The Mechanistic Study Of The Ozone Depletion By Halomethylidyne Radicals And The Carboxylation Reaction Of Benzene With Carbon Dioxide

Halogenated hydrocarbon radicals can be produced due to the ultravioletirradiation of halogenated hydrocarbon wastes spreading into the ozone layer. They willreact with ozone and deplete ozone. The clarification of their reaction mechanisms ishelpful to provide a theoretical basis and practical guidance for the control of ozonedepletion by halogenated hydrocarbon radicals. The reaction mechanisms of theCX(X=F, Cl, Br) radicals with O3were studied using density functional methods at theB3LYP/6-311G(d, p) level. It is found that the CF+O3reaction possesses five productchannels: P1(FCO+O2), P2(FCO2+O), P3(CO2+O+F), P4(CO2+FO) and P5(CO+O2+F);the CCl+O3reaction has five product channels: P1(ClCO+O2), P2(CO2+Cl+O), P3(CO2+ClO), P4(CO+O2+Cl) and P5(OCO2+Cl); for the CBr+O3reaction,there are six product channels, P1(BrCO+O2), P2(OCO2+Br), P3(CO2+O+Br),P4(CO2+BrO), P5(CO+O2+Br) and P6(BrCOO+O). The main products of thethree reactions are P(XCO+O2). The X(X=F, Cl, Br) atom substitutions have effects onthe reaction mechanisms of halogenated methylidyne radicals with ozone. Firstly, theinitial association of the reactants is influenced. In the first step of the CF+O3reaction,CF only attacks the both end oxygen atoms of O3, producing non-planar structureintermediate XCO2O, but in the first step of the reactions, CCl+O3and CBr+O3, CXcan not only attacks the both end oxygen atoms of O3, but also attacks the middleoxygen atom, generating planar structure XCOO2, and secondly different replacementinfluences the isomerization and dissociation ways of the association complex, whichleads to the different product channels and formation pathways.It is greatly significant to utilize carbon dioxide chemically and to produce aromaticcarboxylic acid compounds through benzene carboxylation reactions by carbon dioxideunder the catalysis of aluminium chloride. It is necessary to make the reactionmechanism clear. The four reaction processes were studied using density functionaltheory B3LYP method, which are thatAl2Cl（6orAlCl3）firstly activate carbon dioxide or benzene and then carboxylation reactions are carried out. The reaction pathway that theactivation of benzene, leading to the formation of aryl aluminum halides (C6H5Al2Cl5orC6H5AlCl2), is followed by the carboxylation by using carbon dioxide is more favorablethan that the activation of carbon dioxide followed by the carboxylation, whether thealuminium chloride is dimers or monomer. And the dimers catalysis reactionmechanism is more preferable than monomer catalysis. The results can provide atheoretical guidance for the experimental study of the preparation of aromatic acidcompounds by aromatic hydrocarbons carboxylation with carbon dioxide in the future.