ChemInform Abstract: Estimations of OH Radical Rate Constants from H-Atom Abstraction from C-H and O-H Bonds Over the Temperature Range 250-1000 K.

1986 ◽  
Vol 17 (39) ◽  
Author(s):  
R. ATKINSON
Keyword(s):  
Rate Constants ◽  
Oh Radical ◽  
Temperature Range

Wavelength controlled production of SO4- radicals in the ultraviolet photolysis of ceric sulfate solutions

1984 ◽  
Vol 37 (3) ◽  
pp. 475 ◽  
Author(s):  
RW Matthews
Keyword(s):  
Rate Constants ◽  
Photochemical Reaction ◽  
Transfer Reaction ◽  
Quantum Yields ◽  
Oh Radical ◽  
Transfer Energy ◽  
Fluorescence Measurements ◽  
Sulfate Solutions ◽  
Ultraviolet Photolysis ◽  
Primary Photochemical Reaction

Solutions of cerium(III)/(IV) and formic acid in 0.4 M sulfuric acid have been photolysed under 254 nm and 365 nm light. Marked differences in the reaction kinetics and quantum yields are observed at the two different wavelengths. At 365 nm, the reactions leading to cerium(IV) reduction are caused almost exclusively by the SO4- radical. The ratio of rate constants, k(SO4- + CeIII)/ k(SO4- + HCOOH), is 116 � 11 and the quantum yield of sulfate radicals, ф(SO4-), is 0.023 � 0.002. At 254 nm, the reactions leading to cerium(IV) reduction are caused mainly by the OH radical, but approximately 35% of the oxidizing radicals formed in the primary photochemical reaction are SO4-. Cerium(III) species, excited at 254 nm, transfer energy to cerium(IV) and this results in an additional yield of OH and SO4- radicals. Fluorescence measurements confirmed the efficiency of the energy transfer reaction. The ratio of rate constants, k(OH+CeIII)/k(OH+HCOOH), is 2.22 � 0.18 and ф(CeIV*) and ф(CelIII*) giving oxidizing radicals are 0.116 � 0.010 and 0.0083 � 0.0008 respectively. Thus about 5 times more total oxidizing radicals are produced from excited cerium(IV) species at 254 nm than at 365 nm.

MECHANISM AND KINETICS OF THE CH3CH2C(O)OCH2CH3 + OH REACTION: A THEORETICAL STUDY

2011 ◽  
Vol 10 (05) ◽  
pp. 691-709 ◽  
Author(s):  
CONG HOU ◽  
CHENG-GANG CI ◽  
TONG-YIN JIN ◽  
YONG-XIA WANG ◽  
JING-YAO LIUM
Keyword(s):  
Rate Constants ◽  
Hydrogen Abstraction ◽  
Negative Temperature ◽  
State Theory ◽  
Measured Temperature ◽  
Temperature Range ◽  
Global Rate ◽  
Abstraction Reaction ◽  
Lower Temperature ◽  
Kinetic Calculations

The hydrogen abstraction reaction of CH 3 CH 2 C(O)OCH 2 CH 3 + OH has been studied theoretically by dual-level direct dynamics method. Six H-abstraction channels were found for this reaction. The required potential energy surface information for the kinetic calculations was obtained at the MCG3-MPWB//M06-2X/aug-cc-pVDZ level. The rate constants were calculated by the improved canonical variational transition-state theory with small-curvature tunneling correction (ICVT/SCT) approach in the temperature range of 200–2000 K. It is shown that the "methylene H-abstraction" from the alkoxy end of the ester CH 3 CH 2 C(O)OCH 2 CH 3 is the dominant channel at lower temperature (< 400 K), while the other channels from the acetyl end should be taken into account as the temperature increases and become the competitive ones at higher temperature. The calculated global rate constants are in good agreement with the experimental ones in the measured temperature range and exhibit a negative temperature dependence below 500 K. A four-parameter rate constant expression was fitted from the calculated kinetic data between 200–2000 K.

Inorganic greywater matrix impact on photocatalytic oxidation: does flocculation of TiO2 nanoparticles impair process efficiency?

2011 ◽  
Vol 63 (12) ◽  
pp. 2808-2813 ◽  
Author(s):  
A. Armanious ◽  
A. Özkan ◽  
U. Sohmen ◽  
H. Gulyas
Keyword(s):  
Rate Constants ◽  
Electric Double Layer ◽  
Photocatalytic Oxidation ◽  
Process Efficiency ◽  
Point Of Zero Charge ◽  
Inorganic Salts ◽  
Co2 Absorption ◽  
Oh Radical ◽  
Radical Scavengers ◽  
Subsequent Formation

This study was conducted in order to clarify whether photocatalyst flocculation – as observed in biologically pretreated greywater – contributes to photocatalytic oxidation (PCO) efficiency impairment. Aqueous solutions of tetraethyleneglycol dimethylether spiked with different inorganic salts in concentrations as found in biologically treated greywater were investigated with respect to TiO2 flocculation and PCO mineralisation kinetics. Flocculation of the photocatalyst primarily depended on pH (which was affected by the salts) and how close pH was to the point of zero charge (PZC). Photocatalyst agglomeration was maximum at pH 5.5. With salt concentrations &gt;7 mmol L−1, flocculation was strong even at pH far above PZC due to electric double layer compression. PCO rate constants were not unequivocally related to flocculation. Increasing pH was observed as the clearest factor deteriorating PCO efficiency. This was interpreted to result from impaired adsorbability of negatively charged oxidation intermediates as well as from enhanced CO2 absorption with increasing pH and subsequent formation of HCO3− anions which are OH radical scavengers.

Reaction kinetics of OH radicals with glutaric acid and adipic acid in the aqueous phase

2021 ◽  
Author(s):  
Liang Wen ◽  
Thomas Schaefer ◽  
Hartmut Herrmann
Keyword(s):  
Aqueous Phase ◽  
Adipic Acid ◽  
Rate Constants ◽  
Density Functional ◽  
Glutaric Acid ◽  
Radical Reaction ◽  
Basis Set ◽  
Oh Radicals ◽  
Oh Radical ◽  
Energy Barriers

&lt;p&gt;Dicarboxylic acids (DCAs) are widely distributed in atmospheric aerosols and cloud droplets and are mainly formed by the oxidation of volatile organic compounds (VOCs). For example, glutaric acid and adipic acid are two kinds of the DCAs that can be oxidized by hydroxyl radical (&amp;#8231;OH) reactions in the aqueous phase of aerosols and droplets. In the present study, the temperature- and pH-dependent rate constants of the aqueous OH radical reactions of the two DCAs were investigated by a laser flash photolysis-long path absorption setup using the competition kinetics method. Based on speciation calculations, the OH radical reaction rate constants of the fully protonated (H&lt;sub&gt;2&lt;/sub&gt;A), deprotonated (HA&lt;sup&gt;-&lt;/sup&gt;) and fully deprotonated (A&lt;sup&gt;2-&lt;/sup&gt;) forms of the two DCAs were determined. The following Arrhenius expressions for the T-dependency of the OH radical reaction of glutaric acid, k(T, H&lt;sub&gt;2&lt;/sub&gt;A) = (3.9 &amp;#177; 0.1) &amp;#215; 10&lt;sup&gt;10&lt;/sup&gt; &amp;#215; exp[(-1270 &amp;#177; 200 K)/T], k(T, HA&lt;sup&gt;-&lt;/sup&gt;) = (2.3 &amp;#177; 0.1) &amp;#215; 10&lt;sup&gt;11&lt;/sup&gt; &amp;#215; exp[(-1660 &amp;#177; 190 K)/T], k(T, A&lt;sup&gt;2-&lt;/sup&gt;) = (1.4 &amp;#177; 0.1) &amp;#215; 10&lt;sup&gt;11&lt;/sup&gt; &amp;#215; exp[(-1400 &amp;#177; 170 K)/T] and adipic acid, k(T, H&lt;sub&gt;2&lt;/sub&gt;A) = (7.5 &amp;#177; 0.2) &amp;#215; 10&lt;sup&gt;10&lt;/sup&gt; &amp;#215; exp[(-1210 &amp;#177; 170 K)/T], k(T, HA&lt;sup&gt;-&lt;/sup&gt;) = (9.5 &amp;#177; 0.3) &amp;#215; 10&lt;sup&gt;10&lt;/sup&gt; &amp;#215; exp[(-1200 &amp;#177; 200 K)/T], k(T, A&lt;sup&gt;2-&lt;/sup&gt;) = (8.7 &amp;#177; 0.2) &amp;#215; 10&lt;sup&gt;10&lt;/sup&gt; &amp;#215; exp[(-1100 &amp;#177; 170 K)/T] (in unit of L mol&lt;sup&gt;-1&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;) were derived.&lt;/p&gt;&lt;p&gt;The energy barriers of the H-atom abstractions were simulated by the Density Functional Theory calculations run with the GAUSSIAN package using the M06-2X method and the basis set m062x/6-311++g(3df,2p). The results showed that the energy barriers were lower at the C&lt;sub&gt;&amp;#946;&lt;/sub&gt;-atoms and are higher at the C&lt;sub&gt;&amp;#945;&lt;/sub&gt;-atoms of the two DCAs, clearly suggesting that the H-atom abstractions occurred predominately at the C&lt;sub&gt;&amp;#946;&lt;/sub&gt;-atoms. In addition, the ionizations can enhance the electrostatic effects of the carboxyl groups, significantly reducing the energy barriers, leading to the order of OH radical reactivity as &amp;#160;&lt; &amp;#160;&lt; . This study intends to better characterize the losing processes of glutaric acid and adipic acid in atmospheres.&lt;/p&gt;

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