Partition coefficients of ketones, phenols, aliphatic and aromatic acids, and esters in n-hexane/nitromethane

Article abstract of DOI:10.2478/s11532-011-0060-4

Liquid-liquid partition is used in sample preparation and in countercurrent and liquid-liquid chromatographic separations. Partition coefficients are widely used in toxicology, environmental, and analytical chemistry. The K _hn determination procedure for the n-hexane/ nitromethane system was optimized and partition coefficients for 99 ketones, esters and trimethylsilyl derivatives of phenols, aliphatic and aromatic acids were determined. For 130 compounds, K_hn values were predicted using mathematical relationships between K_hn and other physicochemical and structural parameters. Versita Sp. z o.o.

Full text of DOI:10.2478/s11532-011-0060-4

Cent. Eur. J. Chem. • 9(5) • 2011 • 813-824
DOI: 10.2478/s11532-011-0060-4
Central European Journal of Chemistry
Partition coefficients of ketones, phenols,
aliphatic and aromatic acids, and esters
in n-hexane/nitromethane
Research Article
Urszula Kotowska*, Valery A. Isidorov
Institute of Chemistry, University of Białystok,
ul. Hurtowa 1, 15-399 Bialystok, Poland
Received 20 January 2011; Accepted 30 April 2011
Abstract:
Liquid-liquid partition is used in sample preparation and in countercurrent and liquid-liquid chromatographic separations. Partition
coefficients are widely used in toxicology, environmental, and analytical chemistry. The Khn determination procedure for the n-hexane/
nitromethane system was optimized and partition coefficients for 99 ketones, esters and trimethylsilyl derivatives of phenols, aliphatic
and aromatic acids were determined. For 130 compounds, Khn values were predicted using mathematical relationships between Khn
and other physicochemical and structural parameters.
Keywords: Partition coefficients • n-Hexane/nitromethane system• Structure-partitioning relationships
.
© Versita Sp. z o.o
1. Introduction
plant essential oils [8-11], sodium-bituminous masses
[12], communal wastewaters [13], pesticides, and in
environmental samples containing compounds formed
during treatment and disposal of chemical warfare
agents [14,15]. This application allows us to increase the
identification reliability simply and inexpensively [8-15].
This additional identification parameter is particularly
helpful when analyzing complex unknown mixtures.
n-Hexane/acetonitrile has achieved the highest
applicability of wholly organic biphasic systems, while
Partition between two “largely immiscible” solvents
is widely used in sample preparation for matrix
simplification and isolation of target analytes, as well
as in countercurrent and liquid-liquid chromatographic
separations. The equilibrium concentration ratio is
called the partition (or distribution) coefficient; the
concentration in the less polar phase is the numerator
of Kp = C1/C2. It is a physicochemical constant of the
compound,andiswidelyusedintoxicology,environmental the n-hexane/nitromethane system has been recognized
and analytical chemistry. The key parameter describing as the most promising for identification in terms of
the partitioning behavior of organic toxicants in biological complementarityorinterchangeability[7].Thetwosolvents
and environmental compartments is the n-octanol/water are commonly used as extractant or reaction medium.
partition coefficient, Kow [1,2].
They are also used as mobile phases in countercurrent
Liquid-liquid distribution methods, commonly chromatography [16] and high performance liquid
including the use of water as one component, determine chromatography [17,18]. Nitromethane is also a solvent
descriptors in solvation models [3,4]. Employing systems in capillary electrophoresis [19], so partition coefficients
of two organic solvents makes it possible to use gas in this system could find diverse applications.
chromatography to determine partition coefficients, while
solute descriptors can be based on quantified retention of n-hexane/nitromethane partition coefficients for
factors [5].
different types of organic compounds: ketones, esters,
Anaimofthisstudywastheexperimentaldetermination
Distribution coefficients may also be used as and TMS-derivatized aliphatic and aromatic acids,
identifying parameters in the analysis of complex and phenols. A calculation method to determine Khn
organic mixtures [6,7]. For example, partition coefficients
were employed in the identification of compounds in
values analogous to Quantitative Structure–Retention
Relationships was examined.
* E-mail: ukrajew@uwb.edu.pl
813

Partition coefficients of ketones, phenols, aliphatic
and aromatic acids, and esters in n-hexane/nitromethane
5 µL of n-alkanes mixture and 0.5 µL of n-butylbenzene.
The flask was closed and intensely shaken for 5 minutes.
After the phases were separated, the solution stood for
half an hour. Each phase was then subjected to GC-FID
analysis. Distribution coefficients were calculated from
the ratio of the peak areas by Eq. 1:
2. Experimental procedure
2.1. Materials
n-Hexane (Baker, HPLC grade), nitromethane (Aldrich,
HPLC grade), and anhydrous pyridine (Fluka) were used
withoutadditionalpurificationordrying.Thederivatization
reagent
was
bis(trimethylsilyl)trifluoroacetamide
K
hn = (Sh/Sn)⋅( Bn /Bh)⋅Kb,
(1)
(BSTFA) containing 1% trimethylchlorosilane (Sigma).
SeriesofC6 –C30 n-alkanes, tolueneand n-butylbenzene
(internal standards) were purchased from Sigma.
Other chemicals were obtained from several sources.
where Sh and Sn are the peak areas of the component x
on the chromatograms of the hexane and nitromethane
phases, respectively, and Bh and Bn are the peak
areas of n-butylbenzene (internal standard). Kb is the
2.2. Instrumentation
butylbenzene partition coefficient
(Kb=4.00±0.40).
Gas chromatographic analyses were carried out on
an HP 6890 GC with electronic pressure control, split/
splitless injector, and flame ionization detector (FID)
from Agilent Technologies, USA. It was equipped with a
HP-5 column (30 m × 0.25 mm coated with 0.25 μm 5%
phenylmethylsiloxane). Helium (99.999%, 1 mL min-1)
was the carrier gas. FID flow rates were: hydrogen
40 mL min-1, air 400 mL min-1, nitrogen (make-up gas)
40 mL min-1. The injector and FID temperatures were
250 and 300oC, respectively. The oven temperature was
programmed from 40oC to 300oC at 5oC min-1 and was
maintained for 30 minutes. The split ratio was set to
50:1; septum purge was 1 mL min-1.
The retention times of the compounds and n-alkanes
were used to calculate linear temperature programmed
retention indices (LTPRI) [20].
Phenols and aliphatic and aromatic acids were
analyzed as trimethylsilyl derivatives. 20 μL of pyridine
and 50 μL of BSTFA were added to 1 mg of compound,
the mixture was heated for one hour at 70ºC to form the
TMS derivative and the resulting solution was used for
partition coefficient determination.
3. Results and discussion
3.1. Experimental partition coefficient
determinations
2.3. Partition coefficients determination
The volume of the gaseous phase and the resulting
GC injector pressures after the evaporation 1 μL of
n-hexane or nitromethane were different. This could
affect Khn precision since the higher injector pressure
after nitromethane evaporation pushes out more of the
sample during removal of the needle from the injector.
To avoid this difficulty the needle was left in the injector
for about a minute after injection to allow the sample to
move onto the column.
Samples were prepared at 22oC. A 2 mL flask was
charged by pipette with 0.5 mL of n-hexane solution of
the compounds (at 100 µg mL-1), 0.5 mLof nitromethane,
The determination of a partition coefficient is possible
only when the liquid-liquid system is in equilibrium.
Thus, both shaking time and the phase separation
time required for the distribution coefficient to reach a
constant value were determined. Satisfactory results
were achieved when the shaking time was 5 minutes
and the phase separation time 30 minutes. Relative
standard deviations (rsd) obtained for measurements
carried out between 30 minutes and eight hours after
phase separation did not exceed 3.5%. The difference
between the rsd obtained 24 hours after the partition
and the rsd obtained from earlier measurements was
substantial, i.e., as great as 80%. We conclude that
correct distribution coefficient values can be determined
from 30 minutes to 8 hours after partition.
Figure 1. Log Khn and chromatographic retention indices
relationships: (1) aliphatic monocarboxylic acids, TMS (y
= 0.001390x – 0.8019, R2 = 0.991); (2) phenols, TMS (y
= 0.001297x- 1.0132, R2 = 0.949); (3) monosubstituted
ketones (y = 0.001530x – 1.4972, R2 = 0.934); (4)
unbranched ketones (y = 0.001284x-1.4212, R2= 0.980);
(5) aromatic acids, TMS (y = 0.001371x – 1.7174 R2
=
0.951); (6) phthalic acid esters (y = 0.001519x – 3.4763,
R2 = 0.990).
814

U. Kotowska, V.A. Isidorov
Table 1. Influence of temperature on Khn values
(Tables 2-4). Kb for the internal standard was used as
a check - it could not deviate more than 10% from the
expected value.
Compound
Khn±SD
22oC
18oC
26oC
3.2. Calculation of partition coefficients
Ketones
The partition coefficient in a heterogeneous system
is a physicochemical constant that characterizes a
compound in the same way as, for instance, its boiling
point. There are relationships among physicochemical
and structural properties within a homologous series or
other similarity. Fig. 1 plots log Khn and the compounds’
retention indices on the phenylmethylsiloxane phase
(type DB-5). The slopes (k) are similar for the all
compound classes; this value is a characteristic of
the liquid/liquid system. This coefficient is proportional
to the difference in free energies of solvation for the
homologous difference (k = 10-2 ΔGCH2/2.303RT) in
the two phases [6]. The value of k for the n-hexane/
nitromethane system is (1.4±0.2)×10-3, while for octanol/
water it is (5.4±0.5)×10-3 and for n-hexane/acetonitrile it
is (1.10±0.20)×10-3. The y-intercept in the equation:
2-Pentanone
3-Pentanone
2,4-Dimethyl-3-
0.19±0.01 0.20±0.01 0.21±0.01
0.18±0.01 0.19±0.01 0.20±0.01
0.59±0.01 0.61±0.02 0.63±0.02
pentanone
2-Methyl-3-hexanone
0.54±0.02 0.56±0.02 0.58±0.02
0.29±0.02 0.31±0.02 0.33±0.02
0.33±0.02 0.35±0.02 0.37±0.02
0.74±0.05 0.78±0.04 0.79±0.05
5-Methyl-2-hexanone
2-Heptanone
2-Methyl-3-heptanone
5-Methyl-3-heptanone
0.65±0.04 0.69±0.04 0.70±0.04
Phthalic acid esters
0.02±0.01 0.03±0.01 0.03±0.01
0.05±0.01 0.07±0.01 0.07±0.01
Dimethyl phthalate
Diethyl phthalate
0.12±0.01 0.14±0.01 0.15±0.01
0.25±0.01 0.28±0.01 0.28±0.01
0.23±0.02 0.26±0.01 0.27±0.01
2.99±0.13 2.93±0.17 2.83±0.10
Diisopropyl phthalate
Di-n-butyl phthalate
Diisobutyl phthalate
Di-2-ethylhexyl
log Khn = k · LTPRI – j,
phthalate
is characteristic of a homologous series. Thus the group
Two approaches were studied: (1) injection of each parameter j, a combination of Khn and retention indices,
phase after separation and (2) injection of one layer can be used for compound identification [7].
prior to and after equilibration. The precision of Khn
The relationship between distribution coefficients
values obtained by injecting a single phase was worse and other physicochemical parameters can be used to
(rsd > 10%). When both phases were analyzed rsd did predict unknown Khn values. Mathematical models were
not normally exceed 5%. Khn determinations based on constructed described by a general relationship:
the analysis of both phases is superior and this method
was adopted.
The distribution coefficient depends both on
temperature and pressure. However, atmospheric
log Khn = a log X + b log Y + c.
(2)
Such parameters as molar mass, number of carbon
pressure changes do not significantly affect liquid-liquid atoms in a molecule, density, molar volume, octanol/
equilibria. On the other hand, temperature changes water distribution coefficient, and chromatographic
around room temperature do affect the equilibrium, to retention index were used as variables X and Y.
an extent depending on the structure. Table 1 presents Coefficients a, b and c of Eq. 2 were calculated by the
Khn values for ketones and phthalic acid esters at 18, method of least squares. The coefficient of determination
22 and 26oC. For phthalates the change is the largest (R2) was the matching criterion. F-Snedecor values
o
and is equal to 2-4% per C. We conclude that the [21] characterized the significance of the correlation
determination of Khn values should be carried out at a equations. These equations also served to test the
constant temperature (± 1-2oC).
experimental Khn determinations. Predicted values and
Khn values in n-hexane/nitromethane were the parameters used are in Tables 2-4.
determined for 99 ketones, esters, and TMS-derivatized
The predicted Khn are in good agreement with the
phenols and aliphatic and aromatic carboxylic acids. experimental values; the average difference was 5%.
Linear temperature programmed retention indices The F-test shows is that the equations are meaningful
were determined simultaneously with the distribution at a significance level of at least 95%. The majority of
coefficients. Khn and LTPRI values obtained in R2 values are close to 0.99. A considerably lower R2 was
consecutive measurements (3-5 repetitions) were obtained for acetates of terpene alcohols because the
averaged and the standard deviation calculated compounds belonging to this group differ considerably
815

Partition coefficients of ketones, phenols, aliphatic
and aromatic acids, and esters in n-hexane/nitromethane
Table 2. Experimental and predicted Khn values of ketones and the parameter values used in predicting Khn
calc
Compound
Bp (oC)
MW
LTPRI ± SD
Khnexp± SD
Khn
Unbranched
2-Pentanone
3-Pentanone
3-Hexanone
2-Hexanone
4-Heptanone
2-Heptanone
4-Octanone
2- Octanone
5-Nonanone
2-Nonanone
2- Decanone
6-Undecanone
2-Tridecanone
3-Heptanone
3- Octanone
4-Nonanone
3-Nonanone
3-Decanone
4-Decanone
3- Undecanone
2- Undecanone
5- Undecanone
102.2
102.0
123.5
127.6
144.0
151.5
172.7
172.5
188.4
195.3
210.0
226.0
-
86
688±1
700±1
786±2
790±1
891±2
892±2
970±1
987±2
1069±2
1089±2
1190±2
1269±2
1493±3
887
0.26±0.01
0.25
86
0.26±0.01
0.25
0.37
0.37
0.52
0.52
0.69
0.69
0.90
0.91
1.16
1.44
2.55
0.52
0.69
0.90
0.90
1.15
1.15
1.44
1.44
1.47
100
0.38±0.02
100
0.36±0.02
114
0.54±0.02
114
0.47±0.01
128
0.70±0.02
128
0.61±0.01
142
1.02±0.01
142
0.85±0.01
156
1.18±0.02
170
1.61±0.04
212
2.40±0.05
163.0
172.7
187.5
190.0
205.0
206.0
227.0
231.5
227.0
114
-
-
-
-
-
-
-
-
-
128
986
142
1079
142
1080
156
1174
156
1174
170
1270
170
1272
170
1270
Monosubstituted
3-Methyl-2-butanone
4- Methyl-2-pentanone
3- Methyl-2-pentanone
2- Methyl-3-pentanone
2- Methyl-3-hexanone
5- Methyl-2-hexanone
2- Methyl-3-heptanone
5- Methyl-3-heptanone
4- Methyl-3-hexanone
3-Ethyl-2-pentanone
4- Methyl-2-hexanone
5- Methyl-3-hexanone
94.25
116.8
118.0
114.8
135.0
144.0
158.0
167.5
134.5
139.0
142.0
136.0
86
661±2
750±1
755±2
749±1
838±1
859±1
930±2
943±2
877
0.35±0.02
0.45±0.02
0.38±0.01
0.45±0.02
0.70±0.01
0.62±0.01
0.88±0.04
0.85±0.04
-
0.19
0.41
0.39
0.43
0.69
0.59
0.98
0.88
0.65
0.62
0.60
0.64
100
100
100
114
114
128
128
114
114
114
114
892
-
903
-
836
-
816

U. Kotowska, V.A. Isidorov
ContinuedTable 2. Experimental and predicted Khn values of ketones and the parameter values used in predicting Khn
calc
Compound
Bp (oC)
MW
LTPRI ± SD
Khnexp± SD
Khn
2- Methyl-4-heptanone
3- Methyl-4-heptanone
6- Methyl-2-heptanone
5- Methyl-4-heptanone
6- Methyl-3-heptanone
3- Methyl-2-heptanone
3- Methyl-4-octanone
7- Methyl-4-octanone
5- Methyl-3-octanone
7- Methyl-3-octanone
2- Methyl-3-octanone
4- Methyl-2-octanone
2- Methyl-5-nonanone
2- Methyl-4-nonanone
155.0
156.3
170.5
160.4
163.5
167.0
174.0
178.0
179.0
182.5
183.0
184.0
203.0
207.5
128
923
929
-
-
-
-
-
-
-
-
-
-
-
-
-
-
0.96
128
0.95
0.82
0.91
0.88
0.85
1.48
1.43
1.41
1.37
1.36
1.35
2.14
2.06
128
1024
991
128
128
1001
1012
1064
1077
1080
1091
1093
1096
1188
1202
128
142
142
142
142
142
142
156
156
Disubstituted
4,4-Dimethyl-2-pentanone
2,4-Dimethyl-3-pentanone
2,6-Dimethyl-4-heptanone
125.5
124.5
169.4
114
114
142
788±2
795±2
971±2
0.55±0.01
0.75±0.01
1.44±0.07
-
-
-
Experimentally determined Khnexp and predicted K calc n-hexane/nitromethane partition coefficients; linear temperature programmed retention index (LTPRI)
values and standard deviation (SD) were determhinn ed experimentally; LTPRI values without SD are from the literature [22, 23]; K calc were calculated from
the equations: unbranched ketones: log Khn = 2.3462 log MW + 0.0010 LTPRI – 5.2042, R2 = 0.9942, Fcal = 857.0; Fx,2,α=0.0h5n= 4.1; monosubstituted
ketones: log Khn = -1.6578 log Bp + 0.1935 MW + 1.1373, R2 = 0.9818, Fcal = 134.9; Fx,2,α=0.05 = 5.8.
MW – molar weight; Bp – boiling point.
Table 3. Experimental and predicted Khn values of esters and the parameter values used in predicting Khn
calc
Compound
MW
Log Kow
LTPRI ± RSD
Khnexp± SD
Khn
Aliphatic esters
n-Butyl formate
102.07
116.09
116.09
130.11
116.09
144.12
130.11
144.12
88.05
-
-
-
-
-
-
-
-
-
-
-
737±2
792±2
825±2
927±3
812±1
1008±2
908±3
969±3
724±1
800±2
1094±2
0.30±0.03
0.33±0.03
0.33±0.04
0.44±0.04
0.49±0.04
0.62±0.04
0.57±0.03
0.71±0.03
0.50±0.04
0.56±0.03
0.92±0.08
-
-
-
-
-
-
-
-
-
-
-
iso-Pentyl formate
n-Pentyl formate
n-Hexyl formate
n-Butyl acetate
n-Hexyl acetate
n-Butyl propanoate
iso-Pentyl propanoate
Methyl butanoate
Ethyl butanoate
116.09
158.14
n-Pentyl butanoate
817

Partition coefficients of ketones, phenols, aliphatic
and aromatic acids, and esters in n-hexane/nitromethane
ContinuedTable 3. Experimental and predicted Khn values of esters and the parameter values used in predicting Khn
calc
Compound
MW
Log Kow
LTPRI ± RSD
Khnexp± SD
Khn
n-Hexyl butanoate
Methyl pentanoate
Ethyl pentanoate
Ethyl hexanoate
Propyl hexanoate
172.15
116.09
130.11
144.12
158.14
-
-
-
-
-
1190±3
825±3
898±3
998±2
1089±3
1.24±0.21
0.68±0.04
0.81±0.07
1.29±0.08
1.58±0.14
-
-
-
-
-
Acetates of terpene alcohols
Linalool
196.16
194.14
196.16
196.16
194.14
194.14
196.16
198.17
196.16
196.16
198.17
196.16
196.16
196.16
194.14
196.16
200.19
196.16
196.16
196.16
198.17
196.16
196.16
194.14
196.16
196.16
198.17
194.14
198.17
-
1257±2
1261±1
1289±2
1291±2
1291±2
1294±3
1351±1
1355±1
1171
1.05±0.05
1.10
1.02
1.16
1.16
1.25
1.25
1.31
1.24
0.94
0.94
0.96
1.03
1.03
1.05
1.12
1.10
1.00
1.13
1.13
1.13
1.17
1.15
1.15
1.13
1.23
1.17
1.17
1.11
1.26
cis-Chrysanthenyl
Isobornyl
-
1.10±0.07
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
1.18±0.06
Bornyl
1.23±0.06
trans-Sabinyl
trans-Verbenyl
α-Terpenyl
1.21±0.07
1.27±0.06
1.29±0.07
Citronellyl
1.24±0.05
Santolyl
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Artemisyl
1173
Dihydromyrcenol
cis-Sabinene hydrate
endo-Fenchyl
exo-Fenchyl
1215
1219
1220
1234
Myrtenyl
1235
trans-Sabinene hydrate
Tetrahydrolavandulol
neo-3-Thujyl
Isopulegol
1253
1270
1271
1273
neo-Isopulegol
neo-Menthyl
neo-izo-3-Thujyl
iso-Isopulegol
cis-Verbenyl
Lavandulil
1273
1275
1278
1281
1282
1289
trans-3-Thujyl
Menthyl
1291
1294
trans-Pinocarvyl
cis-Dihydro-α-terpenyl
1297
1298
818

U. Kotowska, V.A. Isidorov
ContinuedTable 3. Experimental and predicted Khn values of esters and the parameter values used in predicting Khn
calc
Compound
MW
Log Kow
LTPRI ± RSD
Khnexp± SD
Khn
iso-3-Thujyl
196.16
196.16
196.16
196.16
198.17
196.16
194.14
198.17
196.16
200.19
196.16
196.16
196.16
194.14
196.16
196.16
196.16
196.16
196.16
194.14
196.16
196.16
196.16
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
1301
1303
1305
1306
1306
1308
1309
1315
1318
1320
1325
1328
1330
1337
1340
1340
1340
1356
1365
1362
1381
1383
1420
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
1.12
neo-Dihydrocarveol
Dihydrocarveol
iso-Verbanol
1.20
1.20
1.21
1.21
1.14
1.21
1.29
1.16
1.23
1.10
1.25
1.26
1.36
1.29
1.29
1.29
1.33
1.35
1.42
1.39
1.39
1.40
Isomenthyl
neo-iso-Isopulegol
cis-Pinocarvyl
trans-Dihydro-α-terpenyl
neo-Verbanol
Dihydrocitronellol
iso-Dihydrocarveol
neo-iso-Verbanol
cis-Piperitol
trans-Carvyl
trans-Piperitol
Verbanol
Terpin-4-ol
neo-Dihydrocarveol
Neryl
cis-Carvyl
trans-Myrtanol
Geranyl
1-Menthen-9-yl
Phthalic acid esters
194.2
Dimethyl phthalate
Diethyl phthalate
1.61
2.54
3.40
4.27
4.27
7.73
3.11
5.12
4.70
6.00
6.87
1455±2
0.03±0.01
0.03
0.07
0.14
0.28
0.28
2.82
0.12
0.20
0.53
0.96
1.67
222.2
250.3
278.4
278.4
390.6
246.2
250.3
312.4
334.4
362.5
1591±2
0.07±0.01
Diisopropyl phthalate
Di-n-butyl phthalate
Diisobutyl phthalate
Di-2-ethylhexyl phthalate
Diallyl phthalate
1773±1
0.15±0.01
1961±2
0.27±0.02
1868±3
0.29±0.02
2555±2
2.83±0.04
-
-
-
-
-
-
-
-
-
-
Di-n-propyl phthalate
Butylbenzyl phthalate
Di-n-hexyl phthalate
Di-n-heptyl phthalate
819

Partition coefficients of ketones, phenols, aliphatic
and aromatic acids, and esters in n-hexane/nitromethane
ContinuedTable 3. Experimental and predicted Khn values of esters and the parameter values used in predicting Khn
calc
Compound
MW
Log Kow
LTPRI ± RSD
Khnexp± SD
Khn
Di-n-octyl phthalate
Butyl-2-ethylhexyl phthalate
Diisooctyl phthalate
Di-n-nonyl phthalate
Diisononyl phthalate
Di-n-decyl phthalate
Diisodecyl phthalate
Diundecyl phthalate
Ditridecyl phthalate
390.6
334.4
390.6
418.6
418.6
446.7
446.7
474.7
530.8
7.73
5.64
7.73
8.60
8.60
9.46
9.46
10.33
12.06
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
2.82
0.89
2.82
4.66
4.66
7.53
7.53
11.96
28.70
Other esters
Citronellyl formate
Linalool propanoate
Nopyl acetate
184.15
210.17
208.15
208.15
224.18
-
-
-
-
-
1271±1
1340±1
1427±1
1517±2
1564±3
0.76±0.02
-
-
-
-
-
0.87±0.18
1.12±0.01
0.72±0.01
1.19±0.40
Citryl acetate
Geranyl butanoate
Experimentally determined Khnexp and predicted K calc n-hexane/nitromethane partition coefficients; linear temperature programmed retention index (LTPRI)
values and standard deviation (SD) were determhinn ed experimentally; LTPRI values without SD are from the literature [24]; Khncalc were calculated from the
equations: acetates of terpene alcohols: log Khn = -5.8349 log MW + 0.0082 LTPRI + 12.3922, R2 = 0.8779, Fcal = 18.0, Fx,2,α=0.05 = 5.8; phthalic acid
esters: log Khn = -4.7198 log MW + 0.0874 log Kow - 12.4570, R2 = 0.9996, Fcal = 1499, Fx,2,α=0.05 = 9.5. MW – molar weight; Kow – octanol/water partition
coefficient.
Experimental and predicted Khn values of TMS derivatives of carboxylic acids and phenols and the parameter values
used in predicting Khn
Table 4.
calc
Compound
MW
LTPRI±SD
Khnexp± SD
Khn
Aliphatic monocarboxylic acids, mono-TMS
2-Methylpropanoic
2.2-Dimethylpropanoic
Hexanoic
88.11
102.13
116.16
144.22
158.24
172.27
200.32
256.43
270.46
284.48
312.54
88.11
832±2
851±2
1074±1
1269±1
1355±2
1458±2
1654±2
2052±2
2153±2
2255±2
2451±3
883
-
2.05
-
2.70
4.51
4.51±0.10
Octanoic
9.01±0.15
8.98
Nonanoic
12.34±0.20
12.42
17.33
33.05
114.34
155.21
208.29
380.49
2.19
Isodecanoic
17.40±0.60
Dodecanoic
-
-
-
-
-
-
-
-
Hexadecanoic
Heptadecanoic
Octadecanoic
Eicosanoic
Butanoic
Pentanoic
102.13
144.22
977
3.15
Dipropylacetic
1151
8.04
820

U. Kotowska, V.A. Isidorov
ContinuedTable 4. Experimental and predicted Khn values of TMS derivatives of carboxylic acids and phenols and the parameter values
used in predicting Khn
calc
Compound
MW
130.19
172.27
188.30
214.35
228.37
242.40
LTPRI±SD
1165
Khnexp± SD
Khn
Heptanoic
-
-
-
-
-
-
6.35
Decanoic
1450
17.23
24.73
45.30
61.73
84.19
Undecanoic
1550
Tridecanoic
1755
Tetradecanoic
1850
Pentadecanoic
1951
Aliphatic dicarboxylic acids, di-TMS
Propanedioic (malonic)
Heptanedioic (pimelic)
Nonanedioic (azelaic)
Decanedioic (sebacic)
Undecanedioic
104.06
160.17
188.22
202.25
216.28
118.09
90.04
1216±1
1612±1
1806±2
1904±2
2005±2
1321±1
1139
1.06±0.09
1.05
1.95
3.03
3.99
5.21
1.13
0.88
1.79
2.34
3.61
1.91
2.95
1.37
2.30
1.25
3.95
1.58
2.50
2.41
3.82
6.98
12.68
1.89±0.19
3.10±0.31
4.02±0.32
5.16±0.42
Butanedioic (succinic)
Etanedioic
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Methylpropanedioic
Ethylpropanedioic
118.09
132.12
146.14
132.12
146.14
132.12
146.14
132.12
160.17
146.14
160.17
174.20
188.23
230.30
258.36
1225
1289
2.2-Dimethylbutanedioic
Methylbutanedioic
meso-2.3-Dimethylbutanedioic
Pentanedioic (glutaric)
2-Methylpentanedioic
3-Methylpentanedioic
3,3-Dimethylpentanedioic
Hexanedioic (adipic)
3-Methylhexanedioic
Octanedioic (suberic)
3-Methyloctanedioic
Dodecanedioic
1320
1333
1365
1410
1423
1431
1431
1514
1544
1710
1743
2102
Tetradecanedioic
2305
Aliphatic hydroxycarboxylic acids, TMS
2-Hydroxypropionic (lactic)
3-Hydroxybutyric
90.08
104.11
132.16
160.21
90.08
1065±1
1167±1
1289±1
1464±1
1151
3.19±0.14
4.52±0.14
9.27±0.25
16.89±0.46
-
3.25
4.52
8.87
17.34
3.21
4.58
2-Hydroxyhexanoic
2-Hydroxyoctanoic
3-Hydroxypropanoic
2-Hydroxyisobutyric
104.11
1071
-
821

Partition coefficients of ketones, phenols, aliphatic
and aromatic acids, and esters in n-hexane/nitromethane
ContinuedTable 4. Experimental and predicted Khn values of TMS derivatives of carboxylic acids and phenols and the parameter values
used in predicting Khn
calc
Compound
MW
LTPRI±SD
Khnexp± SD
Khn
2- Hydroxybutyric
104.11
104.11
118.13
118.13
118.13
118.13
118.13
132.16
132.16
118.13
118.13
132.16
132.13
132.13
132.13
160.21
160.21
1136
1170
1174
1207
1214
1216
1245
1252
1253
1260
1265
1275
1317
1366
1395
1402
1555
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
4.54
3- Hydroxyisobutyric
4.52
6.37
6.35
6.34
6.34
6.32
8.91
8.91
6.31
6.30
8.89
8.84
8.79
8.76
17.46
17.18
2-Hydroxyisopentanoic
2-Hydroxypentanoic
2-Methyl-3-hydroxybutyric
3-Hydroxyisopentanoic
3-Hydroxypentanoic
2-Hydroxyisohexanoic
3-Methyl-2-hydroxypentanoic
4-Hydroxyisopentanoic
4-Hydroxypentanoic
2-Methyl-3-hydroxypentanoic
3-Hydroxyhexanoic
5-Hydroxyhexanoic
2,2-Dimethyl-3-hydroxybutanoic
2-Propyl-3-hydroxypentanoic
7-Hydroxyoctanoic
Phenols
Phenol, mono-TMS
94.11
110.11
110.11
110.11
126.11
126.11
1055±2
1330±2
1390±1
1410±1
1559±2
1659±2
2.09±0.10
5.70 ± 0.08
5.33 ± 0.02
5.74 ± 0.02
9.91 ± 0.69
12.43 ± 0.14
-
-
-
-
-
-
Pyrocatechol (1,2-dihydroxybenzene), di-TMS
Resorcinol (1,3-dihydroxybenzene), di-TMS
Hydroquinone (1,4-dihydroxybenzene), di-TMS
Pyrogallol (1,2,3-trihydroxybenzene), tri-TMS
Phloroglucinol (1,3,5-trihydroxybenzene), tri-TMS
Aromatic acids
Benzoic, mono-TMS
122.12
138.12
138.12
154.12
154.12
170.12
1250±1
1522±1
1635±1
1793±3
1835±2
1981±2
1.30 ± 0.04
2.76 ± 0.04
3.07 ± 0.06
5.98 ± 0.16
6.59 ± 0.12
14.13 ± 0.30
-
-
-
-
-
-
Salicylic (2-hydroxybenzoic), di-TMS
4-Hydroxybenzoic, di-TMS
Gentisic (2,5-dihydroxybenzoic), tri-TMS
Protocatechuic (3,4-dihydroxybenzoic), tri-TMS
Gallic (3,4,5-trihydroxybenzoic), tri-TMS
Alkilaromatic acids
Benzeneacetic, mono-TMS
Mandelic (α-hydroxybenzeneacetic), di-TMS
4-Hydroxybenzeneacetic, di-TMS
136.15
152.14
152.14
1298±2
1489±2
1648±2
0.66 ± 0.01
1.85 ± 0.03
1.46 ± 0.03
-
-
-
822

U. Kotowska, V.A. Isidorov
ContinuedTable 4. Experimental and predicted Khn values of TMS derivatives of carboxylic acids and phenols and the parameter values
used in predicting Khn
calc
Compound
MW
LTPRI±SD
Khnexp± SD
Khn
Homogentisic (2,5-dihydroxybenzeneacetic), tri-
TMS
168.14
1853±2
4.30 ± 0.07
-
Cinnamic acids
o-Coumaric (2-hydroxycinnamic), di-TMS
m-Coumaric (3-hydroxycinnamic), di-TMS
p-Coumaric (4-hydroxycinnamic), di-TMS
Caffeic (3,4-dihydroxycinnamic), tri-TMS
164.15
164.15
164.15
180.16
1818±1
1878±2
1949±1
2151±1
2.07 ± 0.07
2.11 ± 0.07
1.84 ± 0.07
4.99 ± 0.22
-
-
-
-
Experimentally determined Khnexp and predicted Khncalc n-hexane/nitromethane partition coefficients; linear temperature programmed retention index (LTPRI)
values and standard deviation (SD) were determined experimentally; LTPRI values without SD are from the literature [25-27]; Khncalc were calculated from
the equations: aliphatic monocarboxylic acids: log Khn = 1.1377 log LTPRI + 0.0077 MW - 3.6924, R2 = 0.9992, F = 499.5, Fx,2,α=0.05 = 200; aliphatic
dicarboxylic acids: log Khn = -5.9992 log LTPRI + 0.0178 MW + 16.6760, R2 = 0.9996, Fcal = 999.0; Fx,2,α=0.05 = 1c9al; aliphatic hydroxycarboxylic acids:
log Khn = -0.1522 log LTPRI + 0.0107 MW + 0.0106, R2 = 0.9995, Fcal = 499.5, Fx,2,α=0.05 = 200.
MW – molar weight of non-silylated compound.
Table 5 gives the j values calculated using only the
Table 5. Average j ± SD values
experimental Khn values. As can be seen, the j values
Group of compounds
j ± SD
cover a narrow range, but overlap within experimental
error for only a few representatives of different groups.
Hence, j is characteristic of a homologous series and
can be used as a group identification parameter.
Aliphatic ketones
1.40 ± 0.12
1.12 ± 0.17
1.65 ± 0.03
3.17 ± 0.16
Aliphatic esters
Acetates of terpene alcohols
Phthalic acid esters
Aliphatic monocarboxylic acids,
4. Conclusions
0.73 ± 0.03
mono-TMS
Aliphatic dicarboxylic acids, di-TMS
Aliphatic hydroxycarboxylic acids, TMS
Phenols, TMS
1.85 ± 0.15
0.82 ± 0.10
1.01 ± 0.12
1.55 ± 0.11
1.87 ± 0.13
2.19 ± 0.10
Partition coefficients (Khn) in the n-hexane/nitromethane
partition system were determined for 99 ketones,
esters and trimethylsilyl derivatives of phenols, aliphatic
and aromatic acids. Seven tri-parameter correlation
equations between Khn and other physicochemical and
structural parameters were developed. Using these
models Khn values were predicted for approximately
130 compounds. In almost all the equations, R2 > 0.98
indicating good correlation between the experimental
and calculated values. The F values indicate that the
models are meaningful at a significance level of at least
95%. The average deviation of the predicted values
from the experimental ones was 5%.
Aromatic acids, TMS
Alkyl aromatic acids, TMS
Cinnamic acids, TMS
in structure, i.e., the number of rings and number of
double bonds in a molecule. These models can be
called Quantitative Structure – Partition Relationship
(QSPR) or Quantitative Property – Partition Relationship
(QPPR), analogous to the Quantitative Structure –
Retention Relationships (QSRR) used in the predictions
of retention indices [21].
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