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Title: Mechanistic Investigation into the Decarboxylation of Aromatic Carboxylic Acids

Abstract

It has been proposed that carboxylic acids and carboxylates are major contributors to cross-linking reactions in low-rank coals and inhibit its thermochemical processing. Therefore, the thermolysis of aromatic carboxylic acids was investigated to determine the mechanisms of decarboxylation at temperatures relevant to coal processing, and to determine if decarboxylation leads to cross-linking (i.e., formation of more refractory products). From the thcrmolysis of simple and polymeric coal model compounds containing aromatic carboxylic acids at 250-425 °C, decarboxylation was found to occur primarily by an acid promoted ionic pathway. Carboxylate salts were found to enhance the decarboxylation rate, which is consistent with the proposed cationic mechanism. Thermolysis of the acid in an aromatic solvent, such as naphthalene, produced a small amount of arylated products (~5 mol%)), which constitute a low-temperature cross-link. These arylated products were formed by the rapid decomposition of aromatic anhydrides, which are in equilibrium with the acid. These anhydrides decompose by a free radical induced decomposition pathway to form atyl radicals that can add to aromatic rings to form cross-links or abstract hydrogen. Large amounts of CO were formed in the thennolysis of the anhydrides which is consistent with the induced decomposition pathway. CO was also formed in themore » thermolysis of the carboxylic acids in aromatic solvents which is consistent with the formation and decomposition of the anhydride. The formation of anhydride linkages and cross-links was found to be very sensitive to the reactions conditions. Hydrogen donor solvents, such as tetralin, and water were found to decrease the formation of arylated products. Silar reaction pathways were also found in the thermolysis of a polymeric model that contained aromatic carboxylic acids. In this case, anhydride formation and decomposition produced an insoluble polymer, while the O-methylated polymer and the non-carboxylated polymer produced a soluble thermolysis product.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
7910
Report Number(s):
ORNL/CP-103341
KC 03 02 01 0; ON: DE00007910
DOE Contract Number:  
AC05-96OR22464
Resource Type:
Conference
Resource Relation:
Conference: National American Chemical Society Meeting, New Orleans, LA, Aug. 22-26, 1999
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; Pyrolysis; Cross-Linking; Decarboxylation

Citation Formats

Britt, P F, Buchanan, III, A C, Eskay, T P, and Mungall, W S. Mechanistic Investigation into the Decarboxylation of Aromatic Carboxylic Acids. United States: N. p., 1999. Web.
Britt, P F, Buchanan, III, A C, Eskay, T P, & Mungall, W S. Mechanistic Investigation into the Decarboxylation of Aromatic Carboxylic Acids. United States.
Britt, P F, Buchanan, III, A C, Eskay, T P, and Mungall, W S. Sun . "Mechanistic Investigation into the Decarboxylation of Aromatic Carboxylic Acids". United States. https://www.osti.gov/servlets/purl/7910.
@article{osti_7910,
title = {Mechanistic Investigation into the Decarboxylation of Aromatic Carboxylic Acids},
author = {Britt, P F and Buchanan, III, A C and Eskay, T P and Mungall, W S},
abstractNote = {It has been proposed that carboxylic acids and carboxylates are major contributors to cross-linking reactions in low-rank coals and inhibit its thermochemical processing. Therefore, the thermolysis of aromatic carboxylic acids was investigated to determine the mechanisms of decarboxylation at temperatures relevant to coal processing, and to determine if decarboxylation leads to cross-linking (i.e., formation of more refractory products). From the thcrmolysis of simple and polymeric coal model compounds containing aromatic carboxylic acids at 250-425 °C, decarboxylation was found to occur primarily by an acid promoted ionic pathway. Carboxylate salts were found to enhance the decarboxylation rate, which is consistent with the proposed cationic mechanism. Thermolysis of the acid in an aromatic solvent, such as naphthalene, produced a small amount of arylated products (~5 mol%)), which constitute a low-temperature cross-link. These arylated products were formed by the rapid decomposition of aromatic anhydrides, which are in equilibrium with the acid. These anhydrides decompose by a free radical induced decomposition pathway to form atyl radicals that can add to aromatic rings to form cross-links or abstract hydrogen. Large amounts of CO were formed in the thennolysis of the anhydrides which is consistent with the induced decomposition pathway. CO was also formed in the thermolysis of the carboxylic acids in aromatic solvents which is consistent with the formation and decomposition of the anhydride. The formation of anhydride linkages and cross-links was found to be very sensitive to the reactions conditions. Hydrogen donor solvents, such as tetralin, and water were found to decrease the formation of arylated products. Silar reaction pathways were also found in the thermolysis of a polymeric model that contained aromatic carboxylic acids. In this case, anhydride formation and decomposition produced an insoluble polymer, while the O-methylated polymer and the non-carboxylated polymer produced a soluble thermolysis product.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {1999},
month = {8}
}

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