Enhancement of free-radical chain rearrangement, cyclization, and hydrogenolysis during thermolysis of surface-immobilized bibenzyl: implications for coal chemistry
Condensation of p-HOC/sub 6/H/sub 4/CH/sub 2/CH/sub 2/C/sub 6/H/sub 5/ (15c) with the surface hydroxyls of fumed silica gave a surface-immobilized form of bibenzyl (16c) whose thermolysis was compared with that studied earlier for liquid and gaseous bibenzyl (1). The objective was to explore the effects of restricted mobility on a multipathway free-radical reaction, with particular emphasis on modeling dimethylene linking units between aromatic clusters in coal. The initial rate of thermolysis of 16c at 350-400/sup 0/C was accelerated some fourfold compared with 1, and the product composition was notably altered. The major initial product classes in order of decreasing amounts, were the following: (1) rearrangement to form surface-attached 1,1-diphenylethane (18); (2) cyclization-dehydrogenation to form surface-attached 9,10-dihydrophenanthrene (20) (and subsequently surface-attached phenanthrene (21)); (3) symmetrical cleavage to form both surface-attached and gas-phase toluene (19 and 3) in similar amounts; (4) dehydrogenation to form surface-attached stilbene (24); and (5) unsymmetrical hydrogenolysis to form surface-attached ethylbenzene (22) plus gas-phase benzene (10) and the analogous pair, 23 plus 11, in similar amounts. For liquid 1, cyclization and unsymmetrical cleavage had been barely detectable and rearrangement was only a minor pathway. The rate constant for unimolecular C-C homolysis in 16c, based on 3 and 19, was 10/sup 15.3/ exp(-62,900/RT) s/sup -1/, not significantly different from that of 1 and not dependent on surface coverage. However, the initial extent of rearrangement, expressed as a chain length, was accelerated some 30-fold compared with that of liquid 1; cyclization and unsymmetrical cleavage were similarly enhanced.
- Research Organization:
- Oak Ridge National Lab., TN
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 7203843
- Journal Information:
- J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 108:24; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
AROMATICS
BIBENZYL
CARBONACEOUS MATERIALS
CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
COAL
DATA
DECOMPOSITION
DEHYDROCYCLIZATION
DEHYDROGENATION
ENERGY SOURCES
EXPERIMENTAL DATA
FOSSIL FUELS
FUELS
INFORMATION
KINETICS
MATERIALS
MATHEMATICAL MODELS
MEDIUM TEMPERATURE
NUMERICAL DATA
ORGANIC COMPOUNDS
PYROLYSIS
RADICALS
REACTION KINETICS
SIMULATION
TEMPERATURE DEPENDENCE
THERMOCHEMICAL PROCESSES
YIELDS