Retention Indices and Sorption Enthalpies of Pentaerythritol and С2–С8 Acid Esters on Nonpolar Stationary Phases

Article abstract of DOI:10.1134/S003602442010009X

Abstract: The retention and sorption enthalpy characteristics of 38 pentaerythritol esters of C₂–C₈ carboxylic acids of different structures were determined by gas-liquid chromatography on a nonpolar phase in the temperature range 433.2–563.2 K. The molecular structure was shown to affect the temperature dependence of the retention indices of the esters. The average change in the sorption enthalpy of pentaerythritol tetraesters per CH₂ group is lower in magnitude than the similar contribution for normal alkanes. The excess mixing enthalpy at 298.2 K was evaluated for four fully substituted pentaerythritol esters.

Full text of DOI:10.1134/S003602442010009X

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2020, Vol. 94, No. 10, pp. 2168–2176. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Fizicheskoi Khimii, 2020, Vol. 94, No. 10, pp. 1567–1575.
PHYSICAL CHEMISTRY OF SEPARATION
PROCESSES. CHROMATOGRAPHY
Retention Indices and Sorption Enthalpies of Pentaerythritol
and С2–С8 Acid Esters on Nonpolar Stationary Phases
V. V. Emel’yanova, E. L. Krasnykha,*, and S. V. Portnovaa
aSamara State Technical University, Samara, 443100 Russia
*е-mail: kinterm@samgtu.ru
Received November 19, 2019; revised March 11, 2020; accepted March 17, 2020
Abstract—The retention and sorption enthalpy characteristics of 38 pentaerythritol esters of C2–C8 carbox-
ylic acids of different structures were determined by gas-liquid chromatography on a nonpolar phase in the
temperature range 433.2–563.2 K. The molecular structure was shown to affect the temperature depen-
dence of the retention indices of the esters. The average change in the sorption enthalpy of pentaerythritol
tetraesters per CH2 group is lower in magnitude than the similar contribution for normal alkanes. The
excess mixing enthalpy at 298.2 K was evaluated for four fully substituted pentaerythritol esters.
Keywords: pentaerythritol esters, gas-liquid chromatography, logarithmic retention indices, sorption
enthalpy
DOI: 10.1134/S003602442010009X
Pentaerythritol (2,2-bis(hydroxymethyl)propan- The correlation between the sorption enthalpy and the
enthalpy of vaporization of compounds makes it pos-
sible to evaluate the enthalpies of vaporization of com-
plex organic compounds [19–23].
1,3-diol) esters are used to produce plasticizers, var-
nishes, paints, and cosmetic products. They are of
greatest interest for the production of synthetic oils for
various purposes. Pentaerythritol esters of monocar-
boxylic acids have good thermal oxidative stability [1,
2]; low crystallization temperatures allow the use of
synthetic oils based on them in the Arctic zone [3–5].
These oils are mixtures based on pentaerythritol esters
of monocarboxylic acids with various additives [4, 5].
Their quantitative analysis is performed by gas-liquid
chromatography, and the components are identified
using logarithmic retention indices [6–9]. The reten-
tion indices obtained by gas-liquid chromatography
on a capillary column with a nonpolar stationary
phase are widely used in practice; in addition to iden-
tification, these values can be used to calculate the
boiling point [10, 11] and vapor pressure [12, 13]. Cor-
relations between the retention indices and enthalpies
of vaporization within the same homologous series
make it possible to evaluate the enthalpies of vaporiza-
tion for compounds for which experimental data are
unavailable [14–18].
An analysis of the literature data showed that for
pentaerythritol esters, the characteristics of retention
on a nonpolar stationary phase under gas-liquid chro-
matography conditions were not studied. Therefore,
the goal of this study was to determine the retention
indices and sorption enthalpies and analyze their tem-
perature dependences and changes in the homologous
series of pentaerythritol esters of С2–С8 acids with dif-
ferent structures. This paper is a continuation of the
series of publications on sorption under conditions of
gas-liquid chromatography on the nonpolar phase of
esters of carboxylic acids and polyhydric alcohols with
different contents of ester and hydroxyl groups in the
molecule [24–29].
EXPERIMENTAL
The esters were synthesized by esterification of the
corresponding carboxylic acids with pentaerythritol
using an eightfold molar excess of acid [1]. The reac-
tion was performed in an inert gas (nitrogen) atmo-
sphere without a catalyst to reduce the possibility of
formation of condensation products and to prevent the
oxidation of pentaerythritol. The synthesis tempera-
ture corresponded to the boiling point of the carbox-
ylic acid used. The water formed during esterification
was removed using a Dean–Stark trap. The reaction
Chromatographic analysis allows us to obtain not
only the retention indices, but also the thermody-
namic characteristics of sorption. The sorption
enthalpy is important for understanding the mecha-
nism of chromatographic retention and investigating
the intermolecular sorbate–sorbent interactions [11]. mixture was sampled (20 μL) with a syringe in 1–1.5 h
2168

RETENTION INDICES AND SORPTION ENTHALPIES
after the start of water separation, diluted with metha-
2169
O
nol (1 mL), and analyzed by GLC. All the samples
were in a liquid state. n-Alkanes (1 μL of each alkane)
were added to the sample; they were chosen such that
the retention time of the test compounds was between
the retention times of alkanes. The sample was intro-
duced in the chromatograph using a syringe. The vol-
ume of the injected sample was 0.2 μL.
H2C O C R
O
R C O CH2 C CH2 O C R
R C O CH2
O
O
Pentaerythritol tetraester
where R = n-CnH2n–1 (n = 1–6), iso-C3H7, iso-C4H9,
tert-C4H9, 2-ethyl-C5H11.
The retention times were determined in an isother-
mal mode using the procedures presented in [24, 25].
The reaction mass was analyzed and retention
times were determined using the Chromatech-Ana-
lytic hardware-software complex based on the Crys-
tal-2000M chromatograph. For analysis of pen-
taerythritol esters of С2–С6 acids, a capillary column
of 100 m × 0.2 mm × 0.5 μm with a grafted DB-1 sta- equation [30]:
tionary liquid phase was used. For analysis of pen-
taerythritol esters of C7–C8 acids, a capillary column
of 30 m × 0.32 mm × 0.5 μm with a grafted BP-1 sta-
tionary liquid phase was used. The DB-1 and BP-1
phases have the same chemical composition (100%
polydimethylsiloxane) and are nonpolar. Analysis
conditions: helium carrier gas, split ratio 1/50, flame
ionization detector, injector temperature 623.2 K,
detector temperature 573.2 K, column temperature
433.2–563.2 K, sample volume 0.2 μL.
The retention indices were calculated by the Kovats
'
'
log(tx) − log(tz)
(1)
Ix =
100 + 100z,
'
'
(tz)
(tz+1) −
log
log
'
'
'
t t
where t , , z+1 is the reduced elution time of the com-
pound and n-alkanes with z and z + 1 carbon atoms,
z
x
respectively.
The experimental retention indices were deter-
mined from three to seven measurements; the reliable
range of indices was no more than 1.0 index units
(i.u.).
The mixture components were identified using a
Finnigan Trace DSQ mass spectrometer with NIST
2002, Xcalibur 1.31.Sp 5 software. Conditions of anal-
ysis: capillary column ZB-5MS with a weakly polar
phase, length 30 m; inner diameter 0.32 mm; injector
temperature 623.2 K; transfer line temperature
The changes in the internal energy
(kJ/mol)
Δ
sorpU
(kJ/mol) at the average
sorpH
and sorption enthalpy
Δ
temperature of experiment were determined by the
equations [26, 31]
573.2 K; column temperature control mode tinit
=
Δ
RT
sorpU
353 K, 1 min, temperature rise rate 10 K/min to
573.2 K; helium carrier gas; carrier gas flow rate
1.3 mL/min.
k
T
(2)
(3)
ln
= C −
,
)
(
Δ
sorpH = ΔsorpU − RT,
The following expected products were identified in
the reaction mixture:
where R is the gas constant (8.314 J/(mol K)), and k is
the retention index calculated by the equation
H2C OH
O
tR − tM
(4)
k =
,
HO CH2 C CH2 O C R
tM
HO CH2
Pentaerythritol monoester
where tR is the elution time of the compound under
study, and tM is the elution time of the nonsorbing
compound.
The sorption enthalpies obtained by Eq. (2) corre-
spond to the average temperature of experiment.
Reduction to the standard temperature (298.2 K) was
performed by Eq. (5) [26]:
H2C OH
O
O
R C O CH2 C CH2 O C R
HO CH2
Pentaerythritol diester
Δ
sorpH(298.2) = ΔsorpH(Tav)
O
(5)
v
°
+ (−Δl Cp )(298.2 − Tav),
R C O CH2
O
v
R C O CH2 C CH2 O C R
°
where
is the change in the heat capacity of the
Δl Cp
HO CH2
O
liquid–gas transition determined by the procedure
proposed in [32].
Pentaerythritol triester
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 94 No. 10 2020

2170
The excess mixing enthalpy
EMEL’YANOV et al.
E,∞
It was shown that the retention indices also decreased
was cal-
(6)
ΔH (298.2)
at elevated temperature in the given temperature
ranges for the majority of linear esters (ΔI/ΔT is from
–1.7 to –0.5 i.u. on the average), except for dimethyl
oxalate and malonate.
culated by the equation [31]
ΔH E,∞(298.2) = ΔvapH°(298.2) + ΔsorpH°(298.2).
On the other hand, for hydroxycarboxylic esters
obtained on a capillary column with a DB-1 nonpolar
stationary phase, the retention indices increase in the
given temperature range [25]. For glycolic and lactic
esters, ΔI/ΔT is small and amounts to 0.2–1 i.u., while
for malic and tartaric esters the increase in the reten-
tion index at elevated temperatures is more pro-
RESULTS AND DISCUSSION
Retention Indices
The obtained retention indices of pentaerythritol
esters and the coefficients of the equation of the tem-
perature dependence of retention indices are pre-
sented in Table 1.
The temperature dependences of retention indices nounced (ΔI/ΔT is in the range 1.7–4.0 i.u.).
in the given temperature range are linear, which is
Thus, it can be assumed that for compounds con-
taining hydroxyl and ester functional groups, the
retention index increases with temperature. This ten-
dency is associated with the presence of a hydroxyl
group in the molecule because for completely substi-
tuted esters, the retention index changes slightly or
decreases with increasing temperature.
confirmed by the high correlation coefficients R2
(Table 1). This indicates that there is no interaction
between the sorbate molecules on the sorbent surface
[33].
An analysis of changes in the indices at a tempera-
ture increased by 10 K (ΔI/ΔT), calculated for the
homologous series of mono-, di-, tri-, and fully sub-
stituted pentaerythritol esters, showed that the average
increment of the retention index decreases when the
hydroxyl group is replaced by an ester group and
becomes negative in the case of fully substituted tet-
raesters (Table 2).
The dependences of the retention indices of esters
on the number of carbon atoms (nC) in a linear alkyl
substituent at a column temperature of 513.2 K are
described by the following equations:
One of the reasons for the decrease in the index at
elevated temperature may be the overloading of the
chromatographic column [34]. However, this is not so
because the peak asymmetry factor is close to unity for
all esters. Another reason may be a change in the prop-
erties of the stationary phase because of its dynamic
modification by the analytes [35]. However, as indi-
cated above, the analyte concentration was minimum
due to dilution; therefore, phase modification is
unlikely.
The temperature dependences of the retention
indices of the homologous series of mono-, di-, and
fully substituted esters of three polyhydric alcohols
(glycerol, neopentylglycol, and trimethylolpropane)
determined on a capillary column with a nonpolar sta-
tionary phase were analyzed (Table 2) [24, 27, 28].
The obtained values confirm the tendency toward a
decrease in the average value of ΔI/ΔT for the case
with hydroxyl groups replaced by ester ones.
I513.2 = 96.0nC + 1387, R2 = 0.999
(7)
for monoesters;
I513.2 = 184.2nC + 1385, R2 = 0.999
(8)
for diesters;
I513.2 = 264.6nC + 1380, R2 = 0.999
(9)
for triesters; and
I513.2 = 341.1nC + 1350, R2 = 0.998
(10)
for tetraesters.
In the method for calculating the retention index it
is postulated that the change in the retention index per
carbon atom (ΔI/nC) for normal alkanes is 100. As is
known, for some mono- and dicarboxylic esters, the
retention index increases by 90–95 i.u. per CH2 group
[29, 37]. The change in retention indices for pen-
taerythritol esters with the alkyl substituent (R)
increased by one CH2 group was 95.8 i.u. for mon-
oesters, 92.1 i.u. for diesters, 88.2 i.u. for triesters, and
85.3 i.u. for tetraesters. In this case, the dependence of
the index change by a CH2 group is almost linear
(Fig. 1), which confirms the absence of interactions
The temperature dependences of retention indices
were studied on a capillary column with a TBR-1 non-
polar stationary phase (100% polydimethylsiloxane)
in a wide temperature range (333–423 K) for various
classes of organic compounds, including monocar-
boxylic esters [36]. An analysis of the results of the
study reported in [36] revealed that the retention indi-
ces for esters decrease at elevated temperatures, and
ΔI/ΔT is, on the average, –1.1…–0.5 i.u. Earlier, we
determined the retention indices of dicarboxylic acid
esters on a capillary column with an OV-101 nonpolar
stationary phase in the temperature range of 30 K [29]. between ester molecules on the phase surface. A simi-
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 94
No. 10
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RETENTION INDICES AND SORPTION ENTHALPIES
2171
Table 1. Experimental retention indices and coefficients of the temperature dependences of pentaerythritol esters (I =
aTc + b; Tc is the column temperature, K. The values are italicized)
I513.2
units*
,
R2
nС
I, units
ΔI/ΔT
a
b
Pentaerythritol monoesters
453.2 463.2
1451.9 0.1 1455.7 0.1 1459.7 0.1 1464.2 0.1 1483.4
453.2 463.2 473.2 483.2
1551.5 0.1 1556.1 0.1 1561.0 0.1 1566.2 0.1 1580.8
493.2 503.2 513.2 523.2
1660.3 0.1 1666.3 0.1 1672.8 0.1 1679.9 0.1 1673.0
513.2 523.2 533.2 543.2
1772.8 0.1 1778.4 0.1 1784.5 0.1 1795.2 0.1 1771.4
503.2 513.2 523.2 533.2
1862.2 0.1 1868.9 0.1 1875.3 0.1 1882.2 0.1 1868.1
493.2 503.2 513.2 523.2
1617.0 0.1 1622.9 0.1 1629.1 0.1 1635.5 0.1 1629.1
503.2 513.2 523.2 533.2
1359.1 0.1 1364.0 0.1 1369.3 0.1 1374.3 0.1 1364.5
513.2 523.2 533.2 543.2
1726.91 0.1 1733.2 0.1 1739.9 0.1 1746.9 0.1 1726.1
1
2
3
4
5
3
433.2
443.2
4.1
4.9
6.5
7.3
6.7
6.2
5.1
6.7
4.7
0.409
0.492
0.65
1274.6
1329.3
1338.0
1395.6
1528.1
1311.8
1103.7
1384.5
2026.4
0.998
0.999
0.999
0.974
0.999
0.999
0.999
0.999
0.999
0.732
0.664
0.619
0.508
0.667
0.486
iso-
4
tert-
4
iso-
5
533.2
543.2
553.2
563.2
2-ethyl- 2285.7 0.1 2290.4 0.1 2295.4 0.1
–
2276.2
Pentaerythritol diesters
453.2 463.2
1549.4 0.1 1552.8 0.1 1555.4 0.1 1559.6 0.1 1575.9
453.2 463.2 473.2 483.2
1734.5 0.1 1738.6 0.1 1742.6 0.1 1746.9 0.1 1758.2
493.2 503.2 513.2 523.2
1918.5 0.1 1923.1 0.1 1927.5 0.1 1932.6 0.1 1927.6
513.2 523.2 533.2 543.2
2116.8 0.1 2120.8 0.1 2125.3 0.1 2135.2 0.1 2114.5
503.2 513.2 523.2 533.2
2304.6 0.1 2306.1 0.1 2311.2 0.1 2316.1 0.1 2307.5
533.2 553.2 263.2
2509.7 0.1 2521.6 0.1 2526.5 0.1
493.2 503.2 513.2
1
2
3
4
5
6
433.2
443.2
3.3
4.1
4.7
6.0
3.4
5.6
5.1
4.9
5.1
5.8
0.332
0.412
0.467
0.597
0.396
0.564
0.506
0.494
0.510
0.580
1405.5
1547.8
1688.1
1809.2
2104.3
2208.6
1579.3
1302.9
1761.5
2175.1
0.992
0.999
0.999
0.947
0.957
0.998
0.999
0.999
0.999
0.993
–
2498.4
3
523.2
iso-
4
1828.9 0.1 1833.8 0.1 1838.8 0.1 1844.1 0.1 1838.7
503.2 513.2 523.2 533.2
1551.6 0.1 1556.2 0.1 1561.2 0.1 1566.4 0.1 1556.12
513.2 523.2 533.2 543.2
2023.8 0.1 2028.9 0.1 2033.8 0.1 2039.2 0.1 2023.4
533.2 543.2 553.2
tert-
4
iso-
5
2-ethyl- 2484.7 0.1 2489.6 0.1 2496.3 0.1
–
2472.7
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 94 No. 10 2020

2172
EMEL’YANOV et al.
Pentaerythritol triesters
Table 1. (Contd.)
I513.2
units*
,
R2
nС
I, units
ΔI/ΔT
a
b
1
433.2
1648.5 0.1 1649.4 0.1 1651.3 0.1
453.2 463.2 473.2
443.2
463.2
–
1655.3
1.0
1.6
0.094
0.159
1608.0
1836.0
0.998
0.998
2
3
483.2
1908.1 0.1 1909.6 0.1 1911.1 0.1 1912.9 0.1 1917.2
493.2 503.2 513.2 523.2
2154.7 0.1 2156.4 0.1 2157.9 0.1 2159.8 0.1 2157.6
513.2 523.2 533.2
2425.7 0.1 2427.2 0.1 2428.7 0.1
503.2 513.2 523.2
1.7
1.5
1.2
1.8
2.3
4.1
1.9
1.3
0.168
0.15
2071.8
2348.7
2645.6
2892.9
1910.3
1528.8
2191.1
2850.5
0.998
0.997
0.955
0.964
0.999
0.999
0.994
0.971
4
5
6
–
2425.0
533.2
2703.8 0.1 2704.2 0.1 2705.8 0.1 2707.1 0.1 2704.3
533.2 543.2 553.2 263.2
2986.6 0.1 2987.5 0.1 2989.4 0.1 2991.8 0.1 2982.0
493.2 503.2 513.2 523.2
2020.8 0.1 2022.9 0.1 2025.2 0.1 2027.5 0.1 2025.24
503.2 513.2 523.2 533.2
1734.6 0.1 1738.7 0.1 1742.7 0.1 1746.9 0.1 1738.4
513.2 523.2 533.2 543.2
2287.1 0.1 2288.9 0.1 2290.5 0.1 2292.8 0.1 2286.4
533.2 543.2 553.2 563.2
0.115
0.175
0.224
0.409
0.187
0.127
3
iso-
4
tert-
4
iso-
5
2-ethyl- 2918.4 0.1 2919.4 0.1 2920.4 0.1 2922.3 0.1 2916.2
Pentaerythritol tetraesters
1
2
3
4
5
6
433.2
1721.5 0.1 1719.8 0.1 1718.2 0.1 1717.1 0.1 1709.0
453.2 463.2 473.2 483.2
2053.1 0.1 2052.2 0.1 2051.5 0.1 2050.8 0.1 2050.0
493.2 503.2 513.2 523.2
2350.4 0.1 2348.5 0.1 2346.8 0.1 2345.2 0.1 2346.2
443.2
453.2
463.2
–1.5
–0.8
–1.7
–2.4
–2.9
–3.5
–0.9
0.7
–0.148
1785.5
0.991
0.993
0.999
0.997
0.999
—
–0.076 2089.0
–0.173 2435.6
–0.250 2815.8
–0.288 3187.0
–0.347 3593.0
–0.087 2217.5
0.067 2208.2
513.2
2687.5 0.1 2685.1 0.1 2682.5 0.1
503.2 513.2 523.2
523.2
533.2
—
—
2686.2
533.2
3042.0 0.1 3039.3 0.1 3036.3 0.1 3033.4 0.1 3039.1
543.2
3445.1 0.1 3438.1 0.1
493.2 503.2
563.2
—
—
—
—
3455.7
3
513.2
523.2
iso-
4
2174.6 0.1 2173.7 0.1 2172.8 0.1 2172.0 0.1 2172.9
503.2 513.2 523.2 533.2
2223.7 0.1 2224.1 0.1 2224.8 0.1 2225.7 0.1 2223.8
0.999
0.973
—
tert-
4
533.2
2494.4 0.1 2492.6 0.1
533.2 543.2
543.2
—
—
—
—
iso-
5
2497.8
–1.8
–0.18
2541.2
553.2
563.2
2-ethyl- 3259.6 0.1 3255.9 0.1 3252.3 0.1 3249.2 0.1 3266.4
–3.5
–0.348 3445.0
Vol. 94 No. 10
0.998
2020
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A

RETENTION INDICES AND SORPTION ENTHALPIES
2173
Table 2. Average increment of retention indices at a temperature raised by 10 K for esters of polyhydric alcohols
Alcohol
Pentaerythritol
Glycerol [27]
Trimethylolpropane [24] Neopentylglycol [28]
Ester
Mono-
Di-
Tri-
Tetra-
5.9
4.5
1.5
2.3
0.9
–0.9
—
4.1
3.7
0.6
—
2.7
1.0
–
–2.1
—
lar increase (of less than 100 per CH2 group) was
obtained for glycerol esters (88–95 units) [27],
neopentylglycol (91–96 units) [28], and trimethylol-
propane (82–90 units) [24] (Fig. 1).
values of
coincide almost completely
Δ(ΔsorpH°)/nC
for these compounds.
The average change in the sorption enthalpies per
methylene fragment is 6.9, 5.1, 4.3, and 3.9 kJ/mol for
mono-, di-, tri-, and fully substituted pentaerythritol
esters, respectively. It was shown [31] that in the tem-
perature range 323–328 K, the sorption enthalpy for
normal alkanes on the nonpolar phase (HP-1)
decreases on average by 4.4–4.5 kJ/mol per CH2
group. In our previous work, we determined a similar
contribution to the sorption enthalpy (298.2 K) for
linear alkanes, which amounted to 5.4 kJ/mol [28].
Thus, a lower contribution of the methylene fragment
to the sorption enthalpy of fully substituted pen-
taerythritol esters is most likely responsible for the
decrease in the retention index at elevated tempera-
ture.
Sorption Enthalpy
The results of calculation of sorption enthalpy for
pentaerythritol esters are presented in Table 3. An
analysis of these data shows that the sorption enthalp-
ies at 298.2 K depend linearly on the number of carbon
atoms (nC) in the linear alkyl substituent for mono-,
di-, tri-, and tetraesters (Fig. 2).
The change in the sorption enthalpies calculated
for the homologous series of mono-, di-, tri-, and
completely substituted pentaerythritol esters per car-
bon atom in the alkyl substituent
Δ(ΔsorpH°)/nC
To evaluate the excess enthalpy of mixing
depending on the number of COOR groups in the
ester molecule is also linear (Fig. 3). which is indica- ΔH E,∞(298.2) based on the literature data on saturated
tive of the additive contribution of hydroxyl and ester vapor pressures [38], the enthalpies of vaporization at
groups to the sorption enthalpy. A similar dependence 298.2 K were calculated for four pentaerythritol esters.
was also observed for trimethylolpropane and neopen- The excess mixing enthalpy is a negative value
tylglycol esters [24, 28] (Fig. 3), and the numerical (Table 4); i.e., the intermolecular interactions
98
nC
2
3
4
5
6
7
−80
−100
−120
−140
−160
−180
1
94
90
86
PE
TMP
GL
NPG
0
2
3
4
5
1
nCOOR
1
2
3
4
Fig. 1. Dependences of the change in the retention index
per carbon atom in a linear alkyl substituent on the number
of COOR groups in the molecule of pentaerythritol (PE),
trimethylolpropane (TMP), glycerol (GL), and neopen-
tylglycol (NPG) esters.
Fig. 2. Dependences of
on the number of
Δ
sorpH°(298.2)
carbon atoms in a linear alkyl substituent for pentaerythri-
tol (1) mono-, (2) di-, (3) tri-, and (4) tetraesters.
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 94 No. 10 2020

2174
EMEL’YANOV et al.
Table 3. Calculated sorption enthalpies
v
°
(298.2),
−ΔsorpH°
,
−Δl Cp
(Т ),
−ΔsorpH
av
kJ/mol
nC
Тav, K
kJ/mol
J/(mol K)
Pentaerythritol monoesters
1
2
3
4
193.2
200.4
207.6
214.7
221.8
205.1
212.5
208.4
233.9
448.2
468.2
508.2
528.2
518.2
508.2
528.2
518.2
57.5 0.3
58.7 0.2
58.5 0.4
60.4 0.5
63.9 0.3
57.2 0.4
59.0 0.4
56.1 0.1
73.3 2.1
86.5
92.8
102.1
109.8
112.7
100.3
107.8
94.2
5
3, iso-
4, iso-
4, tert-
5, 2-ethyl-
548.2
131.7
Pentaerythritol diesters
1
2
3
4
5
6
185.2
194.9
205.6
216.9
228.7
240.9
201.2
213.1
205.7
249.2
448.2
468.2
508.2
528.2
518.2
548.2
508.2
528.2
61.5 0.3
65.2 0.2
67.6 0.4
71.9 0.5
78.2 0.3
79.7 2.6
64.6 0.4
68.9 0.4
56.1 2.3
96.2 0.5
89.2
98.4
110.8
121.8
128.6
139.9
106.9
117.9
101.3
158.5
3, iso-
4, iso-
4, tert-
5, 2-ethyl-
518.2
548.2
Pentaerythritol triesters
1
2
3
4
5
6
174.1
185.6
199.4
214.6
230.9
247.9
193.2
209.1
259.5
448.2
468.2
508.2
528.2
518.2
548.2
508.2
528.2
66.6 0.4
72.6 0.3
76.9 0.5
83.3 0.4
92.3 0.5
95.8 0.7
72.4 0.5
78.5 0.4
94.8 2.8
92.7
104.1
118.7
132.6
143.1
157.7
112.9
126.6
159.7
3, iso-
4, iso-
4, tert-
548.2
Pentaerythritol tetraesters
1
2
3
4
5
6
160.6
173.6
190.3
209.3
230.0
251.8
182.3
202.2
188.1
266.6
448.2
488.2
508.2
528.2
518.2
548.2
508.2
528.2
518.2
548.2
70.6 0.4
77.0 0.3
84.9 0.6
93.2 0.5
104.8 0.5
109.6 0.4
79.1 0.5
84.6 0.7
79.0 0.3
106.8 1.2
94.7
110.0
124.9
141.4
155.4
172.6
117.4
131.1
120.4
173.4
3, iso-
4, iso-
4, tert-
5, 2-ethyl-
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 94
No. 10
2020

RETENTION INDICES AND SORPTION ENTHALPIES
2175
E,∞
Table 4. Calculated excess mixing enthalpies
for pentaerythritol esters
ΔH (298.2)
ΔH E,∞(298.2), kJ/mol
nC
, exp., kJ/mol
, kJ/mol
Δ
vapH°(298.2)
−ΔsorpH°(298.2)
4
134.0
141.4
172.6
206.1*
173.4
–7.4
–5.1
6
167.5
193.6
151.6
8
–12.5
–21.8
5, 2-ethyl-
* Evaluated from the dependence of the sorption enthalpy of pentaerhythritol tetraesters on the number of carbon atoms in the linear
alkyl substituent (Fig. 2).
between the ester and the nonpolar phase are greater responsible for the decrease in the retention index at
than those between the fully substituted pentaerythri- elevated temperatures in fully substituted pentaeryth-
tol ester molecules during evaporation. Evaluation of ritol esters.
these interactions requires more data on the enthalpies
of vaporization of pentaerythritol esters.
The intermolecular interactions between pen-
taerythritol tetraesters and the nonpolar phase are
greater than those between the ester molecules during
evaporation, which is proved by the negative values of
excess mixing enthalpies.
To summarize, the retention and sorption charac-
teristics of pentaerythritol and С1–С8 acid esters of
various structures were determined by gas-liquid chro-
matography on a nonpolar phase in the temperature
range 433.2–563.2 K. The retention indices and sorp-
tion enthalpies were analyzed for esters containing dif-
ferent numbers of ester and hydroxyl groups. For fully
substituted esters, the retention index changes insig-
nificantly or decreases at elevated temperatures. For
homologous series of mono-, di-, tri-, and fully sub-
stituted pentaerythritol esters, the change in the index
per methylene fragment decreases from 95.8 to
85.3 i.u.
FUNDING
This study was financially supported by the Russian Foun-
dation for Basic Research (project no. 19-08-00928 A).
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2020