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Kinetic H/D isotope effects for gas phase hydroxylation of benzene and chlorobenzene between 520–1080 K. Hydroxyl radical versus O( 3 P) atom attack
Author(s) -
Mulder Peter,
Louw Robert
Publication year - 1988
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550200707
Subject(s) - chemistry , chlorobenzene , kinetic isotope effect , cyclohexane , intramolecular force , benzene , arrhenius equation , phenol , medicinal chemistry , methanol , photochemistry , stereochemistry , deuterium , activation energy , organic chemistry , catalysis , physics , quantum mechanics
Gas phase slow combustion of (chloro)benzene in O 2 /N 2 mixtures, and induced by addends such as tert butylhydroperoxide, cyclohexane, or methanol, leads to (chloro)‐phenol as the only important aromatic product. Using C 6 H 6 /C 6 D 6 mixtures, formation of phenol/perdeuterophenol was studied between 520–1080 K. The temperature dependence of this product ratio was found to obey the Arrhenius expression for the intermolecular isotope effect log k H / k D = −0.14 ± 0.03 + (1240 ± 80)/2.303 RT ( R in cal/mol K). Essentially the same result was obtained for the intramolecular isotope effect, measuring the change in isomer distribution for the chlorophenols formed from p‐deuterio‐chlorobenzene versus those for chlorobenzene. These results are in accordance with H(D)‐abstraction by ·OH, via a linear transition state, as the first and (relative) rate determining step. Whereas above 1000 K, at reduced pressure, the intramolecular isotope effect continues to prevail, C 6 H 6 /C 6 D 6 do not show differences in rate of formation of C 6 H 5 OH/C 6 D 5 OH. Under these conditions, the only effective reaction of arene to phenol appears to be set in by addition of O( 3 P).