Reactions of resorcinol and its chlorinated derivatives with monochloramine: Identification of intermediates and products

Article abstract of DOI:10.1002/etc.5620181104

An investigation of the reaction of resorcinol (compound 1) and its chlorinated derivatives 4-chlororesorcinol (compound 4), 4,6- dichlororesorcinol (compound 5), and 2,4,6-trichlororesorcinol (compound 2) with monochloramine (NH₂Cl) in ether and aqueous solution (pH 7) is reported. NH₂Cl reacted with compounds 1, 2, 4, and 5 to give the pentachloro intermediate, 2,2,4,4,6-pentachloro-5-cyclohexen-1,3-dione (compound 3), which underwent ring opening with H₂O and loss of CO₂ in the presence of NH₂Cl to produce the following: 1,1,3,5,5-pentachloro-3-penten- 2-one (compound 6), 1,1,1,3,5,5-hexachloro-3-penten-2-one (compound 7), and 1,1,3,5,5,5-hexachloro-3-penten-2-one (compound 8). Compound 6 reacted further with NH₂Cl to give compounds 7 and 8; in the presence of NH₂Cl, compound 7 rearranged to compound 8. Mechanisms for the preceding reactions are analyzed in detail. Another aspect of the investigation involved a determination of the amounts of chloroform, CHCl₃, which is produced from compound 3 with NH₂Cl (4%) and with NaOCl (50%). The low production of CHCl₃ from compound 3 and NH₂Cl is discussed in connection with the probable reactions of compounds 7 and 8 with NH₂Cl and H₂O.

Full text of DOI:10.1002/etc.5620181104

Environmental Toxicology and Chemistry, Vol. 18, No. 11, pp. 2406–2409, 1999
1999 SETAC
Printed in the USA
730-7268/99 $9.00 .00
᭧
0
ϩ
Environmental Chemistry
REACTIONS OF RESORCINOL AND ITS CHLORINATED DERIVATIVES WITH
MONOCHLORAMINE: IDENTIFICATION OF INTERMEDIATES AND PRODUCTS
V
ICTOR L. HEASLEY,* MICHAEL B. ALEXANDER, RYAN H. D
AWNYA C. M EE, BRIAN D. WADLEY, and DALE F. S HELLHAMER
Department of Chemistry, Point Loma Nazarene University, San Diego, California 92106, USA
EBOARD, JOHN C. HANLEY, JR.,
T
CK
(
Received 14 September 1998; Accepted 16 February 1999)
Abstract—An investigation of the reaction of resorcinol (compound 1) and its chlorinated derivatives 4-chlororesorcinol (compound
), 4,6-dichlororesorcinol (compound 5), and 2,4,6-trichlororesorcinol (compound 2) with monochloramine (NH Cl) in ether and
4
2
aqueous solution (pH 7) is reported. NH Cl reacted with compounds 1, 2, 4, and 5 to give the pentachloro intermediate, 2,2,4,4,6-
2
pentachloro-5-cyclohexen-1,3-dione (compound 3), which underwent ring opening with H O and loss of CO in the presence of
2
2
NH Cl to produce the following: 1,1,3,5,5-pentachloro-3-penten-2-one (compound 6), 1,1,1,3,5,5-hexachloro-3-penten-2-one (com-
2
pound 7), and 1,1,3,5,5,5-hexachloro-3-penten-2-one (compound 8). Compound 6 reacted further with NH Cl to give compounds
2
7
and 8; in the presence of NH Cl, compound 7 rearranged to compound 8. Mechanisms for the preceding reactions are analyzed
2
in detail. Another aspect of the investigation involved a determination of the amounts of chloroform, CHCl , which is produced
3
from compound 3 with NH Cl (4%) and with NaOCl (50%). The low production of CHCl from compound 3 and NH Cl is discussed
2
3
2
in connection with the probable reactions of compounds 7 and 8 with NH Cl and H O.
2
2
Keywords—Resorcinol
Monochloramine
Chloroform
Intermediates
Mechanisms
INTRODUCTION
tachloride (2,2,4,4,6-pentachloro-5-cyclohexen-1,3-dione,
compound 3) (Fig. 1) preparation procedure has been described
previously [4]; a modified, simpler procedure is reported here.
Five grams (45 mmol) of compound 1 were dissolved in 30
ml of ether and 60 ml of methylene chloride. Chlorine gas
Resorcinol (compound 1) (Fig. 1) is an important model
for examining the reactions of chlorinating agents on humic
acids because it is postulated to be a substituent in the humic
acids and is assumed to be partially responsible for the pro-
(
Cl ) was passed slowly into the solution for 45 min to 1 h.
2
duction of the chloroform (CHCl ) that is formed when drink-
3
At this point, GC analysis was performed to determine con-
version to compound 3. Chlorine gas was passed into the so-
lution until the conversion of compound 1 to compound 3 was
approx. 95%. The solvent was then removed using a rotary
evaporator, and the remaining liquid was cooled in ice until
crystallization occurred. The crystals were isolated and washed
with pentane. Purity, as determined by GC, was 98%. Mono-
ing water is chlorinated [1–3]. Recently, we reported on the
reaction of resorcinol (compound 1) and its chlorinated deriv-
Ϫ
atives with hypochlorite ion (OCl ) in methanol, identifying
the early generation products and the intermediate, which un-
dergoes ring opening [4].
In the investigation described here, we examined the re-
action of monochloramine, NH Cl, with resorcinol (compound
2
chloramine, NH Cl, was made as described previously [8].
2
1
(
) and its chlorinated derivatives, 2,4,6-trichlororesorcinol
compound 2), 4-chlororesorcinol (compound 4), and 4,6-di-
chlororesorcinol (compound 5) (Fig. 1), in ether and in H O.
NH Cl is a chlorinating agent that is widely used for treating
municipal drinking water because it does not react with humic
acid contaminants to produce significant amounts of CHCl3
and related halomethanes [5,6]. The reaction of the model
Usually, the NH Cl/ether layer was isolated, dried over
2
MgSO , titrated iodometrically (ϳ0.3 M) according to the stan-
4
2
dard analytical chemistry procedure, and used directly in re-
2
actions. On one occasion, the NH Cl/ether layer was distilled
2
to eliminate the possibility of impurities in the ether solution
[
8]. NCl was made as described previously [9]. Hypochlorous
3
acid (HOCl) was prepared by chlorination of aqueous
compound resorcinol (compound 1) with NH Cl has not been
2
NaHCO /ether. Hypochlorous acid in the ether layer was iden-
3
investigated. It was our goal in this study to determine whether
resorcinol (compound 1) and its chlorinated derivatives reacted
with NH Cl and, if a reaction occurred, whether CHCl was
tified by its ultraviolet absorption at 298 nm.
2
3
Instrumentation and analysis
produced, the structure of the intermediate, and final products.
1
The 300-MHz H nuclear magnetic resonance (NMR) and
7
5.4-MHz 13C NMR spectra were obtained using a Varian
MATERIALS AND METHODS
Unity 300 instrument (Varian, Walnut Creek, CA, USA) and
are reported relative to Me Si or CDCl . Mass spectral analyses
Starting materials
4
3
Compounds 1, 4, and 5 and molecular sieves (8–12 mesh)
were obtained from Aldrich (Milwaukee, WI, USA). Com-
pound 2 was prepared as described previously [7]. The pen-
were obtained at 70 eV using a Hewlett-Packard gas chro-
matograph (model 5890, Hewlett-Packard, Avondale, PA,
USA) interfaced with a Hewlett-Packard mass selective de-
tector (model 5970B). Results are expressed as electron impact
(
m
/
z
) and as relative intensity (%). Products were analyzed
*
To whom correspondence may be addressed
(
vheasley@ptloma.edu).
using a Hewlett-Packard gas chromatograph (model 5890).
2
406

Reaction of resorcinol with monochloramine
Environ. Toxicol. Chem. 18, 1999
2407
Rate study on the reactions of compounds 3 and 6 with
NH Cl
2
We added 0.64 mg (2.25 mmol) of compound 3 to 1 ml of
0
.22 M (0.22 mmol) monochloramine (10:1 molar ratio). Gas
chromatography analysis showed essentially no reaction at the
end of 1 min; little reaction had occurred even by 10 min:
compound 3, 95.5%; compound 6, 1.4%; compound 7, 1.1%;
and compound 8, 2.0%. In a similar manner, 0.57 mg (0.22
mmol) of compound 6 was added to 1 ml of 0.225 M (0.22
mmol) chloramine (1:1 molar ratio). Compound 6 reacted rap-
idly with NH Cl. In 1 min, the analysis showed the following:
2
compound 6, 82.5%; compound 7, 3.0%; and compound 8,
1
4.5%.
Synthesis and structure confirmation of the products
The structure of compound 6 was reported previously [4].
It was synthesized as follows: 0.15 g (0.53 mmol) of compound
Fig. 1. Structures of reactants 1, 2, and 3 and products 6, 7, and 8.
3 was suspended in H O (25 ml) and stirred overnight. The
2
resulting compound, formed by ring opening by water and
decarboxylation of the intermediate acid, was extracted with
ether and dried over MgSO . The solvent was removed on a
rotary evaporator, and the liquid was distilled under vacuum
4
The GC and GC–MS analyses were performed using a 25-m
Hewlett-Packard ultraperformance column with an internal di-
ameter of 0.20 mm and a methyl silicone stationary phase of
(
72–76ЊC at 1 torr) to give compound 6 with 90% purity.
1
The structure of compound 7 was established by H NMR,
0
.33 ␮m film thickness. Liquid infrared spectra were recorded
13
1
C NMR, GC-MS, and infrared spectrometry. H NMR (300
with a Nicolet 610 Fourier transform spectrometer (Nicolet
Instruments, Madison, WI, USA). Gas-phase infrared spectra
were obtained with a Nicolet 610 interfaced with a Hewlett-
Packard gas chromatograph (model 5890).
MHz):
␦5.90 (d, 1 H, J ϭ 1.8 Hz) and 6.28 (d, 1 H, J ϭ 1.8
Hz). 13C NMR (75.4 MHz): 50.8, 123.3, 129.1, 139.4, and
ϩ
ϩ
1
82.4. GC-MS: M : 290 (1.4) and 288 (0.86); M-Cl : 261
(
0.11), 259 (0.59), 257 (1.8), 255 (2.9), and 253 (1.8); M-Cl-
Starting compounds and products were analyzed by GC at
ϩ
CO : 233 (0.40), 231 (2.1), 229 (6.4), 227 (9.3), and 225 (6.4);
1
20 to 220
retention times (min): 1, 5.5; 2, 9.8; 3, 7.8; 4, 6.0; 5, 6.2; 6,
.5; 7, 6.8; and 8, 7.2.
ЊC at a rate of 10ЊC/min and showed the following
M-CCl -CO: 149 (3.4), 147 (32), 145 (97), and 143 (100);
3
CCl : 123 (1.2), 121 (5.9), 119 (18), and 117 (14); and CHCl :
3
2
5
8
7 (3.2), 85 (14), and 83 (20). Infrared spectrometry, gas phase
Ϫ
1
(
cm ): CO, 1774; C ϭ C, 1614. Compound 7 was synthesized
Reaction of the pentachloride with NH Cl
2
as follows: 0.15 g (0.53 mmol) of compound 3 was stirred
into 11 ml of aqueous 0.2 M NH Cl (2.2 mmol of NH Cl) at
General reaction conditions: to a stirred solution of NH Cl
2
2
2
in ether (ϳ0.3 M) was added 0.21 g (0.75 mmol) of the pen-
ice temperature and pH 6.15. (NH Cl solution at pH 6.15 was
2
tachloride (compound 3). Usually, the reaction was run in a
molar ratio of 1:3 (compound 3:NH Cl; 2.5 ml of NH Cl/ether)
obtained by titration of aqueous NH Cl [pH ϭ ϳ11] with 0.1
2
2
2
M HCl.) The reaction was stirred at ice temperature for 45
min and then extracted with ether. After drying over MgSO4
and removal of the solvent under vacuum with a rotary evap-
orator, the remaining liquid was distilled (80ЊC at 1 torr) to
give compound 7 with 69% purity. The major impurity was
to speed up the conversion of compound 3 to the mixture of
compounds 6 (1,1,3,5,5-pentachloro-3-penten-2-one), 7
(
1,1,1,3,5,5-hexachloro-3-penten-2-one), and 8 (1,1,3,5,5,5-
hexachloro-3-penten-2-one) (Fig. 1). The yield under these
conditions was 88%. The stoichiometry in the reaction of com-
pound 3:NH Cl was 1:1 because 1 Meq of NH Cl and com-
isomer 6. Perhaps at pH 6.15, dichloramine (NHCl ) is the
2
2
2
chlorinating agent because NH Cl is known to disproportion
2
pound 3 reacted completely.
Reactions in ether establishing that compounds 4 and 5 were
on the reaction pathway used the general reaction conditions
ϩ
to NH4 and NHCl at acidic pH.
2
1
The structure of compound 8 was established by H NMR,
13
1
C NMR, GC-MS, and infrared spectrometry. H NMR (300
described above: Sufficient tetrahydrofuran (
ϳ
50:50 with wa-
13
MHz): ␦6.81 (s, 1 H) and 6.92 (s, 1 H). C NMR (75.4 MHz):
ter) was added to water to bring the reactants into solution at
a final volume of 2.5 ml.
ϩ
6
2
2.8, 78.0, 124.9, 133.6, and 182.8. GC-MS: M-Cl : 261 (0.2),
ϩ
59 (1.1), 257 (3.6), 255 (5.7), and 253 (3.1); M-Cl-CO : 233
(
0.1), 231 (0.9), 229 (3.4), 227 (5.3), and 225 (3.6); M-CHCl -
2
ϩ
CO : 183 (12), 181 (43), 179 (100), and 177 (79); CHCl CO:
2
1
13 (4.5) and 111 (9.9); CHCl : 87 (6.7), 85 (33), and 83 (47).
2
Ϫ
1
Infrared spectrometry, liquid phase (cm ): CO, 1763; C
ϭ C,
1
610. Compound 8 was synthesized as follows: 0.21 g (0.75
mmol) of compound 3 was stirred into 10 ml of 0.3 M NH Cl
2
in ether (3 mmol of NH Cl). After 6 h, the ether was removed
2
under vacuum with a rotary evaporator, and the liquid was
distilled (80ЊC at 1 torr) to give compound 8 with 85% purity.
Compounds 6, 7, and 8 were stable under distillation con-
ditions and were stored indefinitely in the freezer.
Fig. 2. In the presence of NH Cl, compound 6 gives compounds 7
and 8; compound 7 rearranges to compound 8.
2

2
408
Environ. Toxicol. Chem. 18, 1999
V.L. Heasley et al.
Fig. 3. Conversion of compound 3 to compound 6 by hydrolysis and
decarboxylation.
Fig. 5. Chlorination of compound 8 to give compound 9 does not
occur.
RESULTS
We observed that compounds 1, 2, 4, and 5 reacted with
NH Cl in ether or H O to give compound 3, confirming that
proving that NH did not interfere with the normal reaction.
3
2
2
In the absence of NH Cl, compound 3 and NH reacted to give
2
3
resorcinol (compound 1) and its derivatives (compounds 2, 4,
and 5) are all on the reaction pathway from compound 1 to
compound 3. Furthermore, we established that the penta-
chloride (compound 3), prepared by independent synthesis,
reacted with NH Cl in ether or in H O (pH 7) to give a mixture
trace amounts of compounds 6, 7, and 8; other products were
not detected by GC. No amides from the reaction of compound
3
and NH were observed in the GC analysis, although an
3
amide of comparable molecular weight (4-chlorobenzanilide)
did emerge.
2
2
of ring-opened products (compounds 6, 7, and 8), as shown
in Figure 1. We also observed that compound 6 reacted with
We assumed that our chlorinating agent was monochlora-
mine (NH Cl) and not dichloramine (NHCl ) or trichloramine
2
2
NH Cl to give compounds 7 and 8. Subsequently, compound
2
(
NCl ). We based this assumption on the following facts: NCl
3
3
7
in the presence of NH Cl rearranged to compound 8 (Fig. 2).
2
in ether, by our own investigation, does not react with com-
Therefore, compound 8 becomes the major product (85%)
if compounds 6, 7, and 8 are allowed to stand in solution with
pound 3; NH Cl is confirmed in the ether solution by its max-
2
imum absorbance at 243 nm [6]; and reaction of compound 3
with aqueous monochloramine solutions that had been titrated
with dilute HCl to pH values of 6.4 and 4 gave primarily
compound 7. (This is, in fact, the procedure used to make
excess NH Cl. If a stoichiometric amount of compound 3 and
2
NH Cl (1:1 molar ratio) are reacted, the percentages of prod-
2
ucts are as follows: compound 6, 51%; compound 7, 25%; and
compound 8, 24%.
compound 7.) At pH 4, NHCl is known to be the major com-
2
The reaction of compound 3 with NH Cl in ether to give
2
ponent, with NH Cl and NCl also being present [6]. Therefore,
2
3
compound 6 definitely depended on the presence of trace
amounts of H O. When the trace amounts of H O were re-
NHCl may be the reacting species at lower pH, but we have
2
2
2
no proof that it is not NH Cl.
2
moved with molecular sieves from ether solutions of com-
Our investigations show that hypochlorous acid (HOCl)
does not react with compound 3 in ether.
pound 3 and NH Cl, the reaction rate decreased proportionally
2
to the drying time. Additions of small amounts of H O to sieve-
2
Only a small amount of CHCl (4%) by internal standard
3
dried solutions of compound 3 and NH Cl restored the reaction
2
was formed when resorcinol (compound 1) and the penta-
chloride were reacted in H O at pH 7 with NH Cl to 700%
rate.
2
2
Without NH Cl, ring opening of compound 3 by H O fol-
2
2
(
compound 1:NH Cl/1 mol:7 mol) and 200% (compound 3:
2
lowed by decarboxylation is too slow to be on the reaction
pathway, as we previously confirmed [4] (Fig. 3).
NH Cl/1 mol:2 mol), respectively. Under the same reaction
2
conditions, reaction of compound 1 with NaOCl to 700% gave
We established that the reaction of the pentachloride (com-
approx. 50% CHCl (by internal standard).
3
pound 3) and NH Cl does not depend on catalysis by an un-
2
known component in the NH Cl/ether solution. After careful
DISCUSSION
2
purification by distillation under vacuum, NH Cl/ether also
2
Our data show that resorcinol (compound 1) and its chlo-
rinated derivatives (compounds 2, 3, 4, and 5) all react with
NH Cl in H O and ether. The reaction pathway involves the
reacted at the same rate with compound 3 in ether to give the
expected products. Ring opening of compound 3 in ether sat-
urated with H O, NH ·H O, NaOH·H O, and HCl·H O did not
2
2
2
3
2
2
2
intermediate pentachloride (compound 3), which undergoes
ring opening with NH Cl/H O to give compound 6, which
occur (no NH Cl was present).
2
2
2
In a rate study, we determined that the reaction of com-
pound 6 with NH Cl to give compounds 7 and 8 is much more
2
rapid than the ring-opening reaction of the compound 3 with
NH Cl and trace amounts of H O to give compound 6.
2
2
NH Cl and compound 3 in ether saturated with NH gas
2
3
reacted to give the normal products (compounds 6, 7, and 8),
Fig. 4. Hydrolysis of compound 7 to give chloroform and a carboxylic
acid.
Fig. 6. Mechanisms for the formation of compounds 7 and 8 from
compound 6 and NH Cl.
2

Reaction of resorcinol with monochloramine
Environ. Toxicol. Chem. 18, 1999
2409
Fig. 7. Mechanisms for base-catalyzed rearrangement of compound
7
to compound 8.
chlorinates further to compounds 7 and 8. Compound 7 in the
presence of NH Cl rearranges rapidly to compound 8.
2
Fig. 8. Mechanism for the rearrangement of compound 7 to com-
pound 8.
The mechanism of ring opening of the pentachloride is not
clear. Our data show that NH Cl and H O are involved in the
2
2
ring opening to give compound 6 and, we presume, CO . Per-
2
haps NH Cl, via a NH Cl-H O complex, assists as a catalyst
rearrangement of chlorine by NH
cause compound 7 and NH in ether do not give compound 8.
Perhaps the rearrangement of compound 7 to compound 8
3
, as shown in Figure 7, be-
2
2
2
in the nucleophilic attack of H O on the carbonyl group be-
3
2
tween the two CCl groups, providing two protons for the
2
terminal carbons and an oxygen for the formation of CO . The
involves compound 6 and dichloramine (NHCl ) as interme-
2
2
NH Cl molecule is now left to chlorinate compound 6. This
diates, as shown in Figure 8.
2
type of mechanism requires the formation of compound 6 be-
fore compounds 7 and/or 8. We could not prove this point,
however, because the rate study showed that the ring opening
Acknowledgement—We acknowledge support from the following
sources: the National Science Foundation (grant CHE-9528446); the
National Institutes of Health (grant 1-R15-ES05671-01); Howard
Hughes Medical Institute (award 71196-552001); the Mass Spectrom-
etry Facility, University of California, Riverside; the Center for Wes-
leyan Studies for the 21st Century; and Research Associates of Point
Loma Nazarene University.
of compound 3 is slow compared to the reaction of NH Cl
2
with compound 6. Consequently, GC analysis in the very early
stages of the reaction of compound 3 and NH Cl indicated
2
only mixtures of compounds 6, 7, and 8.
Our data show that little CHCl is formed in the reaction
3
REFERENCES
of compounds 1 and 3 with NH Cl and H O. The small amount
2
2
1
2
. Rook JJ. 1976. Haloforms in drinking water. J Am Water Works
Assoc 68:168–172.
of CHCl formed probably arises from nucleophilic displace-
3
ment of the weak leaving group CCl by H O, as shown in
3
2
. Norwood DL, Johnson JD, Christman RF, Haas JR, Bobenrieth
MJ. 1980. Reactions of chlorine with selected aromatic models
of aquatic humic material. Environ Sci Technol 14:187–190.
. Boyce SD, Hornig JF. 1983. Reaction pathways of trihalomethane
formation from the halogenation of dihydroxyaromatic model
compounds for humic acid. Environ Sci Technol 17:202–211.
4. Heasley VL, Anderson ME, Combes DS, Elias DS, Gardner JT,
Hernandez ML, Moreland RJ, Shellhamer DF. 1993. Investiga-
tions of the structure and reactions of the intermediate in the
chlorination of resorcinol. Environ Toxicol Chem 12:1653–1659.
. Carswell JK, et al. 1977. Ozone, chlorine dioxide and chloramines
as alternatives to chlorine. In Jolley RL, Gorchev H, Hamilton
DH JR, eds, Water Chlorination: Environmental Impact and
Health Effects, Vol 2. Ann Arbor Science, Ann Arbor, MI, USA,
pp 555–560.
. Wolfe RL, Ward NR, Olson BH. 1984. Inorganic chloramines as
drinking water disinfectants: A review. J Am Water Works Assoc
76:74–88.
Figure 4. Absence of significant CHCl formation probably
3
arises from the fact that compound 7 is present in a relatively
3
low percentage, hydrolyzes extremely slowly with H O, and
2
rearranges quite rapidly to compound 8 in the presence of
NH Cl. We established that compound 8 does not chlorinate
2
further with NH Cl to give compound 9 (Fig. 5), which could
2
hydrolyze to give CHCl (Fig. 5). The pentachloride (com-
3
Ϫ
pound 3) and OCl probably produced a large amount of
5
CHCl , because most of the degradation intermediates and
3
products contain the
rearrangement pathways are impossible for these intermediates
and products (because of the absence of an -carbon, carbon
double bond as exists for compounds 7 and 8), hydrolysis
ϪC(O)CCl leaving group [4]. Because
3
␣, ␤
6
leading to CHCl becomes a major pathway.
3
The mechanisms for the reactions of compound 6 with
7. Heasley VL, Burns MD, Kemalyan NA, McKee TC, Schroeter
H, Teegarden BR, Whitney SE, Wershaw RL. 1989. Aqueous
chlorination of resorcinol. Environ Toxicol Chem 8:1159–1163.
. Coleman GH, Johnson JL. 1939. Monochloramine. Inorg Syn-
thesis 1:59–62.
NH Cl to form compounds 7 and 8 probably involve attack of
2
the two enol forms of compound 6 on the chlorine of NH Cl,
2
8
as shown in Figure 6. The mechanism for the conversion of
compound 7 to 8 in the presence of NH Cl is not clear. We
2
9. Kovacic P, Chaudhary SS. 1973. 1-Amino-1-methylcyclohexane.
know that the mechanism does not involve a base-catalyzed
Org Synthesis 5:35–38.