Energy & Fuels 1993, 7, 589-597
589
Aqueous Organic Chemistry. 6. Reactivity of Hydroxynaphthalenes Michael Siskin," Glen Brons, and Stephen N. Vaughn Corporate Research Science Laboratory, Exxon Research and Engineering Company, Annandale, New Jersey 08801
Alan R. Katritzky,' Marudai Balasubramanian, and John V. Greenhill Department of Chemistry, University of Florida, Gainesville, Florida 3261 1-2046 Received March 18, 1993. Revised Manuscript Received May 26, 1993
Hydroxyaromatics are abundant in lignite and subbituminous coals. Cleavage of ethers in coals generates additional hydroxyaromatics. Reduction of the carbonyl intermediates of these hydroxyaromatics in 15% formic acid or 15% sodium formate provides hydrogenated species which can act as hydrogen donors during coal liquefaction. At 315 "C over a period of 3 days, 1- and 2-hydroxynaphthalenesshowed little change under simple thermolytic or aquathermolytic conditions. These compounds underwent reduction to a small extent on aquathermolysis in 15% formic acid and to a larger extent in 15% sodium formate. 1,2-, 1,3-,1,4-, and 2,3-Dihydroxynaphthaleneswere all highly reactive at 315 "C in all four systems (cyclohexane, water, 15% formic acid, and 15% HCOzNa). The major products resulted from dehydroxylation or decarbonylation followed by ring opening, and self-condensation. In the presence of reducing agents (HCOzH or HCOZNa), large amounts of indane, tetralin, naphthalene, and methylated hydroxynaphthalenes resulted. 1,4Dimethoxynaphthalene underwent ether cleavage and was transformed into various mono- and dihydroxynaphthalenes. Some of the hydroxynaphthalene products had been C-methylated. In the presence of HCOZNa, large amounts of reduction products were obtained.
Introduction The relationship of coal liquefaction behavior to coal structure has been a subject of study for several years, particularly with respect to loss of oxygen.14 Most common liquefaction media employ an H-donor component such as tetralin, which transfers hydrogen to the coal. In such a medium, the coal is depolymerized and reduced to yield a more soluble, lower molecular weight product with a higher H/C atomic ratio. Thermal treatments of coal in H-donor media always yield the product contaminated with the solvent through chemical incorporation. Conversions conducted in a carbon monoxide/ water system circumvent this problem because the medium is totally inorganic and yields an organic product which is derived solely from the coal. The results of several studies show that conversions in CO/HzO systems generally decrease with decreasing oxygen content of the starting goal. Appell et al.,5 using synthesis gas (Hz and CO) and water, found that lignite underwent higher conversion when compared to a bituminous coal. Ouchi and Takemura,G using a CO/HzO system and a cobalt-molybdenum catalyst, found that (1) Szladow, A. J.; Given, P. H. Prep. Pap.-Am. Chem. SOC.,Diu. Fuel Chem. 1978,23, 161. (2) Youtcheff, J. S.; Given, P. H. Fuel 1982, 61, 980. (3) Youtcheff, J. S.; Given, P. H. Prep. Pap.-Am. Chem. SOC.,Diu. Fuel Chem. 1984,29, 1. (4) Whitehunt, D. D. In Organic Chemistry of Coal; Larsen, J. W., Ed.;ACSSymposiumSeries 71;AmericanChemicalSociety Washington,
DC, 1978; pp 10-35. (5) Appell, H. R.;.Miller, R. D.; Illig, E. G.; Moroni, E. G.; Steffgen, F. W. 'Coal Liquefaction in Synthesis Gas"; U S . Department of Energy Representative PETCITR-79, Technology Information Center, U.S. Department of Energy, Washington, DC. (6) Ouchi, K.; Takemura, Y. Fuel 1983,62,1133.
conversion decreased with increasing carbon content for a series of coals ranging from 50% to 90% carbon. Oelert and Siekmann7 found that conversion increased with increasingO/C ratio of the starting material. These results, taken together, suggestthat oxygen functionalities strongly influencethe conversion behavior of the coal. It was found' that roughly 40% of the oxygen in coal was phenolic. The remaining 60 % ,referred to as unaccounted oxygen, was assumed to be etheric. It was noted that the main oxygen loss during conversion was from this "unaccounted oxygen" pool, with considerably smaller losses of phenolic oxygen. Graff and Brandesa found that steam pretreatment of an Illinois No. 6 bituminous coal between 320 and 360 "C dramatically improves the yield of liquids obtained on subsequent conversion or solvent extraction. The steam modified coals also swelled more in water and contained twice as many hydroxyl groups as the raw coal, leading to the hypothesis that steam reacts with ether linkages in coal forming hydroxyl groups and thereby substantially hydrolyzing an important covalent cross-link in the coal s t r u ~ t u r e .Model ~ compound studies on aryl ether reactivity in hot water to form hydroxyaromatics are consistent with these conclusions.10Jl The concentration of hydroxyaromatics, especially in lower rank coals, is high, and this level is increased by aqueous treatment. (7) Oelert, H.; Siekmann, R. Fuel 1976,55, 39. (8)Graff, R. A.; Brandes, S. D. Energy Fuels 1987, I , 84. (9) Brandes, S. D.; Graff, R. A.; Gorbaty, M. L.; Siskin, M. Energy
Fuels 1989,3,494. (10)Siskin, M.; Brons, G.; Vaughn, S. N.; Katritzky, A. R.; Balasubramanian, M. Energy Fuels 1990,4,488. (11) Siskin, M.; Katritzky, A. R.; Balasubramanian, M. Energy Fuels 1991, 5, 770.
0 1993 American Chemical Society Q887-0624/93/25Q7-Q589$Q4.Q0/Q
Siskin et al.
590 Energy &Fuels, Vol. 7,No. 5, 1993 The hydroxyaromatic-keto equilibrium provides carbonyl groups in the coal and coal liquids at low, steadystate levels. McMillenI2 has proposed keto structures as intermediates in the hydrogenolysis of hydroxydiphenyl methanes and ethers in tetralin. Ross13suggested that the mechanism of coal reduction begins with phenol-keto equilibrium followed by reduction of the carbonyl intermediates by a hydroaromatic structure (free radical) or by hydride ion transfer from formate ion in CO/water (ionic). Our previous studies11J4 of the aquathermolytic chemistry of diary1ethers demonstrated that hydroxyaromatics are formed from the ether cleavage reaction and these react via a reductive dehydroxylation mechanism to form polycyclic aromatic hydrocarbons in the presence of 15% HC02Na. The present paper deals with the aquathermolysis chemistry of various hydroxynaphthalenes in an attempt to sort out the reductive dehydroxylation mechanism. We believe that this pathway represents the underlying mechanism for increasing the H/C atomic ratio during water/carbon monoxide treatments of coals and other low-rank resource materials. In coals, the molecules generated are capable of donating hydrogen during liquefaction.161B It should also be applicable to water/ carbon monoxide treatments of hydroxylated wastewater streams, removal of aromatics from diesel fuel, etc. The model compounds selected for this investigation were l-hydroxynaphthalene (15),2-hydroxynaphthalene(161, 1,2-dihydroxynaphthalene(23),1,3-dihydroxynaphthalene (27),1,4-dihydroxynaphthalene(13),2,3-dihydroxynaphthalene (25), and 1,4-dimethoxynaphthalene(22). Each was heated (1g of compound/6 g of solution) at 315 "C under four sets of conditions: (i) in cyclohexane, (ii) in water alone, (iii) in 15% aqueous formic acid, and (iv) in 15% aqueous sodium formate. Aquathermolyses under conditions ii-iv were compared with the purely thermal reactions of condition i. Experimental Section 1,4Dimethoxynaphthalene(22) was prepared accordingto the literatureprocedure (methylationof 1,4-dihydroxynaphthalene using dimethyl sulfate).M The other compounds were obtained from commercial sources. All the starting materials were found by gas chromatography to be of suitable purity (>99%) and were used without further purification. The gas chromatographic behavior of all the compounds employed for this study (starting materials and products) is summarized in Table I. Table IA (supplementarymaterial) records the source and mass spectral fragmentation patterns of the authentic compounds used, either as startingmaterialsor for the identificationof products. Tables IB (supplementary material) and I1 record the mass spectral fragmentation patterns of products for which authentic samples were not availableand which were identifiedby comparison with literaturemass spectral data (Table IB), or by deduction (Table 11). Tables IA and IB and mass spectral assignments associated (12) McMillen, D. F.; Ogier, W. C.; Ross, D. S.J. Org. Chem. 1981,46, 3322.
(13) Ross, D. S.In Coal Science; Gorbaty, M. L., Ed.; Academic Press: New York, 1984; Vol. 3, pp 329-331. (14) Part 5 of this series: Siskin, M.;Katritzky,A. R.;Balasubramanian, M. Fuel, in press. (15) Stuntz, G. F.; Culross, C.; Reynolds, S. D. U.S. Patent 5,026,475 (June 25, 1991). (16) Culross, C.; Reynolds, S. D. U.S. Patent 5,071,540 (Dec. 10,1991). (17) Culross, C.; Reynolds, S.D. U.S.Patent 5,110,450 (May 5,1991). (18) Vaughn, S.N.; Siskin, M.; Katritzky, A. R.; Brons, G.; Reynolds, S.D.; Culross, C.; Neskora, D. R. U.S.Patent 5,151,173 (Sept. 29,1992). (19)Neskora, D. R.; Vaughn, S. N.; Mitchell, W. N.; Culross, C.; Reynolds, S.D.; Effron, E. U.S. Patent 5,200,063 (April 6, 1993). (20) Sha, P. P. T. Recl. Trau. Chim. 1940,59,1029.
with Table IB are available as supplementary material (see paragraph at end of paper regarding supplementary material). The reactions were conducted as previously described21and the results are collected in Tables III-IX. The major products from all of the reactions are summarized in Tables X and XI.
Results and Discussion The reactions are summarized in eqs 1-16. In the equations, numbers 1100 are used for intermediates which are not detected by the GC-MS system. l-Hydroxynaphthalene (15) (Table 111). At 315 "C l-hydroxynaphthalene (15) has low thermal reactivity. After 3 days in cyclohexane it showed only 7.3% thermal conversion to give 1,l'-dinaphthyl ether (42) as the only product. Aquathermolysis of 15 for 3 days showed only 9.3% conversion with the major product again 1,l'dinaphthyl ether (8.0 % ). Byproducts were l-tetralone (10) (1.0%)and traces of tetralin (8) and naphthalene (9). In 15% HC02H there was still only 10% conversion with 1,l'-dinaphthyl ether (2.9%), tetralin (2.8%),and l-tetralone (2.0%) prevalent. There were also significant amounts of naphthalene (9, 1.2%), 1,l'-bisnaphthalene (34,0.2 %),andthe ring-methylated hydroxynaphthalenes 19and 21. In the presence of 15% HCOZNa, the reactivity of 15was enhanced resulting in 81% conversion,the major products being naphthalene (38.8%), tetralin (23.7 96 ), and 1,l'-dinaphthylether (42) (8.5%1. Theother above-named products were all present in trace amounts along with l-methylnaphthalene (11,2.2% ). The much higher conversion in the presence of the formate salt is consistent with the reduction products observed since the formate ion is known to be a better hydride donor than free formic acid. Suggested reaction pathways are shown in eqs 1-4 (Scheme I). The methylated hydroxynaphthalenes 19and 21 probably arise from reductions of intermediate aldehydes 100 and 102 (eq 1). The aldehydes result from the ortho and para formylation of 15 by formic acid. The higher percentage of methylated products in the sodium formate runs indicates the presence of a small proportion of naphthalate anion in the more basic medium. The tautomerism (15 103 104) is important in several of the transformations. Hydride reduction of the carbonyl group leads via the alcohol 101 and subsequent easy dehydration to naphthalene (9) (eq 2). Reduction of the conjugated double bond of 104 gives the l-tetralone (10) (eq 2). Further reduction gives the alcohol 107 which undergoes acid catalyzed elimination to 112 and a find reduction step to tetralin (8) (eq 2). Equations 3 and 4 also contain suggestionsfor the formation of the dinaphthyl deriyatives 42 and 34 via nucleophilic attack by the activated carbon at position 4, or the oxygen atom of l-naphthol on tautomer 103. 2-Hydroxynaphthalene (16) (Table IV). 2-Hydroxynaphthalene is less reactive than the l-hydroxynaphthalene (15) under both thermal and aquathermal conditions. In cyclohexane over 72 h, at 315 "C,16 showed
