Influence of H₂SO₄···H₂O and (H₂SO₄)₂ on the Hydrolysis of Formaldehyde: A Potential Source of Methanediol in the Troposphere

Abstract

The hydrolysis of formaldehyde [HCHO + H 2 O → H 2 C-(OH) 2 ] assisted by bimolecular acidic catalyst of X (X = H 2 SO 4 •••H 2 O and (H 2 SO 4 ) 2 ) under different concentrations of H 2 SO 4 and H 2 O was performed by quantum chemical calculations of CCSD(T)-F12a/cc-pVDZ-F12//M06-2X/6-311++G(3df,3pd) and the master equation method. The calculated results show that the hydrolysis reaction of HCHO catalyzed by X can occur through both HCHO•••H 2 O + X (one-step reaction) and H 2 O•••X + HCHO (stepwise reaction) routes. The stepwise reaction assisted by H 2 SO 4 •••H 2 O is the most favorable reaction among all the hydrolysis reactions assisted by X, with its effective rate constant larger by at least 2 orders of magnitude. In comparison with the hydrolysis of HCHO without X, the favorable route for the hydrolysis of HCHO with H 2 SO 4 •••H 2 O can reduce the energy barrier by 32.0 kcal•mol −1 . Meanwhile, the energy barrier of this reaction is also lower by another 0.8−17.6 kcal•mol −1 than those of the hydrolysis reaction of HCHO assisted by H 2 SO 4 , HCOOH, HNO 3 , CH 3 COOH, H 2 O, and (H 2 O) 2 . From the viewpoint of the calculated effective rate constant k′, the hydrolysis of HCHO with H 2 SO 4 •••H 2 O {[H 2 SO 4 ] = 10 6 molecules•cm −3 and [H 2 O] at 40−100% relative humidity (RH) along with [H 2 SO 4 ] = 10 7 −10 8 molecules•cm −3 and [H 2 O] at 20−100% RH} is more effective than the hydrolysis reaction assisted by H 2 O, (H 2 O) 2 , HCOOH (0.01−10 ppbv), HNO 3 (10 9 −10 11 molecules•cm −3 ), and CH 3 COOH (1−5 ppbv) within the temperature range of 280−320 K. Under the same condition, the hydrolysis of HCHO with H 2 SO 4 •••H 2 O can compete well with the hydrolysis of HCHO assisted by H 2 SO 4 (10 6 −10 8 molecules•cm −3 ). Therefore, this work predicts that H 2 SO 4 •••H 2 O can play a significant role in the hydrolysis of HCHO in the condition of wet areas with relatively high H 2 SO 4 pollution.

Effect of formic acid on O2 + OH˙CHOH → HCOOH + HO2 reaction under tropospheric condition: kinetics of cis and trans isomers

“…To understand this, the mechanism for the formation of methanediol (OHCH 2 OH) from the CH 2 O + H 2 O reaction is re-calculated. The barrier height for CH 2 O + H 2 O is ∼38 kcal mol −1 , which is in very good agreement with that from the recent study by Zhang et al 32 This barrier height is quite high for atmospheric reaction to form methanediol. Due to the high barrier heights, the reaction may lead to the formation of CH 2 O⋯H 2 O, as suggested by Zhang et al 32 The reported rate constants are in the range of (∼10 −10 cm 3 molecule −1 s −1 ), which are similar to the two body complex values.…”

“…The barrier height for CH 2 O + H 2 O is ∼38 kcal mol −1 , which is in very good agreement with that from the recent study by Zhang et al 32 This barrier height is quite high for atmospheric reaction to form methanediol. Due to the high barrier heights, the reaction may lead to the formation of CH 2 O⋯H 2 O, as suggested by Zhang et al 32 The reported rate constants are in the range of (∼10 −10 cm 3 molecule −1 s −1 ), which are similar to the two body complex values. 32 Zhang et al have also reported the rate constants for the effect of H 2 O, H 2 SO 4 , HNO 3 , and CH 3 COOH on the CH 2 O + H 2 O reaction.…”

“…Due to the high barrier heights, the reaction may lead to the formation of CH 2 O⋯H 2 O, as suggested by Zhang et al 32 The reported rate constants are in the range of (∼10 −10 cm 3 molecule −1 s −1 ), which are similar to the two body complex values. 32 Zhang et al have also reported the rate constants for the effect of H 2 O, H 2 SO 4 , HNO 3 , and CH 3 COOH on the CH 2 O + H 2 O reaction. They found that the barrier heights for three body collisions were reduced significantly by ∼32.0 kcal mol −1 compared to the two body reactions, i.e.…”

“…They suggested that the catalytic effect is negligible under atmospheric conditions when the concentration of FA is included. 29–32 In recent studies by Zhang et al 32 proposed that acid catalysis is more efficient than a water-catalyzed reaction, which also motivated us to understand the effect of FA on the formation of formic acid rather than the effect of H 2 O. In addition, the formation of formic acid and its own effects on the same reaction system was interesting to explore the reaction mechanism and chemical kinetic data.…”

“…In the last few years, there has been increasing experimental 20,21 and theoretical [22][23][24][25][26][27][28][29][30][31][32] evidence suggesting that the hydrogen atom transfer (HAT) chemistry is enhanced by acid catalysts. Many research groups 5,6,11,27,[29][30][31][32] have proposed the effect of a FA on many atmospheric reactions, i.e., CH 4 + OH, 11 27 and CH 3 O + O 2 6 reactions.…”