Elementary reaction

About: Elementary reaction is a research topic. Over the lifetime, 2972 publications have been published within this topic receiving 76110 citations.

On the mechanism of boron-subphthalocyanine chloride formation

Abstract: A mechanistic study of chloroboron subphthalocyanine (SubPc) formation from phthalonitrile and BCl3 in aromatic solvents such as p-xylene or toluene suggests that rearrangement of the initial phthalonitrile-BCl3 adduct produces (1Z)-3-chloro-N-(dichloroboryl)-1H-isoindol-1-imine 3, following rearrangement of the initial phthalonitrile-BCl3 adduct. From three molecules of (1Z)-3-chloro-N-(dichloroboryl)-1H-isoindol-1-imine 3, by successive addition, the dichlorosubstituted macrocycle 7 is formed. Quantum-chemical computation shows that the postulated elementary reaction steps leading up to the formation of the SubPc-precursor macrocycle are indeed exothermic, or at least kinetically allowed. The formation of the SubPc is concluded by the elimination of chlorine which is probably catalyzed by BCl3 in a concerted process which might be represented as: dichlorosubstituted macrocycle 7 + BCl3 → SubPc·Cl+ + BCl4- → SubPc + Cl2 + BCl3. The chlorine formed may be photolytically affected if the reaction is carried out under ordinary laboratory lighting (fluorescent lamps), giving rise to a free-radical chain reaction involving the solvent. Alternatively, molecular chlorine may react with aromatic solvents such as toluene and p-xylene in a Friedel-Crafts-type reaction catalyzed by BCl3. In this way, such solvents which are reactive in both ways can protect the reactant phthalonitrile, the reaction intermediates, and the product SubPc from degradation by chlorination.

Preparation of Silicon Nitride Powder from Silica

Abstract: Although thermodynamic data predict the difficulty in advancing the reaction, 3SiO2(S) + 6C(S) + 2N2(G) = Si3N4(S) + 6CO(G), in a closed system, it has been proved that heating fine powder mixtures of silica and carbon in nitrogen gas flow results in sufficient formation of silicon nitride powder, without detectable coexisting silicon carbide. Apparent activation energy (≃163 kcal/mol) on the reaction approximates to the value of ∆Hr (≃l60 kcal/mol at 1700 K) calculated on the elementary reaction, SiO2(S) + C(S) = SiO(G) + CO(G), which therefore seems to be a rate-determining one. The observation of fibrous silicon nitride growing out into gaps among aggregated powder lumps and that of weight losses of samples larger than expected suggest that SiO gas should be generated as an intermediate product. Silicon nitride powder prepared from silica through the improved reaction process possesses excellent characteristics such as high α-phase content, homogeneous shape and size, and very low content of metallic impurities.

The mechanism and activity of oxygen reduction reaction on single atom doped graphene: a DFT method

Abstract: Heteroatom doped graphene as a single-atom catalyst for oxygen reduction reaction (ORR) has received extensive attention in recent years. In this paper, the ORR activity of defective graphene anchoring single heteroatom (IIIA, IVA, VA, VIA and VIIA) was systematically investigated using a dispersion-corrected density functional theory method. For all of the 34 catalysts, 14 of which were further analyzed, and the Gibbs free energy of each elementary reaction was calculated. According to the scaling relationship between ΔGOOH* and ΔGOH*, we further analyzed the rate-determining step of the remaining 20 catalysts. The results show that when the ORR reaction proceeds in the path O2 → OOH → O → OH → H2O, the reaction energy barriers are lower than 0.8 eV for Te-SV, Sb-DV, Pb-SV, Pb-DV, As-SV, As-DV, B-SV, Sn-SV and N-SV. Our result provides a theoretical basis for further exploration of carbon-based single-atom catalysts for ORR.

Complex chemical kinetics in supersonic nozzle flow

Abstract: The subject to be discussed is that in which many elementary chemical reactions occur simultaneously in a gas undergoing laminar, steady, adiabatic flow through a supersonic expanzion nozzle. Some general comments on the techniques involved in the numerical analysis of this type of non-equilibrium flow with a high-speed digital computer will be given, but the emphasis throughout is on the chemical kinetic aspects of the problem. All internal degrees of freedom of the molecules are assumed to be in equilibrium with the local translational temperature everywhere. The flow is taken to be one dimensional in the usual fluid dynamic sense. The interaction between chemical and fluid dynamic variables is illustrated by actual results on two types of mixtures. The first is characteristic of many ordinary solid or liquid rocket propellant exhaust gases and contains the species H2, H2O, CO, CO2, H, and OH. The reasons for assuming that these take part in four elementary (reversible) reactions of importance are given. The second example considers a mixture containing the active species H2, H2O, O2, H, OH, and O such as would be involved in a hydrogen-fueled ramjet, where eight elementary reactions are used. The relative significance of two-body and three-body reactions in influencing the gas composition and other flow variables is discussed. Some indication of the sensitivity of the results to the magnitudes assumed for the rate constants will be given. The degree of utility and validity of various popular approximations in this field is assessed, and some practical implications pointed out.