Atmospheric Vinyl Alcohol to Acetaldehyde Tautomerization Revisited

Abstract

The atmospheric oxidation of vinyl alcohol (VA) produced by photoisomerization of acetaldehyde (AA) is thought to be a source of formic acid (FA). Nevertheless, a recent theoretical study predicted a high rate coefficient k1(298 K) of ≈10(-14) cm(3) molecule(-1) s(-1) for the FA-catalyzed tautomerization reaction 1 of VA back into AA, which suggests that FA buffers its own production from VA. However, the unusually high frequency factor implied by that study prompted us to reinvestigate reaction 1 . On the basis of a high-level ab initio potential energy profile, we first established that transition state theory is applicable, and derived a k1(298 K) of only ≈2 × 10(-20) cm(3) molecule(-1) s(-1), concluding that the reaction is negligible. Instead, we propose and rationalize another important VA sink: its uptake by aqueous aerosol and cloud droplets followed by fast liquid-phase tautomerization to AA; global modeling puts the average lifetime by this sink at a few hours, similar to oxidation by OH.

The reaction of methyl peroxy and hydroxyl radicals as a major source of atmospheric methanol

“…Hydrogen abstraction starting from 1 RC and 3 RC to form the Criegee intermediate 1 CH 2 OO and the triplet biradical 3 CH 2 OO via TS2 and TS3 , respectively, involve significant barriers. In absence of intersystem crossing (ISC) 3 RC → 1 RC , the reaction CH 3 O 2 +OH ↔ 3 RC will be quasi-equilibrated such that the bimolecular rate constant for the overall triplet channel CH 3 O 2 +OH→ 3 CH 2 O 2 +H 2 O can be found from transition state theory (TST)181920, yielding 3 k bi,3 (298 K)=2.6 × 10 −15  cm 3  molecule −1  s −1 . This channel is therefore entirely negligible, as are the other triplet entrance routes described by Bian et al 16,.…”

Oxidation of Volatile Organic Compounds as the Major Source of Formic Acid in a Mixed Forest Canopy

“…• Figure S2 • Figure S3 1-50% (Larsen et al, 2001;Lee, Goldstein, Kroll, et al, 2006), depending on the species; average yields of 16% (OH) and 8% (ozonolysis) have been assumed in recent large-scale modeling studies (Millet et al, 2015;Paulot et al, 2011). Additional known secondary HCOOH sources include OH-driven oxidation of terminal alkynes (Hatakeyama et al, 1986) and photo-tautomerization of acetaldehyde followed by oxidation of the resulting enol (Millet et al, 2015;Peeters et al, 2015;Shaw et al, 2018).…”

Formic acid catalyzed keto‐enol tautomerizations for C2and C3enols: Implications in atmospheric and combustion chemistry

“…This approach considers the curvature of the reaction path and yields more accurate results than the Eckart approximation used in previous works. [5,6] The final rate constant has been calculated as…”

“…Table 1. Those calculated by Peeters [6] and da Silva [5] for the reaction R3 are also plotted for comparison. Our rate constants for the reaction R3 are significantly smaller than those calculated by da Silva, but larger than the ones reported by Peeters.…”

“…The unimolecular gas-phase tautomerization of enols to aldehydes/ketones has a high barrier height, [4] but these reactions can be catalyzed by HCOOH. [5,6] These HCOOH-catalyzed reactions proceed via a double hydrogen shift mechanism: i− C 3 H 5 OH + HCOOH , CH 3 COCH 3 + HCOOH ðR1Þ CH 3 CHCHOH + HCOOH , CH 3 CH 2 CHO + HCOOH ðR2Þ…”