Reaction of Criegee Intermediates with SO₂─A Possible Route for Sulfurous Acid Formation in the Atmosphere

Abstract

The reaction of a Criegee intermediate (CI) with SO 2 is of significant interest due to its negative impact on the environment and ecosystem. In the present work, the formation of H 2 SO 3 through the reaction of the CIs CH 2 OO, syn-CH 3 CHOO, and (CH 3 ) 2 COO with SO 2 is studied by using high-level electronic structure calculations. The reaction of CIs with SO 2 is a stepwise process; in the first step an O atom from a CI is transferred to the S atom of SO 2 , which results in the formation of SO 3 through a heterozonide (HOZ) formation in a barrierless reaction, and in the next step, the two hydrogen atoms of a CI are transferred to SO 3, resulting in the formation of H 2 SO 3 and other carbon-containing compounds. The calculated thermochemical parameters associated with the formation of intermediates and products show the spontaneity of the reactions. The rate constant calculated for the studied reactions shows that the formation of sulfurous acid through the reaction of CH 2 OO with SO 2 is faster than the reaction of syn-CH 3 CHOO or (CH 3 ) 2 COO with SO 2 . Our results show that the reaction of CIs with SO 2 is one of the significant processes in the atmosphere and is responsible for the formation of H 2 SO 3 , carbon monoxide, ketene, cyclopropanone, 2-oxopropyl hydrogen sulfite, and other sulfur-containing compounds in the atmosphere.

Kinetics of the Gas-Phase Reactions of syn- and anti-CH3CHOO Criegee Intermediate Conformers with SO2 as a Function of Temperature and Pressure

“…However, the possible impacts of pressure were not fully discussed, and the reaction of anti -CH 3 CHOO + SO 2 was not considered. The calculations predicted a positive temperature dependence for reactions of CH 2 OO, syn -CH 3 CHOO, and (CH 3 ) 2 COO with SO 2 , despite the reactions being barrierless, and this is in contrast to the experimental results for syn -CH 3 CHOO + SO 2 obtained in this work, our previous experiments for CH 2 OO + SO 2 , and experimental results for (CH 3 ) 2 COO + SO 2 (see the Supporting Information for further details). Where potential impacts of pressure have been considered in detail in theoretical studies of SCI + SO 2 reactions, there is an agreement with the lack of observed pressure dependence in the kinetics for CH 2 OO + SO 2 under atmospheric conditions, ,,, but there are differences in the predicted pressure dependence of the reaction between (CH 3 ) 2 COO and SO 2 . , Vereecken et al suggested that >80% of the SOZ formed by (CH 3 ) 2 COO + SO 2 undergoes prompt decomposition to acetone (CH 3 C­(O)­CH 3 ) and SO 3 at 298 K and a pressure of 4 Torr, while >97% of the SOZ collisionally stabilizes at 298 K and 760 Torr, with the difference compared to CH 2 OO + SO 2 attributed to the greater number of degrees of freedom in the SOZ formed via (CH 3 ) 2 COO + SO 2 , which would also be relevant to the comparison between the SOZ formed via CH 2 OO + SO 2 and those from reactions of CH 3 CHOO conformers with SO 2 .…”

“…The reaction between syn -CH 3 CHOO and SO 2 has been investigated using theoretical approaches, which indicate a barrierless reaction with a 98% yield of acetaldehyde (CH 3 CHO) + SO 3 at 298 K and 200 Torr of He and a rate coefficient for CH 3 CHO + SO 3 production of 4.49 × 10 –11 cm 3 s –1 at 298 K . However, the possible impacts of pressure were not fully discussed, and the reaction of anti -CH 3 CHOO + SO 2 was not considered.…”

“…The reaction between syn -CH 3 CHOO and SO 2 has been investigated using theoretical approaches, which indicate a barrierless reaction with a 98% yield of acetaldehyde (CH 3 CHO) + SO 3 at 298 K and 200 Torr of He and a rate coefficient for CH 3 CHO + SO 3 production of 4.49 × 10 –11 cm 3 s –1 at 298 K. 13 However, the possible impacts of pressure were not fully discussed, and the reaction of anti -CH 3 CHOO + SO 2 was not considered. The calculations 13 predicted a positive temperature dependence for reactions of CH 2 OO, syn -CH 3 CHOO, and (CH 3 ) 2 COO with SO 2 , despite the reactions being barrierless, and this is in contrast to the experimental results for syn -CH 3 CHOO + SO 2 obtained in this work, our previous experiments for CH 2 OO + SO 2 , 6 and experimental results for (CH 3 ) 2 COO + SO 2 40 (see the Supporting Information for further details). Where potential impacts of pressure have been considered in detail in theoretical studies of SCI + SO 2 reactions, there is an agreement with the lack of observed pressure dependence in the kinetics for CH 2 OO + SO 2 under atmospheric conditions, 3 , 4 , 11 , 12 but there are differences in the predicted pressure dependence of the reaction between (CH 3 ) 2 COO and SO 2 .…”

“…For the reaction of the simplest SCI, CH 2 OO, with SO 2 , there is now general consensus regarding the kinetics at room temperature, with a current IUPAC recommendation of (3.7 –0.40 +0.45 ) × 10 –11 cm 3 s –1 at 298 K . The kinetics of CH 2 OO + SO 2 have been demonstrated to be independent of pressure under typical atmospheric conditions, , with a negative temperature dependence and reaction products dominated by formaldehyde (HCHO) , and sulfur trioxide (SO 3 ). , Theory indicates that the reaction of an SCI with SO 2 proceeds via the barrierless formation of a cyclic secondary ozonide (SOZ), followed by collisional stabilization of the SOZ or further rearrangement via one or more submerged barriers to form products including SO 3 . − In the case of CH 2 OO + SO 2 , there is negligible stabilization of the SOZ under atmospheric conditions, , and contributions from two stereochemical pathways lead to the production of HCHO + SO 3 via submerged barriers . For reactions of other SCIs with SO 2 , there is greater potential for stabilization of the SOZ, leading to the potential for pressure-dependent kinetics and product yields …”

New insights into the mechanism and kinetics of the addition reaction of unsaturated Criegee intermediates to CF3COOH and tropospheric implications

“…However, their reaction with TFA is as high as that of CH 2 O + O − with SO 2 , HCl, and (CF 3 ) 2 CO, as well as the self-reaction, which is about 1 × 10 −11 cm 3 s −1 . 68–71 This interesting finding suggests that the 1,4-CC addition reaction of C3–C4 unsaturated SC -CH 2 R z CR y CO + O − + TFA will be a significant loss for larger unsaturated CIs with acids.…”