Atmospheric Chemistry of Enols: The Formation Mechanisms of Formic and Peroxyformic Acids in Ozonolysis of Vinyl Alcohol

Abstract

Vinyl alcohol (VA), for a long time, is thought to be a missing source of formic acid (FA) in the atmospheric models. However, a recent study has shown that FA is just a byproduct in the OH-initiated oxidation of VA, which stimulates investigation on the other sinks of VA in the atmosphere. In this study, the detailed ozonolysis mechanism of VA was investigated theoretically for the first time. The results show that two primary ozonides (syn-and anti-POZ) can be formed in the ozonolysis of VA and that FA coupled with the simplest Criegee intermediate (CH 2 OO) can be produced as the main nascent products. Thus, the ozonolysis of VA is predicted to be a more efficient process to produce FA in the atmosphere compared with its OH-initiated oxidation. Moreover, it is found that the syn-POZ can directly decompose to peroxyformic acid plus formaldehyde, breaking the known "Criegee mechanism" to form carbonyl oxide with carbonyl compound. This special mechanism by providing a new source of peroxy acids in the atmosphere enriches the atmospheric chemistry of enols. The atmospheric lifetime of VA by ozonolysis is predicted to be 30 h, comparable with its prevalent reaction with the OH radical. Therefore, the obtained theoretical results can be usefully incorporated into a future modeling study of enols.

Unimolecular and water reactions of oxygenated and unsaturated Criegee intermediates under atmospheric conditions

“…Hydroxy substituents have a strong impact on the chemistry of SCI. As already reported earlier, 13,39,40 syn-a-OH-substituted SCI converts very quickly to a peracid, while anti-a-OH SCI undergo fast 1,3-ring closure reactions (R3) as their dominant pathway, where the rate of competing processes on the syn-substituent (e.g. 1,4-H-migration, R4) is little affected.…”

Estimation of mechanistic parameters in the gas-phase reactions of ozone with alkenes for use in automated mechanism construction

“…However, two recent theoretical studies examined the ozonolysis of enols. The first (Lei et al, 2020) on the simplest enol, vinyl alcohol (ethenol), suggested that formation of CH 2 OO + HCOOH is strongly favoured (∼ 78 %). The second (Wang et al, 2020), on the complex ketene-enol species 4-hydroxy-1,3-butadien-1-one, also suggests that formation of HCOOH and the corresponding CI is strongly favoured (84 %).…”

“…most strongly favouring formation of the carbonyl containing the functional group) observed in the database is for enol ethers (-OR), giving an F value of −0.655. This is assumed to also be the same case for enols (-OH) based on the theoretical calculations of Lei et al (2020) and Wang et al (2020) and for vinyl esters (-OC(=O)R), based on the observed values for vinyl acetate. By contrast, an acrylate ester (-C(=O)-OR) substituent adjacent to the double bond does not appear to have a strong effect on fragmentation, and F = 0 is used.…”

Competition between Abstraction and Addition Channels for the Reaction between the OH Radical and Vinyl Alcohol in the Interstellar Medium

“…The tautomerization can also take place through a photochemical process at the low pressures and temperatures characterizing Earth’s atmosphere and stratosphere. , However, under these conditions, the Vy lifetime is strongly enhanced by the synergistic effect of its intrinsic kinetic stability and the absence of chemical agents able to catalyze conversion into acetaldehyde. This situation increases, in turn, the probability of Vy reactions with other chemical species, and indeed, the involvement of Vy in the production of organic acids in the atmosphere has been demonstrated unambiguously. , These findings led da Silva et al . to compute accurately the thermodynamic properties of Vy in order to characterize its reactivity in the atmosphere with OH and molecular oxygen (O 2 ).…”

“…This situation increases, in turn, the probability of Vy reactions with other chemical species, and indeed, the involvement of Vy in the production of organic acids in the atmosphere has been demonstrated unambiguously. 7,8 These findings led da Silva et al 9 thermodynamic properties of Vy in order to characterize its reactivity in the atmosphere with OH and molecular oxygen (O 2 ). In even more extreme environments, such as those characteristic of the ISM, the kinetic stability and lifetime of thermodynamically unstable species increase considerably.…”