Effect of sodium chloride on the solubility and hydrolysis of epichlorohydrin in water

Article abstract of DOI:10.1007/s11172-018-2269-2

The mutual solubility of the components in the epichlorhydrin–water–sodium chloride system was studied in the temperature range of 20–90 °С. It was found that epichlorohydrin is salted out as the concentration of NaCl increases. The Sechenov coefficient was determined to be equal to 0.29. It was found that epichlorohydrin reacts with an aqueous solution of sodium chloride to form glycerol dichlorohydrins. Alkali formed during this reaction catalyzes the hydrolysis of epichlorohydrin to glycerol monochlorohydrin, acts as a reagent in the glycidol formation and accelerates its subsequent conversion to glycerol.

Full text of DOI:10.1007/s11172-018-2269-2

Russian Chemical Bulletin, International Edition, Vol. 67, No. 9, pp. 1627—1630, September, 2018
1627
Effect of sodium chloride on the solubility and hydrolysis
of epichlorohydrin in water
G. S. Dmitriev, L. N. Zanaveskin, and S. N. Khadzhiev
A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences,
2
9 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (495) 633 8520. E-mail: dmitriev.gs@mail.ru
The mutual solubility of the components in the epichlorhydrin—water—sodium chloride
system was studied in the temperature range of 20—90 °С. It was found that epichlorohydrin
is salted out as the concentration of NaCl increases. The Sechenov coefficient was determined
to be equal to 0.29. It was found that epichlorohydrin reacts with an aqueous solution of so-
dium chloride to form glycerol dichlorohydrins. Alkali formed during this reaction catalyzes
the hydrolysis of epichlorohydrin to glycerol monochlorohydrin, acts as a reagent in the glycidol
formation and accelerates its subsequent conversion to glycerol.
Key words: epichlorohydrin, water, sodium chloride, solubility, hydrolysis.
Epichlorohydrin (ECH) is a large-tonnage product of
organic synthesis used for the production of epoxy and
ion-exchange resins, epichlorohydrin rubbers, surfactants,
and much more.
The purpose of the present work is the study of the
mutual solubility of components in the ECH—water—
NaCl system.
In industry, ECH is produced by alkaline dehydro-
Experimental
1
chlorination of glycerol dichlorohydrins (Scheme 1).
The reaction products are ECH and an aqueous solu-
tion of sodium chloride. As a rule, the addition of salts to
aqueous solutions of organic compounds with limited
Epichlorohydrin (99.9%, Sigma-Aldrich), NaCl (reagent
grade), and distilled water were used in the work.
The experiments were carried out in a 200 mL glass reactor
equipped with a jacket, a thermocouple sleeve and a reflux con-
denser. Stirring was carried out with a magnetic stirrer. Aqueous
NaCl (120 g) and ECH (40 g) were placed into the reactor. The
reaction mixture was heated to a desired temperature (20—90 °С)
with stirring and kept for 20 min. After the stirring was stopped,
the formation of layers was observed: the upper layer was the
aqueous NaCl and the lower one was ECH. The composition of
each layer was analyzed.
2
solubility such as ECH leads to their salting out, i.e., to
a decrease in the solubility of the substances in the salt
3
solution.
Scheme 1
The analysis of water, ECH, and organic products of its
hydrolysis was carried out by GLC on a Tsvet-800 chromatograph
with a thermal conductivity detector. The column (2 m×3 mm)
was packed with a polysorb-1 phase, the detector temperature
was 200 °С, the injector temperature was 220 °С, the column
temperature was programmed from 70 to180 °С.
The NaCl content was determined by potentiometric titration
of the chloride anion with aqueous AgNO3.
Results and Discussion
To optimize the dehydrochlorination of glycerol di-
chlorohydrins, the data on the solubility of ECH in sodium
chloride solutions of various concentrations and at differ-
ent temperatures, as well as the information on the com-
position of the organic phase equilibrated with the aque-
ous salt layer, may be of practical importance, but they
are not available from the literature.
The solubility of the components of the system under
study in each other is limited in both binary and trinary
mixtures.
The limiting solubility of these components in binary
2
mixtures at 20 °С is 6.55 wt.% for ECH in water, 1.42 wt.%
2
4
for water in ECH, 26.39 wt.% for NaCl in water, and
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1627—1630, September, 2018.
066-5285/18/6709-1627 © 2018 Springer Science+Business Media, Inc.
1

1628
Russ. Chem. Bull., Int. Ed., Vol. 67, No. 9, September, 2018
Dmitriev et al.
0
.073 wt.% for NaCl in anhydrous ECH (experimen-
tal data).
The results of experiments on determination of the
lnCECH
0.2
0.4
0.6
0.8
–
–
–
–
solubility of ECH in aqueous solutions of NaCl of various
concentrations at 20 and 60 °С are presented in Table 1.
As it was expected, ECH undergoes salting out by
sodium chloride. The concentration of ECH in the satu-
rated solution of the salt at 20 °С is 5.8 times lower than
in water and is only 1.1 wt.%.
–
–
–
–
–
1.0
1.2
1.4
1.6
1.8
The ECH phase is in equilibrium with the aqueous salt
layer. The content of NaCl in this phase is 0.08—0.10 wt.%.
The increase in the solubility of NaCl in ECH is caused
by the presence of water dissolved in it. The ECH phase
contains 0.5—0.6 and 1.9—2.0 wt.% of water at 20 and
1
2
3
4
CNaCl/mol L–1
Fig. 1. Salting out of ECH with sodium chloride at 20 °С (lin-
earization of the Sechenov equation).
6
0 °С, respectively. Note that an increase in the concentra-
tion of NaCl reduces the solubility not only of ECH in the
aqueous salt layer, but also that of water in ECH. The
presence of NaCl in the ECH phase leads to a decrease in
the concentration of water in it by about 2.5 times at 20 °С
starting compound for the synthesis of ECH) by sodium
2
chloride is 0.36 (calculated from reference data ). Epi-
chlorohydrin is less soluble in water than glycerol dichloro-
hydrin (162 g L– at 20 °С). The observed decrease in
the salting-out coefficient with the growth of the nonelec-
trolyte hydrophobic properties is confirmed by the well-
1
2
and 1.6 times at 60 °С (the solubility of water in ECH at
2
6
0 °С is 3.23 wt.%).
The salting out process of nonelectrolytes is described
3
5
by the Sechenov equation:
known regularities in the salting-out effect.
It follows from the experimental data that an increase
in temperature from 20 to 60 °С has very little effect on
the solubility in water of separate components NaCl and
ECH, as well as of ECH in NaCl solutions of various
concentrations. As the salt concentration in the aqueous
solution increases, the raising temperature has an in-
creasingly less significant effect on the solubility of epi-
chlorohydrin. If the increase in the solubility of epichloro-
hydrin in water with raising temperature from 20 to 60 °С
is 1.48 wt.%, in the salt-saturated solution it is only
lnC = lnC + kСsalt,
(1)
0
where C is the nonelectrolyte concentration, mol L–1
С is the solubility of nonelectrolyte in pure water,
;
0
–
1
mol L– ; Сsalt is the concentration of salt solution,
mol L 1
.
The result of processing the experimental data by
Eq. (1) is shown in Fig. 1.
The salting-out constant of ECH from aqueous sodium
chloride solutions at 20 °С is k = 0.29. The average error
of approximation does not exceed 4%. For comparison,
the salting-out constant of glycerol dichlorohydrin (the
0
.3 wt.%.
The contact of ECH with water leads to the formation
of some by-products, the proportion of which increases
with increasing temperature. The main product of the
hydrolysis of ECH in water is glycerol 1-monochlorohydrin
Table 1. The solubility of ECH in aqueous solutions of NaCl of
various concentrations at 20 and 60 °С
(
Scheme 2).
Т/°С
Content of NaCl
in aqueous solution (wt.%)
Solubility of
ECH (wt.%)
Scheme 2
2
6
0
0
0.00
6.552
5.9
3.4
2.4
1.9
1
.9
.9
4.9
9.5
9
1
The pH value of the aqueous layer obtained by keeping
1
5.8*
0.00
2
1.1
ECH (25 wt.%) in distilled water for 4 h at 60 °С remains
constant and equal to 6. When this mixture is refluxed at
90 °С, the pH of the solution decreases to 2—3, which
indicates the formation of an acid in the reaction mix-
ture. This results from the intensive reaction according
to Scheme 2 and subsequent hydrolysis of glycerol mono-
chlorohydrin with the evolution of hydrogen chloride
(Scheme 3).
2
8.03
1
.9
.5
4.9
9.4
6.6*
6.5
3.8
2.8
2.2
1.4
9
1
1
2
*
Saturated solution of NaCl.

Epichlorohydrin solubility in NaCl(aq)
Russ. Chem. Bull., Int. Ed., Vol. 67, No. 9, September, 2018 1629
Scheme 3
An oxonium form of ECH protonated at the oxygen
atom is formed as an intermediate compound. Further
addition of chloride anion results in the formation of two
isomers of glycerol dichlorohydrins. In the ECH molecule,
as well as in its oxonium form, the chlorine atom due to
its negative inductive effect contributes to the formation
of a partial positive charge on the carbon atom from the
opposite end of the carbon chain. This substantiates the
predominant formation of glycerol 1,3-dichlorohydrin
through the nucleophilic attack by the agent according to
Scheme 6.
Upon increase in temperature to 80 °С or higher, the
solubility of ECH in salt solutions remains practically
unchanged as compared to the process at 60 °С, but the
processes of its hydrolysis to monochlorohydrin according
to Scheme 2, as well as to glycidol (Scheme 7) and glycerol
(Scheme 8), are accelerated due to the formation of an
alkaline medium.
The conversion of ECH to monochlorohydrin is 10%.
The selectivity on glycerol does not exceed 0.3%.
The experimental data show that hydrolysis of epi-
chlorohydrin in the presence of NaCl follows a different
pathway. An aqueous salt solution of ECH is an alkaline
medium with pH of 9—10. This solution also contains
glycerol 1,3-dichlorohydrin and glycerol 1,2-dichloro-
hydrin, the starting compounds for obtaining ECH ac-
cording to Scheme 1. Under conditions of the experiments,
the conversion of epichlorohydrin is 0.8 wt.%, while the
selectivity on glycerol dichlorohydrins is 100%. It should
be noted that glycerol dichlorohydrins do not form in the
absence of NaCl. The observed fact indicates that ECH
reacts with an aqueous solution of NaCl to form glycerol
dichlorohydrins and an alkali (Scheme 4).
Scheme 7
Scheme 4
Scheme 8
The obtained experimental data confirm the revers-
ibility of the reaction of formation of ECH by dehydro-
chlorination of glycerol dichlorohydrins, which was not
previously noted in the scientific and technical literature.
Another epoxy compound, ethylene oxide in an aqueous
solution, also reacts with sodium chloride to form ECH
For the standard time of the experiments (heating from
0 to 40 min and maintaining the reaction mixture for
0 min at a given temperature), an increase in temperature
2
2
from 60 to 80 °С led to an increase in the conversion of
ECH from 0.8% to 4.3%, but the selectivity on glycerol
dichlorohydrin decreased to 90% due to the reactions
shown in Schemes 7 and 8.
6
and an alkali. Apparently, the reaction with an aqueous
solution of NaCl is characteristic of all epoxy compounds.
The reaction of ECH with an aqueous solution of NаCl
can be represented by Schemes 5 and 6.
1
The technology of preparation of ECH from glycerol
allows one to obtain concentrated solutions of glycerol
dichlorohydrins with the content of the main compound
more than 80 wt.%. Unlike the traditionally used method
of dehydrochlorination of diluted (3—5%) aqueous solu-
tions of glycerol dichlorohydrins in a distillation column
with simultaneous hot-steam distillation off of forming
ECH, the synthesis of ECH from the concentrated start-
ing material can be carried out in a mixing reactor, followed
by separation of the aqueous salt and epichlorohydrin
phases formed. This can significantly reduce the energy
consumption of the process.
Scheme 5
Scheme 6
The obtained results allow us to draw a conclusion
about the optimal conditions for the synthesis. Since the
solubility of epichlorohydrin in the aqueous salt layer
decreases with increasing NaCl concentration, the process
of dehydrochlorination of glycerol dichlorohydrins should

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Russ. Chem. Bull., Int. Ed., Vol. 67, No. 9, September, 2018
Dmitriev et al.
be carried out with a 20 wt.% solution of NaOH. This will
give a close to saturation concentration of NaCl in the
solution with a minimum content of ECH dissolved in it.
Despite the fact that the reaction rate and reactor produc-
tivity increase with increasing temperature, it is better to
conduct the process at temperatures below 60 °С to avoid
intensive hydrolysis of ECH. The results of the studies
showed that the solubility of ECH in the NaCl solution
varies insignificantly with the temperature increase from
chlorohydrins. The formed alkali (pH 9—10) accelerates
the hydrolysis of ECH to glycerol monochlorohydrin and
is involved in further transformations with the formation
of glycidol and glycerol.
The work was carried out within the State Assignment
to the A. V. Topchiev Institute of Petrochemical Synthesis
of the Russian Academy of Sciences.
2
0 to 60 °С and, consequently, practically does not depend
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6
Received April 4, 2018;
in revised form June 7, 2018;
accepted June10, 2018