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Organic bromine as a source of electrophilic bromine in aqueous chlorination reactions
Chemosphere, Vol.17, No.7, pp 1337-1342, Printed in Great Britain
1988
0045-6535/88 $3.00 + .00 Pergamon Press plc
ORGANIC BROMINE AS A SOURCE OF ELECTROPHILIC BROMINE IN AQUEOUS CHLORINATION REACTIONS Su-Ching
Hwang I, Richard A. Larson *,1,2, and Vernon L. Snoeyink I
Department o f Civil Engineering I and Institute for Environmental Studies 2 University
of Illinois
at Urbana-Champaign
Urbana, IL 61801 Aqueous HOCI displaces p - b r o m o substituents from phenol and aniline electrophilic species capable of brominating some aromatic compounds.
nuclei
to
produce
an
Introduction Aqueous
chlorine has
been
widely
used
as a disinfectant
in water treatment
plants.
Its usual
reactant behavior with organic carbon and with amino nitrogen is as an electrophilic agent (I). bromide ion is present,
chlorine also oxidizes the bromide rapidly to form hypobromous acid (1,2). an electrophilic agent, but reacts much more rapidly than HOCI (I), organobromine organic
compounds,
reaction
bromophenol,
to
of
subsequent
bromination
Materials
and
Chlorine
such
aqueous
form
If
as it is in some freshwaters, brackish waters, and sea water, the added
as
chlorine
bromine-containing
is
trihalomethanes
with bromine-containing compounds,
dibromocompounds.
A
reaction
mechanism
The HOBr formed is also
resulting in the formation of (3).
We
report
p-bromoaniline
involving
an
and p -
debromination
and
postulated.
Methods
Solution
- Chlorine solution was prepared by bubbling high purity chlorine gas (Linde
Specialty Gas, Union Carbide, New York, NY) into weakly alkaline (NaOH) distilled-deionized water and buffered to the required pH with I x 10 -3 M phosphate salts. Procedur~
- To 10 L of chlorine solution (1.4 x 10.4 M ) buffered at pH 8.0, 15 mL of methanol
solution containing p-bromophenol
(Aldrich Chemical Company, Inc.) or p - b r o m o a n i l i n e
(Eastman
* Address correspondence to this author at Institute for Environmental Studies, 1005 Western Ave. , Urbana, IL 61801.
1337
1338
Kodak Co.) was added so that the mole ratio of chlorine to organic compound was 1.5 : 1.
After 10 min
reaction time, the excess chlorine was destroyed with sodium sulfite (Fisher Scientific Company). The chlorine-bromophenol reaction mixture was acidified to pH 3.0 with H 2 S O 4. The reaction mixtures were then passed over XAD-2 resins (Rohm and Haas) previously cleaned by sequential 8 hour Soxhlet extractions with ether, eluted
with
sulfate
methanol-methylene
(Mallinckrodt,
concentrator
equipped
Inc.) with
acetonitrile, and methanol.
chloride.
and
The
organic
concentrated
a Snyder
to
column.
After adsorption,
extracts
1.5
mL
Further
were
in
a
dried
the resins were
over
baked
Kuderna-Danish
concentration
was
done
sodium
evaporator
by
directing
a
stream of high purity nitrogen above the extract. Product
A n a l y s i s - T w o p.L of the concentrate was injected into a DB-1 30 m fused silica capillary
column (Hewlett-Packard 5985A GC/MS system). min hold to 240 °C at 4 °C/min.
The column was programmed from 40 °C with a 5-
Compounds were identified by comparing their mass spectra with
those in standard reference collections (4,5), those from reference compounds of known structures, or by comparison or extrapolation from literature data. Results 1.
and
Discussion
Reaction of aqueous chlorine with p - b r o m o a n i l i n e
Compounds
identified
by
GC/MS
from
the
chlorine-p-bromoaniline reaction are listed in Table 1.
The total ion current chromatogram is shown in Figure 1. products,
mono-
bromoaniline 3 and 4).
to
and give
dichlorinated bromoanilines (compounds bromination
products,
dibromoaniline
In addition to the expected chlorination 1 and 2), and
chlorine
reacted
dibromochloroaniline
with p-
(compounds
The result indicates that bromination of the aromatic ring took place in the course of the
chlorination reaction with p-bromoaniline.
We postulate that HOCI reacts with p - b r o m o a n i l i n e
form an intermediate that releases HOBr, which then attacks another p - b r o m o a n i l i n e
molecule
to to
give a dibrominated compound. 2.
Reaction of aqueous chlorine with p - b r o m o p h e n o l
The experiment on p-bromophenol was carried out in the same way as p-bromoaniline. shows the reaction products of chlorine with p-bromophenoi. is shown in Figure 2. reaction.
The
Table 2
total ion current chromatogram
The product distribution was similar to that of the c h l o r i n e - p - b r o m o a n i l i n e
In addition to four major products (compounds 7, 8, 9, and 10), traces of debrominated
compounds, chlorophenol and dichlorophenol (compounds 5 and 6), were detected. 3.
Reaction mechanism for the formation of dibromocompounds
The proposed mechanism is composed of two electrophilic substitution reactions, as shown in Figure 3.
In the first step, the Br at the p - p o s i t i o n
of
the
organic
electrophilic CI of HOCI to form HOBr and chlorocompounds.
compound
is
displaced
by
the
A similar ipso substitution, with loss of
1339
C O 2, has phenolic
been proposed
acids
(6).
to account
The
for the formation
production
of
chlorophenols
experiments is consistent with this mechanism. H
from
another
chlorination
brominated
of water
or
molecule
wastewater
to
of chlorophenols from
The resulting
give
p-bromophenol
certain
in
the
organobromine
Our
results
compounds
No.
HOCl-p-bromoaniline
1.
Compounds
M+(in MS)
reaction products
Relative
Concentration
1
Bromochloroaniline
205
100.0
2
Bromodichloroaniline
239
2.2
3
Dibromoaniline
249
2.1
4
Dibromochloroaniline
283
1.2
Table
No.
2.
HOCI-p-bromophenol
Compounds
M+(in MS)
present
suggest may
the formation of new brominated substances, even in the absence of bromide ion.
Table
of
electrophile, HOBr, then displaces a
a dibromocompound.
containing
in the chlorination
reaction
products
Relative
Concentration
5
Dichlorophenol
162
0.2
6
Chlorophenol
128
0.1
7
Bromochlorophenol
206
100.0
8
Dibromophenol
250
0.8
9
Bromodichlor, ophenol
240
41.5
10
Dibromochlorophenol
284
1.0
result
that in
Figure
1.
ion
Numbered
Total peaks
are
eurre11[
S. M.
2
identified
['rOllt in Table
cllroluatograul
ii
1.
the
(S.
M.
reactiou
with material)
chloriue = starting
of
i)-brolu~auil[ue.
F~ t~ ¢= 0
.
Figure
i .
.
.
.
ion
.
Numbered
2. Total
.
.
curren~
.
.
.
.
,,.._ .
chromatogram
.
I,I.
.
.
from
Io .
.
the
peaks ~re identified in Table 2.
.
7
.
.
(S. M.
.
of
chlorine
-
xvith p-hromophenol. = starting material)
reaction
.
d~ pa
p.J
1342
Figure
3.
Reaction
mechanism
for
the
formation
of
HO" ! HOC!
dibromocompounds
CI
~
"1"
HOBr
RH Br
0
Br -Br
RH
RH * R=NH
or O
References
1. Morris,J. C.
In Water Chlorination: Environmental Impact and Health Effects, vol. 1, R. L. Jolley,
ed., Ann Arbor Science Publishers, New York, p. 21 (1978). 2. Jolley, R. L., and J. H. Carpenter.
In Water Chlorination: Environmental Impact and Health
Effects, vol. 4, R. L. Jolley at el., eds., Ann Arbor Science Publishers, New York, p. 3 (1983). 3. Stevens, A. A., C. J. Slocum, D. R. Seeger, and G. G. Robeck.
J. Amer. Water Works Assoc., 68. 615
(1976). 4. Eight Peak Index of Mass Spectra. 5. Registry of Mass Spectral Data.
Mass Spectrometry Data Centre, AWRE Reading, U. K. (1983). E. Stenhagen, S. Abrahamson, F. W. McLafferty, eds., John Wiley,
New York (1974). 6. Larson, R. A., and A. L. Rockwell. Environ. Sci. Technol., 13, 325 (1979).
(Received in USA 5 April 1988; accepted 13 May 1988)
1988
0045-6535/88 $3.00 + .00 Pergamon Press plc
ORGANIC BROMINE AS A SOURCE OF ELECTROPHILIC BROMINE IN AQUEOUS CHLORINATION REACTIONS Su-Ching
Hwang I, Richard A. Larson *,1,2, and Vernon L. Snoeyink I
Department o f Civil Engineering I and Institute for Environmental Studies 2 University
of Illinois
at Urbana-Champaign
Urbana, IL 61801 Aqueous HOCI displaces p - b r o m o substituents from phenol and aniline electrophilic species capable of brominating some aromatic compounds.
nuclei
to
produce
an
Introduction Aqueous
chlorine has
been
widely
used
as a disinfectant
in water treatment
plants.
Its usual
reactant behavior with organic carbon and with amino nitrogen is as an electrophilic agent (I). bromide ion is present,
chlorine also oxidizes the bromide rapidly to form hypobromous acid (1,2). an electrophilic agent, but reacts much more rapidly than HOCI (I), organobromine organic
compounds,
reaction
bromophenol,
to
of
subsequent
bromination
Materials
and
Chlorine
such
aqueous
form
If
as it is in some freshwaters, brackish waters, and sea water, the added
as
chlorine
bromine-containing
is
trihalomethanes
with bromine-containing compounds,
dibromocompounds.
A
reaction
mechanism
The HOBr formed is also
resulting in the formation of (3).
We
report
p-bromoaniline
involving
an
and p -
debromination
and
postulated.
Methods
Solution
- Chlorine solution was prepared by bubbling high purity chlorine gas (Linde
Specialty Gas, Union Carbide, New York, NY) into weakly alkaline (NaOH) distilled-deionized water and buffered to the required pH with I x 10 -3 M phosphate salts. Procedur~
- To 10 L of chlorine solution (1.4 x 10.4 M ) buffered at pH 8.0, 15 mL of methanol
solution containing p-bromophenol
(Aldrich Chemical Company, Inc.) or p - b r o m o a n i l i n e
(Eastman
* Address correspondence to this author at Institute for Environmental Studies, 1005 Western Ave. , Urbana, IL 61801.
1337
1338
Kodak Co.) was added so that the mole ratio of chlorine to organic compound was 1.5 : 1.
After 10 min
reaction time, the excess chlorine was destroyed with sodium sulfite (Fisher Scientific Company). The chlorine-bromophenol reaction mixture was acidified to pH 3.0 with H 2 S O 4. The reaction mixtures were then passed over XAD-2 resins (Rohm and Haas) previously cleaned by sequential 8 hour Soxhlet extractions with ether, eluted
with
sulfate
methanol-methylene
(Mallinckrodt,
concentrator
equipped
Inc.) with
acetonitrile, and methanol.
chloride.
and
The
organic
concentrated
a Snyder
to
column.
After adsorption,
extracts
1.5
mL
Further
were
in
a
dried
the resins were
over
baked
Kuderna-Danish
concentration
was
done
sodium
evaporator
by
directing
a
stream of high purity nitrogen above the extract. Product
A n a l y s i s - T w o p.L of the concentrate was injected into a DB-1 30 m fused silica capillary
column (Hewlett-Packard 5985A GC/MS system). min hold to 240 °C at 4 °C/min.
The column was programmed from 40 °C with a 5-
Compounds were identified by comparing their mass spectra with
those in standard reference collections (4,5), those from reference compounds of known structures, or by comparison or extrapolation from literature data. Results 1.
and
Discussion
Reaction of aqueous chlorine with p - b r o m o a n i l i n e
Compounds
identified
by
GC/MS
from
the
chlorine-p-bromoaniline reaction are listed in Table 1.
The total ion current chromatogram is shown in Figure 1. products,
mono-
bromoaniline 3 and 4).
to
and give
dichlorinated bromoanilines (compounds bromination
products,
dibromoaniline
In addition to the expected chlorination 1 and 2), and
chlorine
reacted
dibromochloroaniline
with p-
(compounds
The result indicates that bromination of the aromatic ring took place in the course of the
chlorination reaction with p-bromoaniline.
We postulate that HOCI reacts with p - b r o m o a n i l i n e
form an intermediate that releases HOBr, which then attacks another p - b r o m o a n i l i n e
molecule
to to
give a dibrominated compound. 2.
Reaction of aqueous chlorine with p - b r o m o p h e n o l
The experiment on p-bromophenol was carried out in the same way as p-bromoaniline. shows the reaction products of chlorine with p-bromophenoi. is shown in Figure 2. reaction.
The
Table 2
total ion current chromatogram
The product distribution was similar to that of the c h l o r i n e - p - b r o m o a n i l i n e
In addition to four major products (compounds 7, 8, 9, and 10), traces of debrominated
compounds, chlorophenol and dichlorophenol (compounds 5 and 6), were detected. 3.
Reaction mechanism for the formation of dibromocompounds
The proposed mechanism is composed of two electrophilic substitution reactions, as shown in Figure 3.
In the first step, the Br at the p - p o s i t i o n
of
the
organic
electrophilic CI of HOCI to form HOBr and chlorocompounds.
compound
is
displaced
by
the
A similar ipso substitution, with loss of
1339
C O 2, has phenolic
been proposed
acids
(6).
to account
The
for the formation
production
of
chlorophenols
experiments is consistent with this mechanism. H
from
another
chlorination
brominated
of water
or
molecule
wastewater
to
of chlorophenols from
The resulting
give
p-bromophenol
certain
in
the
organobromine
Our
results
compounds
No.
HOCl-p-bromoaniline
1.
Compounds
M+(in MS)
reaction products
Relative
Concentration
1
Bromochloroaniline
205
100.0
2
Bromodichloroaniline
239
2.2
3
Dibromoaniline
249
2.1
4
Dibromochloroaniline
283
1.2
Table
No.
2.
HOCI-p-bromophenol
Compounds
M+(in MS)
present
suggest may
the formation of new brominated substances, even in the absence of bromide ion.
Table
of
electrophile, HOBr, then displaces a
a dibromocompound.
containing
in the chlorination
reaction
products
Relative
Concentration
5
Dichlorophenol
162
0.2
6
Chlorophenol
128
0.1
7
Bromochlorophenol
206
100.0
8
Dibromophenol
250
0.8
9
Bromodichlor, ophenol
240
41.5
10
Dibromochlorophenol
284
1.0
result
that in
Figure
1.
ion
Numbered
Total peaks
are
eurre11[
S. M.
2
identified
['rOllt in Table
cllroluatograul
ii
1.
the
(S.
M.
reactiou
with material)
chloriue = starting
of
i)-brolu~auil[ue.
F~ t~ ¢= 0
.
Figure
i .
.
.
.
ion
.
Numbered
2. Total
.
.
curren~
.
.
.
.
,,.._ .
chromatogram
.
I,I.
.
.
from
Io .
.
the
peaks ~re identified in Table 2.
.
7
.
.
(S. M.
.
of
chlorine
-
xvith p-hromophenol. = starting material)
reaction
.
d~ pa
p.J
1342
Figure
3.
Reaction
mechanism
for
the
formation
of
HO" ! HOC!
dibromocompounds
CI
~
"1"
HOBr
RH Br
0
Br -Br
RH
RH * R=NH
or O
References
1. Morris,J. C.
In Water Chlorination: Environmental Impact and Health Effects, vol. 1, R. L. Jolley,
ed., Ann Arbor Science Publishers, New York, p. 21 (1978). 2. Jolley, R. L., and J. H. Carpenter.
In Water Chlorination: Environmental Impact and Health
Effects, vol. 4, R. L. Jolley at el., eds., Ann Arbor Science Publishers, New York, p. 3 (1983). 3. Stevens, A. A., C. J. Slocum, D. R. Seeger, and G. G. Robeck.
J. Amer. Water Works Assoc., 68. 615
(1976). 4. Eight Peak Index of Mass Spectra. 5. Registry of Mass Spectral Data.
Mass Spectrometry Data Centre, AWRE Reading, U. K. (1983). E. Stenhagen, S. Abrahamson, F. W. McLafferty, eds., John Wiley,
New York (1974). 6. Larson, R. A., and A. L. Rockwell. Environ. Sci. Technol., 13, 325 (1979).
(Received in USA 5 April 1988; accepted 13 May 1988)