Energy & Fuels 1994,8, 990-1001
990
Aqueous High-Temperature Chemistry of Carbo- and Heterocycles. 23.' Reactions of Pyridine Analogs and Benzopyrroles in Supercritical Water at 460 "C Alan R. Katritzky' and Richard A. Barcock Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville, Florida 32611-7200
Michael Siskin* and William N. Olmstead Corporate Research, Exxon Research and Engineering Company, Annandale, New Jersey 08801 Received January 24, 1994. Revised Manuscript Received April 26, 1994'
Eleven nitrogen-containing heterocycles were chosen as fossil fuel model compounds: pyridine, quinoline, 2-methylquinoline (quinaldine), isoquinoline, acridine, phenanthridine, 1,2,3,4-tetrahydroquinoline, indole, 2-methylindole, 2,3-dimethylindole, and carbazole. They were heated at 460 "C for 7 min and for 1h in four different sets of conditions: (i) cyclohexane, (ii) water, (iii) aqueous 15?6 formic acid, and (iv) aqueous 15% sodium formate. Aquathermolyses under conditions (ii)-(iv) could thus be compared with purely thermal reactions under condition (i). Pyridine is almost unreactive at 460 "C under both thermolysis and aquathermolysis conditions, although in 15% aqueous formic acid at 460 "C for 7 min, small quantities of N-alkylpiperidines were observed; however, on extending the reaction time to 1h, small amounts of C-alkylated pyridines were formed. Acridine underwent a much higher conversion than phenanthridine, although no nitrogen removal was observed and both compounds showed mainly hydrogenation and/or oxidation products; after 1h at 460 "C, increased dehydrogenation was observed. Quinoline, 2-methylquinoline, and isoquinoline were much more reactive than the pyridine system, especially in the presence of aqueous 15% formic acid to give mainly hydrogenated derivatives after 7 min; however, after 1h some dehydrogenation back to the aromatic nuclei was observed. Indole and its methylated derivatives (both mono and di) reacted in a similar way: substantial reduction to indolines was observed in aqueous formic acid after only 7 min; however, after 1 h, the indolines seemingly underwent significant dehydrogenation back to indoles. Carbazole was completely unreactive. Structures of the products from all these reactions have been determined, and reaction sequences for their formation are proposed.
Introduction The removal of heteroatoms to give environmentally acceptable products and lower molecular weight materials are both important objectives of fossil fuel processing. Many of the heavier feedstocks now being used and considered for use (tar sands, oil shale, etc.) contain substantial amounts of nitrogen-containing compounds2 and these are detrimental for the following reasons: (i) they poison and deactivate catalysts used in further processing; (ii) they generate toxic nitrogen oxides upon combustion; (iii)they confer instability on the fuel products and cause d i s c ~ l o r a t i o n .Denitrogenation ~~ is currently achieved commercially by hydrodenitrogenation (HDN) Abstract published in Advance ACS Abstracts, June 1, 1994. (1) Part 22: Katritzky, A. R.; Balasubramanian, M.; Siskin, M. Unpublished results. (2) Holmes, S. A. In Shale Oil Upgrading and Refining; Newman, S. A,,Ed.; Butterworth Publishers: Boston, 1983;pp 159-182, and references cited therein. (3) Kartzmark, R.; Gilbert, J. B. Hydrocarbon Process. 1967, 46 (9), 143. (4) Satterfield, C. N.; Giiltekin, S. Ind. Eng. Chem. Process Des. Deu. 1981, 20, 62. (5) Frankenfeld, J. W . ;Taylor,W .F.; Brinkman,D. W .Znd. Eng.Prod. Res. Deu. 1983, 22, 608. (6) Frankenfeld, J. W.;Taylor, W .F.;Brinkman,D. W.Znd.Eng.Prod. Res. Deu. 1983, 22, 615. (7) Frankenfeld,J. W.:Taylor,W .F.;Brinkman,D. W .Znd. Eng.Prod. Res. Deu. 1983, 22, 622.
which involves hydrogenolysis of strong C-N bonds over transition metal catalysts, which in turn, requires significant perhydrogenation of the heteroaromatic and/or aromatic rings. Much current interest from both geologicaland technical perspectives has been focused on the transformation of organic compounds in aqueous environment^.^'^ Most of the world's fossil fuel resources have been naturally formed and modified under aqueous environments, but a detailed understanding of the formation and maturation pathways has been lacking. The potential economic incentives for the conversion and upgrading of fossil fuel (8)Siskin,M.; Brons, G.; Katritzky, A. R.;Balasubramanian, M. Energy Fuels 1990, 4, 475. (9) Siskin, M.; Katritzky, A. R. Science 1991, 254, 231. (10) Katritzky,A.R.;Lapuche,A.R.;Murugan,R.;Luxem,F.J.;Siskin, M.; Brons, G. Energy Fuels 1990,4,493. (11) Abraham, M. A.; Klein, M. T. Znd. Eng. Chem. Prod. Res. Deu. 1985,24, 300. (12) Houser, T. J.; Tiffany,D. M.;Li, 2.;McCarville,M. E.; Houghton, M. E. Fuel 1986,65,827. (13) Stenberg, V. I.; Wang, J.; Baltisberger, R. J.; Van Buren, R.; Woolsey, N. F. J. Org. Chem. 1978, 43, 2991. (14) (a) Clark, P. D.; Hyne, J. B.; Tyrer, J. D. Fuel 1983,62,959. (b) Clark, P. D.; Hyne, J. B.; Tyrer, J. D. Fuel 1984, 63, 125. (15) Clark, P. D.; Dowling, N. I.; Hyne, J. B.; Lesage, K. L. Fuel 1987, 66. 1252 --7
(16) Houser,T.J.;Tsao,C.-C.;Dyla,J.E.;VanAtten,M.K.;McCanille,
M. E. Fuel 1989,68, 323. (17)Townsend, S. H.; Abraham, M. A,; Huppert, G. L.; Klein, M. T.; Paspek, S. C. Znd. Eng. Chem. Res. 1988,27, 143.
0887-0624/94/2508-0990$04.50/00 1994 American Chemical Society
High- Temperature Chemistry of Carbo- and Heterocycles
Energy & Fuels, Vol. 8, No. 4,1994 991
rssources by aqueous treatment (inexpensive, nontoxic, amounts of the Lewis acid zinc chloride (known for its catalytic activity for hydrocracking aromatic structuresa1)plentiful source etc.) rather than by conventionaltreatment are enormous. increased the extent of the reaction in water, with a similar product distribution. It is noteworthy that the reactions Recently, our two research groups have worked extenproceed to a much further extent, and the volatile liquid sively in aqueous organic chemistrylOJaw and we previproduct yields are significantly different, in the presence ously examined the reactivity of various nitrogen-containing compounds in aqueous (subcritical) systems.10~~1@fl~ of supercriticalwater than those from neat pyrolysis, where little reaction was seen. Quinoline was treated similarly The important findings from these earlier studies are in water a t temperatures of 400 and 450 "C for 48 h. summarized in the Results and Discussion section of this Expectedly, quinoline was found to be less reactive than report together with the new results for the relevant model isoquinoline in this medium. The major primary products compounds. As we were interested in investigating the included aniline, phenol, and quinaldine. Notably, for possibility of the removal of nitrogen at high-temperature shorter reaction times (e.g., 3 h) more quinaldine was and pressure in aqueous systems, we have now further observed. When the reaction time was increased the yield extended these investigations to determine the reactivity of volatile products increased, especially phenols which of nitrogen model compounds,thought to be representative were probably derived from aniline and methylaniline. of structures found in fossil fuels, in supercritical aqueous Interestingly, the addition of catalytic amounts of zinc media. This report is the third in a series on the reactivity chloride once again did not change the product distribuof carbo- and heterocycles in 'supercritical" aqueous tion. media.2S*NThe following introduction summarizes some Results for other nitrogen-containing compounds inof the initial work reported by others on the reactions vestigated by Houser are summarized in this paper? of nitrogen-containing compounds in supercritical benzonitrile was found to undergo hydrolysis with subwater. sequent decarboxylation, very quickly and cleanly, in Klein has examined the reactivity of benzylphenylamine supercritical water at 400 "C for 24 h. The yield of benzene in supercritical water and compared the results to those formed was essentially quantitative. Aniline was treated obtained from neat pyr0lysis.~~J7Neat pyrolysis of with supercritical water at 450 "C for 48 h and yielded benzylphenylamine at 386 "C yielded toluene, aniline, and predominantlyphenol, diphenylamine,and ammonia.The benzylaniline as major and primary products; 1,Zdiphenaddition of a catalytic amount of zinc chloride increased ylethane and diphenylmethane were minor primary the conversion with more phenol (from the acid-catalyzed products. In comparison,reaction of benzylphenylamine hydrolysis) being produced. Carbazole was completely in supercritical water yielded benzyl alcohol as a major unreactive at 450 "C for 48 h. Klein has also found that and primary product and benzaldehyde as a minor product carbazole was resistant to reaction in supercritical water in addition to those products obtained from neat pyrolysis. a t both 450 and 550 "C for reaction times of 1 h.17 Stenberg and co-workers13 found that quinoline was Houser later reported the reactivity of 1,2,3,4-tetrahyconverted to 1,2,3,4-tetrahydroquinolineat 425 "C for 2 droquinoline in water a t 400 "C for 3 h and at 450-456 "C h in supercritical water in the presence of carbon monoxide for 3-6 h.'6 At 400 "C the major products were ammonia and that the conversion was enhanced by added sodium and quinoline. Smaller amounts of propylbenzene, indane, carbonate. methylindanes, toluidines, dihydroquinoline, and cresols Houser has published extensive reports of the reactions were also observed. In the presence of a catalytic amount of nitrogen model compounds in supercritical water. of zinc chloride, phenol and aniline were observed in Isoquinoline was treated in water at temperatures of 400addition to the above products. At higher temperatures 450 "C for 48 h.12 Products generated from this reaction (456 "C) and prolonged reaction times (6 h), quinoline included benzene, ethylbenzene, and o-xylene; these was again the major product. Toluene, ethylbenzene, products arise from the exclusive rupture of the heteroxylenes, anilines, propylbenzene,indane, methylindanes, cyclic ring, leaving the homocyclic ring intact. Small toluidines, cresols, dihydroquinoline, xylidenes, xylenols, naphthalene, indole, methylquinolines, and biquinoline (18) Siskin, M.; Katrizky, A. R.;Balasubramanian, M. Energy Fuels 1991,5, 770. were also observed in small amounts. As seen before, the (19) Katritzky, A. R.;Murugan, R.;Balasubramanian,M.; Greenhill, addition of a catalytic quantity of zinc chloride enhanced J. V.; Siskin, M.; Brons, G. Energy Fuels 1991,5,823. the rate of reaction. Benzylamine was treated with water (20) Katritzky, A. R.;Lapucha, A. R.;Siskin, M. Energy Fuels 1992, 6, 439. at 400 and 450 "C for time periods of 1-2 h, and was found (21) Katritzky,A.R.;Luxem,F.J.;Murugan,R.;Greenhill,J.V.;Siskin, to be completely consumed under the mildest conditions M. Energy Fuels 1992,6,460. used, 400 "C for 1h.I2J6 The major products obtained in (22) Katritzky,A. R.;Balasubramanian,M.; Siskin, M. Energy Fuels 1992,6, 431. each case were ammonia, toluene, benzene, biphenyl, and (23) Katritzky, A. R.;Balasubramanian,M.;Siskin, M. J. Chem. SOC., isomeric methylbiphenyls. However, under the milder Chem. Commun. 1992, 1233. (24) Siskin, M.; Katritzky, A. R.;Balasubramanian, M.; Fermghelli, conditions (400 "C) benzaldehyde, benzylidenebenzylD. T.; Brons, G.; Singhal, G. H. Tetrahedron Lett. 1993,34,4739. amine,and a small amount of benzyl alcohol were observed (25) Part 20 of this series; Katritzky, A. R.;Barcock, R. A.; Balaas intermediates, with a reduction in the yield of benzene. subramanian, M.; Greenhill,J. V.; Siskin, M.; Olmstead, W. N. Energy Fuels 1994,8,487. Houser has more recently investigated other nitrogen(26) Part 21 of this aeries; Katritzky, A. R.;Barcock, R. A,;Balacontaining compounds in supercritical water.32 Quinusubramanian, M.; Greenhill, J. V.; Siskin, M.; Olmstead, W. N. Energy clidine in supercritical water a t 400 "C for 4 h yielded Fuels 1994,8,498. (27) Katritzky, A. R.;Lapucha, A. R.;Siskin, M. Energy Fuels 1990, ethylpyridine as the major product as well as traces of 4, 506. toluene and ethylbenzene. Catalytic amounts of zinc (28) Katritzky, A. R.;Lapucha, A. R.;Siskin, M. Energy Fuels 1990, 4, 510. (29) Katritzky,A. R.;Murugan, R.;Balasubramanian,M.; Siskin, M. Energy Fuels 1990,4,547. (30) Katritzky, A. R.;Lapucha, A. R.;Siskin, M. Energy Fuels 1990, 4, 555.
(31)Salim, S.S.;Bell, A. T. Fuel 1984, 63,489. (32) Houeer, T. J.; Zhou, Y.; Teso, C.-C.; Liu, X. The Removal of Heteroatom fromOrganicCompounds by SupercriticalWater:Presented
at the AIChE Annual Meeting, November, 1991.
992 Energy & Fuels, Vol. 8, No. 4, 1994
Katritzky et al.
Table 1. Structure and Identification of Starting Materials and Products no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76
tR(min) 0.53 0.63 0.71 0.72 0.73 1.07 1.11 1.15 1.15 1.20 1.27 1.39 1.44 1.48 1.83 1.87 2.18 2.21 2.39 3.01 3.08 4.13 3.33 3.20 4.17 4.18 4.30 4.30 4.38 4.41 4.48 4.50 5.13 5.21 5.40 5.46 5.70 5.80 5.83 5.90 6.10 6.16 6.26 6.29 6.48 6.48 6.51 6.64 6.67 6.72 6.73 6.78 6.83 6.86 6.95 7.29 7.34 7.62 7.66 7.67 7.75 7.99 8.22 8.26 8.96 9.42 9.88 11.77 12.02 12.04 12.19 12.27 12.33 12.38 12.68 12.92
structure benzene pyridine piperidine toluene 1-methylpiperidine 3-pyridinemethanol 2-picoline 1-ethylpiperidine 3-picoline ethylbenzene 2,4-lutidine 4-ethylpyridine styrene o-xylene 2-ethylpyridine 1-propypiperidine propylbenzene aniline 2-ethyltoluene indane indene 2-methylbenzonitrile o-toluidine 2-ethylbenzonitrile 1-butylpiperidine 1-methylindene 1-methylindane 2-ethylbenzylamine 1-pentylpiperidine naphthalene 2-ethylaniline 2-methyl-N-methylaniline 1-methylindoline indoline 2-methylindoline quinoline 1,a-dimethylindoline 2-propylaniline 1,3-dimethylindoline isoquinoline 1-methylindole 2,3-dimethylindoline 1-methylisoquinoline 3-methylisoquinoline 3-methylindoline indole 1,2,34rimethylindoline 4-methylisoquinoline 2-methylquinoline
1,2-dihydro-2-methylquinoline 3-methylquinoline 1,2,3,4-tetrahydroquinoline 4-methylquinoline 6-methylquinoline 1,2,3,4-tetrahydroisoquinoline 1.2-dimethylindole 2-methyl-1,2,3,4-tetrahydroquinoline 1-methyl-1,2,3,4-tetrahydroisoquinoline 1(W)-isoquinolone 3-methylindole 2-methylindole l-methyl-l,2,3,4-tetrahydroquinoline 2,2’- bipyridine 2,4’- bipyridine 2,3-dimethylindole 1,2,34rimethylindole 2,3,4-trimethylindole 1,2,3,4,4a,9,9a,lO-octahydroacridine 1,2,3,4-tetrahydroacridine 2-(2-methylpheny1)aniline phenanthrene 5,6,6a,7,8,9,10,10a-octahydrophenanthridine 7,8,9,10-tetrahydrophenanthridine acridine phenanthridine 1,2,3,4-tetrahydrophenanthridine
mol wt
equiv wt
identificn baais
response facto+
78 79 85 92 99 109 93 113 93 106 107 107 104 106 107 127 120 93 120 118 116 117 107 131 141 130 132 135 155 128 121 121 133 119 133 129 147 135 147 129 131 147 143 143 133 117 163 143 143 145 143 133 143 143 149 145 147 147 145 131 131 147 156 156 145 161 161 187 183 183 178 187 183 179 179 183
78 79 85 92 99 109 93 113 93 106 107 107 104 106 107 127 120 93 120 118 116 117 107 131 141 130 132 135 155 128 121 121 133 119 133 129 147 135 147 129 131 147 143 143 133 117 163 143 143 145 143 133 143 143 149 145 147 147 145 131 131 147 78 78 145 161 161 187 183 183 89 187 183 179 179
Table 3 Table 2 Table 2 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 4 Table 3 Table 3 Table 3 Table 3 Table 4 Table 3 Table 3 Table 2 Table 3 Table 4 Table 4 Table 2 Table 2 Table 3 Table 3 Table 3 Table 4 Table 2 Table 3 Table 4 Table 2 Table 3 Table 3 Table 2 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 3 Table 2 Table 2 Table 4 Table 3 Table 3 Table 2 Table 3 Table 4 Table 3 Table 3 Table 4 Table 3 Table 3 Table 3 Table 2 Table 2 Table 3
1.00 0.80 0.89 0.96 0.72 0.45 0.83 0.88 0.83 0.96 0.83 0.83 0.96 0.96 0.83 0.71 0.95 0.81 0.95 0.95 0.95 0.79 0.71 0.78 0.70 0.95 0.95 0.70 0.70 0.98 0.71 0.71 0.70 0.71 0.70 0.82 0.70 0.70 0.70 0.82 0.70 0.70 0.81 0.81 0.70 0.71 0.69 0.81 0.81 0.70 0.80 0.70 0.80 0.80 0.70 0.70 0.70 0.70 0.53 0.70 0.70 0.70 0.68 0.68 0.70 0.69 0.69 0.80 0.80 0.68 0.93 0.80 0.80 0.80 0.80 0.80
183
Energy & Fuels, Vol. 8, No.4, 1994 993
High- Temperature Chemistry of Carbo- and Heterocycles Table 1 (Continued) no. tR(min) 13.11 77 13.33 78 13.46 79 14.11 80 14.15 81 14.84 82 15.16 83 15.90 84 16.62 85 17.90 86 18.26 87 18.27 88 18.30 89 18.61 90 18.95 91 19.59 92 20.41 93 20.52 94 20.71 95
structure carbazole 9,lO-dihydroacridine 5,6-dihydrophenanthridie
9[IOHI-acridone 3-cyclohexyl-2-methylindole 4-cyclohexyl-2-methylindole 4-cyclohexyl-2,3-dimethylindole 2,3-benzo[b]fluorene 1,4,7,12-tetrahydroknz[alan~acene
9-cyclohexylacridine
9,1O-dihydro-9-cyclohexylacridine
chryeene biieoquinoliie 4,4'-biquinoline 4-cyclohexylacridine 2-cyclohexylacridine 9-cyclohexen ylacridie 4-cyclohexen ylacridine
2-cyclohexenylacridine
chloride were found to promote the reaction in water, but significant amounts of alkylpyridinesremained. 4-Phenylpiperidine gave a high conversion at 400 O C for 1 h in water. Major products included 4-phenylpyridine, tar, and unknown solids along with lesser amounts of diphenylmethane, propylbenzene, ethylbenzene, and toluene. For extended reaction times (up to 6 h), the yield of the hydrocarbons increased somewhat although significant amounts of pyridine products were still present. 4-Phenylpyridine showed reduced reactivity in water at 450 "C even after 6 h, but considerabletar was produced. Houser concluded that extreme conditions and/or catalysts are necessary to remove the nitrogen contained in pyridines and piperidines. We were interested in investigating the reactivity of various nitrogen-containing model compounds in supercritical aqueousmedia and to determinethe product slates and compare them with those results obtained at the subcritical leve1~*21~24 along with those obtained from simple thermolysis. We now report on the reactions of 11 nitrogen heterocycles at 460 O C in water, 15% aqueous formic acid, and 157% aqueous sodium formate. In every case, a fourth solution in cyclohexane was subjected to the same conditions in order to compare the thermal (radical) decomposition with the aquathermolysis. Initialrunswere carried out for 7 min (i.e., 2 min heat-up time to 460 O C and 5 min residence time at that temperature) and if little or no change was detected they were repeated for 1h.
Experimental Section Pyridine (2), quinoline (36), 2-methylquinoline (quinaldine) (49),isoquinoline (40), 1,2,3,4-tetrahydroquinoline(52), phenanthridine (76),acridine (74),indole (46),2-methylindole(61),2,3dimethylindole (65),and carbazole (77) were all purcbed from Aldrich. All starting materials were checked by GC prior to use; where necessary they were purified to >98%. Water, 15% aqueous formic acid, 15% aqueous sodium formate,and cyclohexane were deoxygenatedwith argon for 1h just before use. All the GC analyseswere carried out on a Hewlett Packard 5890 gas chromatographoperated in the split injection mode (301ratio) and equippedwith a flame-ionizationdetector (FID). A 15-m capillary column (SPB-1)was used and the oven temperature was programmed from W to 250 "Cwith the initial time set at 1min and a subsequent rate of 10 OC/min. The flow rate of the helium carrier gas, hydrogen, and air at room temperature (23 "C)were measured at 29,39, and 380 mL/min.
mol wt 167 181 181 195 213 213 227 216 232 261 263 228 256 256 261 261 259 259 259
equiv wt
167 181 181 195 213 213 227
108 116 261 263 114
128 128 261 261 259 259 259
identificn h i e Table 2 Table 3 Table 3 Table 3 Table 4 Table 4 Table 4 Table 3 Table 3 Table 3 Table 3 Table 3 Table 4 Table 3 Table 3 Table 3 Table 3 Table 4 Table 3
response facto9 0.69 0.68 0.68
0.51 0.84 0.84 0.83
0.91 0.90
0.77 0.66 0.91 0.64 0.84 0.77 0.77
0.77 0.77 0.77
GC/MS analyses of all compounds were performed on a Varian 3400 gas chromatograph and a Finnigan MAT 700 ion trap detector. General Procedure for Aquathermal Reactions. All experiments were carried out in mall (0.75 in.) stainless steel Swagelok (plug and cap) bombs (4 mL capacity) which were not equipped for the collectionor analysis of gaseous products. The model compound (0.16 g) and either cyclohexane or an aqueous solvent (1.14 mL) were charged into the nitrogen-blanketed stainless steel bomb which was then sealed. The reactor was then placed, without agitation, in a Techne fluidized sandbath (Model SBS-4) set at 460 "C using a Techne temperature controller (TC-8D) for a time period of 7 min (Le., 2 min heat-up time to 460 O C and 5 min residence time at that temperature). If little or no reaction was observed, the run was repeated for 1 h. The temperature profile was measured by a Barnant 115 thermocouple thermometer (type J) placed in the sandbath adjacent to the reaction vessel. After the reaction time period, the reaction was immediately quenched by cooling the bomb subsequently with cold air and dry ice, and the bombs were carefully opened while the contents were still solidified (at -78 "C), to minimize loss of material. The reaction mixture was then worked-up as previously described.10 As in earlier parts of this series,'o the GC behavior of all the compounds included in the present paper (starting materials and products) are collated in Table 1. Table 2 records the source and mass spectral fragmentation pattern of the authentic compounds used, either as starting materials or for the identification of products. Table 3 records the mass spectral fragmentation patterns of products which were identified by comparison with published MS data. Table 4 records the MS patterns of products for which no published MS data could be found. These products were assigned from their MS fragmentation patterns, together with a consideration of the reaction conditions, starting materials, and a reasonable mechanistic pathway for their formationfromthe starting materials. In such cases, the assignment ia explained in the text section of the supplementarysection. Tables 2,3, and 4 along with the details of the mass spectral analyses have been deposited as supplementary material (see paragraph at the end of paper regarding supplementary material).
Results and Discussion
All the results and the product yields (mole 7% 1, which have been corrected with regard to their response factor~,9~ (33) Musumarra, G.;P h o , D.;Katritzky, A. R.;Lapucha, A. R.; Luxem, F.J.; MUN~M,R.;Sikh, M.; Brons, G. Tetrahedron Comput. Methodol. lSS9,2, 17.
Katritzky et al.
994 Energy & Fuels, Vol. 8, No. 4, 1994 Table 5. Products of Aquathermolysis of Pyridine (2) at 460 O C
no. 2 3 5 6 7 8 9 10 11 12 15 16 25 29 63 64
solvent
cyclohexane
HzO
time (min) structure
60
60
pyridine piperidine l-methylpiperidine 3-pyridinemethanol 2-picoline l-ethylpiperidine 3-picoline ethylbenzene 2,4-lutidine 4-ethylpyridine 2-ethylpyridine 1-propylpiperidine 1-butylpiperidine 1-pentylpiperidine 2,2'-bipyridine 2,I'-bipyridine
HCOzH (15%) 7
60
97.3 0.2 1.0 0.3 0.3 -
97.6 0.2 0.3
-
0.3 0.3 0.1 0.2 -
HCOzNa (15%) 60
-
0.7
-
0.7 0.1 0.1 0.1 0.2
-
-
Further successiveprotonation and attacks of hydride ion are collected in Tables 5-11 and are represented as at C-6 and C-2 yield piperidine. The N-alkylgroups (other previously described in detail in Part 1.l0 Where apthan methyl) of the alkylated piperidines arise from C-C propriate, the results obtained from the reaction of certain bond cleavages of the pyridine rings, and the mechanisms model compounds are placed in the same table in order deduced for these reactions have been fully discussed that the results can be compared more easily. The elsewhere."*38 Under the new conditions (15% aqueous suggested reaction pathways are illustrated, where necesformic acid, 460 "C, 7 min) we detect the same alkylpisary, in the schemes. Compounds with numbers 1101 are peridines observed at 350 "C for 2 h in the stronger 49% postulated intermediates not detected in the products by aqueous formic acid. Interestingly, these products were the GC/MS system. not observed in the weaker 10% aqueous formic acid at Pyridine (2) (Table 5). Previous work in our labo350 "C for 3 days.20 ratories has shown that at 350 "C for 3 days, pyridine (2) was quite unreactive in cyclohexane and water alone.20 Extending the reaction time to 1h at 460 "C led to only Indeed, only a 9.6% conversion was observed with 10% a very slight conversion in water (0.5%) and aqueous H3P04 to give a varied product slate with 2,2'-bipyridine sodium formate (0.4%) to give 2,4'-bipyridine (64)for both (63)being the major product. In 10% HCOzH, only a cases. In cyclohexane, a 0.4 % conversion was observed to 2.9% conversion was seen with 3-picoline (9)and 4-eth2,2'-(63) and 2,4'-bipyridine (64). In aqueous 15% formic ylpyridine (12)as products. In water containing calcium acid, a 2.4% conversions was observed to ring-alkylated montmorillonite, a 4.9% conversion was observed with pyridines. The mechanisms for alkylation are not clear 2,2'- (63)and 2,4'-bipyridine (64)as the major products. but, evidently, the l-alkylpiperidines (5,8, 16, 25, 29) Recently, we have also observed some unprecedented generated after 7 min undergo cleavage of and/or migration pyridine ring C-C bond cleavages on heating with aqueous of the N-alkyl group (presumably to give volatile hydro49% formic acid at 350 "C for 2 h.H Pyridine (2)underwent carbons) and the piperidine nucleus undergoes dehydroa 16.0% conversion into l-methyl- (5,0.9%), l-ethyl- (8, genation back to pyridine (2). Pyridine (2)then may also 2.3%), l-propyl- (16,3.6%), l-pentyl- (29,1.2%), and undergo ring-methylation, possibly by formylation a t the l-formylpiperidines (8.0 % ): mechanisms were deduced dihydro stage, which would lead to 3- and 5-substitution as discussed later. and by radical reactions at the pyridine stage which would At 460 "C for 7 min, we now find that pyridine (2)is form mainly 2-, and 4-, and 6-substitution, to give essentially completely unreactive in cyclohexane, water, Houser has demonstrated alkylpyridines (7,9,11,12,15). and aqueous 15% sodium formate. In 15% formic acid that 4-phenylpiperidine dehydrogenates to 4-phenylpya 2.7 % conversion was observed to give small quantities ridine in water at 400 "C for 1 h.32 of alkylated piperidines: l-methyl- (5,1.0%), l-ethyl- (8, Acridine (74)(Table 6,Scheme 1). We have already 0.3%), l-propyl- (16,0.3%), l-butyl- (25,0.1%), and shown that at 350 "C for 3 days, acridine (74)in water 1-pentylpiperidines (29,0.276 ) along with some 3-pyridylalone underwent a 50.3 % conversion,mthe major product methanol (6,0.3% ). Formic acid reductions of quaternary being9,lO-dihydroacridine(78). In 10% HCOzHand 10% salts of pyridine and of l-methylpyridinium cation to the HsP04 high conversions (91.3 and 84.6%, respectively) correspondingfully hydrogenated products, uiz.,piperidine were observed,in both cases mainlyto 9,lO-dihydroacridine and l-methylpiperidine, are well d o ~ u m e n t e d . ~The * ~ ~ (78)and 1,2,3,4tetrahydroacridine (69). Aquathermolysis mechanistic pathway to these compounds involves formic in the presence of 10% HzS04 gave 100% of 9(1OH)acid (or formate ion) donating hydride ion to the C-4 of acridone (80). Aquathermolysis of acridine (74)in the the pyridinium cation resulting in 1,4-dihydropy~idine.~*~~presence of nontronite and calcium montmorillonite clays also showed high conversions with high yields of 9-(1OH)(34) Cervinka, 0.;Kriz, 0. Collect. Czech. Chem. Commun. 1965,30, acridone (80)and 9,lO-dihydroacridine (781,while alu1700; Chem. Abstr. 1965,63, 1764. minum-pillared clay gave a mixture of the di- (78)and (35) Yudin, L. G.; Kost, A. N.; Berlin, Y. A.; Shipov,A. E. Zh. Obshch. Khim. 1957,27, 3021; Chem. Abstr. 1957,52,8142. tetrahydroacridines (69). (36) Lukes, R. Collect. Czech. Chem. Commun.1938, IO, 66; Chem. Abstr. 1938, 32, 3764. (37) Lukes, R. Collect. Czech. Chem. Commun. 1947, 12, 71; Chem. Abstr. 1947, 41, 4150.
(38) Katritzky, A. R.; Balaeubramanian,M.; Barcock, R. A.; Ignatchenko, E. S.; Parris, R. L.; Siskin, M. Submitted for publication.
Energy & Fuels, Vol. 8, No. 4, 1994 996
High- Temperature Chemistry of Carbo- and Heterocycles
Table 6, Products of Aauathermolvsis of Acridine (74)and Phenanthridine (75)at 460 "C acridine (74) phenanthridine (75) solvent C6Hl2 H20 HCO2H (15%) HCOzNa (15%) HCOzH (15%) HCO2Na (15%) time (min) 7 60 7 60 7 60 7 60 7 60 7 60 structure 0.4 2.3 2.0 octahydroacridine 1.7 28.1 0.7 20.8 tetrahydroacridine 0.7 0.5 242-methylpheny1)phenylamine 1.0 octahydrophenanthridine 1.0 1.6 0.4 7,8,9,10-tetrahydrophenanthridine 85.5 44.5 99.3 3.5 8.2 63.9 19.5 acridine 74.3 92.0 98.3 96.3 phenanthridine 1.3 2.5 0.7 1,2,3,4-tetrahydrophenanthridine 13.0 43.3 0.7 94.4 61.4 35.0 57.7 9,lO-dihydroacridine 21.7 3.4 1.7 2.6 5,6-dihydrophenanthridine 0.4 9[l0m-acridone 0.4 0.5 9-cyclohexylacridine 9JO-dihydro-9-cyclohexylacridine 0.4 0.5 0.3 0.9 4-cyclohexylacridine 0.4 1.2 2-cyclohexylacridine 0.3 9-cyclohexenylacridine 0.2 4-cyclohexenylacridine 0.2 2-cyclohexenylacridine ~
~
no. 68 69 70 72 73 74 75 76 78 79 80
86 87 91 92 93 94 95
Scheme 2
Scheme 1
0
cOHC
h'HI
(71)
-
(101)
1
+2H
4H
A
I
~~
I
I
1H (73)
" I a
/
H
(691
(78)
+ isomers
(94.951
We now observe a 0.7% conversion to 9,lO dihydroacridine (78)in water at 460 "C for 7 min; increasing the reaction time to 1h, yielded 6.0% of 9,lO-dihydroacridine (78). The reducing agent could be either the metal walls of the reactor vessel or a portion of the organics.20 In cyclohexane, a 14.5% conversion was observed at 460 OC for 7 min to give 9,lO dihydroacridine (78,13.0%). Small quantities of 9-cyclohexylacridine (86),4-cyclohexylacridine (91),2-cyclohexylacridine (92),and 9,lO dihydro-9cyclohexylacridine (87)were also observed as a result of solvent participation. Increasing the reaction time to 1h, led to a 55.5 % conversion with 9,lO-dihydroacridine (78, 43.3 %) and 1,2,3,4-tetrahydroacridine(69,8.4%) as the major products, along with a wide range of cyclohexyl derivatives of acridine, evidently via reactions of cyclohexyl radicals derived from the solvent. Acridine (74)was 96.5% converted at 460 "C for 7 min in aqueous formic acid mainly to 9,lO-dihydroacridine (78, 94.4%), Minor products included 1,2,3,4-tetrahydroacridine (69,1.7 % ) and 1,2,3,4,4a,9,9a,lO-octahydroacridine (68,0.4%). Extending the reaction time to 1h, led to a slightly lower conversion (91.8%1. Interestingly, there was less 9,lO-dihydroacridine (78)generated (61.4%1, while the amount of 1,2,3,4-tetrahydroacridine (69, 28.1 % ) increased significantly. It is clear that acridine (74)is rapidly reduced after 7 min to 9,lO-dihydroacridine (78)
(761
which then probably undergoes further reduction to tetrahydroacridine (69)as the reaction proceeds. However, a point in the reaction is reached where dehydrogenation seems to become the more favored process; the equilibrium elimination of hydrogen is possibly aided catalytically by the surface walls of the reactor. In aqueous sodium formate a 36.1 % conversion after 7 min at 460"C was observed, mainly to 9,lO-dihydroacridine (78,35%1. 1,2,3,4-Tetrahydroacridine(69,0.7% ) was also observed along with some 9(1OH)-acridone (80, 0.4% 1, resulting from an oxidation. Extending the reaction time to 1 h led to an increase in conversion (80.5% ) to give % ), 1,2,3,4-tetrahydroacri9,lO-dihydroacridine (78,57.7 dine (69,20.8%1, and 1,2,3,4,4a,9,9a,lO-octahydroacridine (68,2.0%). Phenanthridine (75) (Table 6, Scheme 2). At 350 "C for 3 days in 10% HzS04 we previously found that 75 gave 51% of 6(5H)-phenanthridone; while a 40% conversion was seen in 10% HCOzH to give 5,6-dihydrophenanthridine (79)and 1,2,3,4-tetrahydrophenanthridine(76). Only a 9.0% conversion was seen in 10% H3PO4 with 1,2,3,4-tetrahydrophenanthridine (76)as the major product. In water containing nontronite clay, and water containing calcium-montmorillonite clays, 1.6 and 12.55% conversions to 6(5H)-phenanthridone were observed. A higher conversion 24.0 % was seen in water with aluminum(76)and pillared clay; 1,2,3,4-tetrahydrophenanthridine 6(5H)-phenanthridone were the products.20 A t 460 "C phenanthridine (75) showed no reaction in either cyclohexane or water after 1 h; in formic acid and
996 Energy & Fuels, Vol. 8,No. 4, 1994
Katritzky et al.
Table 7. Products of Aquathermolysie of 2-Methylquinoline(Quinaldine)(49) and Quinoline (36) solvent
no. 1 4 10 13 17 20 21 27 31 36
38 40 43 46 49
50
tamp ("C) time (min) structure
2-methylquinoline (49) quinoline (36) Ha0 HC02H (15%) HCOaNa (15%) C a 1 ~Ha0 HCOzH (15%) HCOzNa (15%)
Ca12
-460460460460 1 6 0 7 6 0
460
I
benzene toluene ethylbenzene styrene propylbenzene indane indene 1-methylindane 2-ethylaniline quinoline 2-propylaniline isoquinoline 1-methylisoquinoline indole 2-methylquinoline 1,2-dihydro-2-methylquinoline 3-methylquinoline
0
I
0.4 0.6 1.9 0.5 0.9
-
0.1 0.2 2.0
-
2.2
0.9 0.4 35.1
-
-
-
-
-
2.1
1,2,3,4-tetrahydroquinoline 60 3-methylindole 90 4,4"-biquinoliie
sodium formate,it behaves somewhat similarly to acridine (74)but is again less reactive. A 25.7 % conversion in 15% formic acid at 460 OC for 7 min gave 5,6-dihydrophenanthridine (79,21.7% ) as the major product. Other hydrogenated products included 1,2,3,4-(76,1.3%)and 7,8,9,10tetrahydrophenanthridine,(73, 1.0%) 1,1a,2,3,4,4a95,6octahydrophenanthridine (72, 1.0%1, and 242-methylpheny1)aniline (70,0.7 %)-the result of ring opening. At 460 OC for 1h in 15% formic acid, less conversion (8.0%) was observed with an especially reduced amount of 5,6dihydrophenanthridine (79, 3.4% ) which results from a dehydrogenation and rearomatization of the substrate, due to either the metal surface of the reactor or other organics, as the reaction time is prolonged. In 15% sodium formate, low conversions were seen at 460°C bothafter7minandlh(1.7and3.7%,respectively). The typical product in each case, was 5,6-dihydrophenanthridine (79). Smallquantitiesof 7,8,9,1O- (73)and 1,2,3,4 tetrahydrophenanthridines(76) were also observed in the run after 1 h. Quinoline (36) (Table 7, Scheme 3). We previously reported that at 350 OC for 3 days quinoline (36) underwent a 41% conversion in 10% formic acid to give 1,2,3,4tetrahydroquinoline (62) as the major product. In water, little reaction (-5%) was observed but interestingly, isoquinoline (40)was the major product. Similarreaction (6 % ) was seen in cyclohexane; again isoquinoline (40) was the major product. In 10% HsPOl a 42% conversion was seen and the numerous products included alkylquinolines, biquinolines, tetrahydrcquinolines,alkylbenzenes,anilinea, phenols, and indoles. Treatment of quinoline (36) with 10% HzSOlr (8.8% conversion) led to 2(lH)-quinolone along with isoquinoline (40) and 2,2-biquinolyl. In water with nontronite clay, there was a low conversion (4.1%) to a mixture of isoquinoline (40) and l-methylnaphthaleneqm As already mentioned, Houser has reportedQ16 the treatment of quinoline (36)with supercritical water
460 60
0.1 0.2
-
0.1 0.1 0.1
-
95.1 0.1 0.1
-
-
-
53 4-methylquinoline 54 6-methylquinoline 57 2-methyl-
460 4 6 0 4 6 0 4 0 0 4 6 0 6 0 6 0 1 7 6 0
460 60
0.2 0.2 0.1
-
51 52 1,2,3,4-tetrahydroquinoline
1,2,3,4-tetrahydroquinoliie 62 I-methyl-
460
460
6
98.5 0.6
0.2 6.4 0.2 0.2 45.1
-
0.4
-
1.5
-
-
-
-
4.1
-
-
-
0.2
-
-
0.4
-
-
Scheme 3 , ,
I
i)W,H'
n-"
RIM
I
(400,450, or 500 O C for 2 days) alone and water with a catalytic amount of zinc chloride and determined that a wide range of products were formed under all reaction conditions, in every case the moat significant were methylanilines, methylphenols, methylquinolines, and methylindanes. A t 460 "C for 7 min, quinoline (36) was unreacted thermally in cyclohexane,water, and 15%sodium formate, but in 15% aqueous formic acid, 1,2,3,4-tetrahydroquinoline (52) was formed exclusively and in excellent yield (96.5% 1. Interestingly, at the lower temperature of 400 OC for 7 min in 15% formic acid a 98.1% (slightly higher conversion) to 1,2,3,4tetrahydroquinoline(62) was observed. The mechanistic pathway to 1,2,3,4-tetrahydroquinoline (62) from quinoline (36)clearly involves an initial protonation, and then donation of hydride ion to the C-4 of the resulting quinolinium cation, yielding 1,4-dihydroquinoline. Further protonation and attack of hydride ion at C-2 yielded 1,2,3,4-tetrahydroquinoline(52). Reaction
High-Temperature Chemistry of Carbo- and Heterocycles
H (52, 96.5%)
for 1h in 15% aqueous formic acid led to a reduction in the amount of conversion (83.3%). The major product was again 1,2,3,44etrahydroquinoline(52, 79.4% 1. It is clear that quinoline (36) is effectively reduced in 15% formic acid after 7 min, but increasing the reaction time leads to the rearomatization of the hydrogenated portion of the ring to return quinoline (36). Other minor products included benzene (I), toluene (4), ethylbenzene (lo), propylbenzene (17), indane (20), indene (211, and indole (46) from ring-opening reactions. The generation of most of these products can be rationalized by alternative electrocyclic ring-opening of dihydroquinoline 103 at the 2,3 bonds or at the 3,4 bonds of the dihydroquinolinium species 107 as shown in Scheme 3. Houser reported the presence of these same denitrogenated products from the treatment of quinoline with water (in the presence of catalytic ZnClz) at 400 "C for 24 h, but did not propose any mechanism for the reaction.16 l-Methyl-1,2,3,4tetrahydroquinoline (62) was formed via a formylation and subsequent hydride reduction of 1,2,3,4-tetrahydroquinoline (52). 4-Methylquinoline (53) and 2-methyl1,2,3,4-tetrahydroquinoline(57) were also generated in our reactions by mechanisms which are not clear. Houser also reported the presence of methylquinolines from the reaction of water alone at 400 "C for 10 h16 and observed a small quantity of indole from the reaction of quinoline in water containing a catalytic amount of ZnClz at 400 "C for 6 h. Again, he proposed no reaction mechanisms. In 15% sodium formate there was no reaction at 460 "C after 7 min and extending the reaction time to 1 h gave only a 4.9 % conversion, mainly to 1,2,3,4-tetrahydroquinoline (52,4.1%), with smaller amounts of many of the other products, as seen above. The reactions in cyclohexane and water at 460 "C for 1 h gave only a 0.5% conversion in each case mainly to isoquinoline (40); this presumably results from a thermal isomerization reaction, as previously observed (together with its reverse) at 850 "C39 and also in previous aquathermolysis reactions involving quinoline (36) and isoquinoline (40) and a mechanism was suggested.20 2-Methylquinoline (49) (Table 7, Scheme 3). At 350 "C for 3 days 2-methylquinoline (quinaldine) (49) was found to be more reactive than quinoline (36) in 10% H3PO4 (62.0% conversion) and in 10% HzS04 (46% conversion). HzS04 mainly caused a demethylation reaction; 31.9% of quinoline (36) was produced in this solvent and it was suggested that initial oxidation of the methyl group to -CHZOH occurred. A variety of products was obtained in 10% H3P04, but 2,6-dimethylquinoline was the major product. Other prominent products included various propyl-, butyl-, and pentylquinolines formed via the hydrolysis products. Reactions performed in the presence of 10% HCOzH gave more hydrogenated products such as indane (20),tetralin and tetrahydroquinolines, reflecting the inherent reducing properties of this medium.20 We now find that 2-methylquinoline (49) is hydrogenated as easily as quinoline (36) in 15% aqueous formic acid at 460 "C for 7 min. A 94.5% conversion, mainly to (39) Patterson,J. M.; Issidorides, C. H.; Papadopoulos, E. P.; Smith, Jr., W.T.Tetrahedron Lett. 1970, 1247.
Energy & Fuels, Vol. 8, No. 4, 1994 997
2-methyl-1,2,3,4-tetrahydroquinoline (57, 91.1%), was observed. Other minor products included l-methyl1,2,3,4-tetrahydroquinoline(62,2.1% 1, probably resulting from a 1,2-methyl shift from 2-methyl-1,2,3,4-tetrahydroquinoline (57). Ethylbenzene (10, 0.1 % ) and toluene (4,0.1%)were alsoobserved. Increasing the reaction time to 1h led to a decrease in the overall conversion (64.3% ). The major product was 2-methyl-l,2,3,4-tetrahydroquinoline (57, 45.1%). As by the reasoning above, the higher amount of 2-methylquinoline (49) after the longer reaction time probably results from the dehydrogenation of the (57) back generated 2-methyl-1,2,3,4-tetrahydroquinoline to the thermodynamically more stable 2-methylquinoline (49). Most of the products are the exact analogs of those formed from quinoline (36) (see Scheme 3, R = Me) and presumably are formed by similar mechanisms. However, a significant quantity of quinoline (36,2.2% ) and 1,2,3,4tetrahydroquinoline (52, 6.4%) was also formed in this reaction together with propylbenzene (17) and indane (20), and all these involved loss of the 2-methyl group. This is obviously not an oxidation cleavage-we suggest that this reactive methyl becomes formylated and that, after ring opening, loss of a two-carbon fragment occurs. In water at 460 "C for 7 min, a 1.9% conversion was observed, to give quinoline (36)by demethylation (cf.lower temperature resultsx), and 1,2-dihydro-2-methylquinoline (50) by reduction, and a trace of isoquinoline (40). Increasing the reaction time to 1h led to a 2.1 % conversion to give quinoline (36) by demethylation, l-methylisoquinoline (43), and a small amount of 2-propylaniline (38) by ring opening. In aqueous sodium formate at 460 "C for 7 min, a 1.5% conversion was observed with the generation of quinoline (36), 2-propylaniline (38), and 1,2-dihydro-2-methylquinoline (50). Extending the reaction time to 1h gave a 5.8% conversion to yield 2-methyl-1,2,3,4-tetrahydroquinoline (57,2.6%),quinoline (36,2.0%), l-methylisoquinoline (43, 0.5%), ethylbenzene (10, 0.1%), and toluene (4, 0.1%). In cyclohexane at 460 "C for 7 min, a 2.8% conversion was observed. The major product was 1,2-dihydro-2methylquinoline (50,2.4%). Increasing the reaction time to 1h led to a 4.2% conversion to give mainly 2-methyl1,2,3,4-tetrahydroquinoline (57,3.4%)andasmallamount of l-methylisoquinoline (43), isoquinoline (401, and quinoline (36). Isoquinoline (40) (Table 8, Scheme 4). At 350 "C for 3 days, isoquinoline (40) underwent a 31.1% conversion in 10% HCOzH to give a varied product slate. o-Xylene (14, 3.9%), 2-ethyltoluene (19, 5.5%), and indane (20, 2.6 % ) were three significant products formed. Reaction in 10% H3P04 gave a 39.0% conversion and led to an increase in the amount of polyaromatic products like chrysene (88) and dibenzonaphthyridine.zo Houser reacted isoquinoline (40) with supercritical water done and in the presence of catalytic amounts of zine chloride at temperatures of 400,450, and 500 "C and determined the products to be mainly o-xylene (141, ethylbenzene (lo), toluene (41, and benzene (1).lz Isoquinoline (40) showed no reaction at 460 "C in cyclohexane, water, or aqueous sodium formate after 7 min. However, 7 min in aqueous formic acid caused a 55.3% conversion to denitrogenated products, 2-ethyltoluene (19, 29.4%), ethylbenzene (10, 10.6%),o-xylene (14, 7.4%), indane (20, 2.3%), indene (21, 3.0%), and l-methylindane (27,2.4%). Therefore, after just 7 min at
Katritzky et al.
998 Energy &Fuels, Vol. 8, No.4, 1994 Table 8. Products of Aqmthermolysis of Isoquinoline (40) at 460 OC
no.
1 4 10 13 14 19 20 21 22 24 26 27 28 30 36 40 41 43 44 46 48 52 55 58 59 71 84 85 88 89
solvent
cyclohexane
HzO
time (min) structure
60
60
benzene toluene ethylbenzene styrene o-xylene 2-ethyltoluene indane indene 2-meth ylbenzonitrile 2-ethylbenzonitrile l-methylindene l-methyliidane 2-ethylbenzylamine naphthalene quinoline imquinoline l-methylindole l-methyliaoquinoline 3-methylisoquinoline indole 4-methylisoquinoline
1,2,3,4-tetrahydroquinoline 1,2,3,4-tetrahydroisoquinoline l-methyl-l,2,3,4-tetrahydroisoquinoline 1(2H)-isoquinolone phenanthrene 2,3-benzo[bl fluorene
1,4,7,12-tetrahydrobenz[olanthracene chryaene biisoquinolyl
HCOzH (15 % ) 7
60
HCOzNa (15%) 60
0.3 2.7 16.7 0.2 8.1 23.4 4.8 0.5 0.1 0.6 0.2 0.4 3.0 0.2 1.6 30.4 0.2 0.3 0.2 0.1 0.3 0.7 1.1 0.2 1.8 0.1 0.2 0.2 0.4 0.9
0.2 0.5 0.5
-
0.3 0.6 0.3 0.1
-
0.4
-
0.1 94.1
-
0.7
-
2.2
Scheme 4
(125)
460 "C, we see a much greater conversion in this medium and more denitrogenation and ring opening than seen previously after 3 days a t 350 "C. Increasing the reaction time to 1h led to a 69.6% conversion to ethylbenzene (10, 16.7%), o-xylene (14,8.1%), 2-ethyltoluene (19,23.457~1, and indane (20,4.8%) as the major products. These denitrogenated products are the result of hydrogenation, ring opening, and elimination of nitrogen which is easier than for quinoline (36)because cleavage of a phenyl-N bond is not necessary. Other minor products included benzene (1, 0.3%), toluene (4,2.7%), indene (21,0.5%), 2-ethylbenzylamine (28,3.0%),2-methyl- (22,0.1%)and 2-ethylbenzonitrile(24,0.6% ), l-methylindane (27,0.4%), quinoline (36, 1.6 %), 1,2,3,4-tetrahydroquinoline(52, 0.6%), and l(W-isoquinolone (59, 1.8%). The formation of many of these products is rationalized in Scheme 4. Ring opening of the 2,3-bond in 1,2dihydroisoquinoline (1 12)is believed to lead, as shown, to
4,14,19,22,24,and 28. Ring opening of the 1,2-bond in 3,4-dihydroisoquinoline (1 15) is believed to produce 10, 13,20,21,26,and 27,as shown. Formation of 55 and 59 is also shown in Scheme 4. Of the other compounds formed, we observed previously the formation of the polyaromatics such as 71,84,85,and 88.20 There remains the isomerization to quinoline (36) (the reverse of the reaction discussed above), and products of methylation (43,44,48,581 for which the formation route is unclear, although a combination of formylationlreduction and radical methylation cannot be ruled out. In 15% sodium formate at 460 O C for 1 h, a 15.6% conversion was seen. The major products included ethylbenzene (10,8.3% 1, o-xylene (14,2.0%),2-ethyltoluene (19,1.3%), isoquinolone (59, 1.5%),and quinoline (36, 0.1 5%). In water and cyclohexane a t 460 "C for 1h, there was 3.0 and 5.9% conversion, respectively, to give similar product slates comprising toluene (4),ethylbenzene (lo), o-xylene (14),2-ethyltoluene (19),and indane (20). In cyclohexane, where no water is available for hydrolysis, theavailabilityofthedihydroisoquinolines(112)and (115) to undergo electrocyclicring-opening (seeScheme 5)allows the formation of a remarkably similar slate of products to that formed in the aqueous media. 1,2,3,4-Tetrahydroquinoline(52) (Table 9). Our previous work has shown that 1,2,3,4-tetrahydroquinoline (52)after 3 days at 250 "C underwent a 16.7% conversion in water as compared to only a 2.0% conversion in
Energy & Fuek, Vol. 8, No. 4, 1994 999
High- Temperature Chemistry of Carbo- and Heterocycles
Table 9. Products of Aquathermolysis of 1,2,3,4-Tetrahydroquinoline(52) at 460 OC solvent time (min) structure
no.
1 4 10 17 20 27 36 38 52 62
CeHlZ 60
HzO 60
HCOzH (15%) 60
HCOzNa (15%) 60
-
-
0.2 0.2 0.3 0.2 0.2 0.7 3.7
1.3 -
benzene toluene ethylbenzene propylbenzene indane 1-methylindane quinoline 2-propylaniline
0.2 0.5 5.1
4.5 0.9 94.6
1,2,3,4-tetrahydroquinoline 1-methyl-1,2,3,4-tetrahydroquinoline
-
-
-
94.2 -
93.3 1.2
0.2 0.8 23.9 0.2 73.6
-
Table 10. Products of Aquathermolysis of Indole (46)and 2,3-Dimethylindole (65)at 460 O C indole (46)
no.
1 4 10 18 31 33 34 35 37 38 39 41 42
solvent time (min) structure benzene toluene ethylbenzene aniline 2-ethylaniline 1-methylindoline indoline 2-methylindoline 1,2-dimethylindoline 2-prop ylaniline 1,3-dimethylindoline 1-methylindole 2,3-dimethylindoline 3-methylindoline indole 1,2,3-trimethylindoline 3-methylindole 2-methylindole 2,3-dimethylindole 1,2,3-trimethylindole 2,3,4-trimethylindole
C&z 60 0.1 0.1 0.5
0.4 -
2,3-dimethylindole(65)
H20 HCOzH (15%) HCOzNa (15%) 60 7 60 60
0.3 0.2
-
0.1 0.1 0.4 0.2 0.3 45.9
-
0.4 1.1 4.1 4.2 2.8 0.2 5.7
-
45 46 47 60 61 65 66 67 81 3-cyclohexyl-2-methylindole 82 4-cyclohexyl-2,3-dimethylindole
cyclohexane; quinoline (36) was the major product.B In aqueous sodium bisulfite/sodium sulfite, an increased conversion to 68.0 % was observed; as expected increased amounts of quinoline (36, 60.9) were observed in this oxidizing medium. Reaction in 10% phosphoric acid gave an 8.4% conversion with aniline (18) and methylas products. As substituted 1,2,3,4-tetrahydroquinolines mentioned above, Houser reacted 1,2,3,4-tetrahydroquinoline (52) with supercritical water alone and in the presence of catalytic amounts of zinc chloride at 400-456 "Cand determined the main product to be quinoline (36).16 We found 1,2,3,4-tetrahydroquinoline(52) to be essentially unreactive at 460 "C for 7 min in cyclohexane, water, aqueous 15% formic acid or aqueous 15% sodium formate solutions. At 460 "C for 1 h, the most reaction was seen in aqueous sodium formate with a conversion of 26.4%. The major product was quinoline (36, 23.9%). The reasons why substantially more dehydrogenation of 1,2,3,4-tetrahydroquinoline (52) was observed in aqueous sodium formate than in other media are unclear. Small amounts of ethylbenzene (10,1.3 %), 1-methylindane (27, 0.8% ), and 2-propylaniline (38,0.2 % ) were also observed. In cyclohexane, water, and aqueous formic acid, between 5 and 7% conversions were observed in each case. The major product in each case was quinoline (36, -4-5%) resulting from dehydrogenation. In water and aqueous formic acid small quantities of ethylbenzene (lo), l-methylindane (27), and indane (20) were observed. Houser
0.4 0.1
-
0.7
-
98.8 -
-
-
C&Z HzO HCOzH (15%) HCO2Na (15%) ~7
60
7
60
7
60
7
60
-
-
0.8 99.2
4.9 94.8
-
-
-
-
-
-
-
-
-
-
0.2 0.1 0.2
0.1 0.1 0.7 0.3
-
-
0.8
-
0.2
-
0.2
-
0.5 0.2
-
-
-
-
-
0.1
-
-
-
0.1
-
-
-
14.3 0.4
-
0.3
-
-
-
23.7 12.8 0.3
-
0.3 1.7 0.5 4.3 0.5 98.8 95.9 99.5 93.9 46.6 - - - 0.5 0.5 - 0.2 - 1.1 - 0.4 - 0.1 0.7 -
0.8
0.8 1.0 3.0 -
-
35.1 57.0 0.5 0.6 -
-
-
0.2
0.1
-
-
also observed the presence of a similar slate of denitrogenated products including propylbenzene, indanes, and toluidines from the reaction of 1,2,3,4-tetrahydroquinoline (52) in water alone at 400 "C for 3 h, although no mechanisms for their formation were put forward.l6 All the minor products are similar to those formed in the corresponding reaction of quinoline (see Table 7) and we believe that they again arise through dihydroquinolines, although they are now formed by dehydrogenation oxidation rather than reduction. In aqueous 15% formic acid, l-methyl-l,2,3,4-tetrahydroquinoline (62) was also generated via formylation and subsequent hydride reduction. This parallels the reactions previously reported for piperidine itself.24 The reaction in cyclohexane yielded the fewest products with 2-propylaniline (38, 0.9% ) as the only product besides quinoline (36, 4.5% ). Indole (46) (Table 10, Scheme 6). Our previous work has shown that indole (46) was unreactive at 250 "C for 5 days in water and 10% phosphoric acid.21 Increasing the reaction time to 350 "Cfor 5 days indole (46)underwent only slight reaction in water to give small amounts of aniline and o-toluidine. In 10% phosphoric acid at 350 "C for 1 h, a 61% conversion was observed. Major products included phenol, aniline (18), 2-methylindole (611, and 2,3-dimethylindole (65). In our work, we have now found indole (46) to be unreactive in cyclohexane,water, and aqueous 155% sodium formate at 460 "C for 7 min. Indole (46) underwent a
Katritzky et al.
1000 Energy &Fuels, Vol. 8, No. 4, 1994 Scheme 7
Scheme 6
I
k 47.2% conversion in aqueous 15% formic acid at 460 "C for 7 min. The major product resulting from hydrogenation of the nitrogen-containing ring was indoline (34, 45.9% ). Minor products included toluene (4),aniline (181, ethylbenzene (lo),and 2-ethylaniline (31) allresulting from ring cleavage, and 3-methylindoline (60) just from transmethylation, and 1-methylindole (33) from methylation and reduction. The methylations probably involve initial formylation of indoline (34) at the 1-position to form 128 and of indole (46) at the 3-position to give 129. Extending the reaction time to 1 h, there was a lower conversion (20.1%) observed in aqueous 15% formic acid. Much less indoline (34) was generated (5.7 % ) after the reaction for 1h compared to the reaction for 7 min. This is presumably due to the indoline (34) initially generated being dehydrogenated back to indole (46) as the reaction time increases. Other products included an increased amount of 2-ethylaniline (31), ethylbenzene (lo), and aniline (18) all resulting from ring opening. Ring opening of 127 would give 130, and this could undergo internal oxidation reduction to form 131 which would undergo deacylation to form aniline (18). A likely origin of 2-ethylaniline (31) is from (60) by ring opening to 132 and subsequent deformylation. Ethylbenzene (10) could in turn result from deamination of (31). In 15% aqueous sodium formate there was only a 1.2% conversion a t 460 "C for 1 h to give small quantities of 2-ethylaniline (31),aniline (18),and indoline (34). In water at 460 "Cfor 1h, a 0.5% conversion to 2-ethylaniline (31, 0.2%) and aniline (18,0.3%) was seen. In cyclohexane, a 1.8% conversion was observed at 460 "C for 1h, giving small quantities of ethylbenzene (lo),toluene (41, benzene (l),and indoline (34). 2,3-Dimethylindole (65) (Table 10, Scheme 7). We have demonstrated that 2,bdimethylindole (65) is unreactive over 5 days at 250 O C in either water or cyclohexane and underwent only a 4% conversion to 2-methylindole (61) at 350 "C over 5 days in cyclohexane. However, a t 350 "C over 5 days in water alone and at 250 "C for 5 days in 10% H 3 0 4 , for both cases, conversionsof 40 9% to mainly 2-methylindole (61) and 1,2,3-trimethylindole (66) were observed.21 In the current work, we found 2,3-dimethylindole (65) underwent a 53.4% conversion in aqueous formic acid a t 460 "C for 7 min. The major products included 2,3dimethylindoline (42, 23.7%) (whether it was the cis or trans isomer could not be determined from the GUMS), 3-methylindoline (45, 12.8%),and 2-methylindoline (35, 14.3 % ) all resulting from hydrogenation. Minor products included toluene (41, ethylbenzene (lo), from denitroge-
nation and ring opening, and dimethylindolines (37,391, 1,2,3-trimethylindoline(47),and 1,2,34rimethylindole (66) from a trans-methylation processes. The formation of 3-methylindoline (45) could involve formylation at the 3-position and the sequence of intermediates (133), (134), and (135); N-methylation of 45 would give l,&dimethylindoline (39). 2-Methylindole (61) and 2-methylindoline (35) are probably formed by demethylation of the protonated intermediate (136); further N-methylation then gives 1,Zdimethylindoline(37). Toluene (41, ethylbenzene (lo), and aniline (18) are presumed to be formed by processes similar to those for the formation of the same products from indole itself. Extending the reaction time to 1h at 460 "C,there was little increase in conversion observed in cyclohexane,water, and 15% aqueous sodium formate. In 15% aqueous formic acid, a lower conversion (43.0%) was observed, mainly to give 2-methylindole (61, 35.1%). Only a small quantity of 2-methylindoline (35, 0.8%) was observed for this reaction time compared to that after only 7 min (14.3%). This is a similar trend to the following results seen from the other methylated indole derivatives. 2-Methylindole (61) (Table 11, Scheme 7). We have demonstrated previously that at temperatures up to 350 "C over 5 days, 2-methylindole (61) was quite unreactive in water and cyclohexane. In 10% HsP04 at 250 "C for 5 days a 30.1% conversion predominantly to 2,3-dimethylindole (65) was observed, along with traces of indole (46) and trimethylindoles.21 2-Methylindole (61) underwent a 70.7% conversion in 15% aqueous formic acid at 460 "C for 7 min, predominantly reduction to 2-methylindoline (35,61.5% ). Other significant products resulted from transmethylation and included 1,2-dimethylindoline (37), 2,3-dimethylindoline (421, indole (461, and 2,&dimethylindole (65). 2-Methylindole (61) underwent little reaction in cyclohexane, water, and 15% aqueous sodium formate at 460 "C for 7 min. In cyclohexane (0.6% conversion), indole (46), and 2,3-dimethylindole (65) were observed resulting from transmethylation. In water, a 0.9 % conversion was seen to indole (46), 2,3-dimethy€indole (65), and aniline (18). In 155% aqueous sodium formate (0.9 % conversion),indole (46), 2,3-dimethylindole (651, and 2-methylindoline (35) were the products. Extending the reaction time to 1 h at 460 "C led to a decrease in the extent of conversion (44.5%) in 15%
Energy & Fuels, Vol. 8, No. 4, 1994 1001
High-Temperature Chemistry of Carbo- and Heterocycles
Table 11. Products of Aquathermolyeis of 2-Methylindole (61) at 460 OC solvent no. 1 4 10 18 23 31 32 34 35 37 42 46 47 56 61 65 81 82
time (min) structure benzene toluene ethylbenzene aniline o-toluidine 2-ethylaniline 2-methyl-N-methylaniline indoline 2-methylindoline 1,2-dimethylindoline 2,3-dimethylindoline indole 1,2,3-trimethylindoline l,2-dimethylindole 2-methylindole 2,3-dimethylindole
3-cyclohexyl-2-methylindole 4-cyclohexyl-2-methylindole
CSHl2
H2O
HCO2H (15%)
HCOaNa (15%) 7
7
60
7
60
7
60
-
-
-
-
-
0.3
-
0.1 0.3 0.2
-
0.6 0.5
0.1 0.1 0.1 0.4
-
0.5 0.9 0.2 3.0 0.1 0.5 1.9
-
-
-
-
0.2 0.3
-
0.3
1.5 -
99.4 0.3
96.0 0.7 0.3 0.4
-
-
-
aqueous formic acid. Interestingly, very little 2-methylindoline (35) was present after 1h at 460 "C compared with 7 min (compare 1.0 with 61.5%, respectively). However, there was a significant increase in the amount of indole (46,32.2 %) generated. Presumably, the 2-methylindoline (35)generated undergoes dehydrogenation back to 2-methylindole (61) along with demethylation to give indole (46). There was also an increase in the formation of aniline (18,3.0%), ethylbenzene (10,0.2%), toluene (4, 0.9%),and benzene (1,0.5%)via ring opening and of 1,2dimethylindole (56,0.6 7%). New products detected after 1 h, included 2-methyl-N-methylaniline(32, 1.9% ), otoluidine (23,0.1%) and 2-ethylaniline (31,0.5%). The mechanisms are essentially the same as those already discussed. In 15% aqueous sodium formate, there was an 11.6% conversion at 460 "C for 1h. The major product was indole (46,7.6%) along with aniline (18,0.8%), o-toluidine (23, 1.1% ), 2-ethylaniline (31, 0.7%), 2-methylindoline (35, 0.4%), and 2,3-dimethylindole (65, 1.0%). In water at 460 "C for 1h, there was a 6.2% conversion to give indole (46,2.2%) and 2,bdimethylindole (65,2.9%) as the major products. Aniline (18, 0.6%) and o-toluidine (23,0.5%) were the minor products. In cyclohexane at 460 "C for 1 h, there was a 4.0% conversion. Indole (46,1.5% ) and 2,3-dimethylindole (65, 0.7%) were the major products. Aniline (181, 2-methyl(23)and 2-ethylaniline (31),indoline (34),2-methylindoline (35), and 3-cyclohexyl- (81) and 4-cyclohexyl-Zmethylindoles (82) were the other minor products. Carbazole (77). Houser reported that carbazole (77) was unreactive at 450 "C for 48 h12 and Klein found that carbazole (77) was resistant to reaction at both 450 and 550 "C for reaction times of 1h.30 We have now confirmed that this compound (77) is completely unreactive at 460 O C even after 1 h in all four media. Carbazole (77) is evidently highly resistant to aquathermolysis, thermolysis and reduction under these conditions.
Conclusions The reactivity of the nitrogen-containing heterocyclic compounds studied in this paper are similar in cyclohexane and supercritical water, indicating that water by itself does
-
0.2
2.2
-
-
99.1 0.4
93.8 2.9
-
61.5 0.7 0.8 3.7 0.1 0.3 29.3 2.8
-
60
0.8 1.1 0.7 -
-
1.0 0.7 0.4 32.2
-
0.6 55.5 2.5
88.4 1.0
-
0.4
7.6
-
not enter into the free-radical reaction pathways. Addition of either formic acid or sodium formate to the water results in a variety of reductions of aromatic rings. This is strikingly different from what is observed in all carbonor sulfur-containing aromatic rings. It is the result of the basicity of the nitrogen and reduction by sequential proton and hydride ion donation. The amount of denitrogenated products is small for most of the compounds, with the notable exception of isoquinoline. In this case, reduction of the ring leads to a compound with no aromatic carbon nitrogen bond, which makes it easier to thermally denitrogenate. This work indicates that denitrogenation of fossil fuels in supercritical water would need some additional additives in order to be successful on most of the nitrogen-containing heterocycles. Quinoline and 2-methylquinoline (quinaldine) underwent substantial reduction in 15% aqueous formic acid after 7 min. However, extending the reaction time to 1 h did not lead to significant denitrogenation. Indeed, dehydrogenation back to the aromatic nuclei was the favored pathway. Isoquinoline had a useful rate of denitrogenation especially in 15% aqueous formic acid, and a certain amount in 15% aqueous sodium formate after 1 h a t 460 "C. Acridine was more reactive than phenanthridine; both these polycycles underwent significant reduction especially in aqueous formic acid after only 7 min. Indeed, acridine was observed to undergo slight reduction even in water alone. Extending the reaction time led to more extensive dehydrogenation reactions. The monocyclic compound, pyridine, showed very low conversions but some interesting N-alkylpiperidines were generated from the reaction of pyridine in 15% aqueous formic acid. Hydrogenation chemistry of the indole derivatives predominated in 15% aqueous formic acid, where the major reaction was seen. This was followed by lesser amounts of ring opening. Methylations were the only other reaction observed to any significant extent. Carbazole was completely unreactive. Supplementary Material Available: Mass spectral assignmenta of the structures and Tables 2,3, and 4 listing mass spectral fragmentation patterns (10 pages). Ordering information is given on any current masthead page.
