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Applied Chemistry and Physics
Published in Robert A. Burke, Applied Chemistry and Physics, 2020
Hydrocarbon derivatives are formed when one or more hydrogen atoms are removed from a hydrocarbon compound (Figure 3.60). When hydrogen is removed, the compound is no longer complete or the same compound. The compound without the hydrogen is considered a “radical.” Radicals, as they are not complete compounds, do not exist for very long because of the need to bond with some other elements. Therefore, responders will not encounter tanker trucks, or other containers of methyl or other radicals going down the highway. Because the radicals are not the same compounds as they were, the compound name is changed to indicate that the hydrocarbon is a radical of the original compound. The same compound names are used to identify the number of carbons present in a radical as in the hydrocarbon compounds they came from. For example, if methane, an alkane hydrocarbon with all single bonds, has one hydrogen removed, it is no longer methane. There is still one carbon, so “meth” is used, and a “yl” is added to the “meth” to form the name “methyl.” Therefore, a one-carbon radical of methane is the methyl radical.
Chemicals from Paraffin Hydrocarbons
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
The first step in the process involves the breaking of the chlorine-chlorine bond which forms two chlorine (Cl•) free radicals after which the chlorine free radical reacts with methane to form a methyl free radical (CH3•) and hydrogen chloride. The methyl radical then reacts in a subsequent step with a chlorine molecule, forming methyl chloride and a chlorine radical: Cl•+CH4→CH3+HClCH3•+Cl2→CH3Cl+Cl•
Air pollution impacts on ozone
Published in Abhishek Tiwary, Ian Williams, Air Pollution, 2018
The resulting methyl radicals are then involved in further oxidation reactions. One of the major advances in atmospheric chemistry in the last decade has been realisation of the importance of the OH hydroxyl radical in many atmospheric reactions that remove pollutants, despite its low concentration of a few ppt. Hydroxyl radicals oxidise many of the trace constituents in a low-temperature burning of atmospheric rubbish which dominates the daytime chemistry of the troposphere. Production of OH is by reaction of water vapour with O(1D), which is the oxygen atom in the excited singlet state in which it is most reactive. O3→hνO2+O(1D)O(1D)+M→O+MO(1D)+H2O→2OH
Modelling of acetaldehyde and acetic acid combustion
Published in Combustion Theory and Modelling, 2023
Fekadu Mosisa Wako, Gianmaria Pio, Ernesto Salzano
H-abstraction reaction of acetic acid by OH radical has two product channels: R3 and R4. R3 is an important reaction leading to the formation of ketene (CH2CO) since ketene is formed through β-scission decomposition of CH2COOH. In the present study, the rate constants of R3 and R4 were taken from the study reported by Cavallotti et al. [28]. Majorly ketene gets consumed and significantly contributes to the formation of methyl radicals through H-abstraction reaction by; CH2CO + H (+ M) ↔ CH3 + CO (+ M). CH2CO is a key intermediate species in the combustion of acetic acid, which is produced during fuel decomposition [55] or in flames [26]. It has also been shown to play a major role in the consumption of acetylene (C2H2), and to balance the formation of C1 and C2 species in C2H2 flames [62, 63]. Similarly, H-abstraction reactions by H atoms have two decomposition routes for the formation of the carboxymethyl group of acetic acid:
Advanced nanomaterials for highly efficient CO2 photoreduction and photocatalytic hydrogen evolution
Published in Science and Technology of Advanced Materials, 2022
Rashmi Nautiyal, Deepika Tavar, Ulka Suryavanshi, Gurwinder Singh, Archana Singh, Ajayan Vinu, Gurudas P. Mane
The carbene pathway contains CO as an intermediate, along with methanol and formaldehyde. When CO2˙ˉ is linked to the catalyst via the carbon atom, the carbene pathway is preferred. The attachment of ˙H to the O of CO2˙ˉ causes the breaking of the C-O bond. The CO left on the surface can accept 2 additional electrons leaving carbon residues on the surface. These radicals can further combine with 4˙H to form a CH˙ radical, carbene, a methyl radical, and ultimately methane. In case, if methyl radical combines with OH radical, methanol is formed [62]. This methanol is an intermediate rather than a side product, and no traces of HCHO were found. Carbene pathway on isolated Ti4+ species embedded on the zeolite surface has been reported. Here, the quantum confinement effect resulted in the formation of charged transfer excited state species (Ti3+O)*where photogenerated electrons and holes are localized on the neighboring atom. If a metal co-catalyst is not used, then this charge transfer excited state species (Ti3+-O-)* forms methanol as a major product [79].
Active Thermochemical Tables: the thermophysical and thermochemical properties of methyl, CH3, and methylene, CH2, corrected for nonrigid rotor and anharmonic oscillator effects
Published in Molecular Physics, 2021
Methyl radical is a ubiquitous and remarkably stable intermediate in a variety of reactive environments, such as combustion of hydrocarbons, atmospheric reactions, many industrially and ecologically relevant processes, and is present in exoplanetary atmospheres as well as in the interstellar medium. It is, in fact, the first gas-phase radical that was produced in a controlled laboratory experiment (pyrolysis of tetramethyllead) and demonstrated to survive for several milliseconds as a transient species [59]. Spectroscopically, it was first detected by Herzberg [60,61] (obtained by flash photolysis of dimethylmercury). As demonstrated early on [62–65], the radical is planar and belongs to the D3h point group.