Isomerization and Adduction of Hydroaromatic Systems at Conditions

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D O N A L D C . C R O N A U E R , D O U G L A S M. J E W E L L , R A J I V J. M O D I , and K . S. S E S H A D R I Gulf Research and Development Company, P.O. Drawer 2038, Pittsburgh, P A 15230 Y A T I S H T. S H A H University of Pittsburgh, Department of Chemical and Petroleum Engineering, Pittsburgh, P A 15213

Fundamental studies of coal liquefaction have shown that the structure of solvent molecules can determine the nature of liquid yields that result at any particular set of reaction conditions. One approach to understanding coal liquefaction chemistry is to use well-defined solvents or to study reactions of solvents with pure compounds which may represent bond-types that are likely present in coal [1,2]. It is postulated that one of the major routes in coal liquefaction is initiation by thermal activation to form free radicals which abstract hydrogen from any readily available source. The solvent may, therefore, function as a direct source of hydrogen (donor), indirect source of hydrogen (hydrogen-transfer agent), or may directly react with the coal (adduction). The actual role of solvent thus becomes a significant parameter. Our earlier studies [2,3] have measured the reactivity of both hydrocarbon and nonhydrocarbon acceptors with good donor solvents (Tetralin, hydrophenanthrenes), and poor donors (mesitylene). Although the primary role of solvents was observed to be the stabilization of acceptor radicals, appreciable levels of solvent isomerization, polymerization, and adduction also occurred. Herein, these aspects of solvent chemistry have been pursued with the use of 13C labeling techniques to understand the specific reactions. EXPERIMENTAL The experimental procedure to carry out the solvent-acceptor reactions have previously been described [2,3]. In summary, the desired amount of solvent was charged to a stirred autoclave and heated to a temperature about 5°C above reaction temperature. The acceptor with additional solvent was injected into the reactor which rapidly came to the desired temperature. The reactor contents were periodically sampled during the run. 0-8412-0587-6/80/47-139-37l$05.50/0 © 1980 American Chemical Society Whitehurst; Coal Liquefaction Fundamentals ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

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COAL LIQUEFACTION FUNDAMENTALS 1J

i J

Specifically labeled C-octahydrophenanthrene and Ct e t r a l i n were synthesized by Dr. E. J . Eisenbraun. Products from the r e a c t i o n s were analyzed using a combination of the following: (1) GLC using a 100 f t . SCOT c a p i l l a r y column, (2) preparative l i q u i d chromatography using basic alumina [4] , (3) preparative HPLC using a column packed with Lichrosorb ( s i l i c a ) and the solvent n-hexane, (4) C-NMR using a Varian CFT-20 instrument, and (5) GLC-mass spectra using a duPont 491 instrument. REACTIVITY OF HYDROAROMATICS Background Hydroaromatic compounds are among the most common s t r u c t u r e s i n n a t u r a l products making up the b a s i c framework of steroids, alkaloids, and mineral oils (petroleum). Hydroaromatic structures are subject to thermal dehydrogenation, unless s u b s t i t u t e d by gem-dialkyl groups, at bridgehead p o s i t i o n s as e x h i b i t e d by steranes and a l k a l o i d s . Dehydrogenation is usually achieved in the presence of catalysts which promote d e a l k y l a t i o n , which is a typical precursor to dehydrogenation. Hydroaromatic s t r u c t u r e s in heterocyclic compounds are frequently more r e a c t i v e than homocyclics, with respect to dehydrogenation, e.g., t e t r a h y d r o q u i n o l i n e > t e t r a l i n and indoline>indan. Due to the relative ease and reversibility of hydrogenation-dehydrogenation of hydroaromatics, they have been used e x t e n s i v e l y e i t h e r as a source or agent for p l a c i n g hydrogen i n hydrogen-deficient s p e c i e s , such as c o a l . It has f r e q u e n t l y been assumed that hydroaromatics i n the solvents used f o r t h i s purpose c o n t a i n six-membered r i n g s . Little e f f o r t has been d i r e c t e d to determining the isomeric forms. I t i s known that methyl indans are e s s e n t i a l l y s t a b l e to hydrogent r a n s f e r as compared to T e t r a l i n . Due to d i f f i c u l t i e s i n adequately measuring the concentrations of isomeric s t r u c t u r e s , the above assumption may not be t y p i c a l l y v a l i d . Due to i t s simple s t r u c t u r e and a v a i l a b i l i t y , T e t r a l i n i s typically used as a model donor solvent for coal liquefaction. For s i m i l a r reasons, much of the present work was done with T e t r a l i n , as w e l l as octahydrophenanthrene whose s t r u c t u r e i s b e l i e v e d more a l l i e d to true c o a l - d e r i v e d r e c y c l e solvents Γ5 . Curran et a l . [7] observed that T j e t r a l i n decomposed to "C^ benzenes and indan" and that the decomposition seemed to be promoted by coal e x t r a c t s . They a l s o speculated on s e v e r a l s t r u c t u r e s for the benzenes without f i r m s t r u c t u r a l evidence. Recent studies by Whitehurst et a l . [S] have i n d i c a t e d that T e t r a l i n rearranged to 1-methyl indan and that this rearrangement was s o l e l y temperature dependent. These rearrangements were considered reasonably

Whitehurst; Coal Liquefaction Fundamentals ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

21.

Hydroaromatic

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constant a t any t e m p e r a t u r e , proceeded through free radical p r o c e s s e s , and were m i n o r s i d e r e a c t i o n s . The p r e s e n t study i n d i c a t e s t h a t i s o m e r i z a t i o n o f six-membered h y d r o a r o m a t i c s i s n o t l i m i t e d t o t e t r a l i n , i s q u i t e c o m p l e x and may be a more s e r i o u s problem than p r e v i o u s l y c o n s i d e r e d . R e a c t i o n s o f T e t r a l i n and D i h y d r o n a p h t h a l e n e T e t r a l i n has been shown t o undergo t h e r m a l d e h y d r o g e n a t i o n t o n a p h t h a l e n e and r e a r r a n g e m e n t t o m e t h y l i n d a n i n e i t h e r t h e absence or presence of free r a d i c a l acceptors ti,2]. The presence o f free radical acceptors usually accelerates the rearrangement reaction. Even with alkylated Tetralins, r e a r r a n g e m e n t s t i l l o c c u r s w i t h the f o r m a t i o n o f d i - and t r i a l k y l indans. The b a s i c r e a c t i o n s o f T e t r a l i n and d e r i v a t i v e s have been e x t e n d e d t o t h e use o f 1 - C l a b e l s and 1 , 2 - d i h y d r o n a p h t h a l e n e , w i t h and w i t h o u t a s o u r c e o f f r e e r a d i c a l s . The s t u d i e s w i t h Tetralin were m o n i t o r e d e q u a l l y w e l l w i t h C - N M R and GLC techniques. The r a t e c o n s t a n t f o r t h e c o n v e r s i o n o f T e t r a l i n t o m e t h y l i n d a n i n t h e p r e s e n c e o f d i b e n z y l a t 4 5 0 ° C was 6 . 4 χ 10 min" which i s c o n s i s t e n t with that p r e v i o u s l y reported [2]. The most significant observation by NMR i s the r e d i s t r i b u t i o n o f the C l a b e l i n the methyl i n d a n i s o m e r . The l a b e l is found e q u a l l y i n b o t h m e t h y l and 3 - m e t h y l e n e g r o u p s as d e n o t e d b e l o w : 1 3

1 3

1 3

Δ ppm

Position

+

0 0 - C p OCT" 22 as I C

H

34.8 31.4

3

2-CH 3-CH

1 3

2

3

C o n c e n t r a t i o n o f 2 - m e t h y l i n d a n and 2 - C - l - m e t h y l i n d a n were very low. D i h y d r o n a p h t h a l e n e (DHN) i s f r e q u e n t l y assumed t o be an intermediate i n hydrogen t r a n s f e r reactions. While this appears reasonable, efforts to detect a n d / o r measure this i n t e r m e d i a t e have n e v e r b e e n v e r y s u c c e s s f u l . Assuming t h a t DHN i s p r e s e n t , we have b r i e f l y e x p l o r e d i t s r o l e i n h y d r o g e n t r a n s f e r and m e t h y l i n d a n f o r m a t i o n . S e v e r a l e x p l o r a t o r y e x p e r i m e n t s were made w i t h u n l a b e l e d 1,2-dihydronaphthalene, e i t h e r n e a t o r w i t h 10% d i b e n z y l , at 450 C. The r u n s were made u s i n g an a g i t a t e d 10 cc r e a c t o r w h i c h was immersed i n a p r e h e a t e d sand b a t h t o a c h i e v e r a p i d h e a t i n g and c o o l i n g . I t i s f i r s t n o t e d t h a t the p r o d u c t s from e x p e r i m e n t s at e i t h e r 15 o r 180 m i n u t e s c o n t a i n e d no u n r e a c t e d e


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DHN. A p p a r e n t l y DHN b o t h t h e r m a l l y d e h y r o g e n a t e s t o n a p h t h a l e n e and d i s p r o p o r t i o n a t e s t o te&alin and n a p h t h a l e n e . In a l l o f t h e r u n s , t h e r e was a s i z a b l e amount o f h y d r o g e n r e l e a s e d when t h e r e a c t o r s were o p e n e d . When DHN was h e a t e d a t 4 5 0 ° C for either 15 o r 180 m i n u t e s , t h e r a t i o o f n a p h t h a l e n e to e t r a l i n was 1 . 8 . Increased methyl indan formation occurred with time. With the i n t r o d u c t i o n o f d i b e n z y l , the a n t i c i p a t e d [2] increased isomerizat ion of T e t r a l i n to methyl indan occurred. These r e s u l t s suggest that the rearrangement o f hydroaromatics does not proceed through the dihydroi n t e r m e d i a t e s t a g e , but r a t h e r forms d i r e c t l y from t h e s i x raembered ring. The d i h y d r o - i n t e r m e d i a t e o n l y forms d u r i n g hydrogen t r a n s f e r . Reactions o f Hydrogenated

Phenanthrene

The hydrogénation of phenanthrene proceeds stepwise l e a d i n g predominantly to the sym-octahydro-stage r a t h e r than t h e a s y m m e t r i c a l form [5] . E i t h e r form c a n f u n c t i o n as an e x c e l l e n t donor s o l v e n t . Sym-octahydrophenanthrene (HgPh) w o u l d be e x p e c t e d to follow t h e same rearrangement-dehydrogenation reactions as T e t r a l i n , e x c e p t w i t h more i s o m e r and p r o d u c t possibilities. The r e a c t i o n s shown i n F i g u r e 1 i l l u s t r a t e t h e many s t r u c t u r e s expected from sym-HgPh i n the presence of free radical acceptors. U n l i k e T e t r a l i n , h y d r o p h e n a n t h r e n e s have m u l t i p l e structures w h i c h e a c h , i n t u r n , form v a r i o u s i s o m e r s . The amounts o f these isomers a r e dependent upon t h e t y p e o f h y d r o g e n - t r a n s f e r r e a c t i o n s and t h e e n v i r o n m e n t o f t h e s y s t e m . A comparison with T e t r a l i n i s q u i t e u s e f u l , since i t i n d i c a t e s t h e e f f e c t t h a t a d d i t i o n o f h y d r o a r o m a t i c r i n g s have on the b a s i c p r o b l e m . A l t h o u g h a l l t h e s t r u c t u r e s shown i n F i g u r e 1 are t h e o r e t i c a l l y p o s s i b l e , it i s not y e t p o s s i b l e t o s e p a r a t e e a c h from a t o t a l p r o d u c t m i x t u r e by c u r r e n t c a p i l l a r y GLC t e c h n i q u e s . Our t e c h n i q u e s were a b l e t o r e s o l v e c e r t a i n groups of compounds which permitted preliminary kinetic calculations. These i n c l u d e d m o n o - i s o H g P h , d i - i s o - H g P h , i s o H ^ P h , and p h e n a n t h r e n e . Emphasis i n this s t u d y was p l a c e d upon two r e a c t i o n s c a r r i e d o u t a t 4 5 0 C w i t h sample t i m e s between 0 and 180 m i n . The r e f e r e n c e r u n i s t h a t o f HgPh, n e a t , and t h e s e c o n d r u n i s the h y d r o g e n - t r a n s f e r r e a c t i o n o f HgPh w i t h d i b e n z y l , i n w h i c h t h e b e n z y l r a d i c a l i s formed a t c o n d i t i o n s t y p i c a l o f c o a l liquefaction. In the presence of dibenzyl, octahydrophenanthrene u n d e r g o e s b o t h d e h y d r o g e n a t i o n and i s o m e r i z a t i o n . In this study, we u s e t h e k i n e t i c model ( r e f e r to Figure 1 for structures): e



\

ι çst

9 ^

ι +2 MORE

ces?

i

Reactions of octahydrophenanthrene (9)

Industrial and Engineering Chemistry Fundamentals

D l - I S O M E R S OF OCTAHYDROPHENANTHRENE

+ 2 MORE

1

1

+ 2 MORE ISOMERS

Figure 1.

ι

ISOMERS OF T E T R A H Y D R O P H E N A N T H R E N E

MONO ISOMERS OF OCTAHYDROPHENANTHRENE

OCTAHYDROPHENANTHRENE

TETRAHYDROPHENANTHRENE

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COAL LIQUEFACTION FUNDAMENTALS

2

Octahydro phenanthrene I (A)

Tetrahydro phenanthrene ν (B)

Phenanthrene (C)

K-

7

We assume a l l r e a c t i o n s to be f i r s t order and i r r e v e r s i b l e w i t h i n the range of the experimental c o n d i t i o n s . The governing d i f f e r e n t i a l mass balance equations and t h e i r s o l u t i o n s have been reported [9] . The values o f the constants through at 450 C are shown i n Table I . A comparison o f the experimental data with the t h e o r e t i c a l p r e d i c t i o n s i s shown i n F i g u r e s 2 through 4; the above assumption o f a f i r s t order r e a c t i o n appears reasonable. e

Table I KINECTIC CONSTANTS FOR VARIOUS REACTION STEPS e

(Reactor Conditions o f 450 C, 1500 p s i g t o t a l pressure, and a feed c o n c e n t r a t i o n of 30 wt% HgPh, 10 wt% d i b e n z y l , 60 \ mesitylene) CONSTANT

(MIN ) 0.0059 0.003 0.0017 0.0029 0.0001 0.002 0.0035

As shown i n Table I, the a b s t r a c t i o n of hydrogen i s a much more s e l e c t i v e reaction compared to i s o m e r i z a t i o n or d i isomerization. Furthermore, i s o m e r i z a t i o n of tetrahydrophenanthrene i s a very slow process. As noted i n the model, r a t e constant K o i s used to denote the d i r e c t i s o m e r i z a t i o n of H«Ph


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Systems

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TIME (MINS) Industrial and Engineering Chemistry Fundamentals

Figure 2. Concentration of components in the hydrogen abstraction series of reac tions in the presence of an acceptor (9): ( ), model predicted curve; (Φ), octahydrophenanthrene; (O), tetrahydrophenanthrene; ([J), phenanthrene.


378


8K

TIME (MINS) Industrial and Engineering Chemistry Fundamentals

Figure 3.

Isomerization of solvent to monomethyl isomers (9): ( dicted curve.

), model pre-


CRONAUER ET AL.

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379

Systems

Industrial and Engineering Chemistry Fundamentals

Figure 4.

lsomerization of solvent to dimethyl isomer: ( ), model predicted curve (9): (Ah monomethyl (H Ph); (Ηλ monomethyl (H Ph). 8

k


380


to d i - i s o o c t a h y d r o p h e n a n t h r e n e . No d i r e c t e v i d e n c e e x i s t s t o prove that both hydroaromatic rings can simultaneously r e a r r a n g e to the d i - i s o m e t h y l i s o m e r . H o w e v e r , the k i n e t i c d a t a , namely t h e p l o t o f c o n c e n t r a t i o n v e r s u s t i m e , c a n b e s t be f i t w i t h the assumption t h a t t h i s f i r s t o r d e r r e a c t i o n o c c u r s . S t u d i e s d i s c u s s e d below w i t h v a r i o u s hydroaromatic systems i n d i c a t e that these rearrangements proceed through free r a d i c a l p r o c e s s e s as s u g g e s t e d e a r l i e r f o r T e t r a l i n s [.1-3] and do n o t r e q u i r e the i n i t i a l g e n e r a t i o n o f a conjugated o l e f i n g r o u p . T h i s a p p r o a c h c o u l d g e n e r a t e three-membered r i n g i n t e r m e d i a t e s s i m i l a r t o t h o s e i d e n t i f i e d by Goodman and Eastman [10] and more r e c e n t l y by S i n d l e r - K u l y k and L a a r h o v e n [ Π ] . I t i s a l s o noted t h a t the o v e r a l l r a t e o f i s o m e r i z a t i o n o f HgPh i s about t h r e e t i m e s t h a t o f t h e i s o m e r i z a t i o n o f T e t r a l i n [2]. For reference, t h e a c t i v a t i o n e n e r g y o f the T e t r a l i n i s o m e r i z a t i o n r e a c t i o n was i n t h e r a n g e o f 26 t o 32 K c a i / g - m o l e depending upon the presence of a free-radical precursor. Studies have also shown t h a t alkyl Tetralins and recycle s o l v e n t s c o n t a i n i n g a l k y l groups a l s o r e a r r a n g e i n d i c a t i n g that isomerization is not inhibited by substitution on the h y d r o a r o m a t i c r i n g [12] H o w e v e r , some s t e r i c l i m i t a t i o n s may e x i s t w i t h a dependence upon t h e t y p e and s i z e o f t h e a t t a c h e d groups. STRUCTURAL FEATURES OF HYDROPHENANTHRENES The p r e s e n c e o f h y d r o p h e n a n t h r e n e i s o m e r s was i n d i c a t e d by the o b s e r v a t i o n o f numerous GLC peaks w i t h i d e n t i c a l p a r e n t ions but different fragment ions in their mass spectra. Compounds w i t h m e t h y l s u b s t i t u e n t s a l w a y s have more i n t e n s e M 15 ions than those w i t h unsubstituted six-membered rings. C o n s i d e r i n g the c o m p l e x i t y o f t h e total reaction mixtures, liquid chromatography (HPLC) was used to concentrate more discrete solvent fractions for C-NMR s t u d y . The s p e c t r a o f the s a t u r a t e r e g i o n o f pure s y m - H g P h , and two m o n o a r o m a t i c concentrates have been observed and the a s s i g n m e n t o f s i g n a l s i n sym-HgPh have been r e p o r t e d [ 1 3 ] . The a p p e a r a n c e o f new s i g n a l s a t 19 t o 2 1 . 3 ppm were i n d i c a t i v e o f m e t h y l g r o u p s i n a v a r i e t y o f p o s i t i o n s on s a t u r a t e d rings. S i g n a l s between 30 and 35 ppm were i n d i c a t i v e o f f i v e - m e m b e r e d r i n g s b e i n g formed a t t h e expense o f the e i g h t h y d r o a r o m a t i c carbons i n the six-membered r i n g s . The a b s e n c e o f a s h a r p l i n e at a p p r o x i m a t e l y 14 ppm i n d i c a t e d that r i n g opening to a η - b u t y l s u b s t i t u e n t d i d not occur. P r e c i s e mass measurements f u r t h e r showed t h a t each c o n c e n t r a t e has t h e same m o l e c u l a r w e i g h t (186) w h i c h c o n f i r m e d t h a t r i n g o p e n i n g d i d not o c c u r as i m p l i e d by the work o f Curran et al. [7] i n which e x p e r i m e n t i o n was done with Tetralin. +


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When an acceptor was present (ex., d i b e n z y l ) , the solvent products were more complex. The r e a c t i o n s were, t h e r e f o r e , repeated using C labeled octahydrophenanthrene (10% C at p o s i t i o n 1). The presence of a l a b e l not only confirmed the q u a l i t a t i v e nature of r e a c t i o n s shown i n Figure 1, but provided u s e f u l clues as to the r e a l complexity of the s t r u c t u r e s and pathways for t h e i r formation. A sample of hydrophenanthrenes from a d i b e n z y l hydrogent r a n s f e r r e a c t i o n was separated by l i q u i d chromatography i n t o seven f r a c t i o n s . Each f r a c t i o n (>20 mg) was then analyzed by C-NMR, mass spectrometry (70 eV), and ultraviolet spectroscopy and "best f i t " s t r u c t u r e s were then deduced. Minor components were not studied. Pure octahydroand tetrahydrophenanthrene were used as a "reference base" to compare isomers. A d e t a i l e d d i s c u s s i o n of these f r a c t i o n s together with the probable s t r u c t u r e s i n each has been presented e a r l i e r [9] . The most important observations were (1) every possible position isomer of rearranged octahydroand tetrahydrophenanthrene were present but not equally distributed; and (2) the b e n z y l i c carbons of hydroaromatic r i n g s have migrated to a methyl group (confirmed by C label). A small amount of hexahydrophenanthrene was present i n the mixture i n d i c a t i n g that the step-wise t r a n s f e r of hydrogen ( l o s s of two hydrogens) does occur. Three condensed rings apparently provide more s t a b i l i t y for t h i s intermediate than does the naphthalene system. The studies with octahydrophenanthrene confirmed that isomerization i s not unique to Tetralin. The problem becomes more acute with i n c r e a s i n g number of hydroaromatic r i n g s . These s t r u c t u r e studies a l s o suggested that tetrahydrophenanthrene may be a key intermediate and should t h e r e f o r e be studied d i r e c t l y i n order to understand the e f f e c t that condensed aromatics have on the fate of a s i n g l e hydroaromatic r i n g . 13

Studies with Tetrahydroanthracene and

Tetrahydrophanthrene

Since the T e t r a l i n studies showed that isomerization y i e l d e d predominantly the 1-methyl indan isomer and that the c o n t r a c t i o n involves the migration of the b e n z y l i c carbon to a methyl group, we decided to explore the e f f e c t that a d d i t i o n a l r i n g condensation has on t h i s chemistry. 1,2,3,4,-Tetrahydroanthracene i s the l i n e a r benzologue o f T e t r a l i n . This compound behaves i d e n t i c a l to T e t r a l i n i n the presence of d i b e n z y l with respect to r i n g c o n t r a c t i o n , g i v i n g a s i n g l e methyl s i g n a l at 19.6 ppm (Figure 5 ) . Contrary to T e t r a l i n , which does not y i e l d a measurable l e v e l of 1,2dihydro-intermediate, one observes the formation of 9,10dihydroanthrene (36.1 signal). The only other product i s anthracene. The y i e l d of 1-methylcyclopentanoanthracene is


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> G m


384


s l i g h t l y l e s s t h a n t h a t i n the c o r r e s p o n d i n g J e t r a l i n s y s t e m . A n t h r a c e n e and 9 , 1 0 - d i h y d r o a n t h r a c e n e a r e s l i g h t l y g r e a t e r t h a n s t o i c h i o m e t r i c a l l y p r e d i c t e d by hydrogen t r a n s f e r . T h i s may be due to a greater ease of thermal dehydrogenation of three-ring hydroaromatics. 1,2,3,4-Tetrahydrophenanthrene i s the a n g u l a r b e n z o l o g u e of Tetralin. B o t h n a t u r a l and 10% 1C - e n r i c h e d H^Ph were s t u d i e d i n a manner s i m i l a r t o T e t r a l i n . H o w e v e r , one o b s e r v e s a much more c o m p l e x m i x t u r e o f p r o d u c t s w i t h H ^ P h , as s e e n i n t h e C-NMR s p e c t r u m ( F i g u r e 6 ) . T h r e e d i s t i n c t l i n e s between 20-22 ppm a r e o b s e r v e d due t o the m e t h y l g r o u p s on the t h r e e p o s s i b l e i s o m e r s from r i n g c o n t r a c t i o n . I t i s a l s o noted that i n t h e a n g u l a r s y s t e m , t h e s e s i g n a l s a r e at l o w e r f i e l d t h a n i n t h e l i n e a r s y s t e m s ( a p p r o x i m a t e l y 19.6 ppm). The a s s i g n m e n t s o f t h e s e s i g n a l s a r e as f o l l o w s :

2 0 . 6 ppm

2 1 . 7 ppm

2 1 . 4 ppm

A s m a l l amount o f 9 , 1 0 - d i h y d r o p h e n a n t h r e n e is observed (signal at 29.0 ppm) presumably as a result of rapid i s o m e r i z a t i o n o f any 1 , 2 - d i h y d r o p h e n a n t h r e n e formed from the a b s t r a c t i o n o f h y d r o g e n from H^Ph by h y d r o g e n t r a n s f e r . As i s the c a s e w i t h d i h y d r o a n t h r a c e n e , the 9 , 1 0 - d e r i v a t i v e i s the most s t a b l e i s o m e r . An u n e x p e c t e d o b s e r v a t i o n was t h e s c r a m b l i n g o f l a b e l e d carbon in the H^Ph solvent during hydrogen transfer experiments. As d e t e r m i n e d by NMR, about 25% o f the C label at the C - l p o s i t i o n o f H^Ph was found i n the C-4 p o s i t i o n o f phenanthrene i n the p r o d u c t o f a t h r e e - h o u r r u n w i t h d i b e n z y l at 450°C. The following nomenclature and shifts in p h e n a n t h r e n e were used i n t h e d e t e r m i n a t i o n . 3 ^ \ , 2

ΰ C-l

Γ

from TMS

and 8

-

1 2 8 . 5 6 ppm

C-2,3,6,7

-

126.6

C-4 and 5

-

122.6

As shown l a t e r , t h e same s i g n a l enhancement o f C-4 i s s e e n when l a b e l e d sym- o r asym-HgPh a r e u s e d . T h i s t y p e o f e n r i c h m e n t at C-4 i m p l i e s t h a t c o n c u r r e n t c l e a v a g e o f the C ^ - C ^ Q and C ^ - C ^ bonds o c c u r , t o g e t h e r w i t h r i n g i n v e r s i o n . a


a

21.

CRONAUER ET AL.

Hydroaromatic

Systems

385

asym-Octahydrophenanthrene Experiments C a t a l y t i c hydrogénation of phenanthrene to the octahydrostage produces both sym- and asym-isomers, although the former predominate. A d d i t i o n a l l y , i n t e r c o n v e r s i o n of the two forms tends to occur at coal l i q u e f a c t i o n c o n d i t i o n s . Since the asym- form has not been studied p r e v i o u s l y , we b r i e f l y explored both n a t u r a l and 1 - ^ C - e n r i c h e d asym-HgPh with respect to i t s r e a c t i v i t y with d i b e n z y l at 450°C. The spectrum of product of the run with 1-C -asym HgPh i s shown i n Figure 7. The GLC r e s u l t s i n d i c a t e that asym-HgPh decomposes to numerous products that are not normally observed with sym-HgPh. Based on GLC and NMR spectra, the following observations were made: 1.

The condensed c y c l o p a r a f f i n rings crack y i e l d i n g η-butyl groups, c o n t a i n i n g , i n p a r t , the C l a b e l i n a terminal CH^ p o s i t i o n ( s i g n a l at 14.0).

2.

Ring c o n t r a c t i o n has occurred to y i e l d at least two methylcylopentane derivatives ( s i g n a l s at 20.6 and 21.7 ppm).

3.

Tetrahydro- and dihydrophenanthrenes been formed (signals at 25.7 29.0 ppm) .

4.

Phenanthrene has been 128.5 and 122.6 ppm).

5.

About 25% of the 1- C l a b e l has migrated to p o s i t i o n C-4 based upon the NMR s p e c t r a of phenanthrene formed.

formed

have and

(signals

at

13

D i s c u s s i o n of I s o m e r i z a t i o n Results The studies of rearrangement of hydroaromatics suggest that i s o m e r i z a t i o n i s dependent upon the breaking of b e n z y l i c carbon bonds. It i s promoted by the presence of free radicals. A l l of the hydroaromatic molecules y i e l d ring c o n t r a c t i o n products at coal l i q u e f a c t i o n c o n d i t i o n s . Angular hydroaromat i c s are much more l i k e l y to rearrange to a v a r i e t y of p o s i t i o n isomers than l i n e a r hydroaromatics although the rate of i s o m e r i z a t i o n of each separate specie may be d i f f e r e n t than that of T e t r a l i n s . The above r e s u l t s show that the dihydro-aromatics do not d i r e c t l y c o n t r i b u t e to rearrangements. Secondly the dihydroaromatics rapidly aromatize by hydrogen transfer or dispropositionation. This implies that the rearrangement



Figure 7. C-l 3 NMR spectrum of reaction products: asymmetric octahydrophenanthrene plus dibenzyl (saturate region)

31.43

21.

CRONAUER ET AL.

Hydroaromatic

Systems

387

proceeds by a free r a d i c a l process. I t i s also noted that when free r a d i c a l s from the acceptor are present, the rate of rearrangement i s g r e a t l y increased. SOLVENT ADDUCTION The primary r e a c t i o n between good donor s o l v e n t s , such as T e t r a l i n and octahydrophenanthrene, and acceptors can give rather " i d e a l " products. For example, at moderate d i b e n z y l acceptor concentrations (10-20%) dibenzyl i s converted only to toluene i n these s o l v e n t s . However, when poor solvents are introduced, secondary r e a c t i o n s become quite important and " n o n - i d e a l " products are recovered. The type of secondary products are influenced by the solvent used, the temperature o f r e a c t i o n , and the s t r u c t u r e of acceptor molecules. The secondary reactions may well compete with primary r e a c t i o n s to such an extent that k i n e t i c s become d i f f i c u l t to model. As shown e a r l i e r [2] mesitylene forms adducts with b e n z y l r a d i c a l s concurrent with hydrogen t r a n s f e r from T e t r a l i n at 450°C. Although not shown i n the previous paper, m e s i t y l r a d i c a l s also formed adducts with T e t r a l i n i n mixed systems. When reactions with oxygen-containing acceptors were performed [3] i n the 300-400°C region, the formation of adducts occurred with both T e t r a l i n and mesitylene. This r e a c t i o n was observed when benzyl r a d i c a l s were generated from d i b e n z y l ether, d i b e n z y l s u l f i d e , benzyl a l c o h o l , and benzaldehyde. The most surprising observation from low temperature r e a c t i o n s was the formation of adducts between good donor solvents ( T e t r a l i n , octahydrophenanthrene, t e t r a h y d r o q u i n o l i n e ) and acceptor r a d i c a l s . The r e s u l t i n g adducts were not of a s i n g l e predominant s t r u c t u r e . In p a r t i c u l a r , s e v e r a l isomers of toluene-Tetralin were formed as well as di-Tetralin. Several of these r e a c t i o n s were done with D ^ - T e t r a l i n which permitted the f i r m i d e n t i f i c a t i o n of the T e t r a l i n moiety i n the adducts. GLC-MS studies i n d i c a t e d that the T e t r a l i n may be bonded to phenyl, benzyl, benzyloxyor phenoxy-groups, depending on the acceptor used. Bonding is assumed to be predominately on the hydroaromatic r i n g since t h i s should be the most r e a c t i v e s i t e of t e t r a l i n donors. This i s supported by a large fragment ion at M - b e n z y l . However, based on mesitylene experiments, some bonding on the aromatic r i n g also occurs. It appears that the formation of benzyl T e t r a l i n only occurs during the hydrogen transfer reactions at low temperatures (

Isomerization and Adduction of Hydroaromatic Systems at Conditions

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