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Selectivity and reactivity of hot homolytic aromatic substitution by recoil chlorine atoms

Journal Article · · J. Am. Chem. Soc.; (United States)
DOI:https://doi.org/10.1021/ja00451a008· OSTI ID:7311239
; ;
Hot homolytic aromatic chlorination has been studied in simple monosubstituted benzenes C/sub 6/H/sub 5/X (X = F, Cl, Br, I, NH/sub 2/, OCH/sub 3/, NO/sub 2/) using recoil chlorine atoms produced via the /sup 37/Cl(m,..gamma..)/sup 38/Cl reaction. In the gas phase, Cl-for-H substitution is a minor process, proceeding exclusively via hot direct replacement with little selectivity. In the liquid phase, dilution experiments reveal that two processes contribute to hydrogen substitution: a one-step reaction being first order with respect to the concentration of the aromatic substrate and a multistep process involving at least two substrate molecules. In either case the Cl atoms exhibit slight electrophilic features. Application of the Hammett correlation reveals a higher selectivity (rho/sup +/ = -1.43) for the multistep than for the one step process (rho/sup +/ = -0.56). Both chlorination reactions seem to proceed via complex formation. In the case of Cl-for-X substitution, thermoneutral or exothermic processes (X = Cl, Br, I, NO/sub 2/) can be attributed to thermal sigma-complex formation, while endothermic processes (X = F, OCH/sub 3/, NH/sub 2/) are typically low yield, direct hot replacement reactions being first order with respect to the substrate concentration.
Research Organization:
Kernforschungsanlage, Juelich GmbH, Ger.
OSTI ID:
7311239
Journal Information:
J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 99:9; ISSN JACSA
Country of Publication:
United States
Language:
English

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Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400701* -- Radiochemistry & Nuclear Chemistry-- Hot-Atom Chemistry
AROMATICS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISTRY
CHLORINATION
CHLORINE 38
CHLORINE ISOTOPES
HALOGENATION
HOT ATOM CHEMISTRY
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
KINETICS
LIGHT NUCLEI
MINUTES LIVING RADIOISOTOPES
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
RADIOCHEMISTRY
RADIOISOTOPES
REACTION KINETICS
SECONDS LIVING RADIOISOTOPES