Monitoring the phosphorylation of phenol with diethyl chlorophosphate in aqueous medium in the presence of sodium hydroxide by in situ fourier transform infrared spectroscopy

Article abstract of DOI:10.1080/10426500903002537

In situ Fourier transform IR spectroscopy has been found to be an appropriate tool for monitoring the title reaction resulting in the formation of diethyl phenylphosphate.

Full text of DOI:10.1080/10426500903002537

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Phosphorus, Sulfur, and Silicon and the
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Monitoring the Phosphorylation of
Phenol with Diethyl Chlorophosphate
in Aqueous Medium in the Presence of
Sodium Hydroxide by in Situ Fourier
Transform Infrared Spectroscopy
György Keglevich a , Réka Eszter Puskás a , Alajos Grün a b & István
Csontos a
a Department of Organic Chemistry and Technology , Budapest
University of Technology and Economics , Budapest, Hungary
b Research Group of the Hungarian Academy of Sciences at the
Department of Organic Chemistry and Technology , Budapest
University of Technology and Economics , Budapest, Hungary
Published online: 23 Mar 2010.
To cite this article: György Keglevich , Réka Eszter Puskás , Alajos Grün & István Csontos (2010)
Monitoring the Phosphorylation of Phenol with Diethyl Chlorophosphate in Aqueous Medium in the
Presence of Sodium Hydroxide by in Situ Fourier Transform Infrared Spectroscopy, Phosphorus, Sulfur,
and Silicon and the Related Elements, 185:4, 832-837, DOI: 10.1080/10426500903002537
To link to this article: http://dx.doi.org/10.1080/10426500903002537
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Phosphorus, Sulfur, and Silicon, 185:832–837, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500903002537
MONITORING THE PHOSPHORYLATION OF PHENOL
WITH DIETHYL CHLOROPHOSPHATE IN AQUEOUS
MEDIUM IN THE PRESENCE OF SODIUM HYDROXIDE
BY IN SITU FOURIER TRANSFORM INFRARED
SPECTROSCOPY
Gyo¨rgy Keglevich,1 Re´ka Eszter Puska´s,1 Alajos Gru¨n,1,2
and Istva´n Csontos1
1Department of Organic Chemistry and Technology, Budapest University
of Technology and Economics, Budapest, Hungary
2Research Group of the Hungarian Academy of Sciences at the Department
of Organic Chemistry and Technology, Budapest University of Technology
and Economics, Budapest, Hungary
In situ Fourier transform IR spectroscopy has been found to be an appropriate tool for
monitoring the title reaction resulting in the formation of diethyl phenylphosphate.
Keywords Heterogeneous phase; in situ Fourier transform IR spectroscopy; monitoring;
phenol; phosphorylation
INTRODUCTION
In situ Fourier transform (FT) IR spectroscopy is a current method for monitoring or-
ganic chemical transformations.1–8 The time-dependent IR spectra allow the establishment
of formal kinetics, detection of intermediates, and optimization of the reaction investigated.
Hence, in situ FT-IR spectroscopy is a useful tool in environmentally friendly chemistry.
No matter if the reaction mixtures are homogeneous or heterogeneous, they can be studied
by the ReactIR 1000 spectrometer supplied with an attenuated total reflection (ATR) probe
in the range of –80 to 250◦C, even under pressure. In situ FT-IR spectroscopy is becoming a
routine method in the pharmaceutical and fine chemical, and even in the plastics industries.
In earlier studies, esterifications6 and oximation reactions7,8 were investigated. On the one
hand, a formal equilibrium constant was determined,6 while on the other hand, interme-
diates were pointed out under suitable reaction conditions.7,8 The reactions were, in all
cases, optimized. In situ FT-IR spectroscopy has been applied only rarely in organophos-
phorus chemistry.5 We decided to monitor an esterification involving a Schotten–Baumann
phosphorylation of phenol. This type of reaction is important in the industrial synthesis of
organophosphorus insecticides.9,10
Received 20 March 2009; accepted 27 April 2009.
The authors are grateful for the OTKA (T067679) support of this work.
Address correspondence to Gyo¨rgy Keglevich, Department of Organic Chemistry and Technology, Budapest
University of Technology and Economics, H-1521 Budapest, Hungary. E-mail: keglevich@mail.bme.hu
832

MONITORING THE PHOSPHORYLATION OF PHENOL
833
RESULTS AND DISCUSSION
The model reaction to be studied involved the phosphorylation of phenol with diethyl
chlorophosphate in the presence of aqueous sodium hydroxide to yield diethyl phenylphos-
phate (Scheme 1). Under Schotten–Baumann conditions, minor hydrolysis of the phospho-
ryl chloride is inevitable.
OH
26−30 °C
NaOH / H2O
EtO
EtO
O
O
EtO
EtO
O
P
P
+
Cl
Scheme 1
First the phosphorylation was carried out to prepare diethyl phenylphosphonate using
1.1 eq. of diethyl chlorophosphate and 1.05 eq. of sodium hydroxide in 10% aqueous
solution at 5–26◦C. According to GC analysis of the crude product, the proportion of
(EtO)2P(O)OPh and (EtO)2P(O)OH was 9:1. Diethyl phenylphosphate was obtained in
68% yield after the workup procedure.
The next step was to register the IR spectra of the reaction components (phenol,
sodium phenolate, diethyl chlorophosphate, and diethyl phenylphosphate). This was done
by inserting the probe into the water solution of phenol and sodium phenolate, or placing
some oily chlorophosphate and diethyl phenylphosphate on the head of the probe. The
spectra obtained are shown in Figure 1, while selected absorptions together with expected
Figure 1 IR spectra for the reaction components measured neatly.

834
G. KEGLEVICH ET AL.
Table I IR absorptions expected and measured for (EtO)2P(O)Cl and (EtO)2P(O)Ph (cm−1
)
Range11
(EtO)2P(O)Cl (neat)
(EtO)2P(O)Ph (neat)
νP
νP–O–C (alkyl)
νP–O–C (aryl)
1175–1350
990–1050
1180–1240
1282 (1298)a
1007, 1023
—
1180–1320b
1023
1180–1320b
O
aShoulder.
bA broad signal results from νP O/νP–O–C (aryl) vibrations.
ranges are listed in Table I. Diethyl chlorophosphate revealed intensive absorptions at
1007/1023 and 1282 cm−1 due to νP–O–C (alkyl) and νP O stretching vibrations, respectively.
At the same time, the IR spectrum of the mixed ester showed intensive signals at 1023 and
in the range of 1180–1320 cm−1, due to the νP–O–C (alkyl) and νP O/νP–O–C (aryl) stretching
vibrations, respectively. The ester also had absorptions at 961 and 942 cm−1
.
Then the phosphorylation reaction was repeated by inserting the probe into the
reaction vessel. The mixture of phenol in water was kept at ∼2◦C by an ice-water bath.
Then diethyl chlorophosphate was added with intensive stirring over ca. 5 min, followed
by the addition of aqueous sodium hydroxide over ca. 20 min so that the temperature did
not rise above 5◦C. Then the bath was removed, and the mixture was stirred further at
26◦C for 4 h until completion of the phosphorylation. The reaction was monitored by in
situ FT-IR spectroscopy (Figure 2). Appearance of the mixed ester could be seen easily
in the 3D diagram, making use of the frequencies at 1208, 961, and 942 cm−1 mentioned
above. Decreasing bands at 1007 and 1282 cm−1 characteristic to the phosphoryl chloride
could not be observed in the 3D diagram at the start of the reaction. The broad absorption
at 1208 cm−1 is the result of the combination of the νP and νP–O–C stretching vibrations
O
of the mixed phosphoric ester. Decrease in the concentration of diethyl chlorophosphate
cannot be followed, only the increase in the relative quantity of the diethyl phenylphosphate.
The decreasing absorption of (EtO)2P(O)Cl at 1023 cm−1 is suppressed by the increasing
band of (EtO)2P(O)(OPh) at around the same frequency. Formation of the hydrolyzed
Figure 2 A segment of the time-dependent IR spectrum for the phosphorylation of phenol with diethyl chlorophos-
phate in water in the presence of sodium hydroxide at 26◦C.

MONITORING THE PHOSPHORYLATION OF PHENOL
835
Figure 3 Concentration profile for the reaction of phenol with diethyl chlorophosphate.
byproduct, (EtO)2P(O)OH, formed only in 10% could not be identified in the 3D diagram.
The phosphorylation was complete after 3.5 h. The absorbance–time diagram obtained after
deconvolution, which is the separation of the overlapping absorption bands of the reaction
components, is shown in Figure 3.
It was also possible to reproduce the IR spectra of the reaction components, such as
phenol, diethyl chlorophosphate, and diethyl phenylphosphate by deconvolution (Figure 4
and Table II). It can be seen that the real IR spectra of the components are quite similar to
those obtained by deconvolution (Figure 1 vs. Figure 4).
Figure 4 IR spectra for the reaction components obtained from the 3D diagram after deconvolution.

836
G. KEGLEVICH ET AL.
Table II IR absorptions measured and obtained from the 3D diagram after deconvolution (in cm−1
)
(EtO)2P(O)Cl
PhOH
(EtO)2P(O)(OPh)
Obtained
Obtained
Obtained
after deconv. Measured
after deconv. Measured
after deconv. Measured
1502
1475
1371
1235
1502
1475
1378
1235
1490
1475
1490
1475
νP
1270
1282
νP
νP
νP
1255
1231
1208
1166
1027
961
1255
1231
1208
1166
1023
961
O
O
O
O
1166
1019
1166
1023
1007
1170
1073
1170
1073
νP–O–C
νP–O–C
942
942
In summary, the heterogeneous phase Schotten–Baumann phosphorylation of phenol
by diethyl chlorophosphate was monitored by in situ FTIR spectroscopy. The reaction path
could be analyzed by a 3D IR spectrum and an absorbance–time diagram.
EXPERIMENTAL
Equipment
In situ Fourier transform IR measurements were carried out using a ReactIR 1000
spectrometer. The ATR measuring head was placed in a 100-mL four-necked flask equipped
with a dropping funnel, a condenser, a thermometer, and a magnetic stirrer. The temperature
was maintained by using an appropriately adjusted water bath.
Procedure
To phenol (10.8 g, 115.0 mmol) in water (30 mL), diethyl chlorophosphate (18.3 mL,
126.5 mmol) was added dropwise over 5 min with intensive stirring at ≤5◦C. Then a solution
of sodium hydroxide (4.83 g, 120.75 mmol) in water (43.5 mL) was added dropwise over
20 min so that the temperature did not rise above 5◦C. After that, the mixture was allowed
to warm up to 26◦C. The phosphorylation was complete after a stirring period of 3.5 h.
In the preparative experiment, the mixed ester was extracted with chloroform (2 ×
20 mL). The combined extracts were dried (Na2SO4) and purified by column chromatogra-
phy (silica gel, 3% methanol in chloroform) to give 18.0 g (68%) of the diethyl phenylphos-
phate in a pure form. 31P NMR (CDCl3) δ –6.2; δP[ref. 12] (CDCl3) –5.6.
In the monitoring experiment, the ATR measuring head was placed into the flask.
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