Unique variations of the distribution coefficients of homologues in the perfluorodecalin-acetonitrile heterophase system

Article abstract of DOI:10.1134/S1070363211020101

The properties of the heterophase system perfluorodecalin-acetonitrile differ significantly from those of other combinations of the organic solvents limitedly soluble in each other. While for the most of such combinations the distribution coefficients (K _d) of homologues increase in going from the simplest to next members of the series, in the case of perfluorodecalin- acetonitrile they remain almost constant. This provides a possibility to use the values of K _d directly for the group identification of analytes, and first of all allows distinguishing isomeric alkenes and cycloalkanes, as well as the isomers of the hydrocarbons with greater formal unsaturation.

Full text of DOI:10.1134/S1070363211020101

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 2, pp. 337–344. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © I.G. Zenkevich, A.S. Kushakova, 2011, published in Zhurnal Obshchei Khimii, 2011, Vol. 81, No. 2, pp. 237–244.
Unique Variations of the Distribution Coefficients
of Homologues in the Perfluorodecalin–Acetonitrile
Heterophase System
I. G. Zenkevich and A. S. Kushakova
St. Petersburg State University, Universitetskii pr. 26, St. Petersburg, 198504 Russia
e-mail: izenkevich@mail15.com
Received June 17, 2010
Abstract—The properties of the heterophase system perfluorodecalin–acetonitrile differ significantly from
those of other combinations of the organic solvents limitedly soluble in each other. While for the most of such
combinations the distribution coefficients (Kd) of homologues increase in going from the simplest to next
members of the series, in the case of perfluorodecalin–acetonitrile they remain almost constant. This provides a
possibility to use the values of Kd directly for the group identification of analytes, and first of all allows
distinguishing isomeric alkenes and cycloalkanes, as well as the isomers of the hydrocarbons with greater
formal unsaturation.
DOI: 10.1134/S1070363211020101
Chromato-distribution method [1] avanced in mid-
sixties [2] in order to extend the gas-chromatographic
analysis is based on an equilibrium distribution of
components of the analyzed samples in the
heterophase systems of the organic solvents limitedly
mixing with each other followed by the analysis of
each layer under identical conditions. This method
allows the characterization of analytes in addition to
their retention indices (RI) by their distribution coef-
ficients (Kd = Cnon-polar/C polar ≈ Snon-polar/S polar). As to the
informativity of such combination of analytical
parameters, it is only slightly inferior to the RI com-
bination obtained on the columns with phases of
different polarity [3], but devoid of its major draw-
back: the problem of assignment of chromatographic
peaks of the same components in different chromato-
grams. Since the values of both RI and logarithms of
distribution coefficients of the homologues in different
series increase in parallel with the number of carbon
atoms in the molecules for the majority of heterophase
systems, for the solution of the problem of group
identification the differential parameters j have been
proposed that are invariants of homologous series [3]:
meaning is the difference between the free energies of
solvation of homological difference CH2 in the two
layers of heterophase solvent systems [3]. For this
reason, it can be considered as a characteristic of the
selectivity of the chosen system toward the compounds
of different homologous series.
The problems to be solved by the joint application
of Kd and RI include the following tasks (ordered by
the degree of detailing the structural data of analytes):
(1) General conclusions on the degree of
“homogeneity” of the composition of complex
samples, that is, the assignment of the mixture
components to the same or different homologous series
[4].
(2) Identification of isomers and homologues in a
mixture. For isomers Kd ~ const, for homologues Kd ≠
const, but the condition j ≈ const is fulfilled.
(3) Identification of the congeners differing by
certain fragments in their molecular compositions
according to the criterion Δj ≈ const, and the
quantification of such fragments.
j = kRI – log Kd,
(1)
(4) Unambiguous identification of the components,
when the mixtures of similar composition have been
studied previously (comparing the values of j, Kd and
RI with reference data).
The coefficient k (in this case dimensionless)
reduces variations of two compared physical and
chemical constants to a common scale. Its physical
337

338
ZENKEVICH, KUSHAKOVA
Table 1. Mutual solubility of some components of heterophase systems of organic solvents under normal conditions
Mutual Solubility, wt %
Components of the system
B (polar)
Acetonitrile
k×103
A (non-polar)
Hexane
A in B
B in A
3.0±0.2
2.4±0.1
2.7±0.1
1.5±0.1
<0.03
13.5±0.8
1.9±0.1
1.4±0.1
3.0±0.1
<0.2
1.1±0.1
1.33±0.05
1.67±0.12
1.3±0.1
–
Hexane
Nitromethane
Triftoretanol
Acetonitrile
Hexane
Decane
Perfluorodecalin
Octane
Acetonitrile
Perfluorodecalin
Perfluorodecalin
Chloroform
4.8
27.8
0.9±0.1
–
Nonane
3.2
15.3
Perfluorodecalin
5.5±0.4
14.0±1.5
0.5±0.1
A binary heterophase solvent system that has been
characterized in detail is the system 1-octanol–water.
The logarithms of distribution coefficients (P) for this
system (log P) is now considered as a measure of
hydrophobicity of organic compounds [5] and as one
of the characteristics of their polarity [6]. However, the
properties of its constituent fluids are not well ap-
propriate for gas chromatographic analysis, therefore
the most popular for this purpose is the use of low-
boiling organic solvents, in particular, hexane–
acetonitrile [1, 3]. For the same purpose the system
hexane–nitromethane is recommended [7]. Since
recently fluorinated solvents were proposed as the
polar phase, among which the system of heptane–
2,2,2-triftoretanol and heptane–1,1,1,3,3,3-hexafluoro-
2-propanol were described [8].
chloroform) or as a polar phase (combined with
alkanes CnH2n+2, n ≥ 7). With n-hexane, perfluoro-
decalin can be mixed at room temperature in any ratio.
Comparing the data in Table 1 it is seen that for the
majority of heterophase systems the mutual solubility
of their components is no less than 1 wt %. The
differences in the mutual solubility of components
correspond to the variation of values of the coefficient
k in Eq. (1) from ~0.5×10–3 to ~1.7×10–3. In other
words, the greater the mutual solubility, the smaller the
difference in parameters j for the different homologous
series with respect to a given system. The only
exception is the system of perfluorodecalin–aceto-
nitrile that was not considered previously. For this
system the solubility of the nonpolar component in the
polar one is less than 0.2 wt %, of polar in nonpolar is
less than 0.03 wt %. (A feature of the method proposed
in [11] is incomplete characterization of low solubility
by such inequalities.) Hence, one can expect that
anomalous properties may be found in the first place in
this system.
The properties of a heterophase solvent system in
the GC-distribution method are largely defined by the
mutual solubility of the components [9]. Since not all
systems having the practical value are represented in
the NIST database [10], a general method has been
developed for determining the mutual solubility of
their components [11]. Table 1 lists the data on mutual
solubility of components of some systems at the
temperature 20±1°C. Typically, the higher mutual
solubility of a heterophase system components, the
lower the value of the coefficient k in Eq. (1) and the
lower the selectivity of the system with respect to
compounds of different homologous series.
Number of joint references to the considered com-
bination of solvents in the Internet (Google infor-
mation retrieval system, February 2010), except for
links to the publication [11] is only 4/1 in English and
Russian, respectively.
This paper considers the features of the homo-
logous variations of the distribution coef-ficients of
organic compounds in the perfluorodecalin–aceto-
nitrile heterophase system in order to evaluate the
feasibility of its use for identification of analytes in the
chromato-distribution method.
It is interesting to note that such a component of a
heterophase system as perfluorodecalin can act both as
a nonpolar phase (when combined with acetonitrile or
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UNIQUE VARIATIONS OF THE DISTRIBUTION COEFFICIENTS
339
Table 2. Correlation between the logarithms of distribution
coefficients of simple N-alkylarenes in the hexane–
acetonitrile and 1-octanol–water systems and their gas-
chromatographic retention indices on the standard nonpolar
polydimethylsiloxane stationary phases
The algorithm for finding the parameters of Eqs. (1)
in the first stage involves the calculation of the
regression equations coefficients relating the
logarithms of the values of Kd of the homologues in
each series of a considered heterophase solvent system
with the values of their gas-chromatographic RIs,
log Kd = aRI + b. This is followed by averaging the
coefficients a of such dependences for all series, k =
Σai/n, and the computation with the formula (1) of the
parameters j for each homologue, followed by
averaging within the series under consideration.
Typical variations of the values of Kd for simple
homologues, and the correlation of log Kd values with
the values of RI on the standard nonpolar
polydimethylsiloxane stationary phases is illustrated
by Table 2 by an example of mono-n-alkylarenes in
the hexane–acetonitrile system [k ≈ (1.1 ± 0.1)×10–3]
[3] and in much more selective system of 1-octanol-
water [k ≈ (5.5 ± 0.6)×10–3] (estimate from [3, 5, 12–
14]). In the first case the distribution coefficient of n-
pentylbenzene exceeds 4-fold the Kd of unsubstituted
benzene, while in the second case it is more than
600 times larger. Similar variations in the distribution
coefficients of homologues of any series are typical of
all so far characterized heterophase solvent systems.
The only exception is the perfluorodecalin–acetonitrile
system considered in this paper.
R in C6H5R
H
RI
log P
Kd
log Kd
656±8
2.10
0.79
–0.10
CH3
760±9
854±9
2.74
3.15
3.66
4.26
4.90
5.52
1.10
1.41
1.96
2.4
3.1
–
0.04
0.15
0.26
0.38
0.49
–
C2H5
C3H7
C4H9
C5H11
C6H13
945±9
1046±5
1143±9
1240±9
Parameters of equations log P = aRI + b and log Kd = aRI + b
a
(5.8±0.1)×10–3 (1.21±0.01)×10–3
b
–1.74±0.14
0.998
–0.858±0.001
0.9997
r
S0
0.07
0.006
dependence of the distribution coefficients of homo-
logues on the number of carbon atoms in their
molecules (or, alternatively, on their position in the
respective series). Table 3 shows the values of Kd of
some organic compounds in this system grouped
according to the homologous series and within the
series in the ascending order of molecular masses.
These data show that, for example, in the series of
alkylarenes the Kd values of the simplest C6–C9
homologues increase from 0.06 to 0.09, but for the
other (C10–C15) remain almost constant (vary in the
range of 0.09–0.13 with the reproducibility at the level
of ±0.01–0.03). In some cases there is a small (and
comparable to measurement errors) decrease in the Kd
in going from simple to higher homologues, such as in
the case of 1-chloroalkanes C6–C8 (0.15, 0.13 and
0.12, respectively). Figure 1 illustrates a weak linear
dependence of the logarithms of distribution
coefficients of n-alkanes on their retention indices
(RI = 100nC) with the correlation coefficient r = 0.841.
The coefficient a of linear regression log Kd = aRI + b
for the n-alkanes is (1.1 ± 0.3)×10–4 , whereas for
alkylarenes a = (3.1 ± 1.1)×10–4 (with r = 0.578),
roughly by an order of magnitude less than the values
of the coefficients for other heterophase systems.
Consequently, it is just the small variation of Kd for the
A first feature of this system is associated with the
higher density of perfluorodecalin compared with
acetonitrile:
Solvent
Mr
bp, °С
81.6
d420
0.786 1.344 460±13
1.942 1.313 ~550
nD20
RInon-polar
Acetonitrile
41
Perfluorodecalin 462
141.6
The distribution coefficients commonly are considered
as a ratio of equilibrium concentrations of analytes in
the nonpolar and polar layers, Kd = Cnon-polar/Cpolar
.
Since in most of the known heterophase systems the
density of polar solvents is higher than that of non-
polar, then the values of Kd corresponds to the ratio of
concentrations of analytes in the upper and lower
layers, respectively. In the case of perfluorodecalin–
acetonitrile, the nonpolar is the lower layer, so that
Kd = Cbottom/Ctop. Among other solvent systems such
inversion of non-polar and polar layers occurs in the
combination of perfluorodecalin–chloroform.
The principal and perhaps unique feature of the
perfluorodecalin–acetonitrile system is extremely weak
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ZENKEVICH, KUSHAKOVA
Table 3. The distribution coefficients of organic compounds of various series in the heterophase system perfluorodecalin–
acetonitrile
Compound
Mr
Kd
Compound
Arenes CnH2n-6 (FU = 4)
Mr
Kd
Alkanes CnH2n+2 (FU = 0)
n-Nonane
128
142
156
170
184
198
210
0.96±0.14
0.90±0.10
0.99±0.14
1.01±0.05
1.05±0.09
1.03±0.08
1.16±0.08
1.06±0.08
Toluene
92
0.06±0.02
0.07±0.01
0.07±0.01
0.07±0.01
0.09±0.01
0.09±0.01
0.13±0.01
0.10±0.03
0.12±0.02
0.10±0.01
0.13±0.02
0.09±0.01
0.12±0.01
0.10±0.02
n-Decane
Ethylbenzene
106
106
120
120
134
134
134
148
148
148
162
162
162
m-Xylene
n-Undecane
n-Dodecane
n-Tridecane
n-Tetradecane
n-Pentadecane
n-Hexadecane
1,2,4-Trimethylbenzene
1,3,5-Trimethylbenzene
Butylbenzene
tert-Butylbenzene
p-Cymene
224
Alkenes CnH2n (PS = 1)
(2,2-Dimethylpropyl)benzene
(1,2-Dimethylpropyl)benzene
(1-Etilpropyl)benzene
1-Octene
112
0.39±0.08
0.48±0.08
0.46±0.02
0.38±0.02
0.42±0.02
2,2,4-Trimethyl-2-pentene
(Z)-2-Methyl-3-octene
(E)-2-Methyl-3-octene
21-2-Methyl-2-octene
112
126
126
126
Hexylbenzene
1,3-Dimethyl-5-(1,1-dimethylethyl)benzene
1,3,5-Trimethyl-2-(1-methylethyl)benzene
Cycloalkanes (FU = 1)
1,3,5-Trimethyl-2-(1-methylbutyl)benzene
1-Butyl-4-(1-methylethyl)benzene
176
0.11±0.01
Cycloalkanes
84
98
0.64±0.04
0.57±0.14
0.85±0.06
0.83±0.05
0.81±0.08
176
176
190
204
0.10±0.01
0.11±0.01
0.12±0.04
0.10±0.01
Methylcyclohexane
cis-p-Mentane
1-(1-Methylethyl)-4-(1-methylpropyl)-benzene
1-Butyl-4-(1-methylpropyl)benzene
140
140
trans-p-Mentane
1-Pentyl-4-(1-methylpropyl)benzene
(1-Methylpropyl) cyclohexane
140
Sesquiterpenes C15H24 (FU = 4)
204
204
Alkynes CnH2n-2 (FU = 2)
α-Muurolene
β-Bisabolene
0.35±0.03
0.11±0.02
1-Heptyne
96
0.07±0.01
1-Octyne
110
166
0.08±0.01
0.04±0.01
Hydrocarbons of various series
6-Dodecyne
Indene [6] a
116
132
132
138
138
142
154
182
0.04±0.01
0.05±0.01
0.07±0.01
0.56±0.02
0.38±0.05
0.02±0.01
0.02±0.01
~0
Conjugate dienes CnH2n-2 (FU = 2)
(Z)- and (E)-(1-Methyl-1-propenyl)benzene [5]
(1-Ethylethenyl)benzene [5]
trans-Decalin [2]
2,3-Dimethyl-1,3-butadiene
2,5-Dimethyl-2,4-hexadiene
82
0.28±0.01
0.19±0.02
110
Monoterpenes C10H16 (FU = 3)
1-p-Menthene [2]
α-Pinene
β-Pinene
Limonene
3-Carene
4-Carene
γ-Terpinene
136
136
136
136
136
136
0.56±0.02
0.35±0.02
0.21±0.02
0.36±0.02
0.21±0.03
0.17±0.01
1-Methylnaphthalene [7]
Biphenyl [8]
Dibenzyl [8]
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UNIQUE VARIATIONS OF THE DISTRIBUTION COEFFICIENTS
341
Table 3. (Contd.)
Compound
Mr
Kd
Compound
Mr
Kd
Compounds containing heteroatoms
1-Methyl-1,2-epoxycyclohexane
1-Chlorohexane
112
120
0.08±0.02
0.15±0.03
1-Chlorooctane [0]
148
154
0.12±0.02
0.09±0.01
1-Methyl-4-(1-methylethyl)-2,3-
epoxycyclohexane [2]
Benzyl chloride [4]
126
126
130
134
136
143
143
146
0.02±0.01
0.05±0.01
0.19±0.04
0.13±0.02
0.08±0.02
0.78±0.13
0.90±0.06
0.16±0.04
Bromobenzene [4]
1-Bromohexane [0]
1-Bromooctane [0]
1-Iodopentane [0]
1-Bromononane [0]
1-Iodohexane [0]
1-Bromodecane [0]
156
164
192
198
206
212
220
0.04±0.01
0.07±0.02
0.08±0.02
~0.01
1-Methyl-3-chlorobenzene [4]
Dibutyl ether [0]
1-Chloroheptane [0]
1-Bromobutane [0]
Tripropylamine [0]
Dibutylmethylamine [0]
Diisobutylsulfide [0]
0.10±0.01
~0.01
0.10±0.01
a Here and later in brackets after the name is given the value of formal unsaturation (FU) of the compound.
homologues of the same series in the perfluorodecalin–
acetonitrile heterophase system that causes the low
reproducibility and low values of the coefficients of
this regression equations.
The electron impact mass spectra of many alkenes
and cycloalkanes are not enough characteristic and do
not allow a reliable detection of compounds of these
groups [15]. Differences in RI of alkenes and cyclo-
alkanes on standard polar and nonpolar phases (53 ± 7
and 64 ± 11, respectively) overlap within the limits of
standard deviations and therefore also are not
informative for their identification [16]. The dif-
However, if the variations of Kd within a suf-
ficiently large set of different homologues of a series
are small and comparable to the errors in measuring
these quantities, then at a first approximation they can
be neglected. This is equivalent to k→0 in the rela-
tion (1), which implies that j→log Kd. Thus, as the
parameter for the group identification of compounds of
different series can be used directly the arithmetic
mean value of distribution coefficient <Kd> ± sK
instead of the difference (1) as this is shown in Table 4.
log Kd
0.06
0.04
0.02
It follows from these data that the determination of
Kd in the perfluorodecalin–acetonitrile system can be
regarded as a simple and reliable method for the
identification of unsaturated hydrocarbons of different
classes. First of all, by the value of Kd alkenes and
cycloalkanes with the same values of formal
unsaturation (FU = 1) can be distinguished.
0.00
–0.02
–0.04
–0.06
800
1000
1200
1400
1600
FU = 1 – N + Σ(niνi)/2 = (2nIV + nIII – nI + 2)/2,
(2)
Retention index
Fig. 1. Graphical illustration of the poorly defined linear
dependence of logarithms of the distribution coefficients of
n-alkanes in the C10F18–CH3CN system on their retention
indices (RI = 100nC). The linear regression parameters: a =
(1.1±0.3)×10–4, b = –0.14±0.04, r = 0.841, S0 = 0.02.
where N is the total number of atoms in a molecule, ni
is the number of atoms with valence νi, nIV, nIII and nI
are the numbers of four-, three- and univalent atoms in
a molecule, respectively.
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ZENKEVICH, KUSHAKOVA
Table 4. Mean values of distribution coefficients of organic compounds of different homologous series in the heterophase
system perfluorodecalin–acetonitrile
a
Homologous series
Alkanes
General formula
CnH2n+2
FU
0
<Kd>±sK
j±sj
1.02±0.08
–0.40±0.07
Alkenes
CnH2n
1
1
2
2
3
3
4
5
0
0
0
0
0.43±0.04
0.74±0.13
0.06±0.02
0.24±0.06
0.19±0.03
0.37±0.14
0.10±0.02
0.06±0.02
0.13±0.02
0.09±0.02
~0.01
–0.19±0.09
–0.08±0.11
0.54±0.14
–
Cycloalkanes
Alkynes
CnH2n
CnH2n–2
CnH2n–2
CnH2n–4
CnH2n–4
CnH2n–6
CnH2n–8
CnH2n+1Cl
CnH2n+1Br
Conjugated dienes
Cyclodienes
Bicycloalkenes
Arenes
–
–
0.70±0.05
–
Alkenylarenes
Chloroalkanes
Bromoalkanes
Iodoalkanes
Trialkylamines
0.52±0.12
0.60±0.04
0.62±0.18
–0.31±0.19
CnH2n+1
I
CnH2n+3
N
0.84±0.08
a The value of the j parameter [formula (1)] for the system hexane–acetonitrile [3].
ferences in the mass spectra of alkenes and cyclo-
alkanes obtained under chemical ionization (dominate
the signals of the ions [M + H]+ and [M – H]–,
respectively) are clearly expressed only when FU = 1,
whereas at FU > 1 interpretation of such data may be
ambiguous. Perhaps the only characteristic allowing a
reliable differentiation of alkenes and cycloalkanes
hitherto suggested was their ionization energy (9.2 ±
0.4 and 10.1 ± 0.5, respectively), but the difference in
these constants can be identified using the photo-
ionization detectors [17–20] only.
naphthalenes, biphenyls, etc.) do not exceed 0.01 – 0.02.
All compounds with functional groups containing
active hydrogen atoms (OH, NH, SH) obey the
condition Kd = 0. Consequently, the considered hetero-
phase system perfluorodecalin–acetonitrile is charac-
terized by a specific selectivity toward the hydro-
carbons of different classes with formal unsaturation of
no more than approximately 5. Note the relatively high
values of Kd of tertiary amines R3N (0.84 ± 0.08),
dialkylsulfides (0.16, one representative of the series)
and ethers (0.19, the same). In the series of aliphatic
halo derivatives RHal the Kd values decrease in the
sequence of Hal = Cl, Br, I.
It should be noted that in contrast to the above
difficulties the average value of Kd of alkenes (0.43 ±
0.04) and cycloalkanes (0.74 ± 0.13) are so markedly
different and almost independent of the number of
carbon atoms in the molecules of analytes that their
unambiguous assignment to the corresponding groups
of homologues ceases to be a serious problem. Similar
statistically significant differences in the values of Kd
can be traced for other hydrocarbons with the same
values of FU, such as alkynes (0.06 ± 0.02) and
conjugated dienes (0.24 ± 0.06) with FU = 2. With
further increase in FU the intervals of <Kd>±sK
variations naturally begin to overlap within ±2 sK, for
example, in cyclodienes (0.19 ± 0.03) and bicycle-
alkenes (0.37 ± 0.14), arenes (0.10 ± 0.02, FU = 4) and
alkylstyrenes (0.06 ± 0.02, FU = 5). The values of Kd
of more unsaturated compounds (alkyl-substituted
From the correlation dependences linking the Kd
value in the perfluorodecalin–acetonitrile system with
other characteristics of homologous series, it is useful
to compare the properties of this system with the
properties of other systems that do not exhibit the
anomalies discussed above. The series shown in the
Table 4 are characterized additionally by the values of
j±sj [Eq. (1)] for the hexane–acetonitrile system [3].
Figure 2 shows a graphic illustration of the dependence
of Kd(C10F18/CH3CN) = f[j(C6H14/CH3CN)]; its linear
character is confirmed by the high absolute value of
the correlation coefficient r = –0.944. Hence, we can
conclude that the patterns of distribution of organic
compounds of the different series between non-polar
and various aprotic polar solvents are largely similar,
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UNIQUE VARIATIONS OF THE DISTRIBUTION COEFFICIENTS
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1.2
1.0
0.8
0.6
0.4
0.2
0.0
although in one case, the distribution coefficients of
homologues are practically constant, while in another
they are heavily dependent on their position in the
homologous series.
As noted above, the distribution coefficients are
one of the physicochemical criteria of the polarity of
organic compounds [6]. Chromatographic charac-
teristics of the polarity of analytes is the difference
between RI on standard polar and nonpolar stationary
phases, ΔRI = RIpolar – RInon-polar [15]. Accounting for
the existence of the limit value Kd → 0 for highly polar
compounds with high values of ΔRI, it is not proper to
identify the relationship Kd(DRI) as a directly
proportional dependence Kd = aΔRI + b, but as the
inversely proportional, Kd = a/ΔRI + b; the parameters
are: a = 69.6 ± 7.1, b = –0.22 ± 0.06, r = –0.956, S0 =
0.09. Such dependence explains the rapid approach to
zero by the Kd values upon increase in the number of
heteroatoms in the molecule. For example, for
dichloroalkanes ΔRI ≈ 355 ± 66, hence Kd ≈ 69.6/355 –
0.22 ≈ 0.02 ≈ 0.
–0.4 –0.2
0.0
0.2
0.4
0.6
0.8
j for C6H14–CH3CN system
Fig. 2. Graphical illustration of the correlation of the
distribution indices in the C10F18–CH3CN system and
values of the parameter j for the system C6F14–CH3CN; a =
–0.81±0.11, b = 0.56±0.05, r = –0.944, S0 = 0.14.
EXPERIMENTAL
Reagents of different purity (mainly of chemically
pure grade) were used as preparations of compounds of
different homologous series. A mixture of isomeric
(Z)- and (E)-2-methyl-3-octene and 2-methyl-2-octene
was obtained by dehydration of 2-methyl-3-octanol in
the presence of catalytic amounts of sulfuric acid;
identification of the products was carried on the basis
of reference values of their retention indices. Similarly,
the dehydration of 2-phenyl-2-butanol yielded a
mixture of (Z)- and (E)-(1-methyl-1-propenyl)benzene
and (1-ethylethenyl)benzene.
The use of chromato-distribution method is some-
what complicated by the temperature dependence of
mutual solubility of the components of many of
heterophase solvent systems (increases with increasing
temperature) [10], affecting the Kd value. Con-
sequently, if the temperature at the measurement
differs significantly from 20 ± 1°C, the determination
of Kd values in most of the known heterophase systems
requires temperature control. In this connection it
should be noted that another important feature of the
combination perfluorodecalin–acetonitrile is a low
mutual solubility of its constituent components that
corresponds to a low temperature dependence of
solubility itself. The relative variation of the mutual
solubility of the components of this system in the
temperature range of 20–50°C is:
Acetonitrile (chemically pure grade) was pre-dried
to reduce water content below 0.01 wt % (chromato-
graphic control) with the molecular sieves NaA
(average pore diameter 0.4 nm) during a day. The
sieves were pre-annealed at 320°C for 3 h. Perfluoro-
decalin was used without further purification.
To determine the distribution coefficient (Kd), in a
vessel of 7–10 ml capacity was placed perfluoro-
decalin and acetonitrile 1.0–1.5 ml each, and to the
mixture was successively dosed 5–10 μl of examined
substance, the vessel was shaken for 15–20 s, held for
2–5 min at room temperature (20 ± 1°C) and analyzed.
In the case of the formation of an emulsion which was
detected visually by turbidity of one of the layers, the
problem layer was homogenized by adding to the
system any solvent (more often, CH3CN).
Т, °С C10F18 solubility in CH3CN CH3CN solubility in C10F18
20
30
40
50
1.0 (<0.2 wt %)
1.0 (<0.03 wt %)
1.14
1.24
1.24
1.02
1.08
1.10
In such cases, the requirements in the accuracy of
maintaining the temperature of determination are
significantly reduced, which simplifies the practical
application of chromato-distribution method.
To characterize the temperature dependence of
mutual solubility of perfluorodecalin and acetonitrile
and the distribution coefficients of analytes, the
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 2 2011

344
ZENKEVICH, KUSHAKOVA
measurements were performed in the temperature
range from 20 to 50°C with 10°C increment using a
UTU-3 ultrathermostat (Poland, the temperature
setting and maintaining precision ±0.1°C).
REFERENCES
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Yagodovskii, V.D., Khromato-raspredelitel’nyi metod
(The Chromato-Distribution Method), Moscow: Nauka,
1976.
Gas-chromatographic analysis was performed on a
Tsvet-100 chromatograph with a flame ionization
detector and a packed column I in the mode of
programming temperature from 50 to 220°C at the rate
4–6 deg min–1. In the case of overlapping the signals of
examined components with the peak of a solvent was
used column II in the same mode of temperature
programming: column I: 3 m × 3 mm with 5% SE-30
on Chromaton N (0.16–0.20 mm); column II: 1.5 m ×
3 mm with 20% Carbowax 20M on Chromaton NAW
HMDS (0.20–0.25 mm).
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Evaporator temperature 220°C, carrier gas nitrogen
(30 ml min–1), sample dosage 2 μl (microsyringe MSh-
10). Registration of chromatographic peaks (scale
100×10–10 Å) was performed using a TR 2213
integrator (Japan) or a software package UniChrom
(Minsk, version 4.x-5). For monitoring changes in the
mutual solubility of perfluorodecalin and acetonitrile
by the method [11] column I was used at 50°C. Under
these conditions almost complete separation of trans-
and cis-isomers of perfluorodecalin was achieved
(ratio 55: 45; peak areas were summed up), the ratio
obtained is consistent with the typical ratio of trans-
and cis-isomers of this substance according to
published data (~1:1) [21] .
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The mathematical processing was performed with
Microsoft Excel and Origin (version 4.1) softwares. To
smooth deviations in sets of Kd values the algorithm
[22] was used.
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Analitika i Kontrol’, 2009, vol. 13, no. 2, p. 106.
ACKNOWLEDGMENTS
A part of the distribution coefficients in the
perfluorodecalin–acetonitrile system was measured by
A.A. Bushueva, the Faculty of Chemistry Master,
St. Petersburg State University. The authors express
their gratitude to the Candidate of chemical sciences
N.G. Ismagilov (Russian Research Center “Applied
Chemistry”) for the perfluorodecalin sample.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 2 2011