New Approaches in Coal Chemistry - American Chemical Society

5 The Interrelationship of Graphite Intercalation Compounds, Ions of Aromatic Hydrocarbons, and Coal Conversion. II LAWRENCE B. EBERT, JOSEPH C. SCANLON, DANIEL R. MILLS, and LOUIS M A T T Y Downloaded by EAST CAROLINA UNIV on January 3, 2018 | http://pubs.acs.org Publication Date: October 26, 1981 | doi: 10.1021/bk-1981-0169.ch005

Corporate Research—Science Laboratories, P.O. Box 45, Linden, NJ 07036

The benzenoid character of both graphite and polycyclic aromatic hydrocarbons leads to certain common features in their respective chemistries (1). In the same sense that aromatic hydrocarbons react with reductants and oxidants to form (radical) anions and cations, graphite will react to form donor or acceptor intercalation compounds. Although more complex than either aromatic hydrocarbons or graphite, coals, especially those of higher rank, also possess benzenoid character, and thus might be expected to undergo some of the same chemistry. We shall discuss the utility, and the limitations, of proposed analogies among graphite, polycyclic aromatic hydrocarbons, and selected coals. To make our talk appropriate to a symposium on modern approaches to characterization, we have chosen several specific examples of common reactions which illustrate the similarities and divergences of these systems: 1.

2.

Many metal and non-metal h a l i d e s i n t e r a c t s t r o n g l y w i t h g r a p h i t e , aromatic hydrocarbons, and c o a l s . We have used wide l i n e n u c l e a r magnetic resonance to compare the graphite i n t e r c a l a t i o n compound "C16BF4" w i t h the product of the i n t e r a c t i o n of Illinois #6 c o a l with B F 3 . Coupli n g our work with the known l i t e r a t u r e of complexes of aromatic hydrocarbons with B F 3 , we f i n d that B F 3 r e a c t s d i f f e r e n t l y with g r a p h i t e , aromatic hydrocarbons, and various coals. The reagent a l k a l i metal/naphthalene i n t e t r a h y d r o f u r a n r e a c t s w i t h g r a p h i t e , p o l y n u c l e a r aromatics, and v a r i o u s c o a l s to form chemically reduced p r o d u c t s . In the present paper, we emphasize the use of e l e c t r o n paramagn e t i c resonance d a t a , i n the form of g v a l u e s , l i n e w i d t h s , r a d i c a l d e n s i t i e s , and s a t u r a t i o n c h a r a c t e r i s t i c s , to analyze the reduced c o a l products and to i n f e r c e r t a i n d i f f e r e n c e s between the reduced c o a l s and the anions of graphite and simple aromatic hydrocarbons. A d d i t i o n a l l y , because the i n t e r a c t i o n of c o a l s with a l k a l i metal/naphthalene r e q u i r e s much time for completion, we have i n v e s t i g a t e d i n t e r n a l decomposition pathways for the

0097-6156/81/0169-0073$05.00/0 © 1981 American Chemical Society

Blaustein et al.; New Approaches in Coal Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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reagent system a l k a l i metal/naphthalene i n THF, as a f u n c t i o n o f a l k a l i metal, by the use o f combined gas chromatography/mass spectroscopy (GC/MS) and h i g h r e s o l u t i o n n u c l e a r magnetic resonance. 3. Potassium carbonate i s a well-known c a t a l y s t f o r the steam g a s i f i c a t i o n o f carbonaceous m a t e r i a l s . We d i s c u s s the use o f i n s i t u high temperature X-ray d i f f r a c t i o n to demonstrate that i n t e r c a l a t i o n compound-like s t r u c t u r e s are not i n v o l v e d as s t a b l e i n t e r m e d i a t e s . Although we s h a l l present each t o p i c s e p a r a t e l y i n the t e x t , we emphasize that the r e s u l t s of each area p o i n t to s e v e r a l gene r a l conclusions: • The s t r o n g e s t s i m i l a r i t y between i o n i c aromatic compounds and i n t e r c a l a t i o n compounds of g r a p h i t e i s charge t r a n s fer. • The s t r o n g e s t divergence between i o n i c aromatic hydrocarbons and i n t e r c a l a t i o n compounds o f g r a p h i t e a r i s e s from v a r i a t i o n s i n the r a t i o o f p e r i p h e r a l carbons t o i n t e r n a l carbons. • The chemistry of aromatic c l u s t e r s i n v a r i o u s c o a l s i s modified by s u b s t i t u e n t s on these c l u s t e r s . We thus i n f e r a great s i m i l a r i t y i n the chemistry of the p i e l e c t r o n s o f g r a p h i t e and o f s m a l l aromatic hydrocarbons. Apparent divergences a r i s e f o r cases i n which the aromatic molecules form sigma complexes, whose c r e a t i o n i s not e a s i l y p e r c e p t i b l e f o r g r a p h i t e , simply because of the low r a t i o of p e r i p h e r a l carbon t o i n t e r n a l carbon. While many c o a l s do c o n t a i n aromatic c l u s t e r s , the chemistry of t h e i r p i e l e c t r o n s i s a l t e r e d by the presence of s u b s t i t u e n t s which a l t e r the e l e c t r o n i c and s t e r i c p r o p e r t i e s of the aromatic core. A d d i t i o n a l l y , added chemical reagents may r e a c t d i r e c t l y not only with these s u b s t i t u e n t s but a l s o with mine r a l phases present i n the c o a l t o y i e l d a product i n which the p i aromatic chemistry i s masked. The I n t e r a c t i o n Of Benzenoid Carbon With Metal And Non-Metal Halides There are many halogen c o n t a i n i n g molecules which r e a c t not only w i t h g r a p h i t e (2) but a l s o with p o l y c y c l i c aromatic hydrocarbons (3)· Recently, B e a l l has proposed that such molecules r e a c t with c o a l t o form i n t e r c a l a t i o n compounds ( 4 ) . Any analogies here must be regarded with c a u t i o n , f o r the i n t e r a c t i o n of halogen c o n t a i n i n g molecules with benzenoid s p e c i e s runs from non-existent a l l the way to o x i d a t i v e halogenation. As an example, while z i n c d i c h l o r i d e r e a c t s f a c i l e l y w i t h c o a l ( 5 ) , i t does not r e a c t a t a l l with g r a p h i t e ( 6 ) . To examine the nature of these d i f f e r e n c e s , we consider the r e a c t i o n of boron t r i f l u o r i d e with p o l y c y c l i c aromatic hydrocarbons, g r a p h i t e , and I l l i n o i s #6 c o a l . Aalbersberg and co-workers (7) examined the i n t e r a c t i o n of BF3 with p o l y c y c l i c aromatic hydrocarbons as anthracene, perylene, and t e t r a c e n e . The i n t e r a c t i o n was weak, and could be reversed


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simply by pumping on the system or adding excess water. The form of t h i s covalent (and presumably diamagnetic) complex was cons i d e r e d analogous to protonated aromatics, i n which the added species i s bound to the edge of the aromatic molecule:

In the presence of both BF3 and a protic acid HX, aromatic hydrocarbons give structures analogous to the following (8):

H

H

In contrast, BF3, which i s not a good oxidant, does not react with graphite to form an intercalation compound (1). Addition of the oxidant C1F (which by i t s e l f does not react with graphite) leads to an intercalation compound containing BF5, rather than BF3 ÇL), with chlorine gas identified as the other reaction product ( 9 ) . That graphite has been oxidized i s demonstrated by the presence of a narrow (0.12 mT = 1.2 G) electron spin resonance signal in the v i c i n i t y of g = 2.0027, present at a l l temperatures between -168°C and 23°C (see Figure 1). Such a signal i s directly analogous to those found i n aromatic radical cations (10). While this signal i s asymmetric and possesses an area independent of temperature, i t i s not Dysonian, as i s discussed below. The wide line fluorine nuclear magnetic resonance of the intercalation compound Ci6BF4 may be used not only to demonstrate the chemical identity of the inserted species but also to establish the translational freedom of this species. The chemical shift of the fluorine resonance i s at (70+10) ppm vs. CF3COOH, consistent (11) with BF4 (71 ppm) but not with BF3 (54 ppm). (The neutral/ anion complex, B2F7, i s also possible (12)). The derivative extremum linewidth i s narrow (0.02 mT = 800 Hz) at a l l temperatures between -168°C and 23°C. A simple calculation suggests that translation, and not rotation, i s the cause of this narrow l i n e . Assuming a f i r s t stage compound (as indicated by X-ray diffraction) ,!

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1 ! 1 1 1 Figure 1. The derivative mode of the ESR absorption (9.11 GHz) of C BF as a function of temperature. Total scan range is 4 mT (= 40 G) and the figures have been offset horizontally for viewing ease. Although the behavior seen here is indica tive of a conduction carrier resonance, the reader should consult the text for a full discussion. 16


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and a uniform hexagonal l a t t i c e o f B F 4 anions, there w i l l be a d i s t a n c e o f 568 pm between t r i - c o o r d i n a t e B F 4 s p e c i e s l e a d i n g t o an i n t e r m o l e c u l a r second moment o f 0.113 G , or a Gaussian model l i n e w i d t h of 0.67 G, three times l a r g e r than that observed. The narrow f l u o r i n e resonance of "CiôBF^ i s q u i t e i n cont r a s t t o the f l u o r i n e a b s o r p t i o n found f o r the product of I l l i n o i s #6 c o a l w i t h B F 3 . At room temperature, we observe a 0.25 mT (=2.5 G) wide, dipolar-broadened, spectrum not i n d i c a t i v e of t r a n s l a t i o n freedom. In c o n t r a s t to the weakly bound complexes o f B F 3 w i t h aromatic hydrocarbons, we a n t i c i p a t e B F 3 t o r e a c t s t r o n g l y with oxygen f u n c t i o n a l i t y i n the c o a l , through h y d r a t i o n w i t h water, h y d r o l y s i s w i t h a c i d s (13), and ether complex formation (14), to give f l u o r i n e a b s o r p t i o n l i n e s which a r e i n the r i g i d l a t t i c e condition. The p o i n t of the preceding examples i s t o demonstrate that a s i n g l e reagent, B F 3 , can r e a c t i n completely d i f f e r e n t ways w i t h p o l y c y c l i c aromatic hydrocarbons, g r a p h i t e and c e r t a i n c o a l s . The mere presence of a r e a c t i o n does not demonstrate a commonality. 2


1

The A l k a l i Metal/Naphthalene/Tetrahydrofuran System Although the c a p a b i l i t y of the a l k a l i metal/naphthalene/ t e t r a h y d r o f u r a n system t o reduce g r a p h i t e and p o l y c y c l i c aromatic hydrocarbons has long been known (15, 16), i t i s the r e s e a r c h o f Sternberg and co-workers on r e d u c i n g , and then a l k y l a t i n g , c o a l which has brought a t t e n t i o n t o t h i s system (17, 18). The products of t h i s r e d u c t i v e a l k y l a t i o n treatment have remarkable s o l u b i l i t i e s i n o r g a n i c s o l v e n t s and thus have stimulated much i n t e r e s t (19, 20). While the model f o r t h i s chemistry could be taken as the r e d u c t i o n o f simple aromatic hydrocarbons, the long r e a c t i o n times r e q u i r e d (^100 hours) and the presence o f h i g h oxygen l e v e l s i n the c o a l s (^10%) suggest that other c h e m i s t r i e s could occur. E l e c t r o n s p i n resonance i n v e s t i g a t i o n of reduced c o a l products demonstrates the r e l a t i v e absence of aromatic r a d i c a l anion s t r u c tures i n the reduced, but not a l k y l a t e d , products. I f there were a one-to-one correspondence between a l k a l i metal consumed and r a d i c a l anions generated i n the reduced c o a l ( i . e . , as i n a l k a l i metal n a p h t h a l e n i d e ) , we would expect an i n t e n s e ( ^ l O ^ l s p i n s / gram ^0.03 spin/C atom), exchange-narrowed resonance near g = 2.0028. In f a c t , treatment o f e i t h e r I l l i n o i s #6 bituminous o r Wyodak subbituminous c o a l s w i t h potassium naphthalenide produces l i t t l e change i n the e l e c t r o n s p i n resonance spectrum with r e s p e c t to g v a l u e , l i n e w i d t h , or r a d i c a l d e n s i t y (1, 21). An a d d i t i o n a l c o n f i r m a t i o n of the absence of r a d i c a l anion s t r u c t u r e s i n the reduced c o a l may be i n f e r r e d from the s a t u r a t i o n behavior of the ESR a b s o r p t i o n , as given i n Figure 2. While c o a l s as I l l i n o i s #6 or Wyodak, p o s s e s s i n g lO^- to 1019 spins/gram, have T^'s of the order o f 10" ^ t o 10~° sec (22), o r g a n i c s o l i d s p o s s e s s i n g h i g h concentrations of r a d i c a l s , as s o l i d d i p h e n y l p i c r y l h y d r a z y l , have T j / s o f the order of 1 0 " to 10~9 sec (10, 23). As i s 8

8



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To.oo

Figure 2. A plot of the apparent area of the ESR absorption against microwave power for Illinois #6 coal and two chemically treated Illinois #6 coal products. In this display, a nonsaturating material would appear as a horizontal line. The reader should note that the initial Illinois #6 and naphthalenide-treated Illinois #6 coals have virtually the same saturation profile. Thermal treatment of the coal with potassium at 300°C actually makes T longer. Dry Illinois #6 (A); Sternberg Illinois #6 (•); K/Illinois #6 (300°CI4h) (#). t



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evident from the f i g u r e , the Ίχ of the reduced c o a l i s , w i t h i n the l i m i t s of e r r o r , equal to the Τ χ of the s t a r t i n g c o a l , and thus we see no evidence f o r the dominance of e l e c t r o n - e l e c t r o n i n t e r a c t i o n s , as would be expected f o r a s o l i d c o n t a i n i n g a h i g h c o n c e n t r a t i o n of f r e e r a d i c a l s . In t h i s absence of evidence f o r increased r a d i c a l d e n s i t y , one could p o s t u l a t e the presence of s p i n - p a i r e d , diamagnetic, dianions i n the reduced c o a l . However, u s i n g the chemistry of p o l y c y c l i c aromatic hydrocarbons as a model, we f i n d that such dianions are n e i t h e r expected to be s t a t i s t i c a l l y abundant (24, 25) nor, as good bases, to be i n e r t to the r e d u c t i v e system on a time s c a l e of 100 hours (26). Of t h i s l a t t e r p o i n t , we have u t i l i z e d combined GC/MS to analyze s o l u t i o n s of a l k a l i metal naphthalenide i n THF (90 mM metal, 40 mM naphthalene, 25 ml THF) quenched w i t h D 2 O , so that we may determine the s t a b i l i t y of the reactant system i t s e l f on a time s c a l e of 100 hours. The predominant product, other than naphthalene i t s e l f , f o r both sodium and potassium naphthalenide quenches was 1 - e t h y l 1 - p r o t i o , 4-deutero 4 - p r o t i o naphthalene (3) (and/or the 1,1 2,2 isomer (4)) r a t h e r than the expected 1-deuteFo 1-protio, 4-deutero 4-protio naphthalene (5). =r

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The product s l a t e f o r the l i t h i u m quench was even more complex, with approximately equal amounts of four products: 1 - e t h y l naph thalene, l-(4-hydroxybutyl) naphthalene, 1-ethyl 1 - p r o t i o , 4deutero 4 - p r o t i o naphthalene, and l-(4-hydroxybutyl) 1 - p r o t i o , 4-deutero 4 - p r o t i o naphthalene. Hydrogen gas, i n the i s o t o p i c form HD, was evolved on quenching the l i t h i u m and sodium systems, but not the potassium system. These r e s u l t s i n d i c a t e that the naphthalene r a d i c a l anion i s not s t a b l e to the s o l v e n t t e t r a h y d r o f u r a n at room temperature on a time s c a l e of 100 hours. Decomposition pathways are a l k a l i metal dependent. Sodium and potassium naphthalene a t t a c k THF through a proton a b s t r a c t i o n , c y c l o r e v e r s i o n mechanism, as p r e v i o u s l y described by Bates f o r the b u t y l l i t h i u m / T H F system (27). L i t h i u m naphthalenide a t t a c k s the THF not only by the Bates mechanism but a l s o by a n u c l e o p h i l i c r i n g opening, as i s i m p l i c i t i n e a r l i e r high temperature work on l i t h i u m naphthalenide i n THF (28) and i n work on the a t t a c k of THF by tritylmagnesium bromide (29). The two s m a l l e r a l k a l i metals, l i t h i u m and sodium, leave behind a



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hydride product, while the potassium does not. High r e s o l u t i o n ? L i NMR of an unquenched, aged s o l u t i o n of l i t h i u m naphthalenide, given i n Figure 3, u n e q u i v o c a l l y shows the presence of two d i f f e r e n t l i t h i u m environments, one of which i s c o n s i s t e n t w i t h para magnetic l i t h i u m naphthalenide ( l e f t ) and one c o n s i s t e n t with a diamagnetic l i t h i u m s a l t ( r i g h t ) . Thus, one reason f o r the apparent divergence between c o a l and graphite/aromatic hydrocarbons with r e s p e c t to r e d u c t i v e chemis t r i e s may a r i s e from the i n s t a b i l i t y of the reducing system on the timescale r e q u i r e d f o r c o a l r e a c t i o n . The n e c e s s i t y of these long r e a c t i o n times r e s u l t s i n p a r t from the presence of many s u b s t i t uents found on aromatic c l u s t e r s i n c o a l s . For the higher rank c o a l s (30), these are expected to be predominantly -R, -OH, and -OR groups (rather than - C 0 0 H or -CHO) which through i n d u c t i v e and resonance e f f e c t s w i l l d e s t a b i l i z e anions and thus r e t a r d r e d u c t i o n (31). A d d i t i o n a l l y , the presence of bulky s u b s t i t u e n t s on aromatic r i n g s , as would be found f o r c o a l rather than simple aromatic hydrocarbons, a l s o r e t a r d s r e d u c t i o n , because of s t e r i c i n t e r f e r e n c e with s o l v a t i o n of the r a d i c a l anion or d i a n i o n (31). Of course, not only the s u b s t i t u e n t s but a l s o m i n e r a l matter can react d i r e c t l y with potassium naphthalenide. Steam G a s i f i c a t i o n Of Carbon Catalyzed By K2CXh The r e a c t i o n of v a r i o u s carbonaceous m a t e r i a l s with steam to y i e l d CO, C O 2 , and H 2 has been i n t e n s i v e l y s t u d i e d . Of s p e c i a l i n t e r e s t has been the c a t a l y s i s of t h i s r e a c t i o n by v a r i o u s a l k a l i metal c o n t a i n i n g compounds, most n o t a b l y potassium carbonate (3237). Various mechanisms have been proposed, some i n c l u d i n g a l k a l i metal atoms (37) or even g r a p h i t e i n t e r c a l a t i o n compounds (38) as intermediates. To evaluate the p o s s i b i l i t y of such i n t e r c a l a t i o n compound i n t e r m e d i a t e s , we have conducted i n s i t u X-ray d i f f r a c t i o n i n v e s t i g a t i o n which would r e v e a l i n t e r c a l a t i o n compound formation both as a change i n the g r a p h i t e B r a v a i s l a t t i c e and as a change i n thermal e x p a n s i t i v i t y . Temperature v a r i a n t X-ray d i f f r a c t i o n experiments, employing a Guinier-Simon camera, were c a r r i e d out on mixtures of g r a p h i t e and potassium carbonate ( 5 - 2 0 wgt%) contained i n open c a p i l l a r i e s exposed to a water s a t u r a t e d (23°C) n i t r o g e n flow. With temperature i n c r e a s i n g from 23°C to 700°C (100°C/hour), only g r a p h i t e and K 2 C O 3 l a t t i c e s were observed, while a t 700°C the graphite Bragg peaks disappeared, unaccompanied by i n t e r c a l a t i o n compound formation. The thermal e x p a n s i v i t y of the g r a p h i t e l a t t i c e was 3 χ 10~5 Ac/(c°C), as f o r normal g r a p h i t e , and i n con t r a s t to the value of 4 χ 10"5 Ac/(c°C) that we have found f o r C 3 K i n the range -158°C to 23°C. The f a i l u r e t o f i n d evidence f o r i n t e r c a l a t i o n compound intermediates i n steam g a s i f i c a t i o n i n d i c a t e s the importance of sigma, r a t h e r than p i , e l e c t r o n s i n the r e a c t i o n , and i s c o n s i s t e n t with the view of the importance of the a t t a c k by gaseous molecules on the edges of g r a p h i t e planes (39).



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3a.

The Li-7 NMR (34.8 MHz) of a two-week-old solution of Li-naphthalenide in THF. With respect to an external standard of aqueous LiClO^ the larger peak is 11.95 ppm downfield, the smaller 1.6 ppm upfield, with the displayed spectrum width in the figure equal to 4000 Hz. The downfield peak arises from Li-naphthalenide, with the shift arising from the Fermi contact term (at room temperature for lithium, a shift downfield of 10 ppm corresponds to a hyper fine constant of + 0.005 mT = 4- 0.05 G). At short reaction times, the downfield peak is even broader than shown here, possessing a full width at half maximum of 880 Hz.

Figure 3b. The Li-7 NMR (34.8 MHz) of n-butyllithium in n-hexane. With the spectrum width equal to 4000 Hz, the single sharp peak comes at 1.6 ppm downfield from LiClO (aq). In the context of this chapter, a positive value of chemical shift refers to an upfield shift. h


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Summary Table 1 summarizes the r e s u l t s of the three s p e c i f i c r e a c t i o n s discussed i n t h i s paper. With some i n t u i t i o n , we can g e n e r a l i z e these f i n d i n g s . The i n t e r c a l a t i o n of g r a p h i t e r e f l e c t s changes i n the p i e l e c t r o n system of g r a p i t e , e i t h e r through r e d u c t i o n ( a d d i t i o n of e l e c t r o n s , as by naphthalenide) or through o x i d a t i o n (removal of e l e c t r o n s , as by BF3/CIF). When the p i e l e c t r o n system i s unchan ged (K2CO3/H2O or BF3 a l o n e ) , i n t e r c a l a t i o n does not o c c u r although chemistry at the edges of g r a p h i t e planes may occur. The formation of aromatic r a d i c a l anions or c a t i o n s from p o l y c y c l i c aromatic hydrocarbons i s d i r e c t l y analogous to i n t e r c a l a t i o n compound formation. A d d i t i o n a l l y , however, Lewis a c i d s (as BF3) can form weak charge t r a n s f e r compounds by a t t a c k i n g the edges of the molecules; such chemistry i s e a s i l y detected because of the high r a t i o of C e r i p h e r a l / C i n t e r n a l these p o l y c y c l i c aromatic molecules r e l a t i v e to g r a p h i t e . Bituminous c o a l s , i n p o s s e s s i n g a l a r g e number of s u b s t i t u ents (as -R, -OH, -OR), both can undergo chemistry at these s i t e s (as with BF3) and can have t h e i r bulk benzenoid chemistry modi f i e d by i n d u c t i v e e f f e c t s of these s u b s t i t u e n t s .


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o f

p

Experimental D e t a i l s and Comments Discussions of both the equipment (40) and chemical procedures C l , 21) have appeared elsewhere. B r i e f l y , w i d e l i n e n u c l e a r magnetic resonance was examined w i t h a V a r i a n WL 112 spectrometer, with r a d i o f r e q u e n c i e s s u p p l i e d by a General Radio 1061 frequency s y n t h e s i z e r . E l e c t r o n paramagnetic resonance i n v e s t i g a t i o n u t i l i z e d a V a r i a n Ε l i n e Century S e r i e s console, an E-102 microwave b r i d g e (9.5 GHz), and an E-231 c a v i t y (TE102 r e c t a n g u l a r ) . A d i s c u s s i o n o f the a p p r o p r i a t e u n i t s f o r r e p o r t i n g EPR and NMR r e s u l t s has been given (41). A G u i n i e r Simon camera, manufactured by Enraf-Nonius D e l f t , was used f o r v a r i a b l e temperature x-ray d i f f r a c t i o n . The high r e s o l u t i o n l i t h i u m - 7 NMR was measured on a JEOL FX-90, and the GC/MS data was taken on a DuPont 21-491. U p f i e l d NMR s h i f t s are taken p o s i t i v e . The d e t a i l s of the EPR i n v e s t i g a t i o n of the g r a p h i t e compound "C16BF4" merit some d i s c u s s i o n . Because the m a t e r i a l i s an e l e c t r o n i c conductor, we suspended the p o l y c r y s t a l l i n e sample i n eicosane, melted the mixture under hot water, v i b r a t e d the sample to get random o r i e n t a t i o n , and f r o z e the mixture under c o l d water. Because Ci6BF4" i s an a n i s o t r o p i c conductor ( i t does not have m e t a l l i c c o n d u c t i v i t y orthogonal to the p l a n e s ) , the i n t e r p r e t a t i o n of the EPR r e s u l t s r e q u i r e s care. Thus, i n a t h i c k p l a t e of an i s o t r o p i c metal as l i t h i u m , one observes a Dysonian asymmetry parameter A/B which i s dependent on temperature, v a r y i n g between M



naphthalene*

Form of complex with BF~

framework by ^COg/l^O

Reduction of benzenoid

framework by

Reduction of benzenoid

no compound found (unless C 1 F present)

not observed

predominant

graphite

predominant

aromatic molecules

Summary Of Reaction Results

Table I


B F 3 hydrate, B F 3 etherate, and s i m i l a r

present, but not predominant

coals

84

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APPROACHES

IN C O A L

CHEMISTRY

2.7 and 19 as the r a t i o of the conduction e l e c t r o n d i f f u s i o n time to the e l e c t r o n Τ 2 v a r i e s from 1 0 t o 10~4 (42). A d d i t i o n a l l y , one can i n t e r r e l a t e the l i n e w i d t h and g value of the EPR absorp t i o n t o the e l e c t r o n i c c o n d u c t i v i t y s c a t t e r i n g time through the theory of E l l i o t t (43, 44). C u r i o u s l y , we see from F i g u r e 1 of t h i s paper that the A/B parameter, the l i n e w i d t h , and the g value of the EPR a b s o r p t i o n o f C i 6 B F 4 " are e s s e n t i a l l y unchanged over the temperature range -168° t o + 23°C. T h i s behavior stems d i r e c t l y from the a n i s o t r o p y of "C^BF^ , which gives t h i s and other graphite i n t e r c a l a t i o n compounds (45) much i n common with the EPR behavior o f other a n i s o t r o p i c conductors (46), magnetic i m p u r i t i e s i n metals (47), and the NMR behavior of m e t a l l i c n u c l e i i n b u l k metals (48), rendering a c a s u a l i n t e r p r e t a t i o n of t h i s "conduction c a r r i e r resonance d i f f i c u l t (49, 50). P a r e n t h e t i c a l l y , i n support o f our analogy between g r a p h i t e acceptor compounds and aromatic r a d i c a l c a t i o n s , we have found the carbon-13 w i d e l i n e NMR s i g n a l s ( d i s p e r s i v e mode at 10 MHz, 12 MHz, and 15 MHz) of the compounds C10ASF5, Ci3Cr03, C14UF6, and C14PF5 a l l to f a l l i n the range (-36+20) ppm v s . e x t e r n a l benzene, c o n s i s t e n t with the des h i e l d i n g e f f e c t s found f o r aromatic r a d i c a l c a t i o n s (51). The s t a b i l i t y of the a l k a l i metal/naphthalene/tetrahydrofuran system a l s o merits some d i s c u s s i o n . Both our r e s u l t s and those of Sternberg (17) suggest that naphthalene w i l l decompose as long as excess a l k a l i metal i s present. I f one deals with s t o i c h i o m e t r i c s o l u t i o n s of the r a d i c a l anion, there i s evidence suggesting long term s t a b i l i t y (52), and we cannot i n f a c t prove that some unknown impurity i s r e s p o n s i b l e f o r the decomposition observed. Our t e t r a h y d r o f u r a n was d i s t i l l e d from L1A1H4 and used immediately under helium i n a VAC atmospheres dry box. F i n a l l y , we note that our i n f e r e n c e s on the nature of the coal/BF3 product a r e c o n s i s t e n t with recent work on products of c o a l with ZnCl2 and AICI3 (53). Neither BF3, ZnCl2, nor AICI3 w i l l d i r e c t l y i n t e r c a l a t e g r a p h i t e C 2 , 6 ) , but a l l are considered to form sigma complexes with aromatic molecules (_7, 54). 2

M


11

1 1

Acknowled gemen t s We thank J . S. Bradley f o r the d i s t i l l e d t e t r a h y d r o f u r a n and K. D. Rose f o r the high r e s o l u t i o n l i t h i u m nuclear magnetic reson ance s p e c t r a . R. H. Schlosberg, B. G. S i l b e r n a g e l , and the three r e f e r e e s f o r t h i s paper made many u s e f u l comments.

Literature Cited 1. 2. 3.

Part I: Ebert, L. B.; Matty, L . ; Mills, D. R.; Scanlon, J. C. Mat. Res. Bull. 1980, 15, 251. Selig, H.; Ebert, L. B. Adv. Inorg. Chem. Radiochem. 1980, 23 281. Burkhardt, L. Α.; Hammond, P. R.; Knipe, R. H.; Lake, R. R. J. Chem. Soc. A 1971, 3789.


5.

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.

EBERT E T AL.

Graphite

Intercalation

Compounds

85

Beall, H. Fuel 1979, 58, 319. Wood, R. E.; Wiser, W. H. Ind. Eng. Chem./Proc. Res. Dev. 1976, 15, 144. Ebert, L. B. Ann. Rev. Mat. Sci. 1976, 6, 181. Aalbersberg, W. I.; Hoijtink, G. J.; Mackor, E. L . ; Weijland, W. P. J . Chem. Soc. 1959, 3055 Perkampus, H. H.; Baumgarten, E. Angew. Chem., Int. Ed. 1964, 3, 776. Leffler, Α.; Selig, H.; manuscript in preparation. Singer, L. S.; Kommandeur, J. J. Chem. Phys. 1961, 34, 133. Emsley, J. W.; Feeney, J.; Sutcliffe, L. H.; "High Resolution Nuclear Magnetic Resonance", Vol. II; Pergamon: Oxford, 1966. Brownstein, S.; Paasivirta, J. Can. J. Chem. 1965, 43, 1645. Diehl, P. Helv. Phys. Acta 1958, 31, 685. Gerrard, W.; Lappart, M. F. Chem. Rev. 1958, 58, 1081. Novikov, Yu. N.; Vol'pin, M. Russ. Chem. Rev. 1971, 40, 733. Hoijtink, G. J.; de Boer, E . , van der Meij, P. H.; Weijland, W. P. Rec. Trav. Chim. 1956, 75, 487. Sternberg, H. W.; Delle Donne, C. L . ; Pantages, P.; Moroni, E. C.; Markby, R. E. Fuel 1971, 50, 432. Sternberg, H. W.; Delle Donne, C. L. Fuel 1974, 53, 172. Alemany, L. B.; King, S. R.; Stock, L. M. Fuel 1978, 57, 738. Dogru, R.; Erbatur, G.; Gaines, A. F.; Yurum, Y.; Icli, S.; Wirthlin, T. Fuel 1978, 57, 399. Ebert, L. B.; Mills, D. R.; Matty, L . ; Pancirov, R. J.; Ashe, T. R. Advances in Chemistry Series, #192, "Coal Structure", American Chemical Society: Washington, D.C., 1981. Smidt, J.; van Krevelen, D. W. Fuel 1959, 38, 355. Austen, D. E. G.; Ingram, D. J. E.; Tapley, J. G. Trans. Far. Soc. 1958, 54, 400. Jensen, B. S.; Parker, V. D. J. Am. Chem. Soc. 1975, 97, 5211. Jensen, B. S.; Parker V. D. Acta Chem. Scand. Β 1976, 30, 749. Carnahan, J. C.; Closson, W. D. J. Org. Chem. 1972, 37, 4469. Bates, R. B.; Kroposki, L. M.; Potter, D. E. J. Org. Chem. 1972, 37, 560. Fujita, T. Suga, K.; Watanabe, S. Synthesis 1972, 11, 630. Jensen, F. R.; Bedard, R. L. J. Org. Chem. 1959, 24, 874. Blom, L.; Edelhausen, L . ; van Krevelen, D. W. Fuel 1957, 36, 135. House, H. O.; "Modern Synthetic Reactions", 2nd ed.; Benjamin: Menlo Park, Ca., 1972; p 198. Taylor, H. S.; Neville, H. A. J. Am. Chem. Soc. 1921, 43, 2055. Long, F. J.; Sykes, K. W. Proc. Roy Soc. (London) 1952, A215, 100. Walker, P. L . ; Shelef, M.; Anderson, R. A. in "The Chemistry and Physics of Carbon", Vol. 4; Dekker: New York; 1968, pp 287-383.


N E W APPROACHES IN C O A L

86

35. 36. 37. 38. 39.


40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54.

CHEMISTRY

Johnson, J . L. Catal. Rev.-Sci. Eng. 1976, 14, 131. Rudolph, P. F. H. Energiespectrum 1977, 1, 311. McKee, D. W.; Chaterjii, D. Carbon 1978, 16, 53. Wen, W.-Y., Catal. Rev.-Sci. Eng. 1980, 22, 1. Walker, P. L. in "Scientific Problems of Coal Utilization", ed. B. R. Cooper; U.S. Department of Energy: Washington, 1978; pp 237-247. Ebert, L. B.; Mills, D. R.; Scanlon, J . C. Mat. Res. Bull. 1979, 14, 1369. Crooks, J. E. J . Chem. Ed. 1979, 56, 301. Feher, G.; Kip, A. F. Phys. Rev. 1955, 98, 337. Elliott, R. J . Phys. Rev. 1954, 96, 266. Beuneu, F.; Monod, P. Phys. Rev. Β 1978, 18, 2422. Ebert, L. B.; Selig, H. Mat. Sci. Eng. 1977, 31, 177. Kahn, A. H. J . Appl. Phys. 1975, 46, 4965. Winter, J . "Magnetic Resonance in Metals"; Clarendon: Oxford, 1971; Chapter 10. Bloembergen, N. J . Appl. Phys. 1952, 23, 1379. Ebert, L. B.; DeLuca, J . P.; Thompson, A. H.; Scanlon, J . C. Mat. Res. Bull. 1977, 12, 1135. Khanna, S. K.; Falardeau, E. R.; Heeger, A. J.; Fischer, J. E. Sol. St. Commun. 1978, 25, 1059. Forsyth, D. Α.; Olah, G. A. J . Amer. Chem. Soc. 1976, 98, 4086. Paul, D. E.; Lipkin, D.; Weissman, S. I. J . Amer. Chem. Soc. 1956, 78, 116. Taylor, N. D.; Bell, A. T. Fuel 1980, 59, 499. Morita, M.; Hirosawa, K.; Sato, T. Bull. Chem. Soc. Jpn. 1977, 50, 1256.

RECEIVED

April 27, 1981.


New Approaches in Coal Chemistry - American Chemical Society

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