Rate constants for the reaction of OH radicals with COS, CS2 and CH3SCH3 over the temperature range 299–430 K

doi:10.1016/0009-2614(78)85653-X

Chemical Physics Letters

Volume 54, Issue 1, 15 February 1978, Pages 14-18

https://doi.org/10.1016/0009-2614(78)85653-X Get rights and content

Abstract

Rate constants for the reaction of OH radicals with COS, CS₂ and CH₃SCH₃, which are involved in the global sulfur cycle, have been determined over the temperature range 299–430 K using a flash photolysis-resonance fluorescence technique. For COs and CS₂ upper limits at room temperature of k(COS) < 7 × 10⁻¹⁵ cm³ molecule⁻¹ s⁻¹ and k(CS₂) < 7 × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹ were determined, while for CH₃SCH₃ the Arrhenius expression k(CH₃SCH₃) = 5.47 × 10⁻¹² exp[(355 ± 300)/RT] cm³ molecule⁻¹ s⁻¹ was obtained with a rate constant at room temperature of (9.8 ± 1.2) × 10⁻¹² cm³ molecule⁻¹ s⁻¹.

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Hydroxyl radical is known as the main degrading agent of organic compounds in the troposphere [5]. However, it is proved that OH radical cannot solely degrade CS2 due to the high barrier involved in the CS2 + OH reaction [6–8]. Some experimental and theoretical investigations have revealed that OH could remove CS2 in the presence O2 molecule [1,9–10].
The oxidation reactions of CS₂ molecules by two simple Criegee intermediates CH₂OO and (CH₃)₂COO are theoretically investigated. The PES of the reactions are explored by M06-2X, G4 and W1RO quantum-chemical methods. The overall rate constants for the reactions are calculated by SCTST. The calculations reveal that in both reactions CS₂ molecules add to Criegee intermediates via a concerted mechanism to form primary cyclic chemically-activated adducts. Next, the chemically-activated adducts decompose to form some products. The activation energies for the reactions of CH₂OO and (CH₃)₂COO with CS₂ are calculated to be 22.2 and 33.5 kJ mol⁻¹, respectively. The activation energy for CH₂OO + CS₂ is comparable with other suggested pathways for atmospheric degradations of CS₂ and it could be a possible pathway for degradation of atmospheric CS₂. The oxidation mechanisms of the sulfur-containing products of f-CI + CS₂ reaction by OH and O(³P) radicals are also investigated and discussed.
On adduct formation and reactivity in the OCS + OH reaction: A combined theoretical and experimental study
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The OCS + OH reaction occurs either via adduct formation or direct S-abstraction. We investigate OH-oxidation of OCS using quantum chemical methods and find that the OC(OH)S adduct reacts rapidly with O₂ forming SOOH + CO₂. SOOH rapidly dissociates under atmospheric conditions regenerating OH. We interpret earlier experimental results based on monitoring OH-loss, and find that OH-regeneration in presence of O₂ may explain the insensitivity of the reaction rate to pressure and O₂. We calculate a rate constant of $3.52 \times 10^{- 16}$ cm³ s⁻¹ at 10 Torr increasing to $7.20 \times 10^{- 16}$ cm³ s⁻¹ at 700 Torr. In addition we present a new experimental determination of the OCS + OH rate constant of $(5.3 \pm 3.6) \times 10^{- 15}$ cm³ s⁻¹ at 296 K and 700 Torr using relative-rate technique.
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Carbonyl sulphide is the predominant sulphur compound in the atmosphere, contributing to the formation of aerosol particles affecting global climate. Human activity has significantly increased its total amount since the beginning of the Industrial Revolution due to its presence in petroleum and coal, reason why it is necessary to understand and control its emissions. On the other hand, carbonyl sulphide is an undesired substance for catalysis in important industrial processes. Hydrolysis is the most promising among the different strategies to reduce its presence, giving as products carbon dioxide and hydrogen sulphide. In the present work, the mechanism of reaction of carbonyl sulphide hydrolysis process in gas phase was studied from 400 K to 1500 K, equilibrium constants were obtained and reaction yields were estimated, by means of composite quantum-computational methods. Good agreement with literature experimental results confirms the suitability of the chosen methods, specially CBS-QB3, in supporting the reaction mechanism, giving accurate equilibrium constant values, and obtaining realistic yields. The effect of isotopic substitution in OCS was also studied, from 300 K to 1500 K, being much less significant than temperature dependence.
Atmospheric oxidation of carbon disulfide (CS<inf>2</inf>)
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Significant variation of CS2 concentration with altitude indicates that, it has a relatively short atmospheric lifetime. Kurylo [6] as well as Atkinson and Pitts [7] adopted pulsed H2O photolysis to produce OH and measured its concentration by means of resonance fluorescence technique to obtain the rate coefficient for R1. Kurylo [6] quoted the rate coefficient of R1 as 1.9 × 10−13 cm3 molecule−1 s−1, while Atkinson and Pitts reported an upper limit for R1 as 7 × 10−14 cm3 molecule−1 s−1 at 298.15 K.
This contribution investigates primary steps governing the OH-initiated atmospheric oxidation of CS₂. Our approach comprises high-level density functional theory calculation of energies and optimisation of molecular structures as well as RRKM-ME analysis for estimating pressure-dependent reaction rate constants. We find the overall reaction OH + CS₂ → OCS + SH too slow to account for the formation of the reported experimental products. The initial reaction of OH with CS₂ proceeds to produce an S-adduct, SCS(OH). Species-formation history for the system OH + CS₂ indicates that, the S-adduct represents the most plausible product with a barrier-less addition process and a stability amounting to 48.5 kJ/mol, in reference to the separated reactants. This adduct then undergoes a bimolecular reaction with atmospheric O₂ yielding OCS and HOSO, rather than dissociating back into its separated reactants. We also find that further atmospheric oxidation of the C-adduct (if formed) yields two of the major experimental products namely OCS and SO₂. The kinetic analysis provided in this study explains the atmospheric fate of reduced sulfur species, an important S-bearing group in the global cycle of sulfur.
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The proposed scheme for methane oxidation to methanol in a vapor–gas system: ${CH}_{4} + \frac{1}{2} O_{2} + (hv / {HNO}_{3}) \to {CH}_{3} OH$ under mild conditions: at a temperature (T = 100 °C), atmospheric pressure (P = 1 atm), ultraviolet radiation of HNO₃ (λ > 230 nm), and autocatalytic influence of nitric acid was investigated. In this way, methanol with 90% selectivity can be achieved at a methane conversion level of 10%. Quantum chemical calculations for the activation reaction of methane by hydroxyl radical (via HNO₃ photo-dissociation) were performed using the density functional theory (DFT) method at the B3LYP/6-311++G(3df,3pd) level. Results of the DFT calculations which are broadly consistent with the experimental data, clearly find physicochemical justification. By and large, a possible extension of the technique here in, for the oxidation of higher alkanes (instead of methane) to methanol, in principle, also enhances the opportunity to recycle nitric acid, and the valuable semi-products (alkene and/or oxide of alkene).
Quantum chemical and theoretical kinetics studies on the reaction of carbonyl sulfide with H, OH and O(<sup>3</sup>P)
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Citation Excerpt :
As mentioned in the introduction section, regarding the rate constants of the reaction R2, there are two groups of contradictory data in the literature. Some laboratories [6,8] have refuted the importance of this reaction and reported an upper limit of 5.0 × 106 L mol−1 s−1 at room temperature for the rate constant of the reaction R2. On the other hand, some laboratories have reported considerable values for the rate coefficients.
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¹: Present address: Aeronomy Laboratories, NOAA Environmental Research Laboratories, Boulder, Colorado 80302, USA.

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Rate constants for the reaction of OH radicals with COS, CS2 and CH3SCH3 over the temperature range 299–430 K

Abstract

Planetary Space Sci.

J. Chem. Phys.

J. Chem. Phys.

Science

Chem. Eng. Progr.

Nature

Nature

Tellus

Tellus

J. Geophys. Res.

J. Air Pollution Control Assoc.

Geophys. Res. Letters

Advan. Environ. Sci. Technol.

Tellus

Advan. Photochem.

J. Atmos. Sci.

Rate constants for the reaction of OH radicals with COS, CS₂ and CH₃SCH₃ over the temperature range 299–430 K