Oxidizing O,O,O-trimethyl phosphorothioate with hydrogen peroxide or ozone

Article abstract of DOI:10.1007/s11164-011-0404-x

Oxidization of O,O,O-trimethyl phosphorothioate to the corresponding oxo (P=O) compound is accomplished under mild conditions with hydrogen peroxide or ozone. Urea hydroperoxide was found to be a serviceable solid-state source of hydrogen peroxide; it was a better oxidizing agent than 30% hydrogen peroxide and resulted in better yield. It was also proved that ozone was the most effective oxidizer, with formation of purer products in higher yield (90.1%) than with hydrogen peroxide. Springer Science+Business Media B.V. 2011.

Full text of DOI:10.1007/s11164-011-0404-x

Res Chem Intermed (2012) 38:645–649
DOI 10.1007/s11164-011-0404-x
Oxidizing O,O,O-trimethyl phosphorothioate
with hydrogen peroxide or ozone
•
Xinzhi Chen Guihua Li Chao Qian
•
Received: 8 July 2011 / Accepted: 8 September 2011 / Published online: 23 September 2011
Ó Springer Science+Business Media B.V. 2011
Abstract Oxidization of O,O,O-trimethyl phosphorothioate to the corresponding
oxo (P=O) compound is accomplished under mild conditions with hydrogen peroxide
or ozone. Urea hydroperoxide was found to be a serviceable solid-state source of
hydrogen peroxide; it was a better oxidizing agent than 30% hydrogen peroxide and
resulted in better yield. It was also proved that ozone was the most effective oxidizer,
with formation of purer products in higher yield (90.1%) than with hydrogen peroxide.
Keywords O,O,O-Trimethyl phosphorothioate Á Hydrogen peroxide Á
Urea hydroperoxide Á Ozone
Introduction
Organophosphate insecticides are an important class of water-soluble pesticides
mainly used in agriculture to control pests (insects) on fruits, vegetables, and cotton
[1]. Acephate is especially useful [2]. The byproduct obtained during production
of O,O-dimethyl phosphorochloridothioate, O,O,O-trimethyl phosphorothioate
(1, TMTP, Scheme 1), is a major disposal problem and affects the purity of the
acephate. Because there are currently no uses of 1, the search for an efficient,
inexpensive, and environmentally sound application of this material is extremely urgent.
As far as we are aware, three methods for conversion of TMTP to other products
have been reported in the literature:
1
2
3
Rearrangement of TMTP;
Chlorination of TMTP; and
Oxidation of TMTP.
X. Chen Á G. Li Á C. Qian (&)
Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027,
People’s Republic of China
e-mail: supmoney@163.com
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X. Chen et al.
O
P
H3CO
H3CO
H3CO
SCH3
i
I
H 3
OCH3
C
S
O
SO2Cl2
or Cl2
H3CO P OCH3
P
SCl
ii
OCH3
OCH3
1
o
x
i
d
O
i
z
e
r
P
OCH3
iii
OCH3
2
Scheme 1 The conversions of TMTP
Unfortunately:
1
2
3
The isomerizing agent used for the rearrangement was methyl iodide which is an
expensive reagent, and a use for the isomeric compound has not been found [3];
Thionyl chloride or chlorine was the chlorination agent, and both are toxic
reagents [4]; and
Ozone was reported to oxidize TMTP to trimethyl phosphate (TMP) at very low
temperature (-75 °C) [5], but this route also suffered from several disadvan-
tages, for example harsh conditions, relatively low ozone utilization, and long
reaction time, although the product has widespread industrial uses as a fire
retardant in plastics production [6].
We therefore further studied the oxidation of TMTP.
The conversion of thiophosphoryl (P=S) compounds to the corresponding oxo
(P=O) compounds by oxidation has been a subject of chemical and biochemical
investigation for a long time. For instance, oxone (2ÁKHSO5ÁKHSO4ÁK2SO4) [7, 8],
trifluoroacetic anhydride ((CF3CO)2O) [9], and magnesium monoperoxyphthalate
(MMPP) [10] have been developed for this purpose. However, many of these
procedures have limitations because of their properties, e.g., low effective oxygen
content, environmentally unfavorable by-products, and high cost.
For these reasons we turned our attention to hydrogen peroxide or ozone to oxidize
TMTP. We used hydrogen peroxide (30%) and solid-state hydrogen peroxide which
can release oxidative species in an organic medium. Solid-state hydrogen peroxide,
for example urea hydroperoxide (CO(NH2)2ÁH2O2; UHP) [11], sodium perborate
(NaBO3ÁnH2O, n = 1 or 4; SPB) [12], and sodium percarbonate (NaCO3Á1.5H2O2;
SPC) [13] can result in formation of highly reactive hydrogen peroxide molecules.
These chemicals are inexpensive and are extensively used in the detergent industry as
bleaching and antiseptic agents. Ozone, because of its high oxidizing power without
pollution, has also received much attention in organic chemistry [14].
Herein we present the results of our studies on the application of hydrogen
peroxide and ozone for oxidation of TMTP.
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Oxidizing O,O,O-trimethyl phosphorothioate
647
Experimental procedure
Materials and methods
1
1H, 13C, and 31P NMR were recorded in CDCl3, using 400 MHz for H, 100 MHz
for 13C, and 160 MHz for 31P. Chemical shifts in parts per million (ppm) were
relative to TMS (1H and 13C) or 85% H3PO4 (31P) as internal references. The
products were analyzed by use of an Agilent 1790F gas chromatograph (GC) with a
hydrogen flame ionization detector and a glass column (45 m 9 0.53 mm). Raw
materials and reagents were purchased commercially and used without further
purification.
The ozone concentration was determined by bubbling the ozone/oxygen gas
mixture through a solution of potassium iodide and then titrating with a standardized
solution of sodium thiosulfate [14]. At a flow rate of 30 L/h (measured by use of a
flow meter), the concentration of ozone is approximately 3–4% (v/v).
General procedure for oxidization of TMTP using hydrogen peroxide
Hydrogen peroxide (50 mmol) was added slowly to a solution of TMTP (7.8 g,
50 mmol) in methanol (20 mL) in a 100-mL, round-bottomed flask fitted with a
paddle stirrer, reflux condenser, and thermometer. After heating the mixture to
reflux with stirring for 1 h, elemental sulfur and the corresponding salt formed in the
reaction were isolated by filtration, for recycling, and the solvent was removed. The
1
residue was dried with magnesium sulfate and yielded TMP. H NMR (CDCl3,
400 MHz) d (ppm): 3.77 (s, 9H, CH3); 13C NMR (CDCl3, 100 MHz) d (ppm): 54.6;
31P NMR (CDCl3, 100 MHz) d (ppm): 2.85.
Ozonation of TMTP
To a 100-mL round-bottomed flask equipped with a magnetic stir bar was added
TMTP (7.8 g, 50 mmol), and the solution was heated at 50 °C. A tube supplying
ozone generated by use of ozonizer was bubbled into the rapidly stirred mixture at a
rate of 30 L/h for 2.5 h. The exiting gas was passed through sodium hydroxide
solution to absorb the sulfur trioxide formed. After completion of the reaction, the
liquid was purified by distillation. The colorless clear liquid 2 (6.31 g, 90.1%) was
obtained. The identity of the product was confirmed by comparison with the
standard sample using GC. 1H NMR (CDCl3, 400 MHz) d (ppm): 3.75 (s, 9H, CH3);
13C NMR (CDCl3, 100 MHz) d (ppm): 54.5; 31P NMR (CDCl3, 100 MHz) d (ppm):
2.85.
Results and discussion
When TMTP was oxidized by hydrogen peroxide (30%), although the conversion
reached 100%, much of the desired product readily hydrolyzed and we obtained low
yield. Concentrated hydrogen peroxide is not readily available and, furthermore,
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X. Chen et al.
contains water, so we choose solid-state hydrogen peroxide, i.e. anhydrous
hydrogen peroxide.
According to reports, UHP [11], SPB [12], and SPC [13] have been used for the
oxidation of a wide range of material and proved to be interesting eco-friendly
reagents. Their stability at room temperature, high hydrogen peroxide content, the
potential for releasing hydrogen peroxide in a controlled manner, and their
solubility in organic solvents make them good and safe substitutes for anhydrous
hydrogen peroxide in most oxidation reactions. The results of oxidizing TMTP with
different oxidizers are shown in Table 1. During investigation, it was found that
UHP was a good and safe oxidizer for the oxidation reaction because of its high
hydrogen peroxide content (36.2%) and good solubility in organic solvents.
Although, the yield was higher when we used solid-state hydrogen peroxide than
when 30% aqueous hydrogen peroxide was used, hydrolysis still occurred because
of the small amount water present in these oxidants. So we turned our attention to an
anhydrous system. Ozone is well known for its oxidizing properties and has been
used in a wide range of oxidation procedures without water. Previous work [5]
indicated ozone had been used for the thionate–oxon conversion with 1,2-
dichloroethane as solvent at -75 °C to yield TMP. This method had great potential
for use under mild reaction conditions.
In this work we used ozone, solvent-free at 50 °C, to oxidize TMTP, and
obtained good yield (90.1%). By testing the exiting gas with KI–starch paper we
found that utilization of ozone reached 99%. The reaction was tried at 20–70 °C. It
was found 50 °C was the optimum temperature to obtain a high yield in a short
reaction time. Increasing the reaction temperature would obviously accelerate the
reaction. However, increasing the temperature to 60 °C or higher is dangerous
because ozone readily explodes at such high concentrations at relatively high
temperature.
Conclusion
In general, because TMP is readily hydrolyzed, the oxidation should be performed
under water-free conditions. Comparison of the results obtained by use of hydrogen
peroxide (30%), solid-state hydrogen peroxide, and ozone revealed the second
Table 1 Oxidizing TMTP with hydrogen peroxide
Entry
Oxidizer
Reaction conditions
Conversion (%)
Yielda (%)
Time (h)
Temp (°C)
1
2
3
4
a
H2O2 (30%)
UHP
1.0
1.0
2.0
2.0
60
60
60
60
100
100
100
100
37.4
85.3
73.7
73.5
SPB
SPC
The yield refers to isolated product
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Oxidizing O,O,O-trimethyl phosphorothioate
649
option results in high yield, and is operationally simple, least expensive, safer, and
easier to handle, whereas ozone results in the highest yield and best quality product.
Acknowledgment The authors are grateful for generous financial support from the National Natural
Science Foundation of China (21076183), the Natural Science Foundation of the Zhejiang Province
(Y4090045, R4090358), and the Fundamental Research Funds for the Central Universities
(2011QNA4018).
References
1. S. Ghadimi, S.L. Mousavi, Z. Rahnama, M. Rahimi, Phosphorus Sulfur Silicon Relat. Elem. 185,
347–354 (2010)
2. C.B. Yeoh, C.L. Chong, Eur. J. Lipid Sci. Tech. 111, 593–598 (2009)
3. W.G. Emmett, H.O. Jones, J. Chem. Soc. Trans. 99, 713–720 (1911)
4. J. Michalski, J. Mikolajczak, A. Skowronska, J. Am. Chem. Soc. 100, 5386–5390 (1978)
5. A. Skowronska, E. Krawczyk, Synthesis-Stuttgart. 6, 509–510 (1983)
6. X.M. Wang, C. Yamada, H. Naito, G. Segami, K. Kibe, J. Electrochem. Soc. 153, A135–A139 (2006)
7. L.A. Wozniak, W.J. Stec, Tetrahedron Lett. 40, 2637–2640 (1999)
8. C.L. Zhang, Z.Q. Du, Chin. Chem. Lett. 20, 1411–1414 (2009)
9. J. Helinski, Z. Skrzypczynski, J. Wasiak, J. Michalski, Tetrahedron Lett. 31, 4081–4084 (1990)
10. J.A. Jackson, C.E. Berkman, C.M. Thompson, Tetrahedron Lett. 33, 6061–6064 (1992)
11. S. Taliansky, Synlett. 12, 1962–1963 (2005)
12. J. Muzart, Synthesis-Stuttgart. 11, 1325–1347 (1995)
13. A. Mckillop, W.R. Sanderson, Tetrahedron 51, 6145–6166 (1995)
14. B.M. Branan, J.T. Butcher, L.R. Olsen, J. Chem. Educ. 84, 1979–1981 (2007)
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