Thermochemical properties of methyl and chloro-methyl hyplochlorites and ethers and reaction of methyl radical with CLO
Department of Chemical Engineering, Chemistry and Environmental Science
Master of Science
Bozzelli, Joseph W.
Grow, James M.
Kebbekus, Barbara B.
Vaporization, Heats of.
Hypochlorites are formed from reactions of chlorine monoxide (ClO) addition to unsaturates and association with radicals. ClO is a prevalent and an important species in chemistry of the atmosphere and in combustion systems where chlorine is present. Thermochemical property data on these oxy-chlorocarbon species are important to understanding the reaction pathways and kinetics in these environments. Enthalpy, DHf°298, entropy, S°298, and heat capacities, Cp(T) from 300 to 1500 K are determined for methyl hypochlorite and three chloro-methyl hypochlorites and formaldehyde-C1 atomcomplex radicals (CH2O--Cl, CHClO--CI, CCI2O--Cl) by density functional, and ab initio calculation methods. Molecular structures and vibration frequencies are determined at the B3LYP /6-3 1 G(d,p) density functional calculation level, with single point calculations energy at the B3LYP/G(d,p), B3LYP/6-311+G(3df,2p), QCISD(T)/6-31G(d,p), and CBS-Q levels of calculation. Enthalpies of formation are determined at each calculation level using the DH°rxn, and known enthalpies of other reactants in each of several working reactions (up to seven). Barriers for intramolecule rotation are calculated and contributions to entropy and heat capacity from internal rotation in the chloro-methyl hypochlorite, chloro-dimethyl ether, chloro-methoxy and formaldehyde-Cl atom coupling radicals are determined. Evaluation of enthalpy data from reaction (up to seven) schemes and the statistical distribution of rotation conformers, result in DHf°298for CH3OCI of - 15,4 ± 1.5, CH2 ClOCL of -22.1 ± 2, CHCl2OCl of -26.1 ± 4 and CCl3OCI of -26.7 ± 5 kcal/mol in CBS-Q//B3LYP/6-31 G(d,p) method. Evaluation of data from all 7 reaction schemes, and the statistical distribution analysis of rotation conformers, result in DHf°298 values for CH2ClOCH3 of -55.4 ± 1, CHCl2OCH3 of -61.8 ± 2, and CCl3OCH3 62.8 ± 3 kcal/mol at the CBS-Q//B** level. Enthalpies of formation are determined at each calculation level using the DHf°rxn298 and known enthalpies of other reactants in each of 6 different working reactions. The statistical distribution analysis of rotation conformers is also considered; DHf°rxn298 values for CH2ClO · of -4.5 ± 0.3, CHCl2O · of -5.6 ± 0.3, CCl3O· of - 7.5 ± 0.3, CH2O--Cl of - 2.1 ± 0.3, CHClO--Cl of - 17.5 ± 0.3, and CCl2O-Cl of -24.7 ± 0.3 kcal/mol at the CBS-Q//B3**. The reaction system (CH3Cl + ClO « CH3OCl « Products) is very important to understanding the depletion effect of chlorine chemistry on stratospheric ozone layer. Monochlorine monoxide radical (ClO) is known the cause of ozone depletion and alkyl and alkyl halides are most abundant atmosphere. The kinetics for the reactions of monochlorine monoxide radical (ClO) methyl radical are analyzed by using quantum Rice- Ramsperger- Kassel (QRRK) theory for k, (E).and a modified strong collision approach for falloff.
njit-etd2000-057 (143 pages ~ 8,706 KB pdf)
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Created January 30, 2006