Identification of bromination products of chloro-substituted anilines in aqueous environment by gas chromatography

Article abstract of DOI:10.1134/S1070427211100132

To reduce the detection limits of aniline and its various chloroderivatives (all isomers of mono- and dichloroanilines, 2,4,5 -, 2,4,6-, and 3,4,5-trichloroanilines, pentachloroaniline) in aqueous media we suggested bromination reaction, followed by gas chromatographic definition bromo derivatives of chloroanilines on a selective electron capture detector. To identify the products of bromination of chloroaniline in combination with mass-spectrometric data we used chromatographic retention indices on standard nonpolar polydimethylsiloxane stationary phase that was determined for 50 compounds in this class. The technique of identifying bromoderivatives of chloroaniline in water was developed at the gas-chromatographic analysis in the selective electron capture detector. To improve the reliability of the identification of additional bromoderivatives of chloroanilines we obtained their trifluoroacetyl derivatives.

Full text of DOI:10.1134/S1070427211100132

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 10, pp. 1748−1759. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © I.V. Gruzdev, M.V. Filippova, I.G. Zenkevich, B.M. Kondratenok, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84,
No. 10, pp. 1656−1667.
ORGANIC SYNTHESIS AND INDUSTRIAL
ORGANIC CHEMISTRY
Identification of Bromination Products
of Chloro-Substituted Anilines
in Aqueous Environment by Gas Chromatography
I. V. Gruzdeva, M. V. Filippovab, I. G. Zenkevichc, and B. M. Kondratenoka
aInstitute of Biology, Komi Scientific Center, Ural Branch of Russian Akademy of Sciences, Syktyvkar, Russia
bSyktyvkar State University, Syktyvkar, Russia
cSt. Petersburg State University, St. Petersburg, Russia
Received March 11, 2011
Abstract—To reduce the detection limits of aniline and its various chloroderivatives (all isomers of mono- and
dichloroanilines, 2,4,5 -, 2,4,6-, and 3,4,5-trichloroanilines, pentachloroaniline) in aqueous media we suggested
bromination reaction, followed by gas chromatographic definition bromo derivatives of chloroanilines on a
selective electron capture detector. To identify the products of bromination of chloroaniline in combination with
mass-spectrometric data we used chromatographic retention indices on standard nonpolar polydimethylsiloxane
stationary phase that was determined for 50 compounds in this class. The technique of identifying bromoderivatives
of chloroaniline in water was developed at the gas-chromatographic analysis in the selective electron capture
detector. To improve the reliability of the identification of additional bromoderivatives of chloroanilines we
obtained their trifluoroacetyl derivatives.
DOI: 10.1134/S1070427211100132
Problem of determination of oxygen- and nitrogen-
containing aromatic compounds in aqueous media is
topical because, for example, at present in portable water
content of 145 such substances is rationed. Aromatic
amines can be assigned in a special group of very common
highly toxic substances. They are distinguished by
an active application in the industry and solubility in water
which is good enough for organic compounds (aniline,
3.6 g per 100 ml, 2-chloroaniline, 0.3, 4-chloroaniline,
0.5), and with decreasing pH of aqueous solutions their
solubility is increased. Anilines are always present
in the industrial wastewater in production of dyes,
synthetic plastics, rubber, pesticides, cosmetics, and
pharmaceuticals [1].
High toxicity of chloroanilines (2nd and 3rd hazard
class) is responsible for their fairly low maximum
permissible concentration (MPC) in different media
comparable to MPC of lead and mercury compounds
[5, 6]. Thus, in the drinking water a concentration of
chloroaniline should not exceed 50 mg dm–3, and for
reservoirs with piscicultural importance MPC is even
lower, 0.1 mg dm–3.
Chromatographic determination of chloroaniline in
aqueous environments is complicated by the relatively
high hydrophilicity and polarity of these analytes.
Therefore, for extracting the anilines from aqueous
matrices and their concentrating are generally used
various types of solid-phase extraction [7–10]. Gas
chromatographic analysis of obtained extracts is
performed with flame ionization [10], thermionic [7],
and mass spectrometric detectors [8, 9]. The detection
limits of the chromatographic determinations of anilines
vary in a range of 0.5–5 μg dm–3 that is in view of MPC
of chloroaniline (0.1 mg dm–3) is not enough.
Chloroanilines can be released into soil and natural
water after hydrolytic or biochemical degradation of
widely applied pesticides and antiseptics [2, 3]. When
aniline gets into drinking water sources formation of
more toxic chloro-substituted anilines can be performed
in a stage of its disinfecting by active chlorine [4].
1748

IDENTIFICATION OF BROMINATION PRODUCTS OF CHLORO-SUBSTITUTED ANILINES
1749
EXPERIMENTAL
The presence of a reactive amino group in chloroaniline
molecules containing active hydrogen atoms allows
production of various derivatives with this group and,
thus, reduction of the limits of their determination to
0.01–0.1 μg dm–3. The most widely used are nitrogen
[11], phosphorus [12] and halogen [13–17] containing
derivatives of aniline obtained for the determination
using selective thermionic, flame photometric detector
and electron capture detectors, respectively.
We used aniline, 2-, 3-, and 4-chloroanilines, 2,3-, 2,4-,
2,5-, 2,6-, 3,5-, and 3,4-dichloroaniline, 2,4,5-, 2,4,6-,
3,4,5-trichloaniline, and pentachloroaniline with a content
of the main substances no less than 99% (Riedel-de-Haen,
PESTANAL®).
Bromoderivatives of aniline and chloroanilines
(separately for each a compound) were obtained in
aqueous solutions at concentration of substrates of
0.1–1 μg dm–3 setting bromine portions by ratios close
to stoichiometric. At the substrate concentrations
0.01–1 μg dm–3 bromination of blends of chloroanilines
in aqueous solutions was carried out in accordance with
techniques of [19, 20].
Positive mesomeric (+M) effect of the amino group
leads to the high reactivity of the anilines and determines
the possibility of production of their derivatives not only
of the group –NH2, but also of aryl fragment, whose
hydrogen atoms enter into reactions of electrophilic
substitution. The amino group refers to o-p-orientants,
therefore, hydrogen atoms in positions 2, 4 and 6 are
of the highest reactivity. Thus, molecular bromine was
suggested as a reagent to produce halogen derivatives
of anilines [18–20]. Introduction of bromine atoms in
the molecule of chloroaniline gives products having
a substantially greater hydrophobicity that ensures their
efficient extraction concentration [20]. In addition, the
definition of bromo derivatives by a highly sensitive
electron capture detector (ECD) reduces the detection
limits of chloroaniline to 0.01 μg dm–3.
The extraction concentration of bromoderivatives of
aniline and chloroanilines at phase ratios r = 10–100 was
carried out in separating funnels of 500 cm3 for 5 min;
at r = 500–1000, in flasks of 500 cm3 using a magnetic
stirrer MM-5 (3000 rpm) for 10 min.
An analysis of bromination products was performed
in a gas chromatography-mass spectrometer RACE
DSQ (Thermo) and chromatograph “Kristall 5000.2”
(Chromatec) with ECD. Conditions of the gas
chromatography-mass spectrometry: temperature
programming from 50 to 300°C at 5°C min–1 evaporator
temperature 320, interface 200°C, carrier gas helium,
volume rate 1 cm3 min–1, flow division at input of samples
1 : 50. Mass spectra were recorded at an ionization energy
of 70 eV in the range of m/z 50–650 Da.
Reaction of chloroanilines with bromine excess
directly in the aqueous solution ensures production of
the final products of exhaustive bromination (Table 1).
Therewith we reach a required unambiguous correlation
of a number of initial analytes and their derivatization
products [21]. However, in the case of lack of
a reagent along with the final products a formation of
a number of intermediates is possible that complicates
the identification of the analysis results and leads
to an increase in the limits of determination of the
initial chloroanilines, an increased error of analytical
measurements, and other negative consequences. These
conditions can arise, e.g., due to partial hydrolysis of
bromine in an alkaline medium or to the presence in the
probes of reducing agents.
For determination of RI extracts of bromoderivarives
of chloroanilines were dosed with a blend of standard
n-alkanes C8–C24 (only homologs with an even number
of carbon atoms in molecules). Linear-to-logarithmic
indices were computed by software QBasic. In this sys-
tem, RI of each component leaving the chromatographic
column between n-alkanes with n and n +1 carbon atoms,
can be calculated in two ways: by the retention time
of three n-alkanes with carbon atoms in the molecules
n–1, n, and n +1 or n, n +1, and n +2. The coincidence of
the RI values, calculated for different sets of reference
components, is a criterion of the correctness of the identi-
fication of references on the chromatograms. In addition,
the registration of chromatograms of the same samples
was carried out three times. Thus, all the analytes were
characterized by average values of six RIs determined
by the ways suggested; their standard deviations did not
exceed unity of index.
In the study we considered identification of the
products of chloroanilines bromination based on mass-
spectrometric data and gas chromatographic retention
indices (RI) on standard nonpolar polydimethylsiloxane
stationary phase. We suggested technique of application of
RI to identification of bromo derivatives of chloroanilines
with the help of ECD.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 10 2011

1750
GRUZDEV et al.
Table 1. Retention indices of chloroaniline and their products of bromination on the standard nonpolar polydimethylsiloxane
stationary phases
Substituent in the
initial aniline
RI
Intermediate of bromination
RI
Final product of bromination
2,4,6-Tribromo-
RI
None
946
2-Bromo-
1173
1248
1465
1370
1377
1284
1388
1468
1370
1701
1570
1675
1371
1601
1646
4-Bromo-
2,4-Dibromo-
2,6-Dibromo-
2-Chloro-
3-Chloro-
1093
1157
4-Bromo-2-chloro-
6-Bromo-2-chloro-
2-Bromo-3-chloro-
4-Bromo-3-chloro-
6-Bromo-3-chloro-
2,4-Dibromo-3-chloro-
2,6-Dibromo-3-chloro-
4,6-Dibromo-3-chloro-
2-Bromo-4-chloro-
4-Bromo-2,3-dichloro-
4,6-Dibromo-2-chloro-
1552
1872
2,4,6-Tribromo-3-chloro-
4-Chloro-
1160
1301
2,6-Dibromo-4-chloro-
1546
1763
2,3-Dichloro-
4,6-Dibromo-2,3-dichloro-
6-Bromo-2,3-dichloro-
None
1474
2,4-Dichloro-
2,5-Dichloro-
1286
1284
6-Bromo-2,4-dichloro-
1455
1762
4-Bromo-2,5-dichloro-
6-Bromo-2,5-dichloro-
None
1576
1473
4,6-Dibromo-2,5-dichloro-
2,6-Dichloro-
3,4-Dichloro-
1202
1373
4-Bromo-2,6-dichloro-
1461
1757
2-Bromo-3,4-dichloro-
6-Bromo-3,4-dichloro-
2-Bromo-3,5-dichloro-
4-Bromo-3,5-dichloro-
2,4-Dibromo-3,5-dichloro-
2,6-Dibromo-3,5-dichloro-
None
1596
1571
1563
1678
1899
1746
2,6-Dibromo-3,4-dichloro-
3,5-Dichloro-
1349
2,4,6-Tribromo-3,5-dichloro-
2089
2,4,5-Trichloro-
2,4,6-Trichloro-
3,4,5-Trichloro-
Pentachloro-
1488
1367
1581
1782
6-Bromo-2,4,5-trichloro-
1671
1977
''
None
2-Bromo-3,4,5-trichloro-
None
1795
2,6-Dibromo-3,4,5-trichloro-
None
of individual components 0.5–1.0 mg cm–3. The resulting
mixture was analyzed by gas chromatography with ECD
under the following conditions: quartz capillary column
TR-1 (Thermo) 30 m × 0.32 mm × 0.25 mm, detector
Technique of identification of chloroanilines in the
aqueous environments. We prepared alcoholic solution
of chloroaniline (2,4,5-trichloro-, 2,4,6-trichloro-,
3,4,5-trichloro-, and pentahloranilin) with concentration
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 10 2011

IDENTIFICATION OF BROMINATION PRODUCTS OF CHLORO-SUBSTITUTED ANILINES
1751
temperature 320°C, evaporator temperature 320°C,
column temperature 170°C (220°C), carrier gas nitrogen;
carrier gas pressure at an inlet 50 kPa, flow dividing 1 :
30; blower of detector 20 cm3 min–1.
was carried out for 2 min (20–25°C), after bromination
ending an excess of bromine was removed by sodium
thiosulfate: the estimated concentration in the sample
was 0.001 mol dm–3. The resulting bromoderivatives
of chloroaniline were extracted by 1 cm3 of toluene for
10 min on a magnetic stirrer. The resulting organic extract
was analyzed by gas chromatography with ECD under
the conditions described above.
Based on the obtained chromatograms we determined
corrected retention time tR [22] of chloroanilines and
computed parameters of linear regression log tR =
f(RI), where RI was retentions index of corresponding
chloroaniline (Table 1). By such equations we calculated
values of retention time tR or tR' of bromoderivatives of
chloroaniline and their trifluoroacetates using the known
RI values (Table 1, 2). To estimate the dead time of the
chromatographic system t0, necessary to calculate the
corrected retention time (tR'–t0), we injected in it a dose
of 5–10 mm3 methane.
Then we placed the sample (500 cm3) in a flask,
created a weakly alkaline medium (glycine buffer, pH
8.5–9), and added an internal standard 4,6-dibromo-
1,2-dimethoxybenzene (1 g cm–3, 0.5 cm3). Then we
injected bromine water: the calculated molecular bromine
content in the sample was 0.0005 mol dm–3. Bromination
Based on the chromatograms we calculated absolute
retention time of all the present components, its value
we compared with previously calculated values for
bromoderivatives of chloroaniline and identified
substances with similar values of tR.
To confirm the identification results 0.2 cm3 of the
organic extract was probed in a glass vial of 1.5 cm3,
20 mm3 of trifluoroacetic anhydride was kept for 2 h
at 65°С and analyzed by gas chromatograph with ECD
under the similar conditions.
The resulting trifluoroacetate were identified with
the aid of values of tR close to calculated, provided
that there were no peaks corresponding to them in the
Table 2. Results of calculation of absolute retention time tR' of bromoderivatives of chloroanilines by their retention
indices
tR'
tR'
tR'
ΔtR'
tR'
ΔtR'
(calculated)
(calculated)
Compound
RI
s
s
column temperature 220°С
column temperature 170°С
2,4,6-Trichloroanilinea
1367
1455
1488
1546
1581
1646
1671
1757
1763
1782
38
53
36b
49
55
67
76
96
2
4
126
123c
177
204
258
298
391
433
618
634
686
3
7
6-Bromo-2.4-dichloroaniline
2,4,5-Trichloroaniline
184
203
269
303
401
440
640
656
700
56
1
1
2,6-Dibromo-4-chloroaniline
3,4,5-Trichloroaniline
73
6
11
5
78
2
2,4,6-Tribromoaniline
103
110
151
153
161
7
10
7
6-Bromo-2,4,5-trichloroaniline
2,6-Dibromo-3,4-dichloroaniline
4,6-Dibromo-2,3-dichloroaniline
Pentachloroaniline
104
6
140
143
153
11
10
8
22
22
14
a
RIs of compounds selected as reference components for the calculation of parameters of equation of linear regressions log tR' = a(RI) + b
are in bold
b
c
Value is computed by equation of linear regression log tR' = 0.0015(RI) – 0.4873 (sa = 3.03 × 10–5, sb = 0.0473).
Value is computed by equation log tR' = 0.0018(RI) – 0.3711 (sa = 1.78 × 10–5, sb = 0.0278).
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 10 2011

1752
GRUZDEV et al.
chromatogram of bromoderivatives of chloroaniline.
final products of bromination of chloroanilines. Since
chlorine and bromine are two isotope elements (natural
abundance 35Cl 75.5%, 37Cl 24.5, 79Br 50.5, 81Br 49.5),
interpretation of mass spectra of compounds containing
atoms of these halogen, is greatly facilitated by the
presence of characteristic multiplets of peaks of halogen-
containing ions (Fig. 1). The intensity of the peaks in the
multiplets depends on the number and type of halogen
atoms and can be calculated by the known formulas [23].
Thus, for mono-subtituted chloroaniline with bromine the
estimated ratio of peak intensities of the ions M : M + 2 :
M + 4 (where M is molecular mass number calculated
by the mass number of light isotopes of halogens) must
be equal to 3 : 4 : 1; the real ratio of the intensities of
the ions 205, 207, and 209 in the mass spectra (Fig. 1) is
close to such estimates.
In addition, for the identified bromoderivatives and
their trifluoroacetates we computed ratios of areas KS:
Si*SS
KS = ––––––,
(1)
*
SS Si
where Si, SS are areas of the peaks of bromoderivatives
of chloroaniline and internal standard, 4,6-dibromo-
1,2-dimethoxybenzene, in the chromatogram of the
extract before acylation; Si*, SS*, areas of the peaks of
trifluoroacetate of bromoderivative of chloroaniline and
internal standard on the chromatogram of the extract
after acylation.
To make definitive conclusions about the presence of
chloroaniline being determined in the sample of water we
compared values of KS with data of Table 3.
For identified initial reagents and products of
bromination of chloroanilines were found the linear-to-
logarithmic RI listed in Table 1.
Identification of the products of bromination of
chloroanilines. Gas chromatography-mass spectrometric
analysis of chloroanilines blends and products of their
bromination gave mass spectra on which basis we
performed identification of all the initial reagents and
Establishing the structures of isomeric intermediates
of bromination of chloroaniline is the greatest difficulty
in identification, since their mass spectra are virtually
identical (Fig. 1). In this case RI dependence on the
Table 3. Increase in sensitivity of ECD relative to trifluoroacetates of bromoderivatives of chloroanilines KS and their retention
inidices
Compound
2,4,6-Tricloroaniline trifluoroacetate
RI
KS
1.89
1.36
1.21
1.41
1.22
1
1433
1513
1523
1598
1607
1622
1694
1696
1784
1785
1793
1794
1885
1971
2081
6-Bromo-2,4-dichloroaniline trifluoroacetate
4-Bromo-2,6-dichloroaniline trifluoroacetate
2,6-Dibromo-4-chloroaniline trifluoroacetate
4,6-Dibromo-2-chloroaniline trifluoroacetate
4,6-Dibromo-1,2-dimethoxybenzene (internal standard)
2,4,6-Tribromoaniline trifluoroacetate
1.25
1.27
1.43
1.19
1.17
1.14
1.12
1.02
1.05
6-Bromo-2,4,5-trichloroaniline trifluoroacetate
Pentachloroaniline trifluoroacetate
2,6-Dibromo-3,4-dichloroaniline trifluoroacetate
4,6-Dibromo-2,3-dichloroaniline trifluoroacetate
4,6-Dibromo-2,5-dichloroaniline trifluoroacetate
2,4,6-Tribromo-3-chloroaniline trifluoroacetate
2,6-Dibromo-3,4,5-trichloroaniline trifluoroacetate
2,4,6-Tribromo-3,5-dichloroaniline trifluoroacetate
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 10 2011

IDENTIFICATION OF BROMINATION PRODUCTS OF CHLORO-SUBSTITUTED ANILINES
(a)
1753
RI
(b)
Fig. 2. The dependence of retention indices RI of chloroaniline
on the number n and the position of chlorine atoms in the
molecule. (1) No substituents in the ortho positions, (2) one
chlorine atom in the ortho position, (3) two chlorine atoms in
the ortho positions.
coefficients. In the series of compounds aniline–4-
chloroaniline–3,4-dichloroaniline–3.4.5-trichloroaniline
(Fig. 2, curve 1) the chlorine atoms in ortho positions
relative to the amino group are absent, and the slope of
the corresponding line has a maximum value a = 212.1
(r2 = 0.996). When the chlorine atom in one of the ortho
positions in the series aniline–2-chloroaniline–2,4-
dichloroaniline–2,4,5-trichloroaniline (Fig. 2, curve 2) the
slope decreases: a = 181.2 (r2 = 0.995). In the presence of
chlorine atoms in both ortho positions (Fig. 2, curve 3)
this effect is enhanced so that in the series of aniline–2,6-
dichloroaniline–2,4,6-trichloroaniline a = 138.8 (r2 =
0.996).
(c)
Thus, the intramolecular steric effects in the molecules
of ortho-substituted chloroaniline, namely, shielding
the amino group containing active hydrogen atoms by
chlorine atoms, appear via a regular decrease in their
boiling points and, consequently, chromatographic
RI compared with isomers having no chlorine atoms
in ortho positions. One of the concepts that explain
the observed effects, assumes that in the molecules
of the ortho-substituted chloroaniline there are weak
intramolecular hydrogen bonds H–Cl [24]. Similarly,
compounds with two intramolecular hydrogen bonds H–
Cl are characterized by lower RI compared with isomers
containing only one chlorine atom in ortho positions.
In the presence of bromine atoms like “ortho-effect” is
also shown that is indicated by a significant difference in
RI values of isomeric 2- and 4-bromoaniline (1173 and
1248), as well as 2,6 - and 2,4-dibromoanilines (1370
and 1465).
Fig. 1. Chromatogram of (a) 2-chloroaniline bromination
products and (b, c) mass spectra of monobromoderivatives
of 2-chloroaniline. (I) Intensity (%), (τ) time, min. (a): (1)
2-chloroaniline, (2) monobromo derivative of 2-chloroaniline
(isomer 1), (3) monobromoderivative of 2-chloroaniline (isomer
2), (4) 4,6-dibromo-2-chloroaniline. Isomer: (b) 1, (c) 2.
position of the halogen atoms in the aromatic ring
relative to the amino group helps to conform RIs
with structures of specific compounds. Analysis of RI
values of chloroaniline containing different numbers of
chlorine atoms in the molecule, reveals three series of
linear dependencies RI = anCl + b with high correlation
Physical, chemical, and chromatographic constants
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 10 2011

1754
GRUZDEV et al.
4
of chlorophenols are subjected to the same regularities,
for examples:
Isomer
Тb, °С
175–176
220
RI
2-Chlorophenol
4- Chlorophenol
2-Bromophenol
4- Bromophenol
977 ± 12
1173 ± 14
1084 ± 15
1307 ± 19
3
1
2
194–195
236
Accounting for of the ortho effect enables easy
association of RI of isomers of virtually identical mass
spectra with corresponding structures of the molecules.
Consequently, from seven pairs of these isomers
(Table 1) each component can be identified uniquely, for
example: RI (2-bromoaniline) < RI (4-bromoaniline),
RI (2.6-dibromoaniline) < RI (2.4-dibromoaniline),
RI (6-bromo-2-chloroaniline) < RI (4-bromo-2-
chloroaniline), RI (6-bromo-2,3-dichloroaniline) <
RI (4-bromo-2,3- dichloroaniline), RI (6-bromo-2,5-
dichloroaniline) < RI (4-bromo-2,5- dichloroaniline),
RI (2-bromo-3,5- dichloroaniline) < RI (4-bromo-3,5-
dichloroaniline), RI (2,6-dibromo-3,5- dichloroaniline) <
RI (2,4-dibromo-3,5- dichloroaniline).
Fig. 3. Chromatogram of a mixture of chloroanilines
(0.5 μg cm–3). (τ) Time, min. (1) 2,4,6-Trichloroaniline,
(2) 2,4,5-trichloroaniline, (3) 3,4,5-trichloroaniline, (4)
pentachlorianiline.
For this pair of isomers such as 2-bromo-3,4-
dichloroaniline and 6-bromo-3,4-dichloroaniline, the
considered rule is not applicable, since both compounds
in the ortho-position to amino group have one atom
of bromine each. But RI of these isomers are quite
different (by 25 units of the index, Table. 1), hence
their identification is possible using more sophisticated
algorithms.
RI
Fig. 4. The dependence of the corrected retention time log tR'
of chloroanilines (2,4,6-, 2,4,5-, 3,4,5-trichloroanilines and
pentachloroaniline) on their retention indices at column
temperature (1) 170 and (2) 220°С.
ABCD being characterized.
In accordance with this concept for the evaluation of
RI of 6-bromo-3,4-dichloroaniline the following version
of “assembly” of its structure can be considered with
molecules of other bromine- and chlorine-containing
anilines according to scheme (1); for RI of 2-bromo-3,4-
dichloroaniline, by scheme (2).
To evaluate RI of virtually any halogenated anilines
on standard nonpolar polydimethylsiloxane stationary
phases can be used a modified version of additive
schemes [25–27]. It provides for the selection of structural
analogues of target compounds as close as possible to
each other to which the missing structural elements are
added or subtracted, excluding the overlapping fragments
of the structure. So if, for forming the structure ABCD
were selected precursors ABC and BCD, then ABC +
BCD – BC → ABCD, and the condition of additivity of
chromatographic RI have the follow form:
The mean values of RI of 6-bromo-3,4-dichloroaniline
and 2-bromo-3,4- dichloroaniline, assessed along
with noted by two different ways, are 1566 and 1590,
respectively. The calculated value of RI sufficiently
close to the experimental (1571 and 1596), and,
most importantly, the values of RI for 6-bromo-3,4-
dichloroaniline in all cases are less than RI of 2-bromo-
3,4-dichloroaniline. This allows assigning a lower
value of two RI of isomeric bromodichloroanilines to
6-bromo-3,4-dichloroaniline (Table 1), i.e., identifying
RI (ABCD) ≈ RI (ABC) + RI (BCD) – RI (BC),
where RI (ABC), RI (BCD) and RI (BC) are known
retention indices of the structural analogs of analyte
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IDENTIFICATION OF BROMINATION PRODUCTS OF CHLORO-SUBSTITUTED ANILINES
1755
both isomers.
taking into account the ortho effect, only 4-bromo-
3-chloroaniline can be identified. In this molecule
substituents at positions 2 and 4 are missing, so this
isomer must have a maximum value of RI = 1468. In the
The same uncertainty in RI assigning is observed
for three mono- and three dibromoderivatives of
3-chloroaniline (Table 1). In the first group of isomers,
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1756
GRUZDEV et al.
4
(a)
3
2
5
6
7
IS
1
4
(b)
3
2
IS
1
5
6
7
9
8
11
10
Fig. 5. Chromatogram of (a) extract of bromoderivatives of 2-chloroaniline registered under optimal conditions of bromination and (b) at
deficiency of bromine. (I) Intensity (mV), (τ) time, min; The same for Fig. 6. (1) 2,4,6-trichloroaniline, (2) 6-bromo-2,4-dichloroaniline,
(3) 2,6-dibromo-4-chloroaniline, (4) 2,4,6-tribromoaniline, (5) 6-bromo-2,4,5-trichloroaniline, (6) 2,6-dibromo-3,4-dichloroaniline, (7)
4,6-dibromo-2,3-dichloroaniline, (8) 2,4,5-trichloroaniline, (9) 6-bromo-2,3-dichloroaniline, (10) 2-bromo-3,4-dichloroaniline, (11)
4-bromo-2,3-dichloroaniline, (IS) 4,6-dibromo-1,2-dimethoxybenzene.
second group of isomers 2,6-dibromo-3-chloroaniline has
two ortho-substituents, and, hence, the minimum value
of RI = 1570.
RI of 4,6-dibromo-3-chloroaniline, according to
scheme (6).
The mean values of RI for 2-bromo-3-chloroaniline
and 6-bromo-3-chloroaniline according to the estimates
of the three options are 1383 and 1355, which agree
well with the experimentally determined values of
RI of bromination products (1388 and 1370). For the
second pair of isomers (2,4-dibromo-3-chloroaniline and
4,6-dibromo-3-chloroaniline) additive estimates of RI
are 1691 and 1663, respectively (experimental values,
1701 and 1675).
The other four compounds (2-bromo-3-chloroaniline,
6-bromo-3-chloroaniline, 2,4-dibromo-3-chloroaniline,
and 4,6-dibromo-3-chloroaniline) have one ortho-
substituent , so their identification is performed using
additive schemes. For example, RI of 2-bromo-3-
chloroaniline can be assessed by scheme (3); RI of
6-bromo-3-chloroaniline, according to scheme (4); RI of
2,4-dibromo-3-chloroaniline, according to scheme (5);
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IDENTIFICATION OF BROMINATION PRODUCTS OF CHLORO-SUBSTITUTED ANILINES
1757
4 + 5
3
2
1
6
IS
7
1000
Fig. 6. Chromatogram of (a) extract of bromoderivatives of chloroanilines after acylation. (1) 2,4,6-trichloroaniline trifluoroacetate, (2)
6-bromo-2,4-dichloroaniline trifluoroacetate, (3) 2,6-dibromo-4-chloroaniline trifluoroacetate, (4) 2,4,6-tribromoaniline trifluoroacetate, (5)
6-bromo-2,4,5-trichloroaniline trifluoroacetate, (6) 2,6-dibromo-3,4-dichloroaniline trifluoroacetate, (7) 4,6-dibromo-2,3-dichloroaniline
trifluoroacetate, (IS) internal standard 4,6-dibromo-1,2-dimethoxybenzene.Arrows indicate the positions of the peaks of bromoderivatives
of chloroanilines before acylation.
As in the previous case, for isomers with the same
number of substituents in ortho positions molecules
with the most asymmetrical arrangement of substitutents
are characterized by lower RIs. It should also be notes
that in the some versions of mounting of the target
structures, e.g., in Schemes 1–4, RIs values are used of
boromoderivatives of chloroanilines which identification
was performed earlier with application of additive
schemes (2-bromo-3,4-dichloroaniline and 6-bromo-
3,4-dichloroaniline). The calculated values are close to
the experimental RI that confirms the correctness of the
identification of the bromination products.
their RIs differ by more than 100 units (Table 1, Fig. 3).
In the isothermal mode of the gas chromatographic
analysis, the logarithms of the corrected retention time
tR' of homologs are associated with the number of carbon
atoms in molecules nC by linear dependence of the
following form [22]
log tR' = anC + b.
(2)
Accounting for that by definition RI values equal
100nC was assigned to the standanrd n-alkanes, relation
(2) can be, first, written in the mathematically equivalent
form (3), and sencondly, extended to chloro-substitutes
anilines whose RI are expressed in the scale of the
standard alkanes:
Features of identification of bromoderivatives
chloroaniline using ECD. Synthesis of bromoderivatives
of chloroaniline is intended primarily for their gas
chromatographic determination in water (0.01–1 μg dm–3)
with halogen selective electron capture detector (GC-
ECD). However, in this version RI of analytes can not
be fully used for identification, accounting for also the
fact that n-alkanes are hardly registered by ECD. The
effective application of RI requires adaptation of these
values for GC-ECD, at least under isothermal conditions
of the analysis. For this purpose a reverse conversion of
RI of chloroaniline can be used in their retention time.
log tR' = a'RI + b'.
(3)
As a result, processing the data for chloroaniline,
we obtain the linear regression relationship by which
we can assess the retention time of bromoderivatives
of chloroaniline on the basis of their RI under the same
isothermal conditions (Table 2, Fig. 4). The relative
deviations of the calculated and experimental values of tR
at different temperatures do not exceed an average 7–8%.
However, with increasing analysis time (at a decrease in
the column temperature) the absolute deviations naturally
also increase, and, therefore, an identification performed
by the considered method is recommended for maximum
temperature, which provides a satisfactory separation of
At equal concentrations of the chloroanilines in
the sample the most intense signals of ECD will be
observed for four compounds with the largest number
of chlorine atoms: 2,4,5-trichloro-, 2,4,6-trichloro-,
3,4,5-trichloro-, and pentachloroanilines. Identification of
these compounds in a chromatogram is not difficult, since
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GRUZDEV et al.
the mixture components.
chloroderivatives (all isomers of mono- and dichloro-
anilines, 2,4,5-, 2,4,6-, and 3,4,5-trichloroanilines, pen-
tachloroaniline) in aqueous environments we suggested
bromination reaction, followed by gas chromatographic
definition of bromoderivatives of chloroanilines on the
electron capture detector. To identify the products of
bromination of chloroanilines in combination with mass
spectrometric data we used chromatographic retention in-
dices on standard nonpolar polydimethylsiloxane station-
ary phase determined for 50 compounds in this class. The
technique of identifying bromoderivatives of chloroani-
lines in water was developed in the gas chromatographic
determination by the electron capture detector. Synthesis
of trifluoroacetyl derivatives of bromoderivatives of
chloroanilines was additionally conducted to improve
the reliability of their identification.
In the case of appearing on the chromatograms
of bromoderivatives of chloroaniline “extra” peaks
(Fig. 5b) the presence in the probe of intermediates
of bromination should be checked using the data in
Table 1. Thus, bromination of mixture of chloroaniline
with a deficiency of bromine leads to a semi-quantitative
formation of 6-bromo-2,4,5-trichloroaniline and a peak
of the initial substance, 2,4,5-trichloroaniline (tR' = 126 s;
calculated tR' = 123 s) appears on the chromatogram.Also
peaks of the intermediate of products of bromination of
2,3- and 3,4-dichloroanilines are identified: 6-bromo-
2,3-dichloroaniline (tR' = 195 s; calculated tR' = 191 s),
4-bromo-2,3-dichloroaniline (tR' = 330 s; calculated
tR' = 324 s) and 2-bromo-3,4-dichloroaniline (tR' = 321;
calculated tR' = 317 s).
The appearance in the probe of the intermediates of
bromination is confirmed, in this case, by a decrease
in the peak intensities of end products of bromination:
4,6-dibromo-2,3-dichloroaniline and 2,6-dibromo-
3,4-dichloroaniline compared with the chromatogram
samples, which were recorded in the bromination under
optimal conditions (Fig. 5a).
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