Kinetics of the OH and Cl reactions with N-methylformamide, N,N-dimethylformamide and N,N-dimethylacetamide

Atmospheric Oxidation of Hydroperoxy Amides

Recently, hydroperoxy amides were identified as major products of OH-initiated autoxidation of tertiary amines in the atmosphere. The formation mechanism is analogous to that found for ethers and sulfides but substantially faster. However, the atmospheric fate of the hydroperoxy amides remains unknown. Using high-level theoretical methods, we study the most likely OH-initiated oxidation pathways of the hydroperoxy and dihydroperoxy amides derived from trimethylamine autoxidation. Overall, we find that the OH-initiated oxidation of the hydroperoxy amides predominantly leads to the formation of imides under NO-dominated conditions and more highly oxidized hydroperoxy amides under HO2-dominated conditions. Unimolecular reactions are found to be surprisingly slow, likely due to the restricting, planar structure of the amide moiety.

The reaction of Criegee intermediates with formamide and its implication to atmospheric aerosols

The reactions of Criegee intermediates (CIs) play an important role in the formation of secondary organic aerosols that have negative effect on visibility, human health, and global climate. New particle formation (NPF) can contribute to more than half of the aerosols in terms of their number concentration. Here, the reactions of CIs with formamide (FA) in the gas-phase and at the air/water interface were investigated using quantum chemistry calculation and Born-Oppenheimer molecular dynamic simulations. The results show that the reaction mechanism of CIs with FA is similar to that with formic acid, and the formation of hydroperoxymethyl formimidate (P4) is the most favorable pathway both in the gas-phase and at the air/water interface. Moreover, the potential contribution of the products to NPF was also evaluated by means of the molecular dynamic simulations. The results indicate that the product (P4) can participate in the SA-based NPF and water molecules are beneficial to enhance the NPF. The exploration will provide insight into the reaction of CIs with amide and the effect of the Criegee chemistry on the atmospheric aerosols.

OH Kinetics with a Range of Nitrogen-Containing Compounds: N-Methylformamide, t-Butylamine, and N-Methyl-propane Diamine

Emissions of amines and amides to the atmosphere are significant from both anthropogenic and natural sources, and amides can be formed as secondary pollutants. Relatively little kinetic data exist on overall rate coefficients with OH, the most important tropospheric oxidant, and even less on site-specific data which control the product distribution. Structure-activity relationships (SARs) can be used to estimate both quantities. Rate coefficients for the reaction of OH with t-butylamine (k₁), N-methyl-1,3-propanediamine (k₂), and N-methylformamide (k₃) have been measured using laser flash photolysis coupled with laser-induced fluorescence. Proton-transfer-reaction mass spectrometry (PTR-MS) has been used to ensure the reliable introduction of these low-vapor pressure N-containing compounds and to give qualitative information on products. Supporting ab initio calculations are presented for the t-butylamine system. The following rate coefficients have been determined: k_1,298K= (1.66 ± 0.20) × 10^-11 cm³ molecule^-1 s^-1, k(T)₁ = 1.65 × 10^-11 (T/300)^-0.69 cm³ molecule^-1 s^-1, k_2,293K = (7.09 ± 0.22) × 10^-11 cm³ molecule^-1 s^-1, and k_3,298K = (1.03 ± 0.23) × 10^-11 cm³ molecule^-1 s^-1. For OH + t-butylamine, ab initio calculations predict that the fraction of N-H abstraction is 0.87. The dominance of this channel was qualitatively confirmed using end-product analysis. The reaction of OH with N-methyl-1,3-propanediamine also had a negative temperature dependence, but the reduction in the rate coefficient was complicated by reagent loss. The measured rate coefficient for reaction 3 is in good agreement with a recent relative rate study. The results of this work and the literature data are compared with the recent SAR estimates for the reaction of OH with reduced nitrogen compounds. Although the SARs reproduce the overall rate coefficients for reactions, site-specific agreement with this work and other literature studies is less strong.

A theoretical study of hydrogen-bonded molecular clusters of sulfuric acid and organic acids with amides

Amides, a series of significant atmospheric nitrogen-containing volatile organic compounds (VOCs), can participate in new particle formation (NPF) throught interacting with sulfuric acid (SA) and organic acids. In this study, we investigated the molecular interactions of formamide (FA), acetamide (AA), N-methylformamide (MF), propanamide (PA), N-methylacetamide (MA), and N,N-dimethylformamide (DMF) with SA, acetic acid (HAC), propanoic acid (PAC), oxalic acid (OA), and malonic acid (MOA). Global minimum of clusters were obtained through the association of the artificial bee colony (ABC) algorithm and density functional theory (DFT) calculations. The conformational analysis, thermochemical analysis, frequency analysis, and topological analysis were conducted to determine the interactions of hydrogen-bonded molecular clusters. The heterodimers formed a hepta or octa membered ring through four different types of hydrogen bonds, and the strength of the bonds are ranked in the following order: SOH•••O > COH•••O > NH•••O > CH•••O. We also evaluated the stability of the clusters and found that the stabilization effect of amides with SA is weaker than that of amines with SA but stronger than that of ammonia (NH₃) with SA in the dimer formation of nucleation process. Additionally, the nucleation capacity of SA with amides is greater than that of organic acids with amides.

Degradation of liquid phase N,N-dimethylformamide by dielectric barrier discharge plasma: Mechanism and degradation pathways

The degradation of liquid phase N,N-dimethylformamide (DMF) using the dielectric barrier discharge (DBD) plasma was studied in the present study. The results showed that 1000 mg L^-1 DMF could be degraded by DBD plasma under different input power, treatment time and initial pH values of aqueous solution. After 40 min with DBD plasma discharge, 52.2% degradation efficiency was achieved at DMF concentration of 1000 mg L^-1 with an input power of 16.19 W under initial pH of 11.14 in aqueous solution, and the energy efficiency of the system was 13.2 mg kJ^-1. The removal efficiency decreased with the presence of radical scavenger, manifesting that •OH plays a critical role in the degradation process. The value of TOC in DMF aqueous solution decreased from 790 mg L^-1 to 507 mg L^-1 in 40 min, which indicated that DBD plasma has the ability to mineralize a portion of DMF in liquid directly. Additionally, the analysis of FTIR, HPLC and the small molecular organic compounds before and after the DBD plasma degradation indicated that the intermediates of DMF in degradation process were N-methylformamide, methanol, formaldehyde and formic acid, which were finally mineralized into ammonia nitrogen, CO₂ and H₂O. Moreover, the possible degradation mechanism and pathways were proposed.

A density functional theory study of the molecular interactions between a series of amides and sulfuric acid

Amides, a class of nitrogen-containing organic pollutants in the atmosphere, may affect the formation of atmospheric aerosols by the interactions with sulfuric acid. Here, the molecular interactions of sulfuric acid with formamide, methylformamide, dimethylformamide, acetamide, methylacetamide and dimethylacetamide was investigated by density functional theory. Geometry optimization and Gibbs free energy calculation were carried out at M06-2X/6-311++G(3df,3pd) level. The results indicate that the addition of amides to H₂SO₄ might have a promoting effect on atmospheric new particle formation at 298.15 K and 1 atm. In the initial stage of new particle formation, the binding capacity of amides and sulfuric acid is stronger than ammonia, but weaker than methylamine. It is worth noting that the trans-methylacetamide could have similar capabilities of stabilizing sulfuric acid as dimethylamine. In the presence of water, amides are found to only have a weak enhancement capability on new particle formation. In addition, we can infer from evaporation rate that the small molecule clusters of formamide and sulfuric acid may be more energetically favorable than macromolecule clusters.

Uptake of Gaseous Alkylamides by Suspended Sulfuric Acid Particles: Formation of Ammonium/Aminium Salts

Amides represent an important class of nitrogen-containing compounds in the atmosphere that can in theory interact with atmospheric acidic particles and contribute to secondary aerosol formation. In this study, uptake coefficients (γ) of six alkylamides (C₁ to C₃) by suspended sulfuric acid particles were measured using an aerosol flow tube coupled to a high resolution time-of-flight chemical ionization mass spectrometer (HRToF-CIMS). At 293 K and < 3% relative humidity (RH), the measured uptake coefficients for six alkylamides were in the range of (4.8-23) × 10^-2. A negative dependence upon RH was observed for both N-methylformamide and N,N-dimethylformamide, likely due to decreased mass accommodation coefficients (α) at lower acidities. A negative temperature dependence was observed for N,N-dimethylformamide under < 3% RH, also consistent with the mass accommodation-controlled uptake processes. Chemical analysis of reacted sulfuric acid particles indicates that alkylamides hydrolyzed in the presence of water molecules to form ammonium or aminium. Our results suggest that multiphase uptake of amides will contribute to growth of atmospheric acidic particles and alter their chemical composition.

Gas-Phase Mechanisms of the Reactions of Reduced Organic Nitrogen Compounds with OH Radicals

Research on the fate of reduced organic nitrogen compounds in the atmosphere has gained momentum since the identification of their crucial role in particle nucleation and the scale up of carbon capture and storage technology which employs amine-based solvents. Reduced organic nitrogen compounds have strikingly different lifetimes against OH radicals, from hours for amines to days for amides to years for isocyanates, highlighting unique functional group reactivity. In this work, we use ab initio methods to investigate the gas-phase mechanisms governing the reactions of amines, amides, isocyanates and carbamates with OH radicals. We determine that N-H abstraction is only a viable mechanistic pathway for amines and we identify a reactive pathway in amides, the formyl C-H abstraction, not currently considered in structure-activity relationship (SAR) models. We then use our acquired mechanistic knowledge and tabulated literature experimental rate coefficients to calculate SAR factors for reduced organic nitrogen compounds. These proposed SAR factors are an improvement over existing SAR models because they predict the experimental rate coefficients of amines, amides, isocyanates, isothiocyanates, carbamates and thiocarbamates with OH radicals within a factor of 2, but more importantly because they are based on a sound fundamental mechanistic understanding of their reactivity.

The reactions of N-methylformamide and N,N-dimethylformamide with OH and their photo-oxidation under atmospheric conditions: experimental and theoretical studies

The atmospheric oxidation of amides is studied with a combination of laser photolysis and smog chamber experiments along with quantum chemical and statistical rate theory calculations.

Experimental and theoretical understanding of the gas phase oxidation of atmospheric amides with OH radicals: kinetics, products, and mechanisms

Atmospheric amides have primary and secondary sources and are present in ambient air at low pptv levels. To better assess the fate of amides in the atmosphere, the room temperature (298 ± 3 K) rate coefficients of five different amides with OH radicals were determined in a 1 m(3) smog chamber using online proton-transfer-reaction mass spectrometry (PTR-MS). Formamide, the simplest amide, has a rate coefficient of (4.44 ± 0.46) × 10(-12) cm(3) molec(-1) s(-1) against OH, translating to an atmospheric lifetime of ∼1 day. N-methylformamide, N-methylacetamide and propanamide, alkyl versions of formamide, have rate coefficients of (10.1 ± 0.6) × 10(-12), (5.42 ± 0.19) × 10(-12), and (1.78 ± 0.43) × 10(-12) cm(3) molec(-1) s(-1), respectively. Acetamide was also investigated, but due to its slow oxidation kinetics, we report a range of (0.4-1.1) × 10(-12) cm(3) molec(-1) s(-1) for its rate coefficient with OH radicals. Oxidation products were monitored and quantified and their time traces were fitted using a simple kinetic box model. To further probe the mechanism, ab initio calculations are used to identify the initial radical products of the amide reactions with OH. Our results indicate that N-H abstractions are negligible in all cases, in contrast to what is predicted by structure-activity relationships. Instead, the reactions proceed via C-H abstraction from alkyl groups and from formyl C(O)-H bonds when available. The latter process leads to radicals that can readily react with O2 to form isocyanates, explaining the detection of toxic compounds such as isocyanic acid (HNCO) and methyl isocyanate (CH3NCO). These contaminants of significant interest are primary oxidation products in the photochemical oxidation of formamide and N-methylformamide, respectively.

Estimation of gas-phase reaction rate constants of alkylnaphthalenes with chlorine, hydroxyl and nitrate radicals

Quantitative structure-property relationship/quantitative structure-activity relationship (QSPR/QSAR) models were developed for rate constants (k) of alkylnaphthalene reactions with chlorine (Cl), hydroxyl (*OH) and nitrate (NO(3)) radicals using partial least squares (PLS) regression. Quantum chemical descriptors computed by Parametric Method 3 (PM3) Hamiltonian were used as predictor variables. The cross-validated Q(cum)(2)values for the optimal QSPR/QSAR models of alkylnaphthalenes are 0.896, 0.728 and 0.774 for Cl, *OH and NO(3) radicals, respectively. Results from this study showed that rate constants with Cl, *OH and NO(3) are governed by different molecular structural descriptors. In the developed optimal QSPR/QSAR models, frontier molecular orbital energies and atomic charges are major descriptors that affect log k values. When the highest occupied molecular orbital (E(HOMO)) energy, the lowest unoccupied molecular orbital (E(LUMO)) energy, E(LUMO)+E(HOMO), and the average of net atomic charges on carbon atoms (Q(Cave)) are higher, the corresponding alkylnaphthalene reaction rate constants would be higher. In contrast, higher values of the most positive net atomic charges on hydrogen atoms (Q(H)(+)) could lead to the decrease of log k values. H-atom abstraction may occur on the hydrogen atom with the highest atomic charge (Q(H)). Radical addition reaction may also occur on the carbon (e.g. the carbon bonded to the alkyl group) with higher atomic charge (Q(C)) values. Other descriptors such as molecular weight (M(w)), standard heat of formation (DeltaH(f)), total energy (TE), electronic energy (EE), core-core repulsion energy (CCR), average molecular polarizability (a) and dipole moment (mu) were also important descriptors in the QSPR/QSAR models.