Chlorination and oxidation products formed from 1,2,4-trimethylbenzene in aqueous solution under the action of chlorine dioxide

Article abstract of DOI:10.1134/S107042720707018X

Products of the reaction of 1,2,4-trimethylbenzene with chlorine dioxide in aqueous solution were studied. A scheme of 1,2,4-trimethylbenzene transformations was suggested. The influence exerted on the number of the reaction products by the ClO₂ dosage and time of its contact with the substrate was examined.

Full text of DOI:10.1134/S107042720707018X

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 7, pp. 1105 1110. Pleiades Publishing, Ltd., 2007.
Original Russian Text Z.R. Khasanova, M.Yu. Vozhdaeva, N.N. Kabal’nova, E.A. Kantor, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80,
No. 7, pp. 1135 1140.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Chlorination and Oxidation Products
Formed from 1,2,4-Trimethylbenzene in Aqueous Solution
under the Action of Chlorine Dioxide
Z. R. Khasanova, M. Yu. Vozhdaeva, N. N. Kabal’nova, and E. A. Kantor
Ufa State Petroleum Technical University, Ufa, Bashkortostan, Russia
Ufavodokanal Municipal Unitary Enterprise, Ufa, Bashkortostan, Russia
Institute of Organic Chemistry, Ufa Scientific Center, Russian Academy of Sciences,
Ufa, Bashkortostan, Russia
Received October 30, 2006; in final form, April 2007
Abstract Products of the reaction of 1,2,4-trimethylbenzene with chlorine dioxide in aqueous solution were
studied. A scheme of 1,2,4-trimethylbenzene transformations was suggested. The influence exerted on the
number of the reaction products by the ClO2 dosage and time of its contact with the substrate was examined.
DOI: 10.1134/S107042720707018X
Disinfection of water with chemical reagents im-
proves its microbiological parameters. Water disin-
fection is usually performed with molecular chlorine,
sodium hypochlorite, chloramine, ozone, or chlorine
dioxide, or by UV irradiation [1 3]. Today it is im-
portant to find a method that would combine the
advantages of various disinfection methods and reduce
the formation of secondary toxicants [4].
Our main analytical procedure for determining
organic compounds was gas chromatography with
mass-selective detector (GS MSD), which is one of
the most reliable methods for identification of compo-
nents of complex organic mixtures [7].
EXPERIMENTAL
Chlorine dioxide was prepared by the reaction of
sodium chlorite with hydrochloric acid [8]. Sodium
chlorite (main substance content 80%) was purchased
from Aldrich. The sodium chlorite concentration was
determined by titration [9, 10]. The chlorine dioxide
concentration was determined spectrophotometrically
with a Specord M40 device (Carl Zeiss, Jena) in
Chlorine dioxide, which is an available and effec-
tive oxidant, finds growing use both in industry and
in water preparation [5]. It improves the microbiologi-
cal and organoleptic parameters of water and consider-
ably reduces the amount of toxic disinfection products
such as trihalomethanes, which are the main by-
products in chlorination of water with molecular chlo-
rine. This is particularly important in disinfection of
water containing not only natural humic compounds
but also manmade organic pollutants. According to
published data, chlorine dioxide is a mild oxidant.
Benzene and its simplest alkyl derivatives (toluene,
ethylbenzene, xylenes, diphenylmethane) do not react
with chlorine dioxide under the conditions of potable
water treatment in the absence of traces of molecular
chlorine [6].
quartz cells (l = 0.1 cm) in the range of the ClO
absorption maximum (354 362 nm) just before each
experiment.
2
In the experiments we used 1,2,4-TMB [GSO
(State Reference Sample) 3309 85] and deionized
water (Milli-Q Gradient). To attain 25 : 1 molar ratio
of ClO to the organic substrate, to Milli-Q water (V =
2
3
3
1 dm ) containing 1,2,4-TMB (10 mg dm , 8.32
5
10 M) we added ClO to a concentration of 2.08
10 M. To attain 40 : 1 ratio, to Milli-Q water (V =
1 dm ) containing the substrate (1 mg dm , 8.32
10 M) we added ClO to a concentration of 3.33
2
3
In this study we examined transformations of or-
ganic compounds of industrial origin in aqueous solu-
tion under the action of chlorine dioxide. As organic
substrate we chose 1,2,4-trimethylbenzene (1,2,4-
TMB), which is a possible water pollutant in regions
adjacent to petrochemical enterprises.
3
3
6
4
2
10 M. The exposure time was 6 and 24 h, respec-
tively. The water treatment with ClO was performed
2
at room temperature. The reaction was stopped by
1105

1106
KHASANOVA et al.
Table 1. Main parameters of devices for analysis of products of the reaction of 1,2,4-TMB with ClO2 aqueous solution
Gas chromatograph
Detector
Agilent 5890N
G6000 Vega Series 2
HRGC Mega Series
MSD
FID
ECD
Column type
HP-5MS
DBWAX
DB-5
30 m 0.25 mm 0.25 m
30 m 0.25 mm 0.25 m
30 m 0.32 mm 1 m
Carrier gas
Helium
2
Helium
2
Nitrogen
2
Carrier gas flow rate,
1
cm3 min
1
Temperature schedule,
C
35 to 60, 30 deg min ;
60 to 280, 6 deg min ;
60, 9 min; 60 to 120,
70
1
1
10 deg min ; 120, 4 min
280, 10 min
Temperature, C:
vaporizer
detector
250
120
300
120
330
ion source
230
quadrupole
150
transition channel
Ionization mode
Electron energy, eV
280
Electron impact
70
235
adding sodium thiosulfate which deactivates excess
For the chloro derivatives of 1,2,4-TMB, the re-
sponse factors, reflecting the extraction coefficient,
ionization cross section, contributiopn of the charac-
teristic ion to the total ion current, and mass discrimi-
nation of the mass spectrometer used, were taken
equal to unity. The concentrations of chloro deriva-
ClO [11]:
2
5Na2S2O3 + 8ClO2 + 9H2O
10NaHSO4 + 8 HCl.
To study the dynamics of formation of volatile
organic compounds, at 15-min intervals we took from
tives of 1,2,4-TMB, c
, were quantitatively esti-
comp
3
3
the reaction volume (V = 1 dm ) 10 cm samples of
water into specially prepared vials with sodium thio-
sulfate and analyzed the samples by GC MSD. Vola-
tile aromatic hydrocarbons (VAHs) were determined
by head space analysis with a flame ionization detect-
or (GC FID; Vega chromatograph, Carlo Erba Instru-
ments). Volatile halogenated hydrocarbons (VHHs)
were determined similarly using an electron capture
detector (GC ECD; Mega device, Carlo Erba Instru-
ments, Head Space 850 unit).
mated with an external reference by the formula
= S /S , where S and S are the
c
c
comp
comp ref ref
comp
ref
areas of the chromatographic peaks of the product and
external reference, respectively (mV s), and c is the
ref
1,2,4-TMB concentration (M). As external reference
we used a 1,2,4-TMB solution. The analysis results
are given in Table 2.
Analysis of the concentrates prepared after extrac-
tion of products of the reaction of 1,2,4-TMB with
chlorine dioxide shows that the 1,2,4-TMB conversion
in 1.75 h at 25-fold molar excess of ClO is 90.2%.
The possible transformation pathways of 1,2,4-TMB
The 1,2,4-TMB transformation products were ex-
tracted from aqueous solution with methylene chloride
(Merck, 2 10 cm ). The extract was dried over an-
2
3
under the action of ClO are shown in Scheme 1.
2
hydrous sodium sulfate and analyzed on a 6890N gas
chromatograph with a mass-selective detector (5973,
Agilent). The characteristics of the quartz capillary
columns used and the analysis and detection condi-
tions for all the three methods are given in Table 1.
The components were identified by comparing the
experimental mass spectra with those from the Wiley
138 and NBS 75 libraries (coincidence quality 70
90% on the average) and by interpreting the fragmen-
tation patterns under electron impact, taking into
account well-known relationships [7].
Among chlorinated transformation products (path-
way II), we identified two compounds formed by
monochlorination of the benzene ring (5-chloro-
1,2,4-trimethylbenzene, 2; 3-chloro-1,2,4-trimethyl-
benzene, 3) and three compounds formed by chlorina-
tion of the methyl group: 1-(chloromethyl)-2,4-di-
methylbenzene (4), 2-(chloromethyl)-1,4-dimethyl-
benzene (5), and 4-(chloromethyl)-1,2-dimethylben-
zene (6). These compounds are virtually indistinguish-
able by mass spectrometry, which complicates the
peak assignment. However, low intensity of the peak
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CHLORINATION AND OXIDATION PRODUCTS
1107
Table 2. Content of products of 1,2,4-TMB transformations on treatment with ClO2 aqueous solution
Content c 107, M
Product
Characteristic ions, %
25-fold excess
of ClO2, 6 h
40-fold excess
of ClO2, 24 h
1,2,4-TMB (1)
0.083
13.4
8.94
1.08
3.53
1.37
1.84
105(100), 120(45), 91(12)
5-Chloro-1,2,4-trimethylbenzene (2)
3-Chloro-1,2,4-trimethylbenzene (3)
1-(Chloromethyl)-2,4-dimethylbenzene (4)
2-(Chloromethyl)-1,4-dimethylbenzene (5)
4-(Chloromethyl)-1,2-dimethylbenzene (6)
5-Chloro-1-(chloromethyl)-2,4-dimethyl-
benzene (7)
9.91
6.98
119(100), 154(50), 139(22), 91(16)
119(100), 154(45), 139(19), 91(16)
119(100), 154(24), 139(2), 91(13)
119(100), 154(21), 139(4), 91(14)
119(100), 154(23), 139(3), 91(13)
153(100), 188(52), 115(34)
1.54
0.82
2.53
5-Chloro-2-(chloromethyl)-1,4-dimethyl-
benzene (8)
1.51
1.53
153(100), 188(54), 115(30)
1,4-Bis(chloromethyl)-2-methylbenzene (9)
1,2-Bis(chloromethyl)-4-methylbenzene (10)
1,1,5-Trichloro-1-pentene (11)
Dichloroacetyl chloride (12)
2,4-Dimethylbenzaldehyde (13)
2,4-Dimethylbenzoic acid (14)
0.072
0.86
+
+
+
153(100), 115(23), 188(9)
153(100), 115(19), 188(14)
65(100), 137(90), 172(17)
83(100), 111(17), 146(2)
134(100), 105(57), 77(25)
132(100), 150(89), 105(52)
+
+
Scheme 1.
11
12
1
13
14
3
2
4
6
5
7
8
10
9
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1108
KHASANOVA et al.
Scheme 2.
(a)
(b)
Isomers 4 6
(c)
(d)
Isomers 2, 3
(a)
c
107, M
108, M
(b)
c
t, h
t, h
109, M
(c)
c
(d)
c
107, M
t, h
t, h
5
Fig. 1. Variation of VHH concentrations c with time t. [1,2,4-TMB] = 8.32 10 M; 25-fold excess of ClO . (a) (1) 1,2-Dichlo-
2
roethane and (2) chloroform; (b) (3) bromoform and (4) tetrachloromethane; (c) (5) bromochloromethane and (6) dibromochloro-
methane; (d) (7) trichloroethylene.
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CHLORINATION AND OXIDATION PRODUCTS
1109
Scheme 3.
Isomers 7, 8
Isomer 9
Isomer 10
at m/z = 139 in the mass spectra of 4 6 indicates that
their fragmentation mainly occurs through elimination
of halogen atom and ethylene molecule from the
molecular ion, with the subsequent formation of the
tropylium cation (Scheme 2, pathway a). According
to the fragmentation rules, this pathway is more prob-
able for the 1,2,4-TMB monochloro derivatives con-
taining the Cl atom in the side chain.
bis(chloromethyl)-4-methylbenzene (10). The strong-
+
+
est peaks correspond to [M Cl] , [M HCl] , and
some other ions formed by dehydrogenation character-
istic of all steps of fragmentation of aromatic com-
pounds under electron impact (Scheme 3) [12].
A distinctive feature of the mass spectra of 9 and
10 is approximately three times lower intensity of the
molecular peak (m/z = 188) compared to 7 and 8. This
is due to the lower ionization potential of the mole-
cule, its more intense fragmentation, and formation of
the larger number of rearranged ions.
The higher intensity of the peak at m/z = 139 in
the mass spectra of 2 and 3 (Table 2; Scheme 2, path-
way c) indicates that the electron density distribution
in these isomers facilitates the loss of the methyl
groups as compared to 4 6 (pathway b).
In the extracts we also identified 1,1,5-trichloro-1-
pentene 11 and dichloroacetyl chloride 12 (pathway
III).
Among dichlorinated products, we identified
5-chloro-1-(chloromethyl)-2,4-dimethylbenzene (7),
5-chloro-2-(chloromethyl)-1,4-dimethylbenzene (8),
1,4-bis(chloromethyl)-2-methylbenzene (9), and 1,2-
In view of the fact that one of major advantages in
chlorination of water with chlorine dioxide is forma-
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1110
KHASANOVA et al.
tion of insignificant amounts of VHHs, we determined
the content of tetrachloromethane, trichloroethylene,
chloroform, 1,2-dichloroethane, bromodichlorometh-
ane, dibromochloromethane, and bromoform (pathway
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