6 Oxidation of Coal by Alkaline Sodium Hypochlorite SUJIT K. CHAKRABARTTY Downloaded by NORTH CAROLINA STATE UNIV on May 3, 2015 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0071.ch006
Fuel Sciences Division, Alberta Research Council, Edmonton, Alberta, Canada
The use of halogens in alkaline solution to effect the oxidation of ketones (1) and of hypochlorite as a bleaching agent are well-known, but the application of alkaline sodium hypochlorite to oxidize coal has only been recently reported. The close proximity of the standard potentials of halogens in various oxidation states and the ease of disproportionation into species with varying degrees of oxidizing power are responsible for rendering aqueous halogen solutions versatile oxidants (2). For this reason, various mechanisms can be encountered in the course of any reaction between a substrate and a halogen in aqueous media. With sodium hypochlorite (at pH above 10, 99 per cent of the available active oxidant is OCl ), the reaction rates depend on several variables, e.g. concentration of the oxidant, pH, buffer-constituents, ionic strength, temperature, presence of catalyst, etc. Under defined reaction conditions, the hypochlorite anion can perform very selective oxidations; the haloform reactions, the oxidation of enolizable ketones to carboxylic acids, the oxidation of active methine, methylene and methyl groups to ketone or carboxyl functions, the replacement of active hydrogen by halogen, decarboxylation and decarbonyl at ion are some of the well-studied reactions used in preparative organic synthesis (lc,2). Since coal contains a fair amount of labile hydrogens, hypochlorite is expected to initiate at least one of these reactions. The cleavage of aromatic rings by hypochlorite anion is a pertinent question f o r coal-oxidation studies. In t h e p r e s e n c e o f a c a t a l y s t , p a r t i c u l a r l y ( 3 ) , R u 0 , 0 s 0 , RhCl and I r C l , sodium h y p o c h l o r i t e d e g r a d e s benzene r i n g s ; 3 - p h e n y l p r o p i o n i c a c i d i s o x i d i z e d t o s u c c i n i c a c i d (94 p e r c e n t y i e l d ) ; p h e n y l c y c l o h e x a n e c a n be o x i d i z e d t o c y c l o h e x a n e c a r b o x y l i c a c i d (25 p e r c e n t ) . W i t h o u t c a t a l y s t , p h e n o l s and n a p h t h o l s (4) a r e known t o r e a c t w i t h s o d i u m h y p o c h l o r i t e a t m o d e r a t e t e m p e r a ture. The r e a c t i o n o f p i c r i c a c i d w i t h h y p o h a l i t e t o g i v e h a l o p i c r i n (5) i s a n o t h e r r e m a r k a b l e r e a c t i o n t h a t r e s u l t s i n t h e c o m p l e t e f r a g m e n t a t i o n o f a benzene r i n g i n t o s i x s i n g l e c a r b o n -
4
4
0-8412-0427-6/78/47-071-100$05.00/0 © 1978 American Chemical Society In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.
3
6.
CHAKRABARTTY
Oxidation
by Alkaline
Sodium
Hypochlorite
u n i t s under v e r y m i l d c o n d i t i o n s . In a l l t h e s e c l e a v a g e r e a c t i o n s , i n i t i a l l y an e x t e n s i v e h a l o g e n a t i o n o f t h e benzene r i n g occurs u n t i l the a r o m a t i c resonance s t a b i l i z a t i o n i s s u f f i c i e n t l y weakened. Low pH c o n d i t i o n s f a v o u r h a l o g e n a t i o n and addition of hypohalite acid. L a n d o l t and c o - w o r k e r s (6) u n d e r t o o k o x i d a t i o n o f a r o m a t i c compounds a t c o n s t a n t pH. I η h t o 6 h o u r s i n a n i t r o g e n atmo s p h e r e , n a p h t h a l e n e , w i t h an e x c e s s o f sodium h y p o c h l o r i t e a t 6 0 - 7 0 C was o x i d i z e d a t pH 8.5~9 t o p h t h a l i c a c i d (70 p e r c e n t ) . A t pH above 11, t h e y i e l d o f c l e a v a g e p r o d u c t s d e c r e a s e s c o n s i d e r a b l y and u n o x i d i z e d n a p h t h a l e n e a l o n g w i t h some c h l o r i n a t e d p r o d u c t s were r e c o v e r e d . A l t h o u g h 2-methy1 n a p h t h a 1ene r e a c t e d s i m i l a r l y t o n a p h t h a l e n e a t pH 8.5-9, 1 - n i t r o - 2 - m e t h y 1 n a p h t h a l e n e r e a c t e d t o g i v e o n l y 10 p e r c e n t y i e l d o f 3 ~ n i t r o - 4 m e t h y 1 p h t h a l i c a c i d and 80 p e r c e n t r e c o v e r y o f s t a r t i n g com pounds. P h e n a n t h r e n e was f o u n d t o be l e s s r e a c t i v e t h a n n a p h t h a l e n e , and a n t h r a c e n e was i n e r t . The o x i d a t i o n o f methy1-3-naphthy1 k e t o n e w i t h sodium hypo c h l o r i t e a t pH above 10 g i v e s 88 p e r c e n t y i e l d o f 2 - n a p h t h o i c a c i d ("7). But f u r t h e r t r e a t m e n t o f 2 - n a p h t h o i c o r 2 , 3 - n a p t h a l e n e d i c a r b o x y l i c a c i d w i t h e x c e s s sodium h y p o c h l o r i t e ( p r e sumably a t pH l o w e r t h a n 10) r e s u l t e d i n c l e a v a g e o f an aroma t i c r i n g ; p h t h a l i c , t r i m e l l i t i c a n d / o r p y r o m e l l i t i c a c i d s were o b t a i n e d as c l e a v a g e p r o d u c t s (k). From t h i s d i s c u s s i o n i t i s q u i t e e v i d e n t t h a t sodium hypo c h l o r i t e i s a v e r s a t i l e o x i d a n t . The d e g r e e o f s e l e c t i v i t y f o r t h i s o x i d a n t w o u l d depend on how p r e c i s e l y t h e r e a c t i o n c o n d i tions are controlled. F o l l o w i n g t h e p r o c e d u r e d e v e l o p e d by Newman and Holms (7) f o r s y n t h e s i s o f 2 - n a p h t h o i c a c i d f r o m m e t h y 1 - 2 - n a p h t h y l k e t o n e , s e v e r a l c o a l samples w e r e t r e a t e d w i t h h y p o c h l o r i t e a n i o n by C h a k r a b a r t t y and c o - w o r k e r s (8). Three moles o f O C l " were used f o r each gram-atom o f c a r b o n i n c o a l . I t was o b s e r v e d t h a t s u b b i t u m i n o u s c o a l s w o u l d r e a d i l y r e a c t under t h i s c o n d i t i o n b u t b i t u m i n o u s c o a l s w i t h d r y , a s h - f r e e c a r b o n g r e a t e r t h a n 82 p e r c e n t r e q u i r e d p r e v i o u s r e a c t i o n w i t h n i t r o n i u m t e t r a f 1 u o r o b o r a t e i n acetonîtrîle s o l v e n t . The s u b b i t u m i n o u s c o a l s and d e r i v a t i z e d b i t u m i n o u s c o a l s r e a c t e d e q u a l l y w e l l w i t h h y p o c h l o r i t e and gave w a t e r s o l u b l e p r o d u c t s ( s t r u c t u r a l l y f a r l e s s c o m p l e x t h a n s o - c a l l e d humic a c i d ) a t 40-60° i n 2-3 h o u r s and a t 20-28° i n 2-3 d a y s . The p r o d u c t s o f o x i d a t i o n were c a r b o n d i o x i d e and c a r b o x y l i c a c i d s . Table 1 l i s t s t h e y i e l d s from d i f f e r e n t c o a l s r e a c t e d a t 60° w i t h i n i t i a l pH = 12. The w a t e r - s o l u b l e p r o d u c t s were i s o l a t e d , w e r e m e t h y l a t e d w i t h d i a z o m e t h a n e , and were a n a l y z e d by g e l p e r m e a t i o n chromat o g r a p h y (GPC), g a s c h r o m a t o g r a p h y ( G L C ) , mass s p e c t r o m e t r y (MS), and 1 M and 13Q nmr a n a l y s i s . Acetic, propionic, succinic, g l u t a r i c , a d i p i c , benzene- and t o l u e n e - ( w i t h 2 t o 6 c a r b o x y l as w e l l a s w i t h some n i t r o g r o u p s ) c a r b o x y l i c a c i d s were i s o l a t e d and i d e n t i f i e d . The a v e r a g e m o l e c u l a r w e i g h t o f t h e e
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101
In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.
102
ORGANIC CHEMISTRY OF COAL
more c o m p l e x p r o d u c t s h a v i n g p o l y c o n d e n s e d a r o m a t i c a n d / o r h e t e r o a r o m a t i c ( m o s t l y s u b s t i t u t e d by numbers o f c a r b o x y l g r o u p s ) , were between 600 and 800. More t h a n 90 p e r c e n t o f c a r b o n i n c o a l c o u l d be a c c o u n t e d f o r f r o m t h i s p r o d u c t a n a l ysis. TABLE I . Y i e l d
of oxidation
p r o d u c t s from d i f f e r e n t c o a l s
Carbon D i o x i d e
Carboxylic Acids a s COOH-Group
Rank
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%Z,dmf.
76.1 80.5 83.1 85.0 86.4 90.2
mmole/gCarbon
43.2 43.4 40.3 38.3
38.1 34.5
%Zoa\-
Carbon
51.8 52.1
48.4 46.0 45.7 41.4
meq/gCarbon
13.6 14.6 16.4 14.1 21.3 14.0
% CoalCarbon
16.3 17.5 19.7 17.0 25.6
16.8
With the help o f nmr measurement, m o l e c u l a r w e i g h t d a t a , and e l e m e n t a l a n a l y s i s , i t was p o s s i b l e t o c a l c u l a t e t h e r e c o v e r y o f c a r b o n i n d i f f e r e n t c a r b o n f u n c t i o n a l g r o u p s (9). For a t y p i c a l b i t u m i n o u s c o a l ( d . a . f . C - 88%), 18 p e r c e n t o f t o t a l c a r b o n s u r v i v e s o x i d a t i o n as a s i n g l e b e n z e n e r i n g , 6 p e r c e n t a s 2, 3 o r 4 c o n d e n s e d a r o m a t i c ( a n d / o r h e t e r o a r o m a t i c ) r i n g s , 7 per c e n t a s m e t h y l o r m e t h y l e n e and 20 p e r c e n t a s c a r b o x y l groups (Table I I ) . From v a r i o u s r e a c t i o n s some k e t o n e s and e t h e r s a l s o were o b s e r v e d o c c a s i o n a l l y as p r o d u c t s . The most r e v e a l i n g d a t a of t h e s e s t u d i e s a r e t h a t , i r r e s p e c t i v e o f t h e rank o f t h e c o a l , a p p r o x i m a t e l y two t h i r d s o f t h e t o t a l c a r b o n i s o x i d i z e d t o c a r b o n d i o x i d e and c a r b o x y l f u n c t i o n s . I t i s p e r t i n e n t t o know the n a t u r e o f c a r b o n f u n c t i o n a l g r o u p s i n c o a l t h a t u n d e r g o t h i s o x i d a t i o n so r e a d i l y . Mayo and K i r s h e n (10) s t u d i e d t h e o x i d a t i o n o f t h e p y r i d i n e i n s o l u b l e r e s i d u e f r o m I l l i n o i s No. 6 c o a l w i t h t h e o b j e c t i v e o f a t t a i n i n g maximum y i e l d s o f s o l u b l e p r o d u c t w i t h minimum c o n s u m p t i o n o f o x i d a n t and minimum l o s s o f c a r b o n a s c a r b o n d i o x ide. B e c a u s e t h e u n r e a c t e d c o a l and t h e s o l u b l e a c i d s compete for the o x i d a n t , repeated o x i d a t i o n s w i t h small p r o p o r t i o n o f NaOCl were employed w i t h e x t r a c t i o n s and s e p a r a t i o n s o f s o l u b l e a c i d s between s t e p s . In one e x p e r i m e n t 80 p e r c e n t o f t h e o r i g i n a l c a r b o n was a c c o u n t e d f o r a s f o l l o w s : 13.6 p e r c e n t i n u n d i s s o l v e d r e s i d u e , 59.4 p e r c e n t i n c o l o u r e d a c i d s s o l u b l e i n aqueous b i c a r b o n a t e , 7.1 p e r c e n t i n l i g h t e r c o l o u r e d a c i d r e a d i l y s o l u b l e i n w a t e r and 19.9 p e r c e n t i n c a r b o n d i o x i d e . The c o l o u r e d a c i d s had a number a v e r a g e m o l e c u l a r w e i g h t o f a b o u t 900 and a n e u t r a l e q u i v a l e n c e o f 352. The w a t e r s o l u b l e
In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.
6. CHAKRABARTTY
TABLE
II.
Oxidation
Percentage soluble
by Alkaline
Sodium
o f coal-carbons
products,
computed
recovered from
103
Hypochlorite
as
water-
nmr and combustion
data C
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Product-Fraction
#1
mono-nuclear
#2
mono-nuclear
#3
polynuclear*
#4
polynuclear*
#5
polynuclear
Fr
Hoi Wt 623
0
Mol
Wt
23.7
s k e l e t a l
4 a r e as
s t r u c t u r a l
C
types
o f
total
a l k y l
4.2 2.1
8.4 4.9 0.8 2.4 3.9 20.4
12.0 5.8 0.8 3.1 2.9
Total Probable
ç ^carboxyl
arom
24.6 12.8 1.6 5.5 5.9 50.4
trace trace
0.6 6.9
t h e compounds
i n F r 3 and
f o l lows :
< ll.7 2.5°2.5 0.7 0.1 c
H
M
S
(
)
C 0 0 M e
)
7
( M e )
0
770
< l*W ™eV™ 4 C
(C
H)
Wl.8 O.I2 S
In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.
ORGANIC CHEMISTRY OF COAL
104
acids The
h a d M.W. a b o u t
structural
Chakrabartty
and Dorn
hypochlorite
oxidation
Until
a
intermediate is
with
oxidation
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ring
on
of
products and
products
isolated
i t
is
coal.
certain
parts
of
cation
carbanion-type
But
carboxylic carbon.
tinent
to
rings rings,
major
reaction, in
is
l a r l y , same may
the
further
fact
that
react
rings
presumed arises
that
the
functional
premise,
groups.
loss
sary
a c t i v a t i n g
a c i d i t y a
are
is
si tes
in
Though ing
agent
cated
that
was
the which
(3)
acid.
How-
from
the
oxidation
deactivate
and
aroma-
ring-cleavage
Thus
i t may be
a f t e r
n i t r a t i o n
ring-cleavage
and co-workers hypochlorite
a c i d i c
is
the decrease
more
with
protons.
probably
(?)
as
been
becomes
a c i d i c
the elemental
H/C
r a t i o ,
postulated
a
(8(d))
once
and the progres-
the
neces-
incorporated,
on a
composition
bridged
the
The
secondary of
coal,
oxygen
content
reactive.
than
the
increases,
However,
would
low-rank
from
in oxygen
occurs.
suggested
oxidation In
arises
t h e rank
e . g . -N02, has
proton or
prim-
coal,
tricycloa1kane
t o accommodate
the
BrOnsted
coal.
nitronium
tetraf1uoroborate
(11), r e c e n t this
carbon
a c i d i t y
the atomic
configuration
of
and the coal
carbon Keeping
p a r t i c u l a r l y
acid,
follow
acid
hypohalite
coals
the
Simi-
1).
arises
groups
is
s i g n i f i -
m e l l i t i c
(Figure
and aromatic
towards
weight
group,
restored
carbon.
aro-
become
to m e l l i t i c
bituminous
Chakrabartty
With
BrOnsted
t e r t i a r y
acid
of
coal
on
in molecular
sive
on
of
a c i d i t y
of
data
(2) s h o u l d
to
of
the coal,
and suppresses
structures
the a c c e s s i b i l i t y
BrBnsted
in
reaction.
this
on
peraro-
complex
Nitro
attack
is
a l i the
more
mechanism
inert
of of
the surviving
and co-workers(6)).
the a c t i v i t y
major
increase
are
n i t r a t e d .
non-aromatic
the r e a c t i v i t y
depend
coals
being
this
i t
i n d i -
structure.
part
To produce
system
of
further
the form
may be o x i d i z e d
with
in the
cleavage
oxidation
(4) a n d f i n a l l y
(see, Landolt
From that
a f t e r
from
not a
to
d i f f i c u l t
f o r electrophi1ic
reactions
is
degrade
that
by m i n e r a l s
t h e more
hypochlorite occur-
standpoint,
structure.
coal
to produce
bituminous
only
coal in
how
reaction
minor on
the
oxidation
Isolation
in
very
one assumes
polycondensed
path
the major
If
1
of
of
non-aromatic
function
hypochlorite
(l)
largest
oxidation
ever,
t i c
then
like
a
in
groups
provides
and the carbon
catalyzed
understanding
structure
on
constitute
formed.
analysis
formulate
polymer.
reactions
groups
stages
c h l o r o - a l k y l
acids
completed.
measurement.
structural
the structural
probably
c h l o r o - a l k y l C-nmr
to
chlorine.
y e t t o be
Haloform-type
how t h e c a r b o x y l
matic
cant
1
the coal
carbon
acids
From
know
matic
a
a
is
the early
of
and d i c a r b o x y l i c
the chloroalkyl
total
at
d i f f i c u l t
suggests
mono-
1 3
r e l i a b l e
quite
a l i p h a t i c
phatic
by
The presence
products
of
i d e n t i f i e d
(9)
per cent
10-15
the products
d e t a i l e d
a v a i l a b l e ,
reacts
and contained
200
analysis
reagent
s i l y l - d e r i v a t i v e s
of
work
by
G. A.
can o x i d i z e
secondary
is
Olah
a well-known et
benzylic
alcohols
to
a l
n i t r a t -
(12) h a v e
alcohols
carbonyl
indi-
and compounds.
In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.
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CHAKRABARTTY
Oxidation
Figure 1.
by Alkaline
[·_•
COOH
Sodium
and/or
Hypochlorite
-CZ/-OH]
In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.
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106
ORGANIC CHEMISTRY OF COAL
The nitrolysis of alkanes, as well as cleavage of ethers could be affected by this reagent very smoothly. Consequently, the reaction of coal with this reagent may introduce, in addition to nitro group, various other oxygen functional groups such as ketone, aldehyde and alcohol. (The total acetylable groups determined after nitration was found to increase considerably.) From this background, it can also be argued that the mechanism of hypochlorite oxidation of coal, after being treated with nitronium tetraf1uoroborate, may be similar to phenol oxidation, and a substantial amount of carbon dioxide is generated from cleavage of aromatic rings. The oxidation studies with hypohalite have been reported on whole coals and few hand-picked vitra in samples. The difference in reactivity between macérais have yet to be studied. Reaction in non-aqueous media can enlarge the scope of applicability of this reagent, e.g. selective oxidation of heterocyclic components by two-phase reactions. All coals are very susceptible to halogenation. With hypohalite, under both high and low pH conditions, halogenation of the substrate is a primary reaction. Consequently, halogenation of coal vis-a-vis hypohalite oxidation would be a useful topic for structural studies. Literature Cited: 1.
2. 3. 4.
5. 6. 7. 8.
a. Fuson, R. C. and Bull, Β. Α., Chem Rev 15, 275 (1934) b. Holst, G., Chem Rev 5 4 , 169 (1954) c. Fieser, L. F. and Fieser, Μ., Reagents for Organic Synthesis, John Wiley & Sons, New York, Vol 1 (1967), Vol 11 (1969) Chakrabartty, S. Κ., in Oxidation in Organic Chemistry, Part D., Chapter 5 , Ed. W. S. Trahanovsky, Academic Press, New York (1978) Wolf, S., Hasan, S. K. and Campbell, J . R., J. Chem. Soc. D ( 2 1 ) , 1420 (1970) a. Moye, C. J. and Sternell, S., Austral. J . Chem., 19, 2107 (1970) b. Landolt, R. C., Fuel 5 4 , 229 (1975) c. Mayo, F. R., i b i d . , 273 (1975) Birch, A. J., Moye, C. J., Richards, R. W. and Vanek, Z., J . Chem. Soc. 3586 (1962) Angert, J . L . , Gatton, S. L . , Reilly, M. T. and Landolt, R. G., Fuel 5 6 , 224 (1975) Newman, M. S. and Holms, H. L., in Org. Syn. C o l l . Vol. 2 , 428 (A. H. Blatt, Ed.) Wiley, New York (1943) Chakrabartty, S. K. and Kretschmer, H. O. a. J . Chem. Soc. Perkin 1, 222 (1974) b. Fuel 51, 160 (1972) c. ibid, 5 3 , 132 (1974)
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Downloaded by NORTH CAROLINA STATE UNIV on May 3, 2015 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0071.ch006
9. 10.
11. 12.
CHAKRABARTTY
Oxidation
by Alkaline
Sodium
Hypochlorite
Chakrabartty, S. K. and Berkowitz, N. d. ibid., 5 3 , 240 (1974) e. ibid., 55, 362 (1976) f. Nature, 261 ( 5 5 5 5 ) , 76 (1976) Chakrabartty, S. K. and Dorn, H., to be published Mayo, F. R., Huntington, T. and Kirshen, N. Paper No. 1 4 , Preprints 1976 Coal Chemistry Workshop Standford Research Institue Mayo, F. R. and Kirshen, N., in Quatarly Reports on "Homogenous Catalytic Hydrocracking Process for Conversion of Coal to Liquid Fuels, Basic and Exploratory Research". US Energy Research and Development Administration Contract No. Ε ( 4 9 - 1 8 ) - 2 2 0 2 for periods ending on (a) Jan. 1976; (b) April 1976; (c) July 1976; (d) October 1976; (e) January 1977 and (f) April 1977 Fieser, L. F. and Fieser, M., Reagent for Organic Synthesis, Vol I, John Wiley & Sons, Inc., 1967 a. Olah, G. A. and Ho T-L, Synthesis 609 (1976) b. Olah, G. A. and Ho T-L, Synthesis (Press) c. Olah, G. A. and Lin, H. C., J . Amer. Chem. Soc. 93, 1259 (1971) d. Olah, G. A. and Ho T-L, J . Org. Chem. 42 (18), 3097 (1977)
RECEIVED
February
10,
1978
In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.
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