Development of the conditions of synthesis of p-chlorophenyl methacrylate of the desired purity grade

Article abstract of DOI:10.1134/S1070427209010236

The process of synthesis of p-chlorophenyl methacrylate by the reaction of p-chlorophenol with methacryloyl chloride was developed, identification and quantitative determination of admixtures in the targeted compound was carried out. The optimal conditions of the synthesis for obtaining the high quality monomer were developed.

Full text of DOI:10.1134/S1070427209010236

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 1, pp. 123−127. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © N.K. Kobyakova, M.V. Kuz’mina, E.P. Beshenova, L.N. Beloded, 2009, published in Zhurnal Prikladnoi Khimii, 2009, Vol. 82, No. 1,
pp. 124−128.
MACROMOLECULAR CHEMISTRY
AND POLYMERIC MATERIALS
Development of the Conditions of Synthesis of p-Chlorophenyl
Methacrylate of the Desired Purity Grade
N. K. Kobyakova, M. V. Kuz’mina, E. P. Beshenova and L. N. Beloded
Polymers Research Institute, Dzerzhinsk, Nizhni Novgorod oblast, Russia
Received November 1, 2008
Abstract—The process of synthesis of p-chlorophenyl methacrylate by the reaction of p-chlorophenol with
methacryloyl chloride was developed, identification and quantitative determination of admixtures in the targeted
compound was carried out. The optimal conditions of the synthesis for obtaining the high quality monomer were
developed.
DOI: 10.1134/S1070427209010236
In the recent years increased the interest to organic
glasses based on the methyl methacrylate (co)polymers
with enhanced thermal stability and low water absorption
that provides their reliable and prolonged exploitation
under various conditions. Such glasses find application
first of all in aviation and also in electrical engineering
and car building industry [1, 2]. As (co)monomers
for the modification of polymethyl methacrylate the
most promising are the methacrylic esters with bulky
cyclic fragments [2]. A special interest is paid to the
methyl methacrylate coplymers with p-chlorophenyl
methacrylate owing to high optical and strength
characteristics, alongside enhanced thermal stability and
low hygroscopicity [3]. However, it has been shown that
when the p-chlorophenyl methacrylate is even slightly
contaminated its physical and optical properties decrease,
e.g., falls thermal stability due to plasticizing effect and
appear optical defects like the glass turbidity. Hence, for
producing organic glass with required set of properties
a modifying monomer of high purity grade should be
synthesized and used.
the high purity p-chlorophenyl methacrylate restricts the
control over the synthesis and the possibility of optimal
technological regimes.
The aim of this investigation is development of the
method of p-chlorophenyl methacrylate synthesis with
the minimal content of contaminants.
EXPERIMENTAL
The IR spectra were registered on a Specord М82
instrument in the region of 4000–400 cm–1 from thin films.
The NMR spectroscopic investigations were carried out
on a DРХ-200 instrument with operating frequency
200 MHz for protons and 50 MHz for the 13C nuclei.
The samples were dissolved in deuterochloroform form
Aldrich, internal reference TMS.
Chromatographic analysis was carried out on a gas
chromatograph Сhrom-5 with the flame ionization
detector and glass column 2.5 m long and 3 mm in diam-
eter, stationary phase Chromosorb WAW (0.16–0.20 mm)
with 8% of poly(ethylene glycol)adipinate and 2% of
H3PO4; the column temperature 170°C, the evaporator
temperature 220°C, the hydrogen and nitrogen flow rate
30 ml min–1. Calculation of the content of contaminants
was performed using internal reference method, as the
reference was used dimethyl succinate.
Unfortunately only scarce information was published
so far on the synthesis of chloro-substituted phenyl
methacrylates [4, 5]. It was only reported that reaction
of p-chhlorophenol with methacryloyl chloride leads to
p-chlorophenyl methacrylate with the yield 53% or less.
The data on the content of contaminants in the ester and
on their influence on the optical and physico-mechanical
properties of the polymeric materials were not reported.
The absence of the data on the features of manufacturing
Methacrylic acid (TU 6-02-917-79, supplement 1),
p-chlorophenol (TU 6-09-4935-80), organic solvents
and other chemicals were corresponding to the technical
documentation and were not purified additionally.
123

124
KOBYAKOVA et al.
times at the chromatography of p-chlorophenyl methyl
p-Chlorophenyl methacryate was prepared by
methacrylate and p-chlorophenyl β-chloroisobutyrate
synthesized and isolated from the bottom we identified
and determined quantitatively the content of saturated
p-chlorophenyl β-chloroisobutyrate in the p-chlorophenyl
methacrylate. It is this ester that works as a plasticizer
at the (co)polymerization of p-chlorophenyl methacrylate
and methyl methacrylate leading to a decrease in thermal
stability and strength characteristics of organic glass.
acylation of p-chlorophenol with methacryloyl chloride
by the Schotten – Baumann method [6]. The reaction
was carried out in organic solvent in the presence of
aqueous alkali:
The most probably, formation of p-chlorophenyl
β-chloroisobutyrate is caused by the presence in the
methacryloyl chloride of the saturated compound,
β-chloroisobutyryl chloride. Metacryloyl chloride
commonly is obtained by the reaction of methacrylic acid
with thionyl chloride. In the course of reaction are formed
gaseous products, including hydrogen chloride, capable
of adding to the double С=С bond of α,β-unsaturated acids
and respective acyl chlorides contrary to the Markovnokov
rule [7]. As a result the saturated acyl chloride is formed.
The gas chromatography analysis confirmed the presence
of up to 5 wt % of chloroisobyutyryl chloride in the
methacryloyl chloride produced by the above method.
The gas chromatographic analysis of the obtained
p-chlorophenyl methyl methacrylate showed that the
monomer contained several contaminating substances
with content of one of them up to 5 wt % (Fig. 1).
The most expectable contaminant is p-chlorophenyl
β-chloroisobutyrate formed at the addition of hydrogen
chloride to the С=С double bond of the methacrylate
[7]:
To confirm this assumption we carried out authentic
synthesis of p-chlorophenyl β-chloroisobutyrate by
the hydrochlorination of methacrylic acid followed by
reaction of β-choroisobutyric acid with thionyl chloride
and of the formed β-chloroisobyutyryl chloride with p-
chlorophenol [6].
For diminishing the content of unwanted impurity
the thionyl chloride was replaced by benzoyl chloride
[6] that afforded methacryloyl chloride containing
0.01–0.1 wt % only of chloroisobyutyryl chloride.
The IR spectrum of the product obtained includes the
band of vibrations of a C–Cl bond in an aliphatic group
(ν=750 cm–1) and the band of carbonyl group, the band is
shifted to higher wavenumbers (ν=1766 cm–1) that attests
the absence of С=О conjugation with С=С bond.
In the 1Н NMR spectrum were not observed groups of
the signal characteristic of cis- and trans-HC=С system (δ
6.34 and 5.76 ppm respectively) but there are the signals
corresponding to the proton groups СНСН3 (δ 3.09 ppm)
and СН2Cl (δ 3.76 – 3.80 ppm)
τ
Fig. 1. Chromatogram of p-chlorophenyl methacrylate. τ
is retention time (min). (1) toluene, (2, 6, 9) unidentified
contaminants, (3) reference compound dimethyl succinate,
(4) phenyl methacrylate, (5) p-chlorophenyl acetate, (7)
p-chlorophenyl methacrylate, (8) 2,4-dichlorophenyl meth-
acrylate, (10) p-chlorophenol, (11) p-chlorophenyl β-chloro-
isobutyrate.
The side product concentrated in the bottoms
after vacuum distillation of p-chlorophenyl methyl
methacrylate had the characteristics analogous to those
of p-chlorophenyl β-chloroisobutyrate prepared by the
authentic synthesis. By comparison of the retention
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DEVELOPMENT OF THE CONDITIONS OF SYNTHESIS OF p-CHLOROPHENYL METHACRYLATE 125
Table 1. Influence of conditions of the synthesis of p-chlorophenyl methacrylate on the formation of contaminants and the
product yield
It is reasonable to assume that in this case the possibility
of formation of p-chlorophenyl β-chloroisobutyrate
during the synthesis of p-chlorophenyl methacrylate is
practically excluded. However, at the optimization of
technological parameters of the reaction of methacryloyl
chloride with p-chlorophenol we found that in the p-chloro-
phenyl methacrylate this contaminant is present and its
amount depends on the synthesis conditions. On raising
the reaction temperature from 0 to 30°C does not increase
considerably the p-chlorophenyl methacrylate yield but
promotes more intense formation of p-chlorophenyl
β-chloroisobutyrate (Fig. 1). When the process is conducted
at 5°C the p-chlorophenyl β-chloroisobutyrate content is
0.03−0.04 wt %, that corresponds to approximate content
of chloroisobutyryl chloride in the parent methacryloyl
chloride, while in the reaction at 20°C its content grows
4–5-fold (to 0.15–0.20 wt %).
At higher temperature the hydrolysis rate increases
resulting in the increased rate of HCl addition at the
С=С bond of the methacrylate, consistently with the
experimental data shown in Fig. 2.
It is expectable that the content of parent reagents also
affects side reaction. Actually, excess of methacryloyl
chloride, which, as was expected, is needed for the
complete consumption of p-chlorophenol, leads to
increased content of p-chlorophenyl β-chloroisobutyrate;
the yield of p-chlorophenyl methacrylate increases
therewith insignificantly (Fig. 3).
Thus, from the viewpoint of the desired monomer yield
and the content of the unwanted saturated contaminant
the optimal conditions of the synthesis are as follows:
temperature in the range 5–10°C and equivalent ratio of
the parent reagents, methacryloyl chloride and p-chloro-
phenol.
Besides, analysis of the obtained results and additional
experiments allowed to conclude that 0.1 mole excess of
alkali relatively to p-chlorophenol should be taken for
the effective binding the hydrogen chloride formed at
the hydrolysis of methacryloyl chloride.
The fact of appearance of the saturated compound
can be explained by the features of phenol acylation with
acyl chlorides by the Schotten–Baumann method under
the phase transfer reaction conditions [4]. Under these
conditions hydrolysis can proceed of the acyl chloride
[7] with the formation of hydrogen chloride that leads to
formation of p-chlorophenyl β-chloroisobutyrate.
By means of gas chromatography we found that the
synthesized monomer can contain unreacted p-chloro-
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126
KOBYAKOVA et al.
Table 2. Characteristics of contaminants prepared in authentic syntheses
Table 3. Characteristics of the samples of p-chlorophenyl methacrylate
phenol, and sometimes phenol, o-chlorophenol and 2,4-
dichlorophenol contaminating p-chlorophenol. Even little
admixture of phenolic contaminants that exhibit inhibiting
action [8] decreases the monomer polymerization activity
that can result in composition ununiformity of the
(co)polymer material and to deterioration of its optical
and strength characteristics.
To provide practically quantitative reaction of phenols
with methacryloyl chloride the reaction mixture after
loading the reagents was kept for some time (Table 1). The
optimal duration of keeping is found to equal to
30 min. Then the total content of residual phenols is not
higher than 0.01 wt %, the content of p-chlorophenyl
β-chloroisobutyrate also remains on the acceptable
Fig. 3. Dependence of yield А(%) of p-chlorophenyl methacrylate
(1) and content В (%) of p-chlorophenyl β-chloroisobutyrate (2)
on the methacryloyl chloride / p-chlorophenol mole ratio c. The
synthesis temperature 10°C, the reaction duration 2.5 h.
Fig. 2. Dependence of yield A(%) of p-chlorophenyl meth-acrylate
(1) and content B (%) of p-chlorophenyl β-chloro-isobutyrate
(2) on temperature Т (°C). The methacryloyl chloride/p-phenol
mole ratio equals 1, the reaction duration 2.5 h.
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DEVELOPMENT OF THE CONDITIONS OF SYNTHESIS OF p-CHLOROPHENYL METHACRYLATE 127
level, less than 0.1 wt %. Longer keeping leads to more
complete consumption of phenols, but simultaneously to
increased amount of p-chlorophenyl β-chloroisobutyrate,
up to 0.2% and ever higher. The saturated compound in
such amount affects negatively the glass properties.
Thus, the original complex modification of the known
method allowed us to solve an important practical
problem of synthesis of methacrylic monomer with
a desired purity grade for the creation of polymers of
special application. With the high purity p-chlorophenyl
methacrylate as a modifying (co)monomer were obtained
poly(methyl methacrylate) organic glasses with a complex
of improved exploitation characteristics.
These phenols also can react with methacryloyl
chloride to form the corresponding methacrylates that
were identified by means of authentic synthesis (Table 2).
But these monomers do not restrict further polymerization
of the target substance, but on the contrary take a part
in it and, as established, practically do not affect the
characteristics of the obtained polymer material.
CONCLUSIONS
1. Main contaminants in the p-chlorophenyl
methacrylate are identified, sources of their formation
are elucidated and optimal condition for the exclusion
of side processes are selected.
Note that we also identified the p-chlorophenyl
acetate formed in the process (Table 2). Its content in
the p-chlorophenyl methacrylate is not significant and
does not depend on the technological parameters of the
synthesis. Its amount is defined by the amount of acetic
acid contaminating the parent methacrylic acid and can be
diminished to 0.001–0.10 wt% by vacuum distillation.
2. The method of synthesis of high purity p-chloro-
phenyl methacrylate with the yield 72% or higher and
main component content 99.7–99.9% is developed.
Identification of the contaminants in the p-chlorophenyl
methacrylate both introduced with the raw material and
formed in the process of the synthesis allowed to chose
the optimal conditions of the synthesis of p-chlorophenyl
merthacrylate. The developed method is based on the
Schotten – Baumann reaction and the optimal temperature
regime and ratio of reagents. For the better removing
the unreacted initial compound the number of the
alkaline washing of the reaction mixture was optimized.
The reasons for exclusion of phenolic inhibitors were
established and the inhibitors of other classes were
applied providing the required polymerization activity of
the monomer. For excluding reaction of the methacrylate
with oxygen to form peroxide, a vacuum distillation under
inert gas atmosphere was introduced.
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As a result, the p-chlorophenyl methacrylate was
synthesized with the yield no less than 72%; d420 =1.1823;
nD20 =1.5292−1.5300; mp 98–99°C/4−5 mm Hg. The
IR spectrum, ν, cm–1: 1740 (С=O); 1640 (С=С); 810,
1490, 1600, 3000, (p-chloro-substituted aromatic ring;
1250– 1050 (С–О–С). The 1Н NMR spectrum, δ, ppm:
2.05 (m, 3Н, СН3), 5.76 (m, 1Н, trans-СН=С), 6.34 (m,
1Н, cis-СН=С), 7.02 – 7.16 (m, 2Н, 2,6-СН), 7.31−
7.38 (m, 2Н, 3,5-СН). The 13C NMR DЕРТ spectrum, δ,
ppm: 18.3 (СН3), 123.0 (2,6-СН), 127.6 (СН2=С), 129.5
(3,5-СН), 131.1 (4-ССl), 135.6 (СН2=С); 149.4 (1-СО),
165.6 [С(О)О]. The characteristics of the monomer
samples synthesized under the developed conditions are
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