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Organic Pollutants
Published in Paul Mac Berthouex, Linfield C. Brown, Chemical Processes for Pollution Prevention and Control, 2017
Paul Mac Berthouex, Linfield C. Brown
An aldehyde contains a formyl group with the structure –CHO. The carbon atom shares a double bond with an oxygen atom. Aldehydes are derived from alcohols by dehydrogenation (removing a hydrogen atom). Many aldehydes have pleasant odors. The low-molecular-weight aldehydes are important for the synthesis of many industrial chemicals.
Mechanistic and kinetic approach on methyl isocyanate (CH3NCO) with OH and Cl
Published in Molecular Physics, 2022
Manas Ranjan Dash, Subhashree Subhadarsini Mishra
Using high-level DFT and ab-initio calculations, the kinetics and mechanisms of the hydrogen atom abstraction reactions of CH3NCO with OH radical and Cl atom are investigated. The rate constants for the H-atom abstraction reactions of CH3NCO with OH radical and Cl atom are 2 × 10−13 and 2.5 ×10−12 cm3·molecule−1·s−1 at room temperature and atmospheric pressure, respectively, which are reasonably consistent with the experimental values. This work represents the first theoretical kinetic investigations on the CH3NCO + OH/Cl reactions as a function of temperature. Moreover, the thermochemical analysis of the tropospheric degradation pathways of the alkyl isocyanate radical indicates that the final products are formaldehyde, formyl isocyanate, NCO, HCO and HO2 radicals, which are known to be harmful and further degraded into CO, CO2 and N2O. However, estimated OH-driven tropospheric lifetimes of CH3NCO are found to be not high enough (∼eighty days) and compete with the reaction of chlorine atoms in the coastal and marine boundary layer (where the chlorine concentration is high). GWPs and POCPs were also found to be small thus indicating slight damage to the Earth’s atmosphere. We hope that the present theoretical studies will strengthen the chemical kinetics database and depth of understanding for further inspection of the reactions concerning analogous species.
Quantum chemical study on ·Cl-initiated degradation of ethyl vinyl ether in atmosphere
Published in Molecular Physics, 2020
Dandan Han, Haijie Cao, Fengrong Zhang, Maoxia He
Schematic potential energy surfaces for the subsequent reactions of IM13 are depicted in Figure 5. H atom could be abstracted from C3 directly or with the help of O2 molecular. Both pathways, forming ethyl chloroacetate (P1), are prone to occur because of the lower energy barriers (10.39 and 15.85 kcal mol−1). The third pathway is the cleavage of C1–C2 single bond and synchronous formation of C2 = O2 double bond. Ethyl formate (P2) and ClCH2 radical (IM14) are formed with the energy barrier of 4.23 kcal mol−1 and the reaction heat of −9.94 kcal mol−1. The fourth dissociation reaction of IM13 is the bond breaking of C2-O1 and the formation of C2 = O2, leading to the generation of 2-chloroacetaldehyde (P5) and OC2H5 radical. The energy barrier and reaction heat of this route are 21.46 and 11.72 kcal mol−1, respectively. The last process is the formation of alcohol (P7) and IM19 via the rupture of C2-O1 and the H-shift from C2 to O1 atom, with the energy barrier of 13.66 kcal mol−1 and the exothermic heat of 0.80 kcal mol−1. The subsequent pathways of IM14, IM18 and IM19 could form formyl chloride (P3), formaldehyde (P4) and acetaldehyde (P6), which have been discussed in our previous work [58,59]. Comparing the energy barriers and the reaction heats of the further reactions of IM13, we can draw a conclusion that ethyl chloroacetate (P1), ethyl formate (P2), formyl chloride (P3) and formaldehyde (P4) are the most favourable products, while 2-chloroacetaldehyde (P5), acetaldehyde (P6) and alcohol (P7) are secondary products.
Experimental Study and a Short Kinetic Model for High-Temperature Oxidation of Methyl Methacrylate
Published in Combustion Science and Technology, 2019
Shanmugasundaram Dakshnamurthy, Denis A. Knyazkov, Artem M. Dmitriev, Oleg P. Korobeinichev, Elna J.K. Nilsson, Alexander A. Konnov, Krithika Narayanaswamy
The other product, formaldehyde, forms formyl radicals, which then forms CO through well-understood pathways. Carbon monoxide predominantly gets consumed via the familiar exothermic reaction, , which displays positive sensitivity coefficient toward laminar burning velocities, whereas the H atom gets consumed mostly via the branching reaction, , which also has positive sensitivity coefficient (see Figure 10) as noted earlier. This discussion explains why the H-abstraction reactions at the alkylic site of MMA have positive sensitive coefficients toward laminar burning velocities.