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Sauerstoff‐Abfang von Radikalen in überkritischem Kohlendioxid; Bildungsenthalpie und Rekombinationsbarriere des Cycloheptatrienyl‐Radikals
Author(s) -
Roth Wolfgang R.,
Hunold Frank,
Neumann Martin,
Bauer Frank
Publication year - 1996
Publication title -
liebigs annalen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0947-3440
DOI - 10.1002/jlac.199619961029
Subject(s) - chemistry , radical , homolysis , oxygen , reaction rate constant , bond dissociation energy , supercritical carbon dioxide , bond cleavage , dissociation (chemistry) , medicinal chemistry , supercritical fluid , photochemistry , organic chemistry , kinetics , catalysis , physics , quantum mechanics
Oxygen Trapping of Radicals in Supercritical Carbon Dioxide; Heat of Formation and Recombination Barrier of the Cycloheptatrienyl Radical The homolytic thermal cleavage of bitropenyl ( 1 ) in supercritical carbon dioxide has been measured in the presence of 1 to 180 bar oxygen between 120 and 170°C. From these data the activation parameters of the dissociation and recombination reaction are derived, which lead to a heat of formation for the tropenyl radical ( 2 ) of Δ H f o = 64.7 kcal · mol −1 . By using this value a radical stabilization energy (RSE) or 31.5 kcal · mol −1 is obtained, which differs by 1.7 kcal · mol −1 from the planar, acyclic isomer ( trans,trans ‐1,3,6‐trien‐5‐yl: RSE = 29.8 kcal · mol −1 ), which is practically equivalent to the relief of ring strain due to the formation of the radical. In agreement with the observed stability of 2 the equilibrium constant for its reaction with oxygen at 143°C is K eq = 727.7 mol −1 , which corresponds to a bond strengths of 31.5 kcal ˙ mol −1 for R–O 2 · . The equipment and the method used for these experiments are described in detail.