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Temperature dependence of the rate constants for the addition of OH to benzene and to some monosubstituted aromatics -aniline, bromobenzene, and nitrobenzene- and the unimolecular decay of the adducts. Kinetics into a quasi-equilibrium

: Witte, F.; Urbanik, E.; Zetzsch, C.

Journal of physical chemistry 90 (1986), pp.3251-3259 : Lit.
ISSN: 0022-3654
Journal Article
Fraunhofer ITA ( ITEM) ()
Addukt; amines; Anilin; Aromat; Benzol; Bindungsenergie; Brombenzol; Geschwindigkeitskonstante; Hydroxylradikal; Nitrobenzol; Zerfall(unimolekular)

The pressure dependence of the rate constant for the reaction of OH with benzene and the temperature dependence of the reaction of OH radicals with benzene, aniline, bromobenzene, and nitrobenzene have been investigated by using the flash photolysis/resonance fluorescene technique. For the high- and low pressure limits of the addition of OH to benzene the rate constants k=1.3x10E-12 cubicmeters s-1 and k sub o = 3x10E-29 cm6 s-1 are obtained in the presence of Ar at 294 K. The following Arrhenius expressions of the rate constants are obtained for the temperature dependence of the addition of OH to the aromatics: 2.3x10 E-12 exp(-(190+-60)/T) cubicmeters s-1 (benzene),1.7x10E-11 exp(+560+-30)/T) cubicmeters s-1 (aniline), 1.3x10E12 exp(-(180 +-60)/T) cubicmeters s-1 (bromobenzene), and 6x10E13 exp(-(440+-80/T) cubicmeters s-1 (nitrobenzene). Biexponential decays of OH are observed in the presence of the aromatics, indicating that an adduct is formed which subsequently decomposes. The so lution of the corresponding system of differential equations allows us to determine the rate constants for the unimolecular decay of the adducts, aromatic-OH, decomposing back to the reactants. A further reaction path is observed in the case of the adduct aniline-OH (8x10E10 exp(-(7400+-1100)/T)s-1) that does not lead back to the reactants. The bond dissociation energies of OH in the adducts benzene-OH, aniline-OH, and bromobenzene-OH have been determined. (ITA)