmentation chain transfer (RAFT) agent. The transformation reaction is proposed to proceed via a hydrogen abstraction from DTBA by radicals and subsequent termination of the formed phenylcarbonothioylsulfanyl radical with propagating radicals. The proposed reaction scheme was implemented into a computer model, by which the rate coefficient of the hydrogen abstraction from DTBA and of the reinitiation of the intermediate phenylcarbonothioylsulfanyl radical was estimated. The model is in agreement with all of the species observable by electrospray ionization mass spectrometry, with the extent of the experimental induction periods, and with the absolute concentrations of dithioesters that act as efficient RAFT agents during the polymerization. A protocol that uses a cocktail of initiators is introduced, by which the induction period in DTBA-mediated polymerization is effectively eliminated.

scholarly journals H–Abstraction from Dimethyl Sulfide in the Presence of an Excess of Hydroxyl Radicals. A Quantum Chemical Evaluation of Thermochemical and Kinetic Parameters Unveil an Alternative Pathway to Dimethyl Sulfoxide.

2020 ◽  
Author(s):  
Zoi Salta ◽  
Jacopo Lupi ◽  
Vincenzo Barone ◽  
Oscar Ventura
Keyword(s):  
Dimethyl Sulfoxide ◽  
Hydroxyl Radicals ◽  
Quantum Chemical ◽  
Dimethyl Sulfide ◽  
Computational Study ◽  
Alternative Pathway ◽  
Oxidation Mechanism ◽  
State Theory ◽  
Rate Coefficients ◽  
Reduced Sulfur Compounds

<div> Elucidation of the oxidation mechanism of naturally emitted reduced sulfur compounds, especially dimethyl sulfide, plays a central role in understanding background acid precipitation in the natural environment. Most frequently, theoretical studies of the addition and H-elimination reactions of dimethyl sulfide with hydroxyl radicals are studied considering the presence of oxygen that further reacts with the radicals formed in the initial steps. Although the reaction of intermediate species with additional hydroxyl radicals has been considered as part of the global mechanism of oxidation, few if any attention has been dedicated to the possibility of reactions of the initial radicals with a second •OH molecule. In this work we performed a computational study using quantum-chemical methods, of the mechanism of H-abstraction from dimethyl sulfide under normal atmospheric conditions and in reaction chambers at different O2 partial pressure, including complete absence of oxygen. Additionally, important rate coefficients were computed using canonical and variational transition state theory. The rate coefficient for abstraction affords a 4.72 x 10-12 cm3 molecule1 s-1 value, very close to the most recent experimental one (4.13 x 10-12 cm3 molecule-1 s-1). According to our best results, the initial methyl thiomethyl radical was obtained at -25.2 kcal/mol (experimentally -22.4 kcal/mol), and four important paths were identified on the potential energy surface. From the interplay of thermochemical and kinetic arguments, it was possible to demonstrate that the preferred product of the reaction of dimethyl sulfide with two hydroxyl radicals, is actually dimethyl sulfoxide. </div><div> </div>

scholarly journals On apparent barrier-free reactions

2020 ◽  
Vol 3 (1) ◽  
pp. 3-8
Author(s):  
Maikel Ballester
Keyword(s):  
Low Temperature ◽  
Chemical Reactions ◽  
Rate Constant ◽  
Kinetic Models ◽  
Rate Coefficient ◽  
Minimum Energy ◽  
Temperature Limit ◽  
Rate Coefficients ◽  
Minimum Energy Path ◽  
Full Dimension

Rate coefficients of bi-molecular chemical reactions are fundamental for kinetic models. The rate coefficient dependence on temperature is commonly extracted from the analyses of the reaction minimum energy path. However, a full dimension study of the same reaction may suggest a different asymptotic low-temperature limit in the rate constant than the obtained from the energetic profile.

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