Aspects of the Hydrogen Atom Transfer Reactions of Macerals - ACS

10 Aspects of the Hydrogen Atom Transfer Reactions of Macerals CHOL-YOO CHOI and LEON M. STOCK

Downloaded by FUDAN UNIV on March 27, 2017 | http://pubs.acs.org Publication Date: May 8, 1984 | doi: 10.1021/bk-1984-0252.ch010

Department of Chemistry, The University of Chicago, Chicago, IL 60637

The i n f l u e n c e s of macerals from s e v e r a l bituminous coals on the hydrogen-deuterium exchange r e a c t i o n between tetralin-d and diphenylmethane and on the r e d u c t i o n of fluorenone have been s t u d i e d . The s p o r i n i t e - r i c h e x i n i t e s are more e f f e c t i v e promoters of the exchange r e a c t i o n than the corresponding vitrinites or alginite. The s e m i f u s i n i t e - r i c h i n e r t i n i t e s are even l e s s e f f e c t i v e promoters of the exchange r e a c t i o n . More important, they are l e s s s e l e c t i v e i n r e a c t i o n s with tetralin. The presence of s u l f u r c o n t a i n i n g compounds i n the macerals has a notable i n f l u e n c e on t h e i r r e a c t i v i t y i n hydrogen t r a n s f e r r e a c t i o n s . 12

The r e a c t i v i t y p a t t e r n f o r the r e d u c t i o n of f l u o r e n o n e - - s p o r i n i t e > vitrinite > a l g i n i t e > s e m i f u s i n i t e > f u s i n i t e > r e s i n i t e - - d e f i n e s a bell shaped dependence on the H/C r a t i o of the maceral and presumably r e f l e c t s the quantity of r e a d i l y o x i d i z e d hydroaromatic compounds i n the maceral. The d i f f e r e n c e s i n the e f f e c t i v e n e s s of the macerals depends i n part upon t h e i r ability to initiate the r e d u c t i o n of the ketone and i n part upon the facility with which they undergo o x i d a t i o n . As a consequence, there may be s y n e r g i s t i c i n t e r a c t i o n s between the components of the d i f f e r e n t macerals i n o x i d a t i v e hydrogen t r a n s f e r processes.

The concept that f r e e r a d i c a l r e a c t i o n s are r e s p o n s i b l e f o r the i n i t i a l fragmentation r e a c t i o n s of large c o a l molecules and f o r the e s s e n t i a l hydrogen t r a n s f e r r e a c t i o n s that occur during c o a l d i s s o l u t i o n r e a c t i o n s i s q u i t e widely accepted (1)· The i n -

0097-6156/ 84/ 0252-Ό157506.00/ 0 © 1984 American Chemical Society

Winans and Crelling; Chemistry and Characterization of Coal Macerals ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

COAL MACERALS

158

t e r a c t i o n s b e t w e e n c o a l s and l a b e l e d m o l e c u l e s s u c h as t e t r a l i n ^12 ^ examined i n s e v e r a l l a b o r a t o r i e s to i n c r e a s e our u n d e r s t a n d i n g o f t h e s e r e a c t i o n s (2-j>)« Recent f i n d i n g s c o n c e r n i n g t h e s e l e c t i v e and r e v e r s i b l e a b s t r a c t i o n r e a c t i o n s o f h y d r o gen atoms f r o m T e t r a l i n by r a d i c a l s f o r m e d d u r i n g t h e t h e r m a l dec o m p o s i t i o n o f I l l i n o i s No. 6 c o a l a t 400°C (2^) and o t h e r b i t u m i nous c o a l s (3-5) are i n a c c o r d w i t h the f o r m u l a t i o n of the d i s s o l u t i o n r e a c t i o n as a f r e e r a d i c a l p r o c e s s . The f a c t t h a t weak o r g a n i c a c i d s and b a s e s h a v e o n l y a m o d e s t i n f l u e n c e on t h e exc h a n g e r e a c t i o n s o f a r o m a t i c , a l i p h a t i c , and b e n z y l i c h y d r o g e n atoms u n d e r t h e s e c o n d i t i o n s w h e r e a s compounds s u c h as b e n z y l p h e n y l e t h e r , b e n z y l p h e n y l s u l f i d e , t h i o p h e n o l , t h e BDPA r a d i c a l , a n t h r a q u i n o n e , a n t h r o n e , t e t r a c e n e , and a c r i d i n e a c t i v e l y p r o m o t e t h e b e n z y l i c h y d r o g e n atom t r a n s f e r r e a c t i o n s s u g g e s t s q u i t e s t r o n g l y t h a t h y d r o a r o m a t i c compounds a r e e s p e c i a l l y r e a c t i v e i n t h e h y d r o g e n t r a n s f e r p r o c e s s e s (2^)· In a d d i t i o n , b e n z y l p h e n y l s u l f i d e and t h i o p h e n o l s i g n i f i c a n t l y e n h a n c e t h e r a t e o f d i s s o l u t i o n o f I l l i n o i s No. 6 c o a l ( 6 ) . Other workers have i n v e s t i g a t e d t h e d e h y d r o g e n a t i o n o f c o a l s w i t h b e n z o q u i n o n e (_7), i o d i n e (8), s u l f u r (9), p a l l a d i u m on c a l c i u m c a r b o n a t e (10), and b e n z o p h e n o n e (.11,12). A l t h o u g h t h e r e a c t i o n s o f many c o a l s w i t h b e n z o p h e n o n e o c c u r r a t h e r s l o w l y a t 400°C, t h e r e a c t i o n c a n be used to d e f i n e t h e i r hydrogen donor c a p a b i l i t y q u i t e conveniently because a s i n g l e p r o d u c t , diphenylmethane, i s formed i n the r e a c tion.


a

v

e

D

e

e

n

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 s o f m a c é r a i s h a v e r e c e i v e d scant a t t e n t i o n . Peover examined the d e h y d r o g e n a t i o n of f i v e p u r e e x i n i t e s and v i t r i n i t e s f r o m t h e same seam u s i n g b e n z o q u i n o n e i n d i m e t h y l f o r m a m i d e a t 153°C f o r s e v e r a l h o u r s (_7). His r e s u l t s s u g g e s t t h a t e x i n i t e s a r e u s u a l l y somewhat b e t t e r h y d r o gen d o n o r s t h a n t h e c o r r e s p o n d i n g vitrinites. R e g g e l and h i s c o w o r k e r s s t u d i e d t h e r e a c t i o n u s i n g p a l l a d i u m on c a l c i u m c a r b o n a t e t o d e h y d r o g e n a t e f o u r m a c é r a i s f r o m an hvA b i t u m i n o u s c o a l c a t a l y t i c a l l y (13). They f o u n d t h a t 31, 25, 18, and 5 h y d r o g e n atoms were removed p e r 100 c a r b o n atoms o f e x i n i t e , v i t r i n i t e , m i c r i n i t e , and f u s i n i t e , r e s p e c t i v e l y . They a l s o c o n c l u d e t h a t t h e e x i n i t e s a r e g e n e r a l l y more r e a c t i v e . D y r k a c z and h i s c o w o r k e r s h a v e r e c e n t l y d e s c r i b e d a new proc e d u r e f o r t h e s e p a r a t i o n o f c o a l s i n t o m a c é r a i s (14). The m a c é r a i s c a n be o b t a i n e d i n p u r e f o r m , b u t o n l y i n l i m i t e d q u a n tity. Inasmuch as many o f t h e methods u s e d f o r t h e s t u d y o f c o a l r e q u i r e r e l a t i v e l y l a r g e amounts o f m a t e r i a l , we h a v e u n d e r t a k e n new work on t h e d e v e l o p m e n t o f s m a l l s c a l e r e a c t i o n s f o r t h e a c c u r a t e d e t e r m i n a t i o n of the d i f f e r e n c e s i n c h e m i c a l r e a c t i v i t y of macérais. 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 s a r e d i s c u s s e d i n t h i s report. P r e l i m i n a r y work r e v e a l e d t h a t v e r y r e p r o d u c i b l e r e s u l t s c o u l d be o b t a i n e d when 25 mg o f a r e p r e s e n t a t i v e m a c e r a l was u s e d as a c a t a l y s t f o r t h e h y d r o g e n e x c h a n g e r e a c t i o n b e t w e e n t e t r a -


10. CHOI AND STOCK

Hydrogen Atom Transfer Reactions

159

l i n - c i ^ and diphenylmethane at 400°C and when 5 mg of a maceral was used as a reagent f o r the r e d u c t i o n of fluorenone at the same temperature. Consequently, these r e a c t i o n s have been employed to study the hydrogen atom t r a n s f e r r e a c t i o n s of macérais from several d i f f e r e n t coals.


Experimental Part M a t e r i a l s . The macérais used i n t h i s study were obtained from G.R. Dyrkacz and R.E. Winans of the Argonne N a t i o n a l Laborat o r y . Some of the samples were separated from the whole c o a l by hand, others were prepared by d e n s i t y gradient c e n t r i f u g a t i o n and others by f l o a t - s i n k techniques as described i n Chapters 5 and 9. The r e s i n i t e from the King 6 Mine of the Hiawatha Seam, the v i r i n i t e and f u s i n i t e from the hvC I l l i n o i s No. 2 bituminous coal and the a l g i n i t e from the hvA Ohio Lower K i t t a n i n g No. 5 b i tuminous c o a l (PSOC-297) c o n t a i n only n e g l i g i b l e amounts of other macérais. The pétrographie information f o r the pure macérais from hvB Indiana No. 1 Block Seam bituminous c o a l (PSOC-106) has been reported p r e v i o u s l y (14). The compositions of the macérais separated from hvC Indiana B r a z i l Block Seam bituminous c o a l (PSOC-828) and hvA Kentucky Upper Elkhorn No. 3 Seam bituminous c o a l (PSOC-1103) were determined by G.R. Dyrkacz. The r e s u l t s are summarized i n Tables I and I I . A l l of the samples prepared by c e n t r i f u g a t i o n and the f l o a t sink method were demineralized and m i l l e d to three micron d i a meter. The separations were conducted i n the presence of a surface a c t i v e agent, polyoxyethylene(23) l a u r y l ether, i n cesium c h l o r i d e s o l u t i o n s (14). The macérais were washed thoroughly to reduce the q u a n t i t y of s u r f a c t a n t i n the maceral to l e s s than 500 ppm and the q u a n t i t y of c h l o r i d e i o n i n the wash water to below the l i m i t d e t e c t a b l e by p r e c i p i t a t i o n with s i l v e r ion (14). Promotion of Hydrogen Exchange. The i n f l u e n c e of the macérais on the exchange of hydrogen between diphenylmethane and t e t r a l i n - d j 2 was determined using degassed s o l u t i o n s of d i p h e n y l methane (0.376 mmole) and t e t r a l i n - d ^ (0.376 mmole) and the macérais (25mg) i n g l a s s tubes i n an argon atmosphere at 400°C. The products were i s o l a t e d and analyzed using high f i e l d nmr spectroscopy as p r e v i o u s l y described (2)· C e r t a i n macérais i n corporate deuterium during the r e a c t i o n and the change i n the deuterium content of t e t r a l i n - d - ^ i s emphasized i n t h i s r e p o r t r a t h e r than the degree of i n c o r p o r a t i o n of t h i s isotope i n t o d i phenylmethane. Control experiments i n d i c a t e that n e i t h e r polyoxyethylene(23) l a u r y l ether nor cesium c h l o r i d e enhance the r a t e of the exchange r e a c t i o n s between t e t r a l i n - d ^ and d i p h e n y l methane. The r e s u l t s f o r the pure macérais and the maceral concentrates are summarized i n Tables I I I and IV.


Winans and Crelling; Chemistry and Characterization of Coal Macerals ACS Symposium Series; American Chemical Society: Washington, DC, 1984. 15.6

1.5

5.6 5.0

76.4 77.1

Vitrinite Inertinite Demineralized whole Exinite

PSOC-828

PSOC-828

PSOC-1103

PSOC-1103

PSOC-1103

4.0

1.6

H i a w a t h a King 6 whole c o a l contained 9.5% ash, I l l i n o i s No. 2 v i t r i n i t e contained 3.1% ash, and I l l i n o i s No. 2 demineralized f u s i n i t e contained 4.0% ash. A l l the other samples contained l e s s than 1% ash.

13.0

0.5

3.2

Demineralized f u s i n i t e

I l l i n o i s No. 2

79.3

18.1

1.1 5.3 73.9

vitrinite

Demineralized


0.5

17.6 1.1 5.1

71.6

Vitrinite

2.2 1.3


N.D.

4.4 18.1

0.1 5.3

10.6

73.1

5.5

69.3

Whole

Hiawatha King 6 83.9

N.D.

14.6 1.1

3.8

70.9

Inertinite

PSOC-1103

Resinite

8.8

15.3 1.2

5.6

80.4

Vitrinite

Demineralized whole

1.0

11.2 1.8

6.4

80.9


1.1

10.1

1.5

5.3

78.1

Hiawatha King 6

2.4 12.0

1.2

0.7

15.8

1.4

0.9

1.6

11.2

1.1

7.5

78.7

Exinite

0.9

15.9

S

1.4

PSOC-828

5.1

76.7

Demineralized whole

PSOC-828

Composition (%) H Ν 0 (diff)

Concentrate

C

Ultimate Analyses of Coals and Macérais Concentrates.

Coal

Table I.


10. CHOI AND STOCK

Table I I .

Pétrographie A n a l y s i s of Maceral Concentrates from PSOC-828 and PSOC-1103 Coals.

Coal


161


Concentrate

Exinite

PSOC-828

Exinite

91.0

PSOC-828

Vitrinite

PSOC-828

Inertinite

PSOC-1103

Exinite

PSOC-1103

Vitrinite

PSOC-1103

Composition Vitrinite

(%) Inertinite

9.0

0.0

4.0

89.8

6.2

0.0

67.5

32.5

45.5

49.6

4.9

Inertinite

5.0

92.5

2.5

82.3

16.2

1.5

P r i n c i p a l Macérais Maceral

PSOC-106

a

PSOC-828

PSOC-1103

Cutinite

0.3

0.6

0.2

Resinite

2.4

0.9

0.6

Sporinite

17.4

13.6

6.6

Total exinite

20.1

15.1

7.4

Vitrinite

35.2

61.8

74.2

Micrinite

3.2

4.9

5.6

Inertodetrinite

15.7

5.2

3.7

Semifusinite

20.7

9.9

6.5

Fusinite Total i n e r t i n i t e

a

5.7

3.1

2.6

45.3

23.1

18.4

R e f e r e n c e 14.


COAL M A C E R A L S

162

Table I I I .

The Influences of C e r t a i n Coals and Pure Macérais on the Deuterium-Hydrogen Exchange Reaction of T e t r a l i n d and Diphenylmethane at 400°C. a

9

Maceral

(mg)

Indiana No.


None

Deuterium Content of T e t r a l i n (%) Aromatic Benzylic Aliphatic Positions Positions Positions 1 Block Seam hvB Bituminous

0

Coal (PSOC-106)

b

95(96)

92(97)

92(94)

Exinite,

ρ = 1.176, (25)

96

84

91

Exinite,

ρ = 1.210, (25)

95

80

89

Vitrinite,

ρ = 1.291, (26)

95

85

90

Vitrinite,

ρ = 1.330, (25)

95

84

90

I n e r t i n i t e , ρ = 1.371, (25)

95

87

89

ρ = 1.447, (25)

95

87

89

91(97)

94(94)

Inertinite,

Hiawatha King 6 Mine hvB Bituminous None

0

91(96)

Coal

Whole (25)

89

80

92

R e s i n i t e (25)

90

85

93

92(97)

93(94)

I l l i n o i s No. None

2 hvC Bituminous

0

Coal 94(96)

Whole (25)

93

74

89

Demineralized whole (26)

93

69

88

Vitrinite

95

77

91

(25) 95

78

91

72

87

(25)

Demineralized v i t r i n i t e Demineralized f u s i n i t e

(26)

87

a

Diphenylmethane (0.376 mmole) and t e t r a l i n - d (0.376 mmole) were reacted f o r 60 minutes i n the presence of these m a t e r i a l s . 0

^The

d e n s i t y , p, i s noted f o r each maceral f r a c t i o n , reference 14.

c The o r i g i n a l i s o t o p i c composition of the T e t r a l i n used i n these experiments i s given i n parentheses. The i s o t o p i c composition of the T e t r a l i n i s o l a t e d from r e a c t i o n s c a r r i e d out without c o a l m a t e r i a l s i s a l s o shown.


10. CHOI AND STOCK

Table IV.


163

The Influence of Macérais from PSOC-828 and PSOC-1103 on the Deuterium-Hydrogen Exchange Reaction of T e t r a lin-d and Diphenylmethane at 4 0 0 ° C . > a

Deuterium Content of T e t r a l i n ( % ) Aromatic Benzylic Aliphatic Positions Positions Positions Indiana B r a z i l Block Seam hvC Bituminous Coal (PSOC-828)


Maceral

b

(mg)

None

95(96)

91(97)

93(94)


94

83

91

Exinite

94

76

91

94

80

91

96

88

89

(25)

Vitrinite Inertinite

(25) (25)

Kentucky Upper Elkhorn No. 3 Seam hvA Bituminous

Coal (PSOC-1103)

None

96(96)

92(97)

92(94)


94

82

90

E x i n i t e (25)

97

74

88

Vitrinite

93

83

88

95

75

90

Inertinite

(25) (25)

The observed experimental r e s u l t s f o r the macérais have been normalized to 100% maceral p u r i t y . ^The experiments of Table I I I .

were conducted

as described i n footnotes a and c


164

COAL MACERALS


Ketone Reduction. Pure samples of r e p r e s e n t a t i v e compounds were reacted w i t h fluorenone to d e f i n e the general p a t t e r n of reactivity. In a t y p i c a l experiment, fluorenone (0.025 mmole), the hydroaromatic compound (0.025 mmole) and benzene ( 5 0 μ 1 ) were reacted i n an argon atmosphere i n a g l a s s v e s s e l at 400°C f o r 60 minutes. The composition of the s o l u t i o n at the end of the r e a c t i o n was determined by gas chromatography. The r e s u l t s f o r the seven compounds examined i n t h i s work are summarized i n Table V. The r e d u c t i o n of the m a c é r a i s by fluorenone was a l s o s t u d i e d u s i n g degassed s o l u t i o n s of fluorenone (0.025 mmol) i n benzene ( 5 0 μ 1 ) and the maceral concentrate (5mg) i n a g l a s s v e s s e l i n an argon atmosphere at 400°C. Most r e a c t i o n s were c a r r i e d out f o r 30 or 60 minutes. The e n t i r e r e a c t i o n mixture was then f i l t e r e d through a short column c o n t a i n i n g 100-200 mesh F l o r i s i l u s i n g me thylene c h l o r i d e as the e l u t i n g s o l v e n t . The extent of conver s i o n of the ketone to f l u o r e n e was determined by gas chromatogra phy of the e l u e n t . The experimental r e s u l t s are summarized i n Tables VI and V I I . Results The hydrogen atom exchange r e a c t i o n s between T e t r a l i n and diphenylmethane and the r e d u c t i o n of the ketones were s t u d i e d i n the presence of a s e l e c t e d group of raw whole c o a l s , demineral i z e d whole c o a l s , and demineralized m a c é r a i s . The m a c é r a i s used i n t h i s work were obtained from two hvA bituminous c o a l s , one from the Kentucky Upper Elkhorn No. 3 Seam (PSOC-1103) and one from the Ohio Lower K i t t a n i n g No. 5 Seam (PSOC-297); two hvB b i tuminous c o a l s , one from the Indiana No. 1 Block Seam (PSOC-106) and one from the Hiawatha King 6 Mine; and two hvC bituminous c o a l s , one from the I l l i n o i s No. 2 Seam and one from the Indiana B r a z i l Block Seam (PSOC-828). The exchange r e a c t i o n of t e t r a l i n - d , ~ and diphenylmethane has p r e v i o u s l y been s t u d i e d u s i n g as l i t t l e as 50mg of m a t e r i a l . P r e l i m i n a r y experiments w i t h smaller q u a n t i t i e s of some r e p r e s e n t a t i v e c o a l s i n d i c a t e d t h a t the r e a c t i o n s could not be conducted r e p r o d u c i b l y at the d e s i r e d l e v e l of accuracy, ± 27o, w i t h l e s s than 25mg of m a t e r i a l . We t h e r e f o r e used t h i s q u a n t i t y of the c o a l m a t e r i a l i n the subsequent experiments. Only very s m a l l a mounts of cesium c h l o r i d e and B r i j 35, the surface a c t i v e agent employed i n the d e n s i t y g r a d i e n t s e p a r a t i o n , are r e t a i n e d i n the m a c é r a i s . C o n t r o l experiments, i n which as much as 25mg of these m a t e r i a l s were added to the r e a c t i o n system, e s t a b l i s h e d that these substances had no measurable i n f l u e n c e on the exchange r e a c t i o n . The c o a l m a c é r a i s obtained from PSOC-106 hvB bituminous c o a l by c e n t r i f u g a t i o n and from Hiawatha hvB and I l l i n o i s No. 2 hvC bituminous c o a l s by hand s e l e c t i o n were very pure. The extent to which these substances i n f l u e n c e the exchange r e a c t i o n i s presented i n Table I I I .


10. CHOI AND STOCK


Table V.


165

Dehydrogenation of Representative Hydrogen Donors by Fluorenone at 400°C

Hydrogen donor

Conversion to fluorene (%)

1,2,3,4-Tetrahydroquinoline

28

5.12-Dihydrotetracene

14

9,10-Dihydroanthracene

14

1,2,3,4,5,6,7,8-0ctahydroanthracene

6

9,10-Dihydrophenanthrene

5

Tetralin

3

Decalin

0.4

Fluorenone (0.025 mmole) and the H-donor (0.025 mmole) were r e acted i n argon at 400°C f o r 60 minutes.


166

COAL MACERALS

Table VI.

The Reduction of Fluorenone to Fluorene by Coals and Macérais at 400°C f o r 1 Hour i n the Presence of Benzene.


a

Conversion to f l u o r e n e ( % )

Coal

Sample (mg)

Hiawatha King 6

Whole

Hiawatha King 6

Resinite

I l l i n o i s No.

2

Whole

I l l i n o i s No.

2

Demineralized whole

I l l i n o i s No.

2

Vitrinite

I l l i n o i s No.

2

Demineralized v i t r i n i t e

I l l i n o i s No.

2

Demineralized f u s i n i t e

39

(5.0)

15

(5.1)

43

(5.0) (5.0)

49 44

(5.0) (5.0) (5.0)

42 19

b

Exinite,

ρ = 1.176,

(5.2)

67

PSOC-106

b

Exinite,

p" = 1.210,

(5.1)

67

PSOC-106

b

Vitrinite,

p" = 1.291,

(5.2)

46

PSOC-106

b

Vitrinite,

"p = 1.330,

(5.0)

38

PSOC-106

b

I n e r t i n i t e , "p = 1.371,

(5.1)

25

b

I n e r t i n i t e , "p = 1.447,

(5.0)

16

PS0C-106

PSOC-106

PSOC-297

Alginite

(5.0)

41

a

T h e s e experiments were c a r r i e d out with 0.025mmole of fluorenone i n benzene ( 5 0 y l ) .

b

T h e average d e n s i t y of the d i f f e r e n t macérais i s noted.


10. CHOI AND STOCK

Table V I I .

167


The Reduction of Fluorenone to Fluorene by Maceral Con centrates from PSOC-1103 and PSOC-828 at 400°C f o r 1 Hour i n the Presence of Benzene


a

Coal

Maceral(mg)

Conversion to f l u o r e n e (%) Measured Normalized

PSOC-1103

E x i n i t e (5.0)

66

87

PSOC-1103

V i t r i n i t e (5.0)

50

50

PSOC-1103

I n e r t i n i t e (5.0)

33

29

PSOC-828

E x i n i t e (5.0)

60

61

PSOC-828

V i t r i n i t e (5.0)

46

47

I n e r t i n i t e (5.0)

41

30

PSOC-828

The experiments were c a r r i e d out with 0.15 mmole of fluorenone i n benzene (50μ1).


168

COAL MACERALS

The maceral concentrates obtained by f l o a t - s i n k methods from and 1 1 0 3 were somewhat l e s s pure than the macérais obtained by hand or by c e n t r i f u g a t i o n . For convenient comparison, the data obtained i n the exchange r e a c t i o n s have been normalized to 1 0 0 7 o maceral p u r i t y on the b a s i s of the pétrographie informat i o n presented i n Table II using simultaneous l i n e a r equations. The normalized r e s u l t s are summarized i n Table IV.


PSOC-828

Benzophenone, as mentioned i n the I n t r o d u c t i o n , has been used to assess the hydrogen donor c a p a c i t y of c o a l s ( 1 1 , 1 2 ) . Unfortunately, most coals r e a c t very slowly with t h i s compound a t 4 0 0 ° C , equation 1 . For example, l e s s than 5 7 o of t h i s ketone i s converted to diphenylmethane by a v i t r i n i t e - r i c h sample of I l l i nois No. 6 coal i n benzene i n one hour a t 4 0 0 ° C . P r e l i m i n a r y work revealed that the e x i n i t e , v i t r i n i t e , and i n e r t i n i t e i s o l a t e d from P S O C - 8 2 8 e x h i b i t small, but apparently s i g n i f i c a n t

Benzophenone + I l l i n o i s No. 6 Coal

Diphenylmethane ( 1 )

differences i n r e a c t i v i t y . However, the extent o f r e a c t i o n was too small f o r accurate work. Consequently, we sought a more r e a c t i v e ketone. Halogenated benzophenones are more r e a c t i v e than the u n s u b s t i t u t e d compound, but competitive dehalogenation react i o n s complicate the i n t e r p r e t a t i o n o f the r e s u l t s . On the other hand, the r e d u c t i o n o f fluorenone proceeds more than twice as r a p i d l y as that of benzophenone to give a s i n g l e product. Quite accurate r e s u l t s can be obtained when 5mg of the maceral are used i n the r e a c t i o n . In a d d i t i o n , the p o s s i b l e contaminants i n the macérais, B r i j 35 and cesium c h l o r i d e , do not a c c e l e r a t e the r e d u c t i o n of fluorenone by T e t r a l i n . Several r e p r e s e n t a t i v e compounds were examined to gain p e r s p e c t i v e on the r e l a t i o n s h i p between the s t r u c t u r e and r e a c t i v i t y of d i f f e r e n t hydroaromatic compounds, Table V. The encouraging r e s u l t s obtained i n these experiments and i n p r e l i m i n a r y experiments with c o a l s prompted study of the r e a c t i o n s of a l l the macérais with fluorenone. The r e s u l t s f o r the q u i t e pure macérais from I l l i n o i s No. 2 c o a l , PSOC-106, and 2 9 7 and the Hiawatha King 6 Seam c o a l are presented i n Table VI. The normalized r e s u l t s f o r the maceral concentrates obtained from P S O C - 8 2 8 and 1103 are summarized i n Table V I I . Several l i n e s of evidence led us to conclude that most of the macérais c o n t a i n compounds that are r e a c t i v e i n hydrogen t r a n s f e r r e a c t i o n s , but that these m a t e r i a l s are present i n d i f f e r e n t amounts i n the d i f f e r e n t macérais. This f e a t u r e of the chemistry was examined by the study of the r e a c t i o n s of the


10.

CHOI AND STOCK

Hydrogen Atom Transfer

169

Reactions

macérais from PSOC-828 a t d i f f e r e n t time i n t e r v a l s as i n Figure 1 .

displayed

Discussion Promotion of Hydrogen Exchange. The r a d i c a l s d e r i v e d from the c o a l molecules by simple thermal homolyses and by moleculeinduced homolyses i n i t i a t e exchange r e a c t i o n s between t e t r a l i n d^^ d the donors i n the r e a c t i o n s y s t e m — p r i n c i p a l l y diphenylmethane and the hydroaromatic compounds i n the macérais (2^)· While i t i s c l e a r that many d i f f e r e n t f a c t o r s i n f l u e n c e the exchange r e a c t i o n s , the s i m p l i f i e d sequence of r e a c t i o n s shown i n equations 2 - 5 i l l u s t r a t e s the p o t e n t i a l dependence of the exchange a n


Coal Molecules R- + T e t r a l i n - d

1 2

T e t r a l i n - d ^ - + Donor-Η And

— · • R-

(2)

^

T e t r a l i n - d ^ + RD

(3)

^

T e t r a l i n - d - ^ + Donor- (4)

so f o r t h

(5)

process on the c o n c e n t r a t i o n and s e l e c t i v i t y of the i n i t i a t i n g r a d i c a l s , R», d e r i v e d from the coal molecules. The r e s u l t s f o r the macérais may be conveniently examined on the b a s i s of t h i s r e a c t i o n sequence. The h i g h l y p u r i f i e d macérais from the Indiana No. 1 c o a l , PSOC-106, a l l modestly enhance the exchange of hydrogen atoms t e t r a l i n - d ^ 2 and diphenylmethane. The same p a t t e r n of r e a c t i v i t y — b e n z y l i c exchange > a l i p h a t i c exchange > aromatic e x c h a n g e — i s observed with each maceral. These f i n d i n g s are compatible with the r e s u l t s obtained i n other studies of whole coals with l a b e l e d Tetralins (2-^))· While the r e a c t i v i t i e s of the macérais from t h i s c o a l do not d i f f e r a p p r e c i a b l y , the low d e n s i t y e x i n i t e s appear to be somewhat more e f f e c t i v e agents f o r the promotion of the hydrogen t r a n s f e r r e a c t i o n . The r e s u l t s obtained f o r the macérais from the Indiana B r a z i l Seam c o a l , PSOC-828, p a r a l l e l the r e s u l t s f o r the macérais of the PSOC-106 c o a l i n a l l respects except that the macérais from the PSOC-828 coal are s i g n i f i c a n t l y more e f f e c t i v e c a t a l y s t s f o r the exchange r e a c t i o n . The macérais from the Kentucky Upper Elkhorn Seam, PSOC-1103, on the other hand, behave somewhat d i f ferently. The i n e r t i n i t e and e x i n i t e e x h i b i t higher r e a c t i v i t y than the v i t r i n i t e . This a l t e r a t i o n i n behavior i s almost c e r t a i n l y the consequence of the high s u l f u r content of the semif u s i n i t e - r i c h i n e r t i n i t e f r a c t i o n , Table I. Although no informat i o n i s a v a i l a b l e concerning the nature of the s u l f u r compounds i n t h i s maceral concentrate, i t i s known that s u l f u r compounds such as hydrogen s u l f i d e , t h i o l s , and c e r t a i n t h i o e t h e r s are esp e c i a l l y e f f e c t i v e agents f o r the promotion of hydrogen exchange


170

COAL MACERALS


r e a c t i o n (6^. The f i n d i n g t h a t t h e w h o l e c o a l s f r o m t h e I l l i n o i s No. 2 Seam and t h e K e n t u c k y No. 3 Seam a r e somewhat more r e a c t i v e t h a n a n t i c i p a t e d on t h e b a s i s o f t h e r e a c t i v i t y o f t h e i n d i v i d u a l m a c é r a i s may a l s o o r i g i n a t e i n t h e g r e a t e r q u a n t i t y o f s u l f u r c o n t a i n i n g compounds i n t h e w h o l e c o a l s , T a b l e I I . The d i f f e r e n c e i n t h e e x t e n t o f e x c h a n g e a t t h e b e n z y l i c and a l i p h a t i c p o s i t i o n s o f T e t r a l i n i s m e a s u r a b l y l e s s when t h e i n e r t i n i t e s r a t h e r t h a n t h e v i t r i n i t e s f r o m PSOC-106 and PSOC-828, are used t o promote the r e a c t i o n . I n d e e d , t h e i n e r t i n i t e obt a i n e d f r o m PSOC-828 e n h a n c e s t h e e x c h a n g e r e a c t i o n s a t t h e benz y l i c and a l i p h a t i c p o s i t i o n s o f T e t r a l i n t o a c o m p a r a b l e d e g r e e . T h i s d e c r e a s e i n s e l e c t i v i t y s u g g e s t s t h a t the r a d i c a l s formed i n the i n i t i a l f r a g m e n t a t i o n r e a c t i o n s of t h e s e s e m i f u s i n i t e - r i c h macérais d i f f e r s i g n i f i c a n t l y i n t h e i r b e h a v i o r from the r a d i c a l s produced from the o t h e r macérais. The e x i n i t e s i s o l a t e d f r o m PSOC-106, 828, and 1103 are r e l a t i v e l y r i c h i n s p o r i n i t e , Table I I . F o r c o m p a r i s o n , we e x a m i n e d the r e s i n i t e i s o l a t e d from a Hiawatha c o a l . The e x c h a n g e datum for t h i s pure maceral, Table I I I , i n d i c a t e s that i t i s a s i g n i f i c a n t l y l e s s e f f e c t i v e agent f o r the p r o m o t i o n o f the exchange r e a c t i o n than the s p o r i n i t e - r i c h macérais i s o l a t e d from the o t h e r s a m p l e s i n s p i t e o f t h e f a c t t h a t t h e w h o l e H i a w a t h a c o a l i s more r e a c t i v e than the o t h e r whole c o a l s . In summary, a l l t h e m a c é r a i s e x a m i n e d i n t h i s s t u d y e n h a n c e t h e h y d r o g e n atom t r a n s f e r r e a c t i o n s b e t w e e n t e t r a l i n - d - . ~ and the h y d r o g e n atom d o n o r s i n t h e r e a c t i o n s y s t e m . A l t h o u g h the range of r e a c t i v i t y i s r e l a t i v e l y narrow, the d i f f e r e n c e s i n r e a c t i v i t y are w e l l beyond the l i m i t s o f e x p e r i m e n t a l e r r o r . The r e s u l t s i n d i c a t e t h a t t h e s p o r i n i t e - r i c h e x i n i t e s a r e s i g n i f i c a n t l y more r e a c t i v e t h a n t h e c o r r e s p o n d i n g v i t r i n i t e s and e v e n o t h e r a l g i nite-rich exinites. The s e m i f u s i n i t e - r i c h i n e r t i n i t e s , i n c o n t r a s t , a r e s i m u l t a n e o u s l y l e s s e f f e c t i v e p r o m o t o r s o f t h e exchange r e a c t i o n and l e s s s e l e c t i v e i n t h e i r r e a c t i o n s w i t h T e t r a lin. I t i s p e r t i n e n t , however, t h a t r e a c t i v e s u b s t a n c e s s u c h as t h e s u l f u r compounds i n t h e i n e r t i n i t e i s o l a t e d f r o m t h e K e n t u c k y Upper E l k h o r n c o a l c a n a l t e r t h e r e a c t i v i t y p a t t e r n s i g n i f i c a n t ly. The a v a i l a b l e i n f o r m a t i o n s t r o n g l y s u g g e s t s t h a t t h e d i f f e r e n t c o a l m a c é r a i s and t h e i n i t i a l p r o d u c t s o f t h e i r d i s s o l u t i o n r e a c t i o n s i n d o n o r s o l v e n t s decompose t o f o r m r a d i c a l s a t somewhat d i f f e r e n t r a t e s and t h a t t h e r a d i c a l s f o r m e d i n t h e s e processes e x h i b i t d i f f e r e n t degrees of r e a c t i v i t y . Ketone R e d u c t i o n . The r e d u c t i o n o f f l u o r e n o n e t o f l u o r e n e was a d o p t e d f o r t h e s t u d y o f t h e d o n o r c a p a b i l i t i e s o f t h e macérais. The m e c h a n i s m o f t h i s r e a c t i o n , w h i c h a p p a r e n t l y t a k e s p l a c e i n s e v e r a l s t e p s , has n o t b e e n d e f i n e d and i s c u r r e n t l y under study i n our laboratory.



10.

CHOI AND STOCK


171

The extent to which démineraiization i n f l u e n c e s the reduct i o n was examined by a comparison of s e v e r a l d i f f e r e n t portions of I l l i n o i s No. 2 c o a l . Very comparable r e s u l t s were obtained for the whole c o a l , the demineralized whole c o a l , the v i t r i n i t e and the demineralized v i t r i n i t e . These observations imply that the démineraiization procedures used f o r the preparation of the macérais do not a l t e r t h e i r r e a c t i v i t y as reducing agents import a n t l y . These observations c o n t r a s t with the r e s u l t s obtained i n the study of the exchange r e a c t i o n s . The d i f f e r e n c e appears to be r e l a t e d to the degree to which these r e a c t i o n s are i n fluenced by s u l f u r - c o n t a i n i n g molecules. This i n t e r p r e t a t i o n i s supported by the f a c t that the r e a c t i o n of fluorenone with T e t r a l i n at 400°C i s accelerated only modestly by the a d d i t i o n of benz y l phenyl s u l f i d e . In c o n t r a s t , the exchange r e a c t i o n i s greatly accelerated by the a d d i t i o n of t h i s substance (2^). For example, T e t r a l i n (0.038 mmole) converts 4 7 o of fluorenone (0.025 mmole) to f l u o r e n e . The a d d i t i o n of benzyl phenyl s u l f i d e (6mg) to T e t r a l i n and fluorenone increases the conversion to 1 2 7 o whereas the a d d i t i o n of I l l i n o i s No. 6 coal (6mg) increases the conversion to 607>. The macérais of the PSOC-828 coal r e a c t at s i m i l a r rates during the i n i t i a l stages of the reduction r e a c t i o n , Figure 1 . These r e s u l t s suggest that a l l the maceral concentrates obtained from t h i s c o a l contain compounds that can r e a d i l y t r a n s f e r hydrogen to fluorenone and undergo aromatization, but that these react i v e substances are present i n d i f f e r e n t q u a n t i t i e s i n the d i f f e r e n t macérais. Although t h i s suggestion must be tested more thoroughly by the examination of the macérais i s o l a t e d from other c o a l s , the observation suggests that there may be important syne r g i s t i c i n t e r a c t i o n s between the components of s e v e r a l macérais i n some r e a c t i o n s . The d i f f e r e n c e s i n the r e a c t i v i t i e s of the macérais become more apparent i n the 30-60 minute r e a c t i o n s . The behavior of the macérais and the reference compounds are compared i n Table VIII· The r e a c t i v i t y p a t t e r n — s p o r i n i t e s > v i t r i n i t e s > a l g i n i t e > s e m i f u s i n i t e s > f u s i n i t e > r e s i n i t e — e s t a b l i s h e d f o r the macérais i n t h i s r e a c t i o n i l l u s t r a t e s the very great d i f f e r e n c e s i n the r e a c t i v i t i e s of the c o a l molecules derived from d i f f e r e n t kinds of n a t u r a l products. However, the s p o r i n i t e s , v i t r i n i t e s , and s e m i f u s i n i t e s i s o l a t e d from s e v e r a l d i f f e r e n t bituminous coals e x h i b i t s i m i l a r behavior. The r e a c t i o n s h i p between the r e a c t i v i ty of the macérais and t h e i r atomic H/C r a t i o i s shown i n Figure 2. The p a t t e r n of r e a c t i v i t y suggests that there i s a b e l l shaped r e l a t i o n s h i p between the e f f e c t i v e n e s s of the maceral as a reducing agent and i t s H/C r a t i o . Such a r e l a t i o n s h i p i s p l a u s i b l e



COAL M A C E R A L S

Figure 1. The extent of conversion of fluorenone to fluorene by the e x i n i t e ( c i r c l e s ) , v i t r i n i t e (squares), and i n e r t i n i t e ( t r i a n g l e s ) macérais i s o l a t e d from PSOC828.

100 80 Sporinites

60 ο

Vitrinites ι

ο ο

40

#

\

20 0 0

Fusinite

Alginite

Semi-Fusinites

• •

• Resinite

_L

0.5

1.0

1.5

Atomic H/C Ratio Figure 2. The r e l a t i o n s h i p between the conversion of fluorenone t o fluorene and the atomic H/C r a t i o f o r the macérais examined i n t h i s study.


10. CHOI AND STOCK

Table V I I I .

Hydrogen Atom Transfer

The Reduction of Fluorenone by Macérais and Represent a t i v e Hydrocarbons at 400°C i n 60 Minutes

Maceral or reference compound


173

Reactions

Conversion of fluorenone (%)

S p o r i n i t e - r i c h e x i n i t e (PSOC-1103)

87

S p o r i n i t e - r i c h e x i n i t e , (p

= 1.176, PSOC-106)

67

S p o r i n i t e - r i c h e x i n i t e , (p = 1.210, PSOC-106)

67

S p o r i n i t e - r i c h e x i n i t e (PSOC-828)

61

Vitrinite

(PSOC-1103

50

Vitrinite

(PSOC-828)

47

Vitrinite

(p" = 1.291, PSOC-106)

46

Vitrinite

(111. No. 2)

42

A l g i n i t e (PSOC-297) Vitrinite

(p

41

= 1.330, PSOC-106)

38

S e m i f u s i n i t e - r i c h i n e r t i n i t e (PSOC-828)

30

S e m i f u s i n i t e - r i c h i n e r t i n i t e (PSOC-1103)

29

1,2,3,4-Tetrahydroquinoline

28

S e m i f u s i n i t e - r i c h i n e r t i n i t e (p

= 1.371, PSOC-106)

F u s i n i t e (111. No. 2) S e m i f u s i n i t e - r i c h i n e r t i n i t e (p

25 19

= 1.447, PSOC-106)

16

R e s i n i t e (Hiawatha)

15

5,12-Dihydrotetracene

14

9,10-Dihydroanthracene

14

1,2,3,4,5,6,7,8-0ctahydroanthracene

6

9,10-Dihydrophenanthrene

5

Tetralin

3

Decalin

Aspects of the Hydrogen Atom Transfer Reactions of Macerals - ACS

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