Characteristics of retention and enthalpies of sorption from the gas phase of esters of trimethylolpropane and С2–С5 acids on DB-1 stationary phase

Article abstract of DOI:10.1134/S0036024417020194

Characteristics of retention and their temperature dependences, along with the thermodynamic characteristics of sorption on DB-1 nonpolar phase, are determined in the temperature range of 220–280°C for 21 mono-, di-, and trisubstituted esters of trimethylolpropane and monobasic acids with a variety of structures containing from 2 to 6 carbon atoms.

Full text of DOI:10.1134/S0036024417020194

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2017, Vol. 91, No. 2, pp. 398–402. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © E.L. Krasnykh, A.Yu. Aleksandrov, A.A. Sokolova, S.V. Levanova, 2017, published in Zhurnal Fizicheskoi Khimii, 2017, Vol. 91, No. 2, pp. 372–376.
PHYSICAL CHEMISTRY OF SEPARATION PROCESSES.
CHROMATOGRAPHY
Characteristics of Retention and Enthalpies of Sorption
from the Gas Phase of Esters of Trimethylolpropane
and С2–С5 Acids on DB-1 Stationary Phase
E. L. Krasnykh*, A. Yu. Aleksandrov, A. A. Sokolova, and S. V. Levanova
Samara State Technical University, Samara, 443100 Russia
*e-mail: kinterm@samgtu.ru
Received February 8, 2016
Abstract—Characteristics of retention and their temperature dependences, along with the thermodynamic
characteristics of sorption on DB-1 nonpolar phase, are determined in the temperature range of 220–280°C
for 21 mono-, di-, and trisubstituted esters of trimethylolpropane and monobasic acids with a variety of struc-
tures containing from 2 to 6 carbon atoms.
Keywords: esters, trimethylolpropane, gas–liquid chromatography, logarithmic retention indices, enthalpy of
sorption
DOI: 10.1134/S0036024417020194
INTRODUCTION
However, there are no physicochemical or thermody-
namic data for these compounds in the literature.
In today’s polymer industry, the modification of
polymers and products based on them is of great
importance. To enhance their performance and envi-
ronmental characteristics, a variety of additives
(mainly plasticizers) are introduced into their compo-
sition [1]. Around 90% of the plasticizers now being
produced are ester plasticizers, i.e., monomer prod-
ucts with a molecular weight range of 300–600, low
vapor pressure, good thermal stability, and chemical
inertness. Over 80% of the world’s plasticizers are
phthalic acid esters, whose main disadvantage is their
toxicity [2].
The aim of this work was to determine the charac-
teristics of retention and their temperature depen-
dences, along with the thermodynamic characteristics
of the sorption of esters of trimethylolpropane and
С2–С6 acids with different structures.
EXPERIMENTAL
Esters of trimethylolpropane were synthesized via
its esterification with a corresponding acid in the pres-
ence of orthophosphoric acid (the catalyst) in an
open-type reactor system equipped with a Dean–
Stark trap for the separation of the reaction water. The
trimethylolpropane/acid molar ratio was 1/6. Benzene
was used as the azeotrope-forming agent for the syn-
thesis of acetates, while toluene was used for the syn-
thesis of the rest of the esters.
Because of the growing pressure of environmental
legislation, a different approach to selecting raw mate-
rials with respect to chemical composition and toxico-
logical characteristics, is now required [3, 4].
As part of this trend, nonphthalate esters (includ-
ing esters of trimethylolpropane) are of great interest.
Reactions proceeded according to the equations
398

CHARACTERISTICS OF RETENTION AND ENTHALPIES
399
O
CH2 OH
O
CH2 O C R
H C CH2C CH2 O C R
+
H3C CH2C CH2 OH
CH2 OH
3
CH2 OH
1-Monoester of trimethylolpropane
−H2O
2-Monoester of trimethylolpropane
O
CH2 O C R
CH2 OH
O
CH2 OH
O
−2H2O
H3C CH2C CH2 OH
O
H3C CH2C CH2 OH + R
+ H3C CH2C CH2 O C R
O
OH
CH2 OH
Trimethylolpropane
CH2 O C R
CH2 O C R
1,3-Diester of trimethylolpropane
1,2-Diester of trimethylolpropane
−3H2O
O
CH2 O C R
O
H3C CH2C CH2 O C R
O
CH2 O C R
Triester of trimethylolpropane
R−С1−С5
The compounds were identified from the kinetic
dependences of the changes in the concentrations of
mono-, di-, and triesters over time, and by means of
combined chromatography and mass spectrometry on
a Shimadzu GCMS QP2010 Ultra instrument. It
should be noted that, as opposed to the esters of glyc-
erol in [5], we failed to quantitatively or qualitatively
identify 2-monoesters and 1,2-diesters of trimethylol-
propane.
The retention indices were calculated using the
Kováts formula [7]:
'
'
log(tX ) − log(tZ )
,
× 100 + 100Z
(1)
I x =
'
'
log(tZ +1) − log(tZ )
where ' , ' , and ' are the corrected retention times
tX tZ
tZ +1
of the ester and n-alkanes with numbers of carbon
atoms Z and Z + 1, respectively.
The characteristics of the retention of ethers were
determined using a Khromatek–Analitik software–
hardware complex based on a Kristall-2000М gas
chromatograph equipped with a flame ionization
detector on a capillary column, 50 m × 0.2 mm ×
0.5 μm in size with a DB-1 bonded nonpolar phase
(an analog of the OV-101 phase [6]). The temperature
of the evaporator was 350°С, the temperature of the
detector was 300°С, the carrier gas was helium, the
split ratio was 1/100, the injection volume was 0.2 μL,
and the temperature of the thermostat was 220–
280°С.
The experimental values of the retention indices
were determined from 5–7 measurements; the confi-
dence interval for the values was no more than
1.0 index unit (i.u.).
The sorption equilibrium in the gas phase–LSP
system was characterized by the value of the sorbate’s
Т
specific retention volume at temperature
(cm3/g)
Vg
of the column, calculated using the equation [7, 8]
3( pi /p0)2 −1
(tR − tM )F
VgТ
=
P0,TC
,
(2)
2( pi /p0)3 −1
g
where tR is the time of retention for the substance
under study in the column of the chromatograph, min;
tM is the time of residence for the unretained com-
pound in the column (the holdup time), min; FP0,Ti is
the space velocity of the carrier gas at pressure p0 and
temperature Тi, cm3/min; g is the weight of the LSP in
the column, determined from the geometrical param-
eters of the column, g; pi is the pressure of the carrier
All measurements were preformed in the isother-
mal mode, according to the procedures described in
[5, 7]. Specimens of 1 μL of the mixtures of esters
under study and 1 μL of n-alkanes were dissolved in
1 mL of methanol. A specimen with a volume of
0.2 μL was injected into the evaporator using an
autosampler.
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 91 No. 2 2017

400
KRASNYKH et al.
I250°C
2600
3
y = 257.267x + 1019.877
R2 = 0.999
2200
1800
1400
1000
2
y = 179.440x + 1109.430
R2 = 0.999
1
y = 82.087x + 1224.017
R2 = 0.995
1
2
3
4
5
6
7
NС, acid
Retention indices at 250°С (I
) as a function of the number of carbon atoms in the acidic radicals of linear esters of trimeth-
250°С
ylolpropane (N ); (1) monoesters, (2) diesters, and (3) triesters.
С
gas at the inlet to the column, atm; and р0 is the atmo- to calculate the retention indices at other temperatures
spheric pressure, atm.
using coefficients a and b (Table 1). Raising the tem-
perature by 10 degrees increases the retention indices
by 3–6 i.u. for monoesters; by 2–5 i.u. for diesters;
and by less than 1 i.u. for triesters.
The standard values of the changes in internal
ꢀ
energy
and enthalpy (
kJ/mol) of sorp-
ΔspU °
ΔspHi
,
tion were determined using the dependences [7, 9, 10]
With linear acids, the dependence of the retention
indices on the number of carbon atoms in an acidic
radical is also of a linear character (see figure), allow-
ing us to use these dependences to calculate the reten-
tion indices of unexamined linear mono-, di-, and tri-
esters of trimethylolpropane.
ΔspU °
ln(VgT ) = B −
,
(3)
RT
°
,
(4)
ΔspH p,T = ΔspU ° − RT
where
is the change in the internal energy of
ΔspU °
The results from calculating
with Eqs. (3)
ΔspU °
sorption, kJ/mol; R is the universal gas constant
(8.314 J/(mol K)). We can use Eqs. (3) and (4)
because the studies were performed within a narrow
range of temperatures, and the change in the density of
the liquid stationary phase resulting from the tempera-
ture was thus negligible [10].
and (5) using coefficients B and С are presented in
Table 2. The good repeatability of the obtained results
(the error in determining
did not exceed
ΔspU °
1.0 kJ/mol) testifies to the correctness of our calcu-
ꢀ
lations. We later calculated
and (4).
using Eqs. (3)
ΔspHi
Т
Since the determination of
for capillary col-
Vg
umns is accompanied by difficulties in finding the
An analysis of the data in Table 2 shows that the
changes in the enthalpies of sorption depend linearly
on the number of carbon atoms in the alkyl radical.
When the length of the chain is increased by one СН2
group, the enthalpy of sorption in monosubstitued
esters falls by 2.5 kJ/mol. In diesters, it falls by
2.4 kJ/mol; and in triesters, by 2.3 kJ/mol. Such neg-
ligible changes are indicative of the uniformity of the
interaction in the series of mono-, di-, and triesters of
trimethylolpropane with LSP. Upon moving from
mono- to di- and triesters (i.e., with an increase in the
number of ester groups), a linear dependence is
observed for all of the esters as well. The contribution
weight of the liquid stationary phase, an equation in
Т
which the values of
verify the obtained values of
are not employed was used to
Vg
[10, 11]:
ΔspU °
ΔspU °
RT
k
T
,
(5)
ln
= C −
)
(
tR − tM
where k is the retention factor:
.
k =
tM
RESULTS AND DISCUSSION
Our experimental results on the retention indices from the ester group is 2.1–2.3 kJ/mol for all of the
and their temperature dependences are presented in esters, about the same as the contribution from the
Table 1. An analysis of our results shows that the tem- methylene fragment. In other words, for enthalpies of
perature dependences of the indices on temperature sorption (as opposed to enthalpies of evaporation), the
are linear for all of the studied compounds, allowing us contributions from the methylene and ester fragments
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
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No. 2
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CHARACTERISTICS OF RETENTION AND ENTHALPIES
401
Table 1. Values of the retention indices (I) of esters of trimethylolpropane and С2–С5 acids at various temperatures (Tc)
Ester of
trimethylolpropane
Tc
Tc
Tc
Tc
I
I
I
I
*
I250
r2
a
b
1-Monoethanoate
1-Monobutanoate
1-Monopentanoate
1-Monohexanoate
220 1369.1 230 1374.2 240 1379.3 250 1384.6 1384.6 0.517 1255.3 0.999
230 1554.0 240 1559.6 250 1565.1 260 1571.0 1565.2 0.565 1423.9 0.999
240 1620.8 250 1623.3 260 1626.1 270 1628.7 1623.5 0.267 1556.7 0.999
250 1718.2 260 1721.6 270 1724.1 280 1727.5 1718.4 0.304 1642.4 0.997
1-Mono(2-methylpro- 230 1512.2 240 1517.5 250 1523.3 260 1528.3 1523.1 0.458 1408.6 0.980
panoate)
1-Mono(2-methylbu- 230 1607.5 240 1613.9 250 1618.4 260 1623.7 1618.5 0.532 1485.5 0.980
tanoate)
1-Mono(2,2-dimeth- 230 1541.9 240 1548.7 250 1555.2 260 1561.3 1555.0 0.648 1393.0 0.999
ylpropanoate)
1,3-Diethanoate
1,3-Dibutanoate
1,3-Dipentanoate
1,3-Dihexanoate
220 1464.5 230 1467.2 240 1470.3 250 1473.5 1473.6 0.303 1397.8 0.998
230 1811.9 240 1815.3 250 1818.5 260 1822.2 1818.8 0.341 1733.5 0.999
240 1998.7 250 2002.6 260 2006.2 270 2010.1 2002.6 0.377 1908.3 0.999
250 2194.0 260 2197.7 270 2199.8 280 2208.1 2193.4 0.443 2082.6 0.924
1,3-Di(2-methylpro- 230 1733.4 240 1734.7 250 1738.9 260 1745.7 1740.2 0.409 1637.9 0.915
panoate)
1,3-Di(2-methylbuta- 230 1910.7 240 1914.5 250 1916.6 260 1920.7 1917.1 0.320 1837.1 0.915
noate)
1,3-Di(2,2-dimethyl- 230 1777.0 240 1782.4 250 1788.0 260 1792.1 1787.4 0.509 1660.1 0.996
propanoate)
Triethanoate
Tributanoate
Tripentanoate
Trihexanoate
220 1540.7 230 1541.1 240 1541.7 250 1542.6 1542.6 0.063 1526.8 0.981
230 2035.4 240 2035.8 250 2036.4 260 2037.2 2036.5 0.062 2021.0 0.980
240 2297.9 250 2298.6 260 2299.8 270 2300.1 2298.6 0.077 2279.3 0.955
250 2575.6 260 2576.1 270 2576.5 280 2577.1 2575.5 0.049 2563.2 0.992
230 1912.0 240 1912.3 250 1913.7 260 1914.5 1913.7 0.091 1890.9 0.953
Tri(2-methylpropa-
noate)
Tri(2-methylbuta-
noate)
230 2162.3 240 2163.2 250 2162.5 260 2163.6 2163.1 0.032 2155.1 0.992
Tri(2,2-dimethylpro- 240 1984.1 250 1986.5 260 1987.6 270 1986.4 1985.8 0.080 1965.8 0.493
panoate)
2
* Calculated values of the retention indices at 250°С with respect to coefficients a and b; r is the coefficient of determination.
are identical, while any difference is probably included
2
ꢀ
,
(7)
(8)
ΔspHi = − 0.026I250 −15.4, R = 0.99
in the enthalpy of mixing.
Considering the dependence of the enthalpy of
sorption on the retention indices (at 250°C), three
dependences described by corresponding equations
with errors not exceeding 1 kJ/mol can be distin-
guished for mono-, di-, and triesters (Table 2). These
can be used to predict the enthalpies of sorption for
other esters of trimethylolpropane:
2
ꢀ
.
ΔspHi = − 0.027I250 −16.4, R = 0.99
The joint processing of the obtained values of the
enthalpies of sorption depending on the retention
indices gives us
2
2
ꢀ
ꢀ
,
(6)
.
(9)
ΔspHi = −0.029I250 − 9.2, R = 0.93
ΔspHi = − 0.031I250 − 7.7, R = 0.97
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 91 No. 2 2017

402
KRASNYKH et al.
ꢀ
Table 2. Values
and
of sorption (kJ/mol) and coefficients B of esters of trimethylolpropane
ΔspHi
ΔspU °
Eq. (3)
Eq. (5)
ꢀ
ꢀ
,
−ΔspHcalc
,
−ΔspHexp
Ester of trimethylolpropane
kJ/mol
kJ/mol
–В
–С
, kJ/mol
, kJ/mol
−ΔspU °
−ΔspU °
1-Monoethanoate
1-Monobutanoate
1-Monopentanoate
1-Monohexanoate
1-Mono(2-methylpropanoate)
1-Mono(2-methylbutanoate)
1-Mono(2,2-dimethylpropanoate)
1,3-Diethanoate
1,3-Dibutanoate
1,3-Dipentanoate
45.4
7.6
8.5
8.7
8.9
8.5
8.4
8.0
8.4
9.6
10.1
10.6
9.4
10.1
9.3
46.0
18.1
18.9
19.1
19.5
18.9
18.9
18.4
18.8
20.1
20.3
21.2
19.8
20.5
19.7
19.5
21.4
22.2
23.2
21.0
22.0
20.9
49.6
55.5
57.4
59.8
55.3
56.4
53.6
54.0
64.0
68.5
72.9
62.0
67.1
62.1
58.0
72.6
79.3
85.9
69.1
76.7
69.5
49.4
54.6
56.3
59.1
53.4
56.2
54.3
53.7
62.7
67.5
72.5
60.7
65.3
61.9
58.0
71.4
78.5
85.9
68.1
74.8
69.8
51.2
53.0
55.3
51.0
52.1
49.3
49.8
59.7
64.1
68.5
57.7
62.8
57.8
53.7
68.3
74.9
81.4
64.8
72.3
65.2
51.5
53.3
56.5
51.3
52.3
49.6
50.2
59.9
64.3
69.6
58.0
63.1
58.0
54.2
68.6
75.2
82.6
65.0
72.6
65.5
1,3-Dihexanoate
1,3-Di(2-methylpropanoate)
1,3-Di(2-methylbutanoate)
1,3-Di(2,2-dimethylpropanoate)
Triethanoate
Tributanoate
Tripentanoate
9.1
11.0
11.8
12.5
10.5
11.6
10.5
Trihexanoate
Tri(2-methylpropanoate)
Tri(2-methylbutanoate)
Tri(2,2-dimethylpropanoate)
3. S. V. Lipp, A. B. Sokolov, E. L. Krasnykh, et al., Khim.
With respect to the coefficients, this is very close to
Prom. Segodnya, No. 8, 26 (2010).
2
ꢀ
,
(10)
ΔspHi = − 0.033I130 − 5.3, R = 0.97
4. S. P. Safronov, E. L. Krasnykh, S. V. Levanova, et al.,
Khim. Prom. Segodnya, No. 9, 4 (2013).
which was obtained for glycerol ethers [7]. The error in
the calculated values when using Eqs. (9) and (10)
does not exceed 2 kJ/mol, a possible sign of the uni-
formity of the processes that occur during the sorption
of ethers and esters of polyatomic alcohols.
5. A. S. Leol’ko, E. L. Krasnykh, and S. V. Levanova,
J. Anal. Chem. 64, 1126 (2009).
6. P. R. Loconto, Trace Environmental Quantitative Anal-
ysis: Principles, Techniques, and Aplications, 2nd ed.
(CRC, Boca Raton, London, New York, 2005).
7. A. A. Zhabina, E. L. Krasnykh, and S. V. Levanova,
ACKNOWLEDGMENTS
Russ. J. Phys. Chem. A 88, 1590 (2014).
This work was supported by the Russian Founda-
tion for Basic Research, project no. 16-08-00383 а.
8. S. N. Yashkin, Russ. Chem. Bull. 59, 2026 (2016).
9. L. A. Onuchak, S. Yu. Kudryashov, and V. A. Davan-
kov, Russ. J. Phys. Chem. A 77, 1508 (2003).
REFERENCES
10. L. A. Onuchak and S. Yu. Kudryashov, Russ. J. Phys.
Chem. A 88, 1785 (2014).
1. H. Zweifel, R. D. Maier, and M. Schiller, Plastics Addi-
tives Handbook 6E, 6th ed. (Hanser, München, 2009;
Professiya, St. Petersburg, 2010).
11. M. Görgényi and K. Héberger, J. Chromatogr. Sci. 37,
11 (1999).
2. T. Niino, T. Ishibashi, T. Itho, S. Sakai, H. Ishiwata,
Translated by E. Boltukhina
et al., J. Health Sci. 47, 318 (2001).
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 91
No. 2
2017