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Thermal Hydrogenolysis of Nitrogen‐Containing (Hetero)arenes at Elevated Temperature and Pressure
Author(s) -
Cieplik Mariusz K.,
Louw Robert
Publication year - 2004
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200400077
Subject(s) - chemistry , benzonitrile , benzene , hydrogen , hydrogenolysis , pyridine , photochemistry , supercritical fluid , hydrogen atom abstraction , thermal decomposition , quinoline , medicinal chemistry , organic chemistry , catalysis
The behaviour of the aromatic nitrogen derivatives pyridine P and quinoline Q − and for comparison benzonitrile and azobenzene − was studied under elevated pressure (20 to 30 bar) in a flow reactor with an atmosphere of hydrogen at temperatures ranging from 773 to 1173 K. Compounds were introduced into the reactor admixed with benzene. Efficient removal of the heteroelement was observed, accompanied by deep gasification of the carbon skeletons, at higher temperatures. P reacts much faster than benzene, while Q is a little less reactive than P . The main products were methane, hydrogen cyanide and ammonia. Mechanisms are discussed based on induced decomposition by hydrogen atoms. The facile reaction of P is explained by hydrogen abstraction to give the 2‐pyridyl radical followed by ring opening, a reaction with much better thermochemistry than that for benzene and the phenyl radical. Reaction via (partially) hydrogenated intermediates may also play a part. “Exocyclic” nitrogen − such as in benzonitrile − is readily displaced by hydrogen, while for azobenzene spontaneous fission of the rather weak C−N bond is the major rate‐ (and product‐) determining step. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)