Investigation of the role of aromatic carboxylic acids in cross-linking processes in low-rank coals [electronic resource].
- Washington, D.C. : United States. Dept. of Energy. Office of Energy Research, 1997.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
- Physical Description:
- 13 pages : digital, PDF file
- Additional Creators:
- Oak Ridge National Laboratory, United States. Department of Energy. Office of Energy Research, and United States. Department of Energy. Office of Scientific and Technical Information
- Restrictions on Access:
- Free-to-read Unrestricted online access
- In the pyrolysis and liquefaction of low-rank coals, low-temperature cross-linking reactions have been correlated with the loss of carboxyl groups and the evolution of CO₂ and H₂O. It is not clearly understood how decarboxylation leads to cross-linking beyond the suggestion that decarboxylation could be a radical process that involves radical recombination or radical addition reactions. We have recently conducted a study of the pyrolysis of 1,2-(3,3′-dicarboxyphenyl)ethane (1) and 1,2-(4,4′-dicarboxyphenyl)ethane (2) and found that decarboxylation occurs readily between 350-425 °C with no evidence of coupling products or products representative of cross-links. We proposed that decarboxylation occurred primarily by an acid-promoted cationic pathway, and the source of acid was a second carboxylic acid. The decarboxylation of 1 and 2 was investigated in diphenyl ether and naphthalene as inert diluents. In each solvent, the rate of decarboxylation dropped by roughly a factor of 2 upon dilution from the neat liquid to ca. 0.4 mole fraction of acid, but further dilution had no effect on the rate. This could be a consequence of hydrogen bonding or an intramolecular protonation. Molecular mechanics calculations indicated that 1 and 2 can adopt an appropriate conformation for internal proton transfer from a carboxy group on one ring to the second aryl ring without a significant energy penalty. In addition, the dicarboxylic acid could internally hydrogen bond, which may further complicate the reaction mechanism. Therefore, we have conducted a study of the pyrolysis of a monocarboxybibenzyl, 1-(3-carboxyphenyl)-2-(4-biphenyl)ethane (3), to determine if decarboxylation occurs by an ionic pathway in the absence of intramolecular pathways.
- Report Numbers:
- E 1.99:conf-970443--11
- Other Subject(s):
- Published through SciTech Connect.
213. national meeting of the American Chemical Society, San Francisco, CA (United States), 13-17 Apr 1997.
Britt, P.F.; Eskay, T.P.; Buchanan, A.C. III.
- Funding Information:
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