Energy & Fuels 1987,1, 300-304
300
0
2 0
40 Time min
80
Figure 6. Change in the product distributionof the liquefaction of Wandoan coal. Keys are the same as shown in Figure 1. Conditions: 0.04 mmol of MO(CO)~, 0.4 mmol of Fe(C0)5,1.0 mmol of S, PHI= 5.0 MPa, in 1-MN, at 425 "C.
catalysts system, which is also active for hydrogenation of aromatic compounds.
Conclusion There are no significant differences in the catalytic effect of Fe and Sn on the hydroliquefaction of Yallourn and
Mi-ike coals. On the liquefaction of subbituminous Wandoan coal, Fe is a more favorable catalyst than BySn, due to a higher ability to hydrogenate aromatic compounds. Although the direct parallel process to oil and asphaltene from coal prevails during the liquefaction of a low-rank coal, the contribution of the stepwise reactions is more significant to the liquefaction of bituminous coal. The catalyst promotes the stepwise reactions to give higher yield of the oil fraction. From the differences in the amount of preasphaltene fraction as a function of reaction time during the liquefaction of Yallourn coal with low and high catalyst levels, repolymerization of the preasphaltene fraction is considered to be the most important factor controlling liquefaction reactions. The catalyst, Fe and/or Sn, seems to stabilize coal fragment radicals or preasphaltenes that tend to recombine. A discrepancy between observed and calculated results using Scheme I11 in a non-hydrogen-donating solvent without catalyst can be attributed to the repolymerization of coal fragments. This case can be described better by using Scheme IV, assuming the rate of coal conversion to preasphaltene is independent of the nature of the catalyst. Registry No. Sn, 7440-31-5; Fe, 7439-89-6; Bu4Sn,1461-25-2; Fe(CO),, 13463-40-6.
Noncovalent Interactions in High-Rank Coals Elaine M. Y. Quinga and John W. Larsen* Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015 Received June 26, 1986. Revised Manuscript Received January 14, 1987
The adducts formed by reacting maleic anhydride and bituminous coals of varying rank have been prepared. The adducts contain between 16% and 19% maleic anhydride. The extractabilities of the coals and their adducts have been measured in pyridine and THF. For coals having less than 88% C (dmmf), the extractabilities of the coal and its maleic anhydride adduct are the same. The adducts of coals containing more than 90% C are much more extractable than the starting coal is. It is suggested that the coals having more than 90% C are associated by London dispersion interactions ("stacking interactions") between PNA systems. These interactions are not important to the extractability of lower rank coals because either the size or the population of the PNA systems is insufficient.
Introduction Coals of low and medium rank behave like covalently cross-linked networks,ld and we know of no reasons for s u p p i n g that they are not covalent networks. It has been established that hydrogen bonds within the coal are structurally important interactions2%~6~' serving as cross(1) Green, T.;Kovac, J.; Brenner, D.; Larsen, J. W. Coal Structure; Meyers, R. A. Ed.,Academic: New York, 1982; pp 199-282. (2) Larsen, J. W.;Green, T.K.; Kovac, J. J. Org. Chem. 1986, 50, 4729-4735. (3) Liotta, R.Fuelel 1979,58,724. Liotta, R.;Rose,K.; Hippo, E. J.Org. Chem. 1981,46,277-283. (4) Matturro, M. G.; Liotta, R.;Isaacs, J. J. J . Org. Chem. 1985, 50, 5560-5566. (5) Brenner, D.Fuel 1984,63, 1324-1328. (6) Hombach,H.-P.Roc.-Znt. Kohlenwiss. Tag. 1981,48,427;Chem. Abstr. 1983,98, 19153~. (7) Brenner, D. Fuel 1985, 64, 167-173.
0887-0624/87/2501-0300$01.50/0
links in untreated coals. The importance of hydrogen k due to the gradual bonds d w " S as Coal m ~ increases, h P p e m a n c e ofhY&OWl f T O U P S ~As Coal rank increases, the potential i n m -for ~ the ~ formation ~ of show "stacking interactions" between the increasing number of larger polynuclear aromatic (PNA) systems. Evidence for an important role for such interactions in high-rank coals has recently been published? We report here more evidence for the existence of stacking interactions in high-rank coals and, perhaps more importantly, evidence of their limited importance in coals containing 88% or less carbon. The "stacking interaction" is more properly called the London dispersion force. I t is an instantan~ous~ ~ d u c e d (8) vitehurat, D. D.;Mitchell, T. 0.;Farwiu, M. Coal Liquefaction; Academic: New York, 1980. (9) Stock, L. M.; Mallya, N. Fuel 1986, 65, 736-738.
0 1987 American Chemical Society
Noncovalent Interactions in High-Rank Coals
b-
c -
d -
Figure 1. Geometry of aromatic stacking interactions.
dipole-induced-dipole interaction that occurs between all molecules and can produce a strong attraction between large PNA systems.loJ1 The size of the interaction builds rapidly with the size and polarizability of the systems involved. The origin of the attraction is the correlation of electron motion in the interacting molecules. It is a short-range interaction, in most systems diminishing with the sixth power of the distance between interacting systems. Excellent descriptions of it exist.lOJ1Since both the size and number of PNA systems in coals increase with rank and since the London forces will grow in size and importance as the PNA systems increase in size and number, it is expected that the importance of London forces will increase with coal rank. The geometry of these interactions is most important to the possible arrangement of the PNA systems in coals. Because of its importanee in biological systems,12stacking interaction geometry is an actively investigated area. The most favorable geometry in most systems so far considered has the aromatic rings at right angles to each other as in Figure la. The often written parallel stack (Figure lb) is one of the least favorable geometries. In solid benzene, perpendicular interactions are found in addition to displaced parallel planes (Figure IC)and cogwheel (Figure Id) arrangement^.'^ The perpendicular orientation is observed in gas-phase benzene.14 A statistical analysis of the phenylalanine rings in proteins of known structure shows a preference for perpendicular interactions between rings lying above one another.16 Finally, molecular orbital calculations reveal a preference for perpendicular orientation.16 Our experimental approach is to modify the coal to selectively disrupt the London forces and to search for the effects of this disruption. The London forces can be reduced sharply by forcing the interacting PNA systems apart because the interaction is very short range. Reducing the size of a system will also reduce the size of the London forces. If this is to be done chemically, it is crucial to use a reaction that will not cleave covalent bonds, because the effects of removing covalent bonds and disrupting London (10) Kauzmann, W. Quantum Chemistry; Academic: New York, 1957; pp 503-517.
(11) Ishida, T.;Matsui, M.; Inoue, M.; Hirano, H.; Yamashita, M.; Sueivama. K.: Sueiura. M.: Tomita. K. J. Am. Chem. SOC. 1985, 107, 336g3314. . (12) Burley, S.K.;Petsko, G. A. Science (Washington,D.C.) 1985,229, 23-28. (13) Cox, E. G.; Cruickshank, D. W. J.; Smith, J. A. Proc. R. SOC. London 1958,247,l-21. (14) Hopkine,J. B.; Powers, D. E.; Smalley, R. E. J.Phys. Chem. 1981, 86,3739-3742. Langridge-Smith, P. R.R.; Brumbaugh, C. A.; Haynam, C. A.; Levy, D. H. J. Phys. Chem. 1981,85, 3742-3746. (15) Singh, J.; Thornton, J. M. FEBS Lett. 1985, 191, 1-6. (16) Pawliszyn, J.; Szczesniak, M. M.; Scheiner, S. J. Chem. Phys. 1984,88,1726-1730. Karlstrom, G.;Lime, P.; Wallqvist, A.; Jonsson, B. J. Am. Chem. SOC. 1983, 105,3777-3782. '
-
Energy & Fuels, Vol. 1, No. 3, 1987 301
interactions will generally be the same. We propose to use the Diels-Alder reaction between coals and maleic anhydride to simultaneously separate interacting PNA systems and to reduce their size. This is discussed in detail below. The experimental probe to be used is extractability. A molecule can be removed from a coal by extraction if it interacts as strongly with a solvent as with the coal matrix. If interactions that are important in holding a molecule to the insoluble part of the coal are diminished, its extractability will be enhanced. If London forces help bind soluble molecules to the coal and if these forces can be diminished, more molecules will be removed by extraction. Thus, our procedure is to compare the extractability of a coal and its maleic anhydride adduct. If London forces are significant, the extractability of the adduct will be greater. This approach has been used by Stock, albeit with another reaction. Methylation of several high-rank bituminous coals led to little change in pyridine extractability while butylation strongly enhanced it.9 This is quite consistent with an important role for London forces. Also, THF and pyridine extractabilities of coals increase after reductive alkylation reactions and after butylation using sodium or potassium amide in liquid ammonia.17 However, the reductive alkylations are known to cleave some covalent bonds, which makes the coal soluble.18 Bond cleavage seems to be a greater problem with low-rank coals. There is evidence that nonreductive alkylation with potassium amide in liquid ammonia breaks no covalent bonds." A cautionary note is necessary here. A very small amount of bond breaking in a macromolecular network can cause large increases in extractability as fragments of the network break Off.lg I t is very difficult, perhaps impossible, to demonstrate that no bonds have been broken when applying energetic reagents to a substance as complex as coal. Yet this demonstration is necessary for the credibility of these arguments. Because similar amounts of bond cleavage (if any) are expected in coal methylation and butylation, the extractability differences caused by these two nonreductive alkylations is the firmest published evidence for an important structural role for London interactions between PNA systems in coals. Our approach is to use a different chemical reaction, one that proceeds under mild conditions and which uses reagents most unlikely to break covalent Q bonds. The Diels-Alder reaction between coal and maleic anhydride has been studied.m*21The reaction is diffusion-controlled and ester formation between hydroxyl groups in the coal and the maleic anhydride does not occur.21 Four different reactions between maleic anhydride and coals are possible. The anthracene structure unit, which can also be part of a larger structure, is a requirement for the Diels-Alder reaction between maleic anhydride and both acene and phene type aromatic hydrocarbon^^^*^^ (reaction 1). This reaction not only reduces PNA size but also introduces a large group perpendicular to the plane of the PNA system, forcing neighboring PNA systems apart. Both of these alterations will reduce London forces between PNAs. The reaction conditions are much dif-
'
(17) Stock, L. M.; Mallya, N. Prepr. Pap.-Am. Chem. SOC., Diu. Fuel Chem. 1985,30, 291-297. (18) Stock, L. M.In Coal Science; Gorbaty, M. L., Larsen, J. W., Wender. I.. Eds.: Academic: New York. 1982: Vol. 1. D 248. (19) Yan, J. F.Macromolecules 1981; 14, 1438-1445. (20) Duty, R.C.;Liu, H. F. Fuel 1980, 59, 546. (21) Larsen, J. W.; Lee, D. Fuel 1983, 62, 1351-1354. 1980, 102, (22) Biermann, D.; Schmidt, W. J. Am. Chem. SOC. 3163-3173, 3173-3181. (23) Trivedi, B. C.;Culbertson, B. M. Maleic Anhydride; Plenum: New York and London, 1982.
Quinga and Larsen
302 Energy & Fuels, Vol. 1, No. 3, 1987
Table I. Elemental Analyses of Coals Used anal.. % coal C H N 0 + Sa Bruceton 78.9 5.05 1.75 9.9 PSOC 1309 76.6 5.23 1.30 7.9 1.58 3.1 PSOC 721 76.9 5.28 PSOC 1133 73.0 5.01 1.13 0.5 PSOC 648 84.2 4.23 1.83 3.7
(1)
ferent and much milder than alkylation reactions, d i g it a nice complement to the alkylation studies. The reaction of maleic anhydride and &naphthol (reaction 2) is II
-0'( C /
QT&o / C
\
(2)
II 0
II 0
also known and may occur in coal^.^*^ Maleic anhydride also reacts with a variety of condensed PNA systems as typified by the reaction with perylene%(reaction 3). The a
0
II
II
a
formation of adducts of this type will not hinder the approach of molecules normal to the ring plane and results in only a small degree of dearomatization. It will interfere strongly with perpendicular stacking. Finally, alkylation by maleic anhydride, shown here proceeding through an ene reaction (reaction 4), is possible but is not known to 0 X
By difference.
Table 111. Elemental Analyses of Pyridine Extracts of Maleic Anhydride-Coal Adducts anal., % coal C H N 0 + Sa ash Bruceton 4.89 1.84 14.8 0.29 77.8 13.2 0.63 PSOC 1309 77.6 5.04 3.49 5.30 2.19 7.7 0.64 PSOC 721 84.2 PSOC 1133 81.7 5.23 2.24 10.0 0.89 PSOC 648 82.4 5.28 2.05 7.3 3.00
0
/H
By difference. Table 11. Elemental Analyses of the Maleic Anhydride-Coal Adducts anal., % coal C H N 0 + Sa ash 4.78 1.45 14.2 4.8 Bruceton 74.8 4.91 15.5 7.0 PSOC 1309 71.5 1.24 4.80 1.60 9.0 PSOC 721 78.5 6.1 PSOC 1133 73.1 4.04 1.48 11.1 10.3 PSOC 648 83.8 4.12 1.84 6.0 4.2
0
0 "OJ - )Q
a
ash 4.4 9.0 13.1 20.4 6.0
!
0
occur. The first two reactions will destroy stacking interactions in two ways. (1)They reduce the size of the aromatic system since the reacted ring is no longer aromatic. The larger the aromatic system, the stronger the stacking interactions, so any size reduction will weaken them. (2) The maleic anhydride unit introduced will be perpendicular to the ring system of acenes and phenes, (24)Oku, A.; Ohmishi, Y.; Mashi, F. J. Org. Chem. 1972, 37, 4264-4269. (25)Wariyar, N. S. hoc.-Indian Acad. Sci., Sect. A 1956, A43, 231-236. (26)Hopff, H.; Schweizer, H. R. Helu. Chim. Acta. 1959, 42, 2315-2333.
By difference.
forcing the two adjacent ring systems far apart. With condensed aromatics, the addition of the maleic anhydride to the edge of the molecule will disrupt the stacking interactions shown in Figure la,d. Stacking interactions fall off as the sixth power of the distance separating the rings and will effectively vanish at the separation caused by the introduction of the maleic anhydride. The ene alkylation reaction will only function in the second manner. A Diels-Alder reaction in an anthracene structure will be most effective in decreasing the London force.
Experimental Section All chemicals used were the purest grade available from common sources (Aldrich, Fisher). Pyridine, benzene, and tetrahydrofuran were dried over potassium hydroxide pellets. The coal samples were obtained from The Pennsylvania State University Coal Bank and the Argonne National Laboratory Premium Coal Sample Bank and were stored under nitrogen. The elemental analyses of the parent coals, Diels-Alder reacted products, and pyridine extracts were performed by Galbraith Laboratory, Inc., Knoxville, TN, and are given in Tables 1-111. The coal (10-12 g) was placed in 250 mL of chlorobenzene in a 500-mL round-bottom flask under nitrogen and was stirred vigorously. The mixture was heated and maleic anhydride (7-9 g) was added when the temperature reached 90 "C. The mixture was then further heated to 105-110 O C and was stirred for 10 days. The oooled mixture was filtered,and the solid product was Soxhlet extracted with 250 mL of distilled water overnight to remove the unreacted maleic anhydride. The coal residue was dried to constant weight in a vacuum oven at 110 "C. The dried coal residue was Soxhlet extracted with 250 mL of pyridine or tetrahydrofuran for 1 week. Solvent was removed from the extract by vacuum distillation,keeping the temperature below 30 "C. The coal extracts and residues were dried to constant weight in a vacuum oven a t 110 "C. Infrared spectra were obtained on a Mattson Serius 100 Fourier transform spectrometer equipped with Harrick optics and a sampling stage for diffuse reflectance. Spectra were recorded from
Noncovalent Interactions in High-Rank Coals Table IV. Weight Gain of Coals due to Formation of Adducts with Maleic Anhydride coal Bruceton PSOC 1309 PSOC 721 PSOC 1133 PSOC 648 101:no.OOO1Ob 101:n0.00012~ 101:n0.00003~
% C (dmmf)
% w t gaina
84.1 84.3 88.3 90.7 92.1 88.8 88.8 88.8
19.0 20.9 20.3 23.3 21.0 19.9 18.6 20.0
a (wt after reacn - wt. before reacn)/wt before reacn. bArgonne premium coal sample.
the coaddition of 200 scans at 8 em-' resolution against a background of KCl. Samples and KCl were ground in a Wig-L-Bug for 3 min. Dilution of the samples by cogrinding with preground KCl for 3 min produced a 5% mixture yielding reproducible sp e ctra.
Results and Discussion Coals react readily with maleic anhydride, increasing in weight by about 20%, as shown by the data in Table IV. This is consistent with earlier results with Bruceton coal, where an 18% increase in weight was obser~ed.~'The amount of maleic anhydride incorporated can 'also be calculated from the elemental analyses. The results of these calculations are nonsensical. This calculation places great demands on the accuracy of the elemental analyses, demands which these data apparently cannot meet. As shown by the data in Table IV, the weight increase on reaction is reproducible. Additionally, our earlier data on maleic anhydride addition to Bruceton coal, obtained by a different individual, were reproduced. We conclude that the directly measured weight increases are accurate. The increase in weight suggests that a reaction has occurred, incorporating maleic anhydride into the coal structure. The occurrence of ester formation with the anhydride has been ruled out e ~ p e r i m e n t a l l y .The ~ ~ ~loss ~ of the double bond in the maleic anhydride is evident from the disappearance of the IR peak at 850 cm-', which has been assigned to C=C stretch.28 The relevant IR spectra are contained in the supplementary material for this paper. The most reasonable candidate for the reactions are the processes shown in reactions 1-4. For our present purposes, it matters little what the balance is between these reactions since all should disrupt stacking interactions. It is important that no reaction is anticipated that would cleave C-C or C-0 u bonds in coal. The FT-IR spectra of the reaction products showed two distinct absorption bands at about 1780 and 1850 cm-I that are assigned to the mechanical coupling of the anhydride carbonyl vibrations.28 Clearly, the product contains the anhydride functionality. The carbon-carbon double-bond absorption of maleic anhydride at about 850 cm-l is not present in the FT-IR spectra of the adducts. Whatever reactions occurred destroyed the C-C double bond. Because of noise in this region of the spectra, we cannot say with certainty that there remains no unreacted maleic anhydride in the products. There was no evidence of carbon-carbon or carbon-oxygen a-bond cleavage. If the stacking interactions play an important role in holding the coal molecules together, the extractability of coal after the Diels-Alder reaction may be greatly changed. The presence of London forces between PNAs that are (27) Lamen, J. W.; Lee,D.; Shawver, S. E. Fuel Process. Technol. 1986, 12, 51-62. (28) All IR band assignments are from: Bellamy, L. J. The Infra-red Spectra of Complex Molecules, 2nd Ed.; Wiley: New York, 1958.
Energy & Fuels, Vol. 1 , No. 3, 1987 303 Table V. Pyridine Extraction of Coals and Their Maleic Anhydride Adducts coal coal adduct %C % % % % coal (dmmf) residue extract residue extract Bruceton 71 30 83.1 72 30 PSOC 1309 72 32 84.3 73 33 PSOC 721 88.3 72 31 70 33 PSOC 1133 90.7 99 2.6 82 20 PSOC 648 92.1 99 3.6 83 21 101:n0.00004~ 88.9 64 40 101:n0.00005~ 88.9 64 40 101:no.OOOIOa 88.9 64 39 101:no.00012' 88.9 65 40 a
Argonne premium coal sample.
Table VI. T R F Extraction of Coals and Their Maleic Anhydride Adducts coal coal adduct %C % % % % coal (dmmf) residue extract residue extract Bruceton 83.1 83 18 83 17 84.3 91 10 90 11 PSOC 1309 PSOC 721 88.3 98 2.1 96 5.0 PSOC 1133 90.7 98 3.0 95 6.1 PSOC 648 92.1 99 1.8 97 4.2
part of the macromolecular network and soluble molecules will reduce the extractability of the coal, since the interaction will make it more difficult to separate the complexed molecule from the coal. The limiting case is a system not covalently cross-linked, which is insoluble because of many and large interactions between PNA groups. Since these interactions can easily rival strong hydrogen bonds in strength," this possibility is reasonable. Tables V and VI present the pyridine and THF extractabilities of five coal samples. If the coal contains at most 88% C, the extractabilities of the coal and its maleic anhydride adduct are essentially the same. If the coal contains at least 90% C, the adduct is more soluble than the coal from which it was prepared. In pyridine, extractabilities of coals greater than 88% C increased from about 2% for the parent coals to about 20% for the adducts, while the extractabilities remained essentially constant for coals with less than 88% C. The Argonne premium coal standard samples in Table V showed no change in extractability after reaction. The amounts extracted are not as large in THF as in pyridine. THF is not as good a solvent for coals as is pyridine. It is significant that all coals respond the same in both solvents; in no case are conflicting extractability changes observed. Does maleic anhydride react to the same extent with the extractable material as with the insoluble portion of the coal? A tentative conclusion that it does can be reached by considering the elemental analyses in Tables 1-111 and the fact that the extractabilities of the lower rank coals are unchanged by adduct formation. There are enough internal inconsistencies in the elemental analyses to render this conclusion tentative. For Bruceton, PSOC 1309, and PSOC 721, the H/C ratios and oxygen contents of the maleic anhydride adducts and the extractable portion of the adduct are similar enough to support that conclusion. For the two high-rank coals, the oxygen contents are similar but the extra& are enriched in hydrogen. Since maleic anhydride has an H/C ratio of 0.5, it will lower hydrogen content. Reaction with maleic anhydride may render extractable a high hydrogen content portion of the coal that was trapped in the network. In pointing this out we take no position in the current controversy over the presence and structure of a "mobile phase" in coals.29
304 Energy & Fuels, Vol. 1, No. 3, 1987
Quinga and Larsen
Table VII. Pyridine Extraction of Coals and ‘Products“ from a Blank’ Reaction coal blank product coal Bruceton
PSOC 1133
%C
90
%
%
%
(dmmf)
residue
extract
residue
extract
83 91
71 99
28 2.6
73 98
27 1.5
’Reaction conditions and workup duplicated with the omission of maleic anhydride
A control reaction was carried out by using the same conditions as the Diels-Alder reaction, but without maleic anhydride. The extractabilities of the parent coals and the “products”were the same, as shown in Table VII. The reaction conditions do not affect coal extractability, and reaction with maleic anhydride is necessary for the observed changes. In another control experiment, pyridine and maleic anhydride were refluxed for 5 days at 110-115 “C.The IR spectrum of the black residue showed a new peak at about 1725 cm-’, which was not present in either the parent coal, its maleic anhydride adduct, or the solid residue from the pyridine extraction of the adduct but was present in the pyridine extracts of the adducts. This indicates that a reaction may have occurred between pyridine and the soluble portion of the adduct. This is a possibility since it is knownNB1that maleic anhydride reacts with tertiary amines to give the product as shown in reaction 5. It is 0
0
also known that this reaction will lead to polymerization reactions.32 Occurrence of this reaction would also explain the increase in nitrogen content in the pyridine extracts as shown in Table 111, column 3, although such increases normally occur due to the difficulty of removing all the pyridine from coal samples.33 The fact that this reaction does not occur in the insoluble portion of the adduct has important consequences. Most importantly, extractabilities based on the weight loss of the adduct on extraction will be accurate. Also, it suggests that the observed IR peak may be the result of reaction between residual, unreacted maleic anhydride and pyridine rather than a reaction of the coal-maleic anhydride adduct. The small
weight increases on extraction due to bound solvent are consistent with this. The data presented here are completely consistent with an important structural role in high-rank coals for London dispersion interactions between PNA systems. However, the data do not reveal how extensive are the stacking interactions in high-rank coals. It is possible that very strong stacking interactions might prevent the Diels-Alder reaction from occurring. To a first approximation, the energy cost of separating the interacting PNA systems must be added to the activation energy for the Diels-Alder reaction. The reaction will thus be slower with more strongly interacting aromatic systems. Reaction may not occur. Thus, the extractability increases reported here give the minimum effect. It is inescapable that some associative forces exist in coals that are overcome by reaction of the coal with maleic anhydride. The existence of London forces is the best explanation. Perhaps more significant is the demonstration of the absence of an effect on extractability of stacking interactions in coals containing less than 88% C. The extractability increase observed with the high-rank coals demonstrates that adduct formation decreases noncovalent interactions. These are expected to be greater in high-rank coals that contain more and larger PNA systems. The fact that no change in extractability is observed for coals containing less than 88% C is strong evidence against an important structural role for “stacking interactions” between PNA’s in these coals. We do not mean to suggest that such interactions do not exist or play no role, but we have provided evidence that they are smaller than the interactions between good solvents and coals. We have not addressed the possible role that London interactions may play in the structural transition that occurs in coals at about 8688% C. This transition affects most coal physical properties and its chemical reactivity.% We believe that London forces are important to the structural changes occurring in coals of this rank and plan to address this issue in a subsequent paper. It has not eecaped our notice that the large amount of maleic anhydride incorporated has implications for the amount and distribution of polynuclear aromatic structures in these coals.
Acknowledgment. The authors thank Dr. Andrew Baskar for obtaining the IR spectra. We are grateful to Public Service Electric and Gas Research Co. for financial support of this work. Registry No. Maleic anhydride, 108-31-6.
(29) Given, P.H.; Marzec, A.; Barton, W. A.; Lynch, L. J.; Gerstein, B. C.; Fuel 1986,65, 155-163. (30) Mayahi, M. F.;El-Bermani, M. F. Can. J. Chem. 1973, 51, 3539-3540.(31) Braun, D.:Seved, A. A.: Pomakis, J. Makromol. Chem. 1969.1%. 249-252. (32) SChoDov. I. Makromol. Chem. 1970.137. 293-295. (33) Colli;ls, C. J.; Hagaman, E. W.; Jones, R: M.; h e n , V. F. Fuel 1981, 60, 359.
Supplementary Material Available: 21 FT-IR spectra for the coals,their maleic anhydride adducts, and the pyridine extracts of those adducts (8 pages). Ordering information is given on any current masthead page. (34) Larsen,J. W.In Coal Structure; Cooper, B. R., Petrakis, L., Ma.; American Institute of Physics: New York, 1981; pp 1-27.
