Gas-Chromatographic identifi cation of products formed in iodination of methyl phenols by retention indices

Article abstract of DOI:10.1134/S1070427212090108

Iodination reaction followed by conversion of iodine-substituted methylphenols to the corresponding trifl uoroacetates was suggested for improving the sensitivity of the gas-chromatographic determination of phenol and its methyl-substituted derivatives (al isomers of mono- and diethylphenols, 2,3,5-, 2,3,6-, and 3,4,5-trimethylphenols) in aqueous media. Acylation products of iodo methylphenols (104 compounds) were identifi ed by linear-logarithmic retention indices on a standard nonpolar polydimethylsiloxane stationary phase, and the pattern of their variation with the number and nature of substituents were characterized. A procedure for identifi cation of methyl-substituted phenols in water in their gas-chromatographic determination with an electron-capture detector was developed. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S1070427212090108

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 9, pp. 1355−1365. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © I.V. Gruzdev, I.M. Kuzivanov, I.G. Zenkevich, B.M. Kondratenok, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 9,
pp. 1440−1450.
SORPTION
AND CHROMATOGRAPHY
Gas-Chromatographic Identification of Products Formed
in Iodination of Methyl Phenols by Retention Indices
I. V. Gruzdeva, I. M. Kuzivanovb, I. G. Zenkevichc, and B. M. Kondratenoka
a Institute of Biology, Komi Scientific Center, Ural Branch, Russian Academy of Sciences, Syktyvkar, Komi Republic, Russia
e-mail: gruzdev@ib.komisc.ru
b Syktyvkar State University, Syktyvkar, Komi Republic, Russia
c St. Petersburg State University, St. Petersburg, Russia
Received May 12, 2012
Abstract—Iodination reaction followed by conversion of iodine-substituted methylphenols to the corresponding
trifluoroacetates was suggested for improving the sensitivity of the gas-chromatographic determination of phenol and
its methyl-substituted derivatives (al isomers of mono- and diethylphenols, 2,3,5-, 2,3,6-, and 3,4,5-trimethylphenols)
in aqueous media. Acylation products of iodo methylphenols (104 compounds) were identified by linear-logarithmic
retention indices on a standard nonpolar polydimethylsiloxane stationary phase, and the pattern of their variation
with the number and nature of substituents were characterized. A procedure for identification of methyl-substituted
phenols in water in their gas-chromatographic determination with an electron-capture detector was developed.
DOI: 10.1134/S1070427212090108
Phenol and its methyl-substituted derivatives are
widely occurring organic toxicants contaminating
various objects of the biosphere. The wide occurrence
of methylphenols in the environment is due to their
good solubility in water (g per 100 mL: ~8.2 for
phenol, 2.5 ± 0.1 for 2-methylphenol, and 2.3 ± 0.1 for
4-methylphenol) and low vapor pressure [1].
poor sensitivity (~10 μg dm–3), which is due to the small
degree of recovery of methylphenols from aqueous
media in extraction concentration because of their high
hydrophilicity [5].
Thefactthatphenolshaveahydroxygroupcontaining
an active hydrogen atom opens up wide opportunities
for their chemical modification [6]. Substitution of the
hydrogen atom in the OH group diminishes the overall
polarity of their molecules and substantially improves
both extraction and chromatographic characteristics
of analytes. Ether derivatives of methylphenols are
obtained directly in water [7–10] or in organic solvents
[11–13] upon an extraction concentration. However,
both these variants have important shortcomings
impairing the determination sensitivity. For example,
etherification in water is accompanied by hydrolysis of
both the resulting ethers and reagents, and preliminary
extraction of methylphenols is inefficient [14].
The unique physicochemical properties (inhibiting
action, aseptic activity) and the high reactivity of
methylphenols create favorable conditions for their
various industrial applications. The main anthropogenic
sourcesfromwhichmethylphenolsfindtheirwayintothe
environmentiswastewaterfromcoke-andpetrochemical
plants, organic syntheses, and pharmaceutical industries
[2].
Determination of phenol and its methyl-substituted
derivatives in aqueous media requires a high detection
selectivity and sensitivity, because the maximum
permissible concentrations strongly vary even between
isomeric methylphenols (mg dm–3): phenol 0.001,
2-methylphenol 0.004, 2,4- and 2.6-methylphenols
0.25, and 3,5-dimethylphenol 0.01 [3, 4]. This problem
can only be solved by chromatographic methods;
however direct chromatographic determinations have
The optimal approach consists in creating condi-
tions for recovery of the maximum possible amounts
of methylphenols from the aqueous into the extract and
performing an additional chemical modification in the
organic solvent medium. We used this approach in the
1355

1356
GRUZDEV et al.
procedure in which iodo derivatives of methylphenols
are obtained in water, liquid extraction with toluene is
performed, the iodo derivatives of methylphenols are ac-
ylated in the extract with trifluoroacetic anhydride, and
a gas-chromatographic determination is made using a
selective electron-capture detector (ECD). Introduction
of iodine into methylphenol molecules markedly raises
the hydrophobicity of the derivatives [15], which pro-
vides effective recovery of iodo derivatives of methyl-
phenols from water into organic extracts in subsequent
liquid extraction (up to 75–95%). In addition, the pres-
ence of iodine atoms in methylphenol molecules enables
their gas-chromatographic determination with an ECD
having high sensitivity and selectivity toward organic
compounds [16]. Acylation of iodo derivatives of meth-
ylphenols is necessary for raising their volatility and
diminishing the asymmetry of chromatographic peaks
[14].
halogenation of phenols [18]. Iodine was introduced
in nearly stoichiometric ratios, the iodination time was
varied, depending on the chemical activity of a substrate,
from 1 to 10 min. On being extracted with toluene, the
iodination products were analyzed on chromatographs
Kristall 2000M (Khromatek) with a flame-ionization
detector and Kristall 5000 (Khromatek) with an ECD.
The iodo derivatives of the methylphenols were
identified, and linear-logarithmic retention indices
determined, with a TRACE DSQ chromato-mass-
spectrometer (Thermo), with electron-impact ionization,
electron energy of 70 eV, and m/z range 50–650 Da. The
determination conditions were the following: program-
med thermostat temperature 50°C–5°C min–1–300°C;
30 m × 0.32 mm × 0.25 μm quartz capillary column
(TR-1, Thermo); carrier-gas helium (99.99%), flow rate
1 cm3 min–1, flow division 1 : 40; temperatures 320,
200, and 200°C for evaporator, interface, and detector,
respectively.
Performing a double-stage chemical modification
makes it possible to lower the detection limit of
methylphenols in water to 0.005–0.01 μg dm–3, which,
in turn, requires a reliable identification of the resulting
derivatives in complex multicomponent mixtures.
Particularly difficult is identification of isomers (three
monomethylphenols, six dimethylphenols, and three
trimethylphenols)becauseoftheirclosephysicochemical
and, accordingly, chromatographic characteristics [17].
To determine RIs, extracts of iodo derivatives of
the methylphenols and their trifluoroacetates were
metered together with a mixture of C8–C24 reference
alkanes (only homologs with even number of carbon
atoms in molecules). The RI of a component situated
in a chromatogram between n-alkane with n and n +
1 carbon atoms was calculated in two ways: from the
retention times of three n-alkanes with n – 1, n, and n +
1 or n, n + 1, and n + 2 carbon atoms in molecules [19].
Coincidence of RI values calculated from different sets
of reference alkanes serves as a criterion of correctly
revealed references in chromatograms. For each
mixture, three chromatograms were obtained, and,
therefore, each analyte is characterized by an average
over six determinations and the determination error does
not exceed ±3 index units.
In the present study, we consider identification
of products formed in iodination and acylation of
methylphenols on the basis of mass-spectrometric
data and chromatographic retention indices (RIs) on
standard nonpolar polydimethylsiloxane stationary
phases. Particular attention is given to adaptation of
calculated RIs to the variant in which iodo derivatives of
methylphenols and their trifluoroacetates are identified
with an ECD.
To perform identification of the methylphenols
in aqueous media, we prepared an alcoholic solution
of chlorophenols (2,4,6-trichloro-, 2,3,6-trichloro-,
2,3,5,6-tetrachlorophenol, and pentachlorophenol)
with concentrations of individual components of 0.5–
1.0 μg cm–3. The resulting mixture was analyzed on a
gas chromatograph with an ECD under the following
conditions: 30 m × 0.32 mm × 0.5 μm ZB-1 quartz col-
umn (Phenomenex); detector and evaporator tempera-
tures 320°C; programmed temperature of the column
thermostat, 140°C–5°C min–1–290°C; carrier-gas nitro-
gen; inlet pressure of the carrier-gas, 50 kPa; flow divi-
sion 1 : 30; detector pressurization 20 cm3 min–1.
EXPERIMENTAL
We used the following preparations: phenol; 2-, 3-,
and 4-methylphenol; 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and
3,5-dimethylphenol; and 2,3,5-, 2,3,6-, and 3,4,5-tri-
methylphenol (Riedel-de-Haen), with ≥99% main sub-
stance. The rest of reagents and solvents were of analyti-
cally or chemically pure grade.
Methylphenols were iodinated individually for
each compound (0.5 mg cm–3) in an ammonia buffer
solution with pH ~9 by using the general procedure for
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 9 2012

GAS-CHROMATOGRAPHIC IDENTIFICATION
tR', s
1357
Basedonthechromatogramsobtained,wedetermined
corrected retention times tR' of the chlorophenols,
necessary for calculation of parameters of the linear
regression tR' = f(RI), where RI is the retention index of
the corresponding chlorophenol (Fig. 1). The resulting
equation was used to calculate the tR' and the absolute
retention time tR of iodo derivatives of the methylphenols
and their trifluoroacetates from the known values of RIs
(Tables 1, 2). The dead time t0 of the chromatographic
system, necessary for calculating the corrected retention
time tR – t0 can be estimated by the leading edge of the
solvent (ethanol, toluene) peak or by introduction of
5–10 mm3 of methane.
Further, we charged a volumetric flask with 500 cm3
of a sample being analyzed, created an alkaline medium
(glycine or ammonia buffer solution with pH ~ 10),
and added the internal standard, 4,6-dibromo-1,2-
dimethoxybenzene (1 μg cm–3, 0.5 cm3). Then we
introduced iodide water; the calculated content of
molecular iodine in the sample was 0.0005 mol dm–3.
The iodination was performed during 3 min (20–25°C);
after the iodination was complete, the excess of iodine
was removed by addition of a sodium thiosulfate
solution; the calculated concentration in the sample
was 0.001 mol dm–3. The resulting iodo derivatives of
the methylphenols were extracted, after the aqueous
solution was acidified to pH 2–3, with 1 cm3 of toluene
in the course of 10 min in a magnetic stirrer (3000 rpm).
The resulting organic extract was analyzed at the same
conditions as those for the mixture of chlorophenols.
RI
Fig. 1. Dependence of the corrected retention time tR' of iodo
derivatives of methylphenols (points) and chlorophenols 1–4
on their retention indices RI. (1) 2,4,6-trichlorophenol, (2)
2,3,6-trichlorophenol, (3) 2,3,5,6-tetrachlorophenol, and (4)
pentachlorophenol.
methylphenols and their trifluoroacetates, we found
from the chromatograms the parameter Ks:
SiSs*
Ks = –——,
SsSi*
where Si and Ss are the peak areas of the iodo derivative of
a methylphenol and the internal standard (4,6-dibromo-
1,2-dimethoxybenzene) in the chromatogram of the
extract before acylation, andSi* and Ss*, peak areas of the
trifluoroacetate of the iodo derivative of a methylphenol
and internal standard in the chromatogram of the extract
after the acylation.
The values of Ks were compared with those in Table 2
and then the final conclusion was made whether the
water sample being analyzed contains the methylphenols
being determined.
RESULTS AND DISCUSSIONS
The chromatograms obtained were used to calculate
tR' and tR for all the components, compared these values
with those previously calculated for iodo derivatives
of the methylphenols, and found substances with close
values of tR (Fig. 2).
The interaction of methylphenols with molecular
iodine in water under the chosen conditions and,
further, with trifluoroacetic anhydride in the organic
extract guarantees that the final analytical forms,
trifluoroacetatesofiododerivativesofthemethylphenols,
are obtained (Table 1). If, however, the reagents are
deficient, a number of intermediate compounds can be
formed together with the final products. This impairs
the determination sensitivity of methylphenols, makes
larger the error of analytical measurements, and leads
to other negative consequences. Such conditions may
appear, for example, because of a deficiency of iodine
(presence reducing agents in a sample being analyzed) or
hydrolysis of trifluoroacetic anhydride (ingress of water
into the extract). Therefore, to monitor the completeness
of the chemical modification of the methylphenols, we
To confirm the identification results, we took a 0.2-
cm3 sample of the organic extract into a vial, introduced
2 mm3 of pyridine and 10 mm3 of trifluoroacetic
anhydride, kept the mixture at a temperature of 60°C
for 15 min, and analyzed under the conditions specified
above.
The trifluoroacetates obtained were identified by
tR close to the calculated values on condition that
the corresponding peaks of iodo derivatives of the
methylphenols are not present in a chromatogram (Fig. 3).
In addition to tR of iodo derivatives of the
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 9 2012

1358
GRUZDEV et al.
Table 1. Retention indices of methylphenols and products of their iodination on a polydimethylsiloxane stationary phase
(retention indices of trifluoroacetates of these compounds are given in parentheses)
Substituent in the
starting phenol
Intermediate
iodination product
Final iodination
product
RI
RI
RI
2-Methyl-
1034 (926)
6-Iodo-
1232 (1235)
1430 (1259)
1259 (1268)
1257 (1261)
1262 (1271)
1453 (1285)
1661 (1573)
1670 (1606)
1677 (1626)
4,6-Diiodo-
1627 (1575)
4-Iodo-
4-Methyl-
3-Methyl-
1055 (958)
1057 (950)
2-Iodo-
2,6-Diiodo-
1666 (1593)
2108 (1979)
6-Iodo-
2,4,6-Triiodo-
2-Iodo-
4-Iodo-
2,6-Diiodo-
4,6-Diiodo-
2,4-Diiodo-
2,6-Dimethyl-
2,4- Dimethyl-
2,3,5-Trimethyl-
1080 (997)
1126 (1028)
1247 (1142)
4-Iodo-
1473 (1331)
1341 (1339)
1925 (1868)
6-Iodo-
6-Iodo-
1482 (1473)
1673 (1498)
1366 (1367)
1564 (1392)
1545 (1536)
1369 (1368)
1558 (1389)
1796 (1725)
1801 (1742)
1392 (1391)
1402 (1406)
4,6-Diiodo-
4-Iodo-
2,3- Dimethyl-
1153 (1047)
6-Iodo-
4,6-Diiodo-
1782 (1729)
4-Iodo-
3,4,5- Trimethyl-
3,5- Dimethyl-
1288 (1194)
1147 (1044)
2-Iodo-
2,6-Diiodo-
2005 (1922)
2270 (2137)
2-Iodo-
2,4,6-Triiodo-
4-Iodo-
2,6-Diiodo-
2,4-Diiodo-
6-Iodo-
3,4- Dimethyl-
1169 (1075)
2,6-Diiodo-
1830 (1751)
2-Iodo-
2,3,6-Trimethyl-
2,5- Dimethyl-
1201 (1118)
1127 (1020)
4-Iodo-
1612 (1465)
1758 (1702)
6-Iodo-
1348 (1343)
1527 (1357)
1163 (1261)
1359 (1186)
1551 (1501)
1546 (1487)
4,6-Diiodo-
4-Iodo-
Phenol
962 (859)
2-Iodo-
2,4,6-Triiodo-
1962 (1834)
4-Iodo-
2,4-Diiodo-
2,6-Diiodo-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 9 2012

GAS-CHROMATOGRAPHIC IDENTIFICATION
1359
4
7
5
6
8
12
10
9
1
11
2
3
tR, min
Fig. 2. Chromatogram of the extract of iodo derivatives of methylphenols (1 μg cm–3). (I) Intensity and (tR) retention time; the
same for Fig. 3. (1) 6-Iodo-2,4-dimethylphenol, (2) 4,6-diiodo-2-methylphenol, (3) 4-iodo-2,3,6-trimethylphenol, (4) 4,6-diiodo-2-
methylphenol, (5) 2,6-diiodo-4-methylphenol, (6) 4,6-diiodo-2,5-dimethylphenol, (7) 4,6-diiodo-2,3-dimethylphenol, (8) 2,6-diiodo3,4-
dimethylphenol, (9) 4,6-diiodo-2,3,5-trimethylphenol, (10) 2,6-diiodo-3,4,5-trimethylphenol, (11) 2,4,6-triiodo-3-methylphenol, (12)
2,4,6-triiodo-3,5-dimethylphenol, and (IS) 4,6-dibromo-1,2-dimethoxybenzene. The arrows show the retention times of the iodo
derivatives, calculated from their RIs.
12
4
6
7
11
8
5
9
10
2
1
3
tR, min
Fig. 3. Chromatogram of trifluoroacetates of iodo derivatives of the methylphenols. The numbering of the trifluoroacetate peaks
corresponds to iodo derivatives of the methylphenols in Fig. 2. The arrows show the positions of the peaks of the iodo derivatives before
acylation.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 9 2012

1360
GRUZDEV et al.
(a)
2
1
4
3
(b)
(c)
m/z
Fig. 4. (a) Chromatogram of 2-methylphenol iodination products and (b, c) mass spectra of monoiodo derivatives of 2-methylphenol:
isomers (b) 1 and (c) 2. (I) Intensity, (tR) retention time, and (m/z) mass-to-charge ratio. (a) (1) 2-Methylphenol, (2, 3) monoiodo
derivatives of 2-methylphenol (isomers 1 and 2), and (4) 4,6-diiodo-2-methylphenol.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 9 2012

GAS-CHROMATOGRAPHIC IDENTIFICATION
RI
1361
RIcalc
Fig. 6. Correlation between the calculated retention
indices RIcalc and those found experimentally, RIexp, for (1)
methylphenols and (2) iodo derivatives of methylphenols.
Fig. 5. Dependence of the retention indices RI of the
methylphenols on the number N and position of methyl groups
in the molecule. (1) No substituents in ortho positions and (2)
one methyl group in the ortho position.
Taking into account the additive nature of RIs [17]
and using contributions from methyl groups, found for
obtained all the possible iodination intermediates and
identified these compounds by mass-spectrometric
data and linear-logarithmic RIs. Here, the most serious
difficulty is posed by identification of isomers because
their mass spectra are nearly identical (Fig. 4).
monomethylphenols (ΔRICH
= 72, ΔRICH
=
3-ortho
95, ΔRICH
= 93), we can estimate RIs o3f-moettaher
variously s3u-bpasrtaituted methylphenols by the formula
Table 1 lists retention indices for the starting,
intermediate, and final products of iodination of the
methylphenols and their trifluoroacetates. Because
methylphenol molecules contain only a ingle active
center (polar OH group), their RIs will be for the most
part determined by two factors, molecular mass of the
molecule and intensity of interaction of the OH group
with the stationary phase. Both a larger mass of the
molecule and the active interaction of the OH group
with the stationary phase lead to a regular rise in the RI.
For example, values of RI linearly increase (a = 109.1,
R2 = 0.997) in the series of compounds containing
different numbers of methyl groups in the molecule:
phenol–4-methylphenol–3,4-dimethylphenol–3,4,5-
trimethylphenol. If, however, a methyl group appears
in the ortho position, the slope ratio of the linear
regression for the series phenol–2-methylphenol–2,5-
dimethylphenol–2,3,5-trimethylphenol decreases: a =
93.8, R2 = 0.984 (Fig. 5). Presence of the CH3 group in
the ortho position leads to shielding of the OH group
and makes weaker its interaction with the stationary
phase, and just these circumstances diminish the RI
of the methylphenols, compared with isomers having
no substituents of this kind. Introduction of a second
methyl group enhances the “ortho effect” (Table 1):
RI(3,4-dimethylphenol) > RI(2,4-dimethylphenol) >
RI(2,6-dimethylphenol), RI(3,4,5-trimethylphenol) >
RI(2,3,5-trimethylphenol) > RI(2,3,6-trimethylphenol).
RI(methylphenol) = RI(phenol) + n1ΔRICH
3-ortho
+ n2ΔRICH3-meta +n3ΔRICH
3-para
where n1, n2, and n3 are the numbers of methyl groups in
the ortho, meta, and para positions, respectively.
The discrepancy between the calculated and experi-
mentally found values for nine di- and trimethylphenols
is rather small and does not exceed 20% (Fig. 6).
Introduction of iodine atoms into the methylphenols
regularly raises the mass of their molecules and their RIs
(Table 1). Presence of heavy substituents makes more
pronounced the dissimilarity of the physicochemical
properties of iodo derivatives (RI variation range
930 units) as compared with the starting methylphenols
(RI variation range 250 units), which markedly
improves their separation selectivity. For example, two
pairs of isomers, 3- and 4-methylphenols and 2,4-and
2,5-dimethylphenols, are inseparable on the stationary
phase we used (polymethylsilicone), the difference
between their RIs (ΔRI) being 2 and 1, respectively.
When being determined in the form of iodo derivatives,
they are eluted from the column as separate peaks
because the difference between their retention indices is
now ΔRI = 442 and 418, respectively. It should be noted
that ΔRI also exceeds 15 for all other iodo derivatives,
and their full separation does not require any careful
choice and reproduction of chromatographic conditions.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 9 2012

1362
GRUZDEV et al.
Similarly to the methyl group, iodine atoms in the
2-methylphenol and 6-iodo-2-methylphenol, leads to a
substantial decrease in the RI of the trifluoroacetates, by
171 units, whereas the RI of the other remains nearly
unchanged: RI = 4. Substitution of the hydrogen atom
of the OH group with an acyl moiety diminishes the
polarity of the molecules, and, consequently, makes
smaller the RI (4-iodo-2-methylphenol). An iodine atom
in the ortho position in 6-iodo-2-methylphenol already
exerts a similar influence (by shielding of the hydroxy
group) and, upon introduction of the acyl fragment,
these effects are mutually canceled out.
positions 2 and 6 also give rise to the ortho effect by
blocking the OH group and weakening its interaction
with the stationary phase. For example, introduction of
an iodine atom into the para position raise the RI of the
compound by ΔRI1-para = 404 ± 25 (for 9 monoiodine-
substituted) and that into the ortho position, by only
ΔRI1-ortho = 216 ± 39 (for 13 mono iodine-substituted).
Taking the ortho effect into account makes it possible to
rather simply relate the RIs of isomers having the corre-
sponding structures: in each pair of this kind, the smaller
RI will be observed for the isomer with a iodine atom in
the ortho position, namely (Table 1): RI(2-iodophenol) <
RI(4-iodophenol), RI(6-iodo-2-methylphenol) < RI(4-
iodo-2-methylphenol, RI(2-iodo-3-mp, RI(2-iodo-
3-m) < RI(4-iodo-3-methylphenol, RI(6-iodo-2,3-
A similar behavior is also observed in acylation
for the remaining six pairs of monoiodine-substituted
isomers whose identification was based on the ortho
effect, which, in turn, confirms its adequacy.
A particular difficulty in identification of iodine-
substituted methylphenols is posed by isomers differing
only in the position of the iodine atom in one of the ortho
positions (Table 1): 6-iodo-3-methylphenol and 2-iodo-
3-methylphenol, ΔRI = 5; 6-iodo-3,4-dimethylphenol
and 2-iodo-3,4-dimethylphenol, ΔRI = 10; 4,6-diiodo-3-
methylphenol and 2,4-diiodine-3-methylphenol, ΔRI = 7.
dimethylphenol)
RI(2-iodo-3,5-dimethylphenol)
dimethylphenol), RI(6-iodo-2,3,5-trimethylphenol) <
RI(4-iodo-2,3,5-trimethylphenol).
<
RI(4-iodo-2,3-dimethylphenol),
RI(4-iodo-3,5-
<
Introduction of a second and third iodine atom into
methylphenol molecules, the values experimentally
found for some iodo derivatives begin to strongly differ
from those calculated equation
The above approach based on the ortho effect
is inapplicable to each pair of these isomers, and,
consequently, more complex algorithms should be used
for their identification.
RI(MP-I) = RI(MP) + n1ΔRI1-ortho + n2ΔRI1-para
,
A modified variant of additive schemes has proven
effective for estimation of chromatographic RIs of
various substances [21–23]. In this approach, structural
analogs as close as possible to the compounds being
identified are chosen, and lacking structural elements
are added or abstracted from these, with duplicate
molecular fragments excluded. For example, if, to form
an ABC structure, its analogs AD and BC are chosen,
then
where RI(MP) is the retention index for the starting
methylphenol, and n1 and n2 are the numbers of iodine
atoms in the ortho and para positions, respectively.
An analysis of the data we obtained demonstrated
that all the points lying away from the straight line
(Fig. 6) correspond to iodo derivatives, in whose
molecules iodine atoms substitute both ortho positions.
The retention indices of these substances are “shifted”
by approximately two hundred units upwards,
compared with the calculated values. The observed
deviations can be attributed to the absence of the
ortho effect upon introduction of an iodine atom to
the second ortho position. Presumably, the activity of
the hydroxy group is fully blocked even by the first
iodine atom and the contribution to the RI from the
second iodine atom is close to ΔRI1-para, rather than to
ΔRI1-ortho, the difference between these two being just
about 200 units. The efficiency of deactivation of the
hydroxy group by the iodine atom is well manifested in
syntheses of trifluoroacetates of monoiodine-substituted
derivatives. For example, acylation of isomers, 4-iodo-
AD + BC – D → ABC.
Because RIs are additive quantities, we can write
RI(ABC) ≈ RI(AD) + RI(BC) – RI(D),
where RI(AD), RI(BC), and RI(D) are known retention
indices of the compounds on a given stationary phase.
In accordance with this approach, we can estimate the
RI of 6-iodo-3-methylphenol by considering the follow-
ing way to “assembly” its structure from molecules of
other methylphenols and their derivatives (Scheme 1).
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 9 2012

GAS-CHROMATOGRAPHIC IDENTIFICATION
1363
Scheme 1.
OH
OH
OH
OH
I
CH3
CH3
I
_
+
CH3
CH3
_
RI = 1057
+
1232
OH
1034
=
1255
Scheme 2.
OH
OH
OH
I
I
CH3
_
+
CH3
CH3
CH3
_
RI
=
1057
+
1259
1055
=
1261
Similarly, we obtain for the RI of 2-iodo-3-
methylphenol
3,4-dimethyphenol trifluoroacetate: 1372 ± 23 against
1384 ± 21 for its isomer.
The values calculated for the RI of 6-iodo-3-meth-
ylphenol and 2-iodo-3-methylphenol by three different
additive scheme are 1255 ± 11 and 1265 ± 19, respec-
tively. These values are rather close to those obtained
experimentally (1257 and 1262), with the values of RI
for 6-iodo-3-methylphenol being in all cases smaller than
those for 2-iodo-3-methylphenol, which makes it pos-
sible to assign the smaller of two values of RI just to this
isomer (Table 1. Estimation of the RIs of trifluoroacetates
of these isomers gives similar results, which confirms the
validity of the conclusion we made (Scheme 2).
For the second pair of isomers, as also in two pre-
ceding cases, a large RI is observed for the isomer with
an in-line arrangement of substituents: 1662 ± 15 for
2,4-diiodo-3-methylphenol, against 1610 ± 25 for its tri-
fluoroacetate (experimental values: 1677 and 1626, re-
spectively). The isomer with a less “compact” arrange-
ment of substituents, 4,6-diiodo-3-methylphenol has a
smaller RI (1649 ± 9), and its trifluoroacetate, 1597 ±
12 (experimental values: 1670 and 1606, respectively).
One of goals pursued in iodination of methylphe-
nols is to enable application of a halogen-selective ECD
for their detection. However, the vast body of chro-
matographic data, and primarily the retention indices,
are in no demand in ECD analyses because the classi-
cal variant of RI calculations is based on values of tR'
for n-alkanes, which are not recorded by this detector.
Therefore, development of ways to adapt RIs for their
full-scale application in the GC-ECD variant remains a
topical task.
RI(6-iodo-3-methylphenol trifluoroacetate) 1260 ±
15 < RI(2-iodo-3-methylphenol
1275 ± 22.
trifluoroacetate)
The experimental values are 1261 and 1271,
respectively.
A stronger retention is observed for molecules with
a “compact” arrangement of substituents, which can
presumably be attributed to weaker steric hindrance
to the interaction of the hydroxyl with the stationary
phase in structures of this kind. This assumption is
confirmed by additive estimates of RIs for two other
pairs of isomeric iodo derivatives. The average values
of RI for 6-iodo-3,4-dimethylphenol and 2-iodo-3,4-
dimethyl phenol, found by using three additive schemes,
are 1365 ± 9 and 1374 ± 18 (experimental values: 1392
and 1402, respectively). Similarly, estimates give for
the RIs of trifluoroacetates a smaller value for 6-iodo-
In the linear temperature-programming mode in
gas-chromatographic analyses, the corrected retention
time tR' of homologs is related to the number of carbon
atomic nC in their molecules by a linear dependence of
the type [20]:
tR' = anC + b.
(1)
Taking into account that RIs equal to 100nC are as-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 9 2012

1364
GRUZDEV et al.
signed to n-alkanes, we can, first, rewrite expression (1)
in a mathematically equivalent form (2) and, second,
extend it to iodo derivatives of methylphenols, whose
RIs are expressed on the scale of reference n-alkanes
(Fig. 1):
values of tR' does not exceed 2–3%, which makes it
possible to sufficiently reliably distinguish peaks of
iodo derivatives of methylphenols in the chromatogram
(Fig. 2). To verify the results of a preliminary
identification of iodo derivatives of methylphenols,
their trifluoroacetates are obtained in the same extract.
Replacement of the hydrogen atom with an acyl group
enhances the volatility of the iodo derivatives and makes
shorter their retention times (Fig. 3, Table 1), whose
vales can also be calculated by the above algorithm from
their RIs. It is important that there will be no peaks of
iodo derivatives of methylphenols in the chromatogram
of trifluoroacetates (Fig. 3) because the acylation occurs
with a nearly quantitative yield. Moreover, N-acylation
of iodo derivatives of methylphenols changes the
sensitivity of the ECD to these substances because
three fluorine atoms are additionally introduced into the
molecule.. The change in the sensitivity Ks of the ECD
can serve as an additional identification parameter for
methylphenols, which also improves the reliability of
their identification.
tR' = a'RI + b'.
To find the coefficients a' and b' in Eq. (2), it
is necessary to calculate tR' for any 3–5 halogen-
containing phenols (detectable by ECD) with RIs
known for the given stationary phase and to construct
the dependence tR' = f(RI). In the case in question, we
chose chlorophenols with RIs close to iodo derivatives
of the methylphenols: 2,4,6-trichlorophenol (1318),
2,3,6-trichlorophenol (1348), 2,3,5,6-tetrachlorophenol
(1508), and pentachlorophenol (1710). The resulting
equation tR' = 1.277RI – 1354 (R2 = 0.9994) was used
to estimate the retention time of iodo derivatives of
methylphenols on the basis of their RIs under the
same conditions of GC analysis (Fig. 1, Table 2). The
discrepancy between the calculated and experimental
Table 2. Results of calculations of the reduced retention time tR' of iodo derivatives of methylphenols from their retention indices
tR', s
Compound
RI
ΔtR', %
Ks
found
367
calculated
357
6-Iodo-2,4- dimethylphenol
4-Iodo-2,6- dimethylphenol
4-Iodo-2,3,6-trimethylphenol
1340
1473
1612
2.7
2.0
1.5
1.13
5.97
3.43
516
526
694
704
4,6-Dibromo-1,2-dimethoxybenzene (internal
standard)
1619
711
713
0.3
1
4,6-Diiodo-2- methylphenol
2,6-Diiodo-4- methylphenol
4,6-Diiodo-2,5-dimethylphenol
4,6-Diiodo-2,3-dimethylphenol
2,6-Diiodo-3,4-dimethylphenol
4,6-Diiodo-2,3,5-trimethylphenol
2,4,6-Triiodophenol
1627
1666
1758
1782
1830
1925
1962
2005
2108
725
772
724
773
0.2
0.1
0.6
0.5
0.5
0.7
1.0
0.2
0.1
1.19
0.96
1.57
1.30
1.30
1.69
4.31
1.64
3.08
896
890
927
922
987
982
1112
1163
1209
1339
1104
1151
1206
1337
2,6-Diiodo-3,4,5-trimethylphenol
2,4,6-Triiodo-3-methylphenol
2,4,6-Triiodo-3,5-dimethylphenol
2270
1526
1544
1.2
5.09
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 9 2012

GAS-CHROMATOGRAPHIC IDENTIFICATION
1365
9. Llompart, M., Garcia–Jares, M., et al., J. Chromatogr. A,
CONCLUSIONS
2006, vol. 1124, pp. 11–21.
10. Faraji, H., Tehrani, M., and Husain, S., J. Chromatogr. A,
To perform a reliable identification of products
formed in iodination and acylation of methylphenols
(104 compounds), linear-logarithmic retention indices
were determined and examined fundamental aspects of
their variation with the number and type of substituents.
A procedure for gas-chromatographic identification of
methylphenols in aqueous media was developed. This
procedure is based on the full-scale application of
retention indices with an electron capture detector.
2009, vol. 1216, pp. 8569–8574.
11. Basheer, C. and Lee, H., J. Chromatogr. A, 2004,
vol. 1057, pp. 163–169.
12. Reitzel, L. and Ledin, A., J. Chromatogr. A, 2002,
vol. 972, pp. 175–182.
13. Jaber, F., Schummer, C., et al., Anal. Bioanal. Chem.,
2007, vol. 387, pp. 2527–2535.
14. Dem’yanov, P.I., Zh. Anal. Khim., 1992, vol. 47, no. 12,
pp.1942–1966.
REFERENCES
15. Korenman, Ya.I., Ekstraktsiya fenolov (Extraction of
Phenols), Gorky: Volgo-Vyat. Knizhn. Izd., 1973.
1. Kharlampovich, G.D. and Churkin, Yu.V., Fenoly
16. Zlatkis, A. and Poole, C.F., Electron Capture: J.
Chromatogr. Library, New York: Elsevier, 1981.
(Phenols), Moscow: Khimiya, 1974.
2. Elin, E.S., Fenol’nye soedineniya v biosfere (Phenolic
Compounds in the Biosphere), Novosibirsk: Sib. Otd.
Ross. Akad. Nauk, 2001.
17. Yashin, Ya.I., Fiziko-khimicheskie osnovy khromato-
graficheskogo razdeleniya (Physicochemical Foundations
of Chromatographic Separation), Moscow: Khimiya,
1976.
3. SanPiN (Sanitary Regulations) 2.1.4.1074–01. Potable
water: Hygienic requirements to the quality of water from
centralized drinking water supply systems, Moscow:
Goskomsanepidnadzor Rossii, 2001.
18. Becker, H., Organicum, New York: Pergamon Press, 1973.
19. Marinichev, A.N., Turbovich, M.L., and Zenkevich,
I.G., Fiziko-khimicheskie raschety na mikro-EVM
(Physocochemical Calculations on Microcomputers),
Leningrad: Khimiya, 1990.
4. Perechen’ rybokhozyaistvennykh normativov (Catalog of
Fishery Regulatins), Moscow: VNIRO, 1999.
5. Vorob’eva, T.V., Terletskaya, A.V., and Kushchev-
skaya, N.F., Khim. Tekhnol. Vody, 2007, vol.29, no. 4,
pp. 370–390.
20. Petsev, N. and Kotsev, N., Spravochnik po gazovoi
khromatografii (Handbook of Gas Chromatography),
Moscow: Mir, 1987.
6. Berezkin, V.G., Khimicheskie metody v gazovoi khro-
matografii (Chemical Methods of Gas Chromatography),
Moscow: Khimiya, 1986.
21. Zenkevich, I.G., Moeder, M., Koeller, G., and Schrader,
S., J. Chromatogr. A, 2004, vol. 1025, pp. 227–236.
22. Zenkevich, I.G., Makarov, A.A., Schrader, S., and
Moeder, M., J. Chromatogr. A, 2009, vol. 1216, pp. 4097–
4106.
7. Ventura, A. and Galceran, M., Anal. Bioanal. Chem.,
2006, vol. 368, pp. 293–298.
23. Zenkevich, I.G., Eliseenkov, E.V., and Kasatochkin,A.N.,
Chromatographia, 2009, vol. 70, no. 56, pp. 839–849.
8. Pavon, J., Ferreira, A., et al., J. Chromatogr. A, 2009,
vol. 1216, pp. 1192–1199.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 9 2012