Organic Chemistry of Coal - American Chemical Society

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


%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


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


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



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


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.



CHAKRABARTTY

Oxidation

Figure 1.

by Alkaline

[·_•

COOH

Sodium

and/or

Hypochlorite

-CZ/-OH]



106


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)


6.

8.


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


107

Organic Chemistry of Coal - American Chemical Society

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