Spectroscopic Characterization of the Reaction Products between the Criegee Intermediate CH 2 OO and HCl

Infrared Spectrum of the Adduct 2-Chloro-2-hydroperoxybut-3-ene [(C2H3)CCl(CH3)OOH] of the Reaction between the Criegee Intermediate Methyl Vinyl Ketone Oxide [C2H3C(CH3)OO] and HCl

Methyl vinyl ketone oxide (MVKO, C2H3C(CH3)OO) is an important Criegee intermediate produced from ozonolysis of isoprene, which is the most abundant nonmethane hydrocarbon emitted into the atmosphere. Reactions between Criegee intermediate and hydrogen chloride (HCl) are important because of their large rate coefficients. In this work, we photolyzed a mixture of (Z)-(CH2I)HC═C(CH3)I/HCl/O2 at 248 nm to produce MVKO to carry out the reaction MVKO + HCl and recorded infrared spectra of transient species with a step-scan Fourier-transform infrared absorption spectrometer. Eleven bands near 1415, 1381, 1350, 1249, 1178, 1118, 1103, 1065, 978, 931, and 895 cm-1 were observed and assigned to the hydrogen-transferred adduct (C2H3)CCl(CH3)OOH (2-chloro-2-hydroperoxybut-3-ene, CHPB) according to the predicted IR spectrum using the B3LYP/aug-cc-pVTZ method; the conformation could not be definitively determined. According to calculations, most low-energy conformers can interconvert, and the most stable conformers anti-trans-CHPB and syn-trans-CHPB might have the major contributions. Four bands near 1423, 1360, 1220, and 1080 cm-1 were observed and tentatively assigned to the OH-decomposition products (C2H3)CCl(CH3)O (1-chloro-1-methyl-2-propenyloxy, CMP); both trans-CMP and cis-CMP might contribute. Unlike in the case of CH2OO + HCl and CH3CHOO + HCl, in which secondary reactions of the OH-decomposition products reacted readily with O2 to produce the dehydrated products HC(O)Cl and CH3C(O)Cl, respectively, the secondary reaction of CMP with O2 was not observed because there is no feasible H atom in CMP for O2 to abstract.

The simplest Criegee intermediate CH2OO reaction with dimethylamine and trimethylamine: kinetics and atmospheric implications

We have used the OH laser-induced fluorescence (LIF) method to measure the kinetics of the simplest Criegee intermediate (CH2OO) reacting with two abundant amines in the atmosphere: dimethylamine ((CH3)2NH) and trimethylamine ((CH3)3N). Our experiments were conducted under pseudo-first-order approximation conditions. The rate coefficients we report are (2.15 ± 0.28) × 10-11 cm3 molecule-1 s-1 for (CH3)2NH at 298 K and 10 Torr, and (1.56 ± 0.23) × 10-12 cm3 molecule-1 s-1 for (CH3)3N at 298 K and 25 Torr with Ar as the bath gas. Both reactions exhibit a negative temperature dependence. The activation energy and pre-exponential factors derived from the Arrhenius equation were (-2.03 ± 0.26) kcal mol-1 and (6.89 ± 0.90) × 10-13 cm3 molecule-1 s-1 for (CH3)2NH, and (-1.60 ± 0.24) kcal mol-1 and (1.06 ± 0.16) × 10-13 cm3 molecule-1 s-1 for (CH3)3N. We propose that the electronegativity of the atom in the co-reactant attached to the C atom of CH2OO, in addition to the dissociation energy of the fragile covalent bonds with H atoms (H-X bond), plays an important role in the 1,2-insertion reactions. Under certain circumstances, the title reactions can contribute to the sink of amines and Criegee intermediates and to the formation of secondary organic aerosol (SOA).

Infrared Characterization of the Products of the Reaction between the Criegee Intermediate CH3CHOO and HCl

The rapid reactions between Criegee intermediates and hydrogen halides play important roles in atmospheric chemistry, particularly in the polluted urban atmosphere. Employing a step-scan Fourier transform spectrometer, we recorded infrared absorption spectra of transient species and end products of the reaction CH3CHOO + HCl in a flowing mixture of CH3CHI2/HCl/O2/N2 irradiated at 308 nm. Bands at 1453.6, 1383.7, 1357.9, 1323.8, 1271.8, 1146.2, 1098.2, 1017.5, 931.5, and 847.0 cm-1 were observed and assigned to the anti-conformer of chloroethyl hydroperoxide (anti-CEHP or anti-CH3CHClOOH). In addition, absorption bands of H2O and acetyl chloride [CH3C(O)Cl, at 1819.1 cm-1] were observed; some of them were produced from the secondary reactions of CH3CHClO + O2 → CH3C(O)Cl + HO2 and OH + HCl → H2O + Cl, according to temporal profiles of H2O and CH3C(O)Cl. These secondary reactions are conceivable because the nascent formation of CH3CHClO + OH via decomposition of internally excited CEHP was predicted by theory, and both HCl and O2 are major species in the system. The nascent formation of CH3CHClO + OH appears to be more important than that of CH3C(O)Cl + H2O, consistent with theoretical predictions. By adding methanol to deplete some anti-CH3CHOO, we observed only anti-CEHP with a reduced proportion; this observation indicates that the conversion from syn-CEHP, expected to be produced from syn-CH3CHOO + HCl, to anti-CEHP is facile. We also estimated the overall rate coefficient of the reaction syn-/anti-CH3CHOO + HCl to be kHCl = (2.7 ± 1.0) × 10-10 cm3 molecule-1 s-1 at ∼70 Torr and 298 K; this rate coefficient is about six times the only literature value kHClsyn = (4.77 ± 0.95) × 10-11 cm3 molecule-1 s-1 reported for syn-CH3CHOO + HCl by Liu et al., indicating that anti-CH3CHOO reacts with HCl much more rapidly than syn-CH3CHOO.

Reactivity and internal dynamics in the Criegee intermediate CH2OOCO2 system: A rotational study

The reaction system between the simplest Criegee intermediate, CH₂OO, and the greenhouse gas CO₂ has been investigated by Fourier transform microwave spectroscopy. The CH₂OO-CO₂ weakly bound complex was identified in the rotational spectrum, where inversion doublets due to the tunnelling motion between two equivalent configurations of the complex, with CO₂ located at one side or the other side of the CH₂OO plane, were observed. Using a two-state torsion-rotation Hamiltonian, a complete set of rotational and centrifugal distortion constants for both tunneling states were derived. In addition, the torsional energy difference between both states could be accurately determined, being 23.9687 MHz. The non-observation of the cycloaddition reaction product is in agreement with our ab initio calculations and with previous results that concluded that the reactivity of CIs toward CO₂ is measured to be quite limited.

Infrared characterization of the products and the rate coefficient of the reaction between Criegee intermediate CH2OO and HCl

Reactions between Criegee intermediates and hydrogen halides might be significant, particularly in the polluted urban atmosphere, because of their large rate coefficients. Employing a Fourier-transform spectrometer in a step-scan mode or a continuous-scan mode, we recorded infrared spectra of transient species and end products in a flowing mixture of CH₂I₂/HCl/N₂/O₂ irradiated at 308 nm. Five bands near 823.2, 1061.1, 1248.4, 1309.2, and 1359.6 cm^-1 were observed and assigned to the gauche-conformer of chloromethyl hydroperoxide (CMHP, CH₂ClOOH). At a later time of the reaction, absorption bands of H₂O and formyl chloride (CHClO) at 1782.9 cm^-1 were observed; these species were likely produced from the secondary reactions of CH₂ClO + O₂→ CHClO + HO₂ and OH + HCl → H₂O + Cl according to temporal profiles of CMHP, H₂O, and CHClO; formation of CH₂ClO + OH via decomposition of internally excited CMHP was predicted by theory and both HCl and O₂ are major species in the system. We investigated also the rate coefficient of the reaction CH₂OO + HCl on probing CH₂OO with a continuous-wave infrared quantum-cascade laser absorption system under total pressure 5.2-8.2 torr at 298 K. The rate coefficient k_HCl = (4.8 ± 0.4) × 10^-11 cm³ molecule^-1 s^-1, is comparable to the only literature value k_HCl = (4.6 ± 1.0) × 10^-11 cm³ molecule^-1 s^-1 reported by Foreman et al.

Observation of hydroperoxyethyl formate from the reaction between the methyl Criegee intermediate and formic acid

The hydroperoxide ester, hydroperoxyethyl formate, has been characterized as the nascent reaction product obtained from the reaction of the Criegee intermediate, CH₃CHOO, and formic acid.

The reaction between the methyl Criegee intermediate and hydrogen chloride: an FTMW spectroscopic study

Reaction of methyl substituted Criegee intermediate, CH₃CHOO, with hydrogen chloride investigated by rotational spectroscopy.