Effect of solvent swelling on diffusion rates in bituminous coal

Reactions of Pittsburgh No. 8 Coal with Maleic Anhydride. Evidence for the Existence of Reactive Diene Structures in Coal

“…Ester Formation. The absence of ester formation reaction between the maleic anhydride and hydroxyl groups has been noted previously by Larsen et al , and Zher'akova et al The single unchanged carbonyl peak at 172 ppm in Figure also demonstrates that esterification is not occurring. The failure of 1-naphthol, 2-naphthol, and phenol to react with maleic anhydride under the conditions used for the reaction with coal and the absence of any change in the carbonyl carbon chemical shift on reaction with coal confirm that ester formation is not occurring.…”

“…A Diels−Alder reaction requires a reactive diene in the coal. Published coal models − do not contain enough reactive diene structures to account for the 10−20% weight increase reported when maleic anhydride reacts with the coal. − 2-Naphthols are also capable of undergoing a Diels−Alder reaction with maleic anhydride in molten maleic anhydride at 250 °C as reported by Wariyar, a temperature far in excess of the 110 °C used in this work. The large incorporations observed with coals and the high reaction temperature required for β-naphthols suggest that either (1) the maleic anhydride does not incorporate via a reaction with naphthols or (2) the coal contains more reactive groups than those that appear in current model structures or (3) something in the coal catalyzes the Diels−Alder reaction.…”

“…Diels − Alder Reaction. The Diels−Alder is the reaction most commonly proposed to explain the reaction of maleic anhydride with coals. − There are not enough anthracenes (whether or not substituted) or other acenes in current coal structures to account for the 15−20% maleic anhydride incorporations observed. − ,− Theoretically, the number of reaction sites could be increased if 2-naphthol type structures in coal also undergo Diels−Alder reactions. The product of reaction between anthracene and maleic anhydride, anthracene-9,10- endo -succinic anhydride, has a 13 C chemical shift at 46 ppm (see Supporting Information Figure A).…”

“…The first reported study was by Duty . This was followed by a series of studies by one of us, a paper by Zher'akova and Kochkan'an, and a study by Nishioka. − There is agreement that coals take up between 10% and 20% of their weight in maleic anhydride. The maleic anhydride double bond disappears in the reaction, and all except Nishioka have assigned this to the occurrence of Diels−Alder reactions.…”

“…As an anhydride, maleic anhydride might be expected to form esters with the abundant phenolic hydroxyls in coals. Larsen et al ruled out ester formation with phenolic hydroxyl groups by hydrolyzing the coal−maleic anhydride adduct using aqueous tetraethylammonium hydroxide at room temperature . This procedure is known to cleave ester groups in coal .…”