Process for preparing styrene oxide

Styrene oxide is prepared by reacting styrene and hydrogen peroxide in a heterogenous system in the presence of a bis(tri-n-alkyltinoxy) molybdic acid and an inorganic anion.

BACKGROUND OF THE INVENTION 
The present invention relates to a process of preparing styrene oxide by 
the reaction of styrene and hydrogen peroxide in the presence of a 
catalyst. 
Styrene oxide is used over a wide range of field, for example as a 
stabilizer for polymers, an ultraviolet ray absorber, a starting material 
in the preparation of drugs, a stabilizer for solvents, or as a starting 
material for phenethyl alcohol and phenethyl aldehyde which are useful as 
synthetic perfumes and sweetening materials. 
For preparing styrene oxide by the epoxidation of styrene there generally 
is adopted a process in which styrene is epoxidized using an organic 
peracid, as described in Japanese Patent Laid Open No. 149271/1980. 
However, this process involves the following drawbacks and is not always 
satisfactory. 
(1) During the reaction of oxidizing styrene with an organic peracid, the 
organic peracid is decomposed and there occurs an addition reaction of the 
resulting radical to styrene, thus resulting in that the selectivity of 
styrene oxide with respect to styrene is deteriorated. 
(2) The resulting styrene oxide cleaves in the presence of an organic acid 
byproduced after the reaction, thereby producing an ester and a hydroxy 
compound, whereby the selectivity of styrene oxide with respect to styrene 
is deteriorated. 
(3) Peracetic acid which is most easily available industrially among 
organic peracids is prepared by a so-called Daicel-Wacker process 
comprising air oxidation of acetaldehyde, but it is a very expensive 
oxidizing agent. 
(4) In order to avoid a possible danger in the use of an organic peracid it 
is necessary to pay close attention to both operation and equipment. 
On the other hand, an oxidation reaction using hydrogen peroxide byproduces 
only water and does not cause the problem of environmental pollution; 
besides, hydrogen peroxide is easily available industrially and is 
inexpensive. In principle, therefore, hydrogen peroxide is a desirable 
epoxidizing agent. In the preparation of an epoxide by the reaction of 
styrene and hydrogen peroxide, however, the styrene conversion and the 
selectivity to the epoxide are both low. The low conversion is because 
hydrogen peroxide remains unreacted in the reaction performed at a low 
temperature, while in the reaction performed at a high temperature 
hydrogen peroxide decomposes and produces oxygen, and thus hydrogen 
peroxide is not effectively consumed in reaction. 
The reason why the selectivity to epoxide is low is that water which is 
introduced into the reaction system together with hydrogen peroxide and 
water resulting from the reaction both cause the formation of polyol. 
The reactivity of styrene in epoxidation is as tabulated below (see 
"Encyclopedia of Polymer Science and Technology" Vol. VI (1967), 
Interscience Publishers, New York, p. 83). The epoxidizing speed of 
styrene is relatively low in comparison with other olefins; for example, 
it is about one tenth as compared with a relative reactivity in the 
epoxidation of cyclohexene, thus indicating that the epoxidation reaction 
rate of styrene is very low. 
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Olefin Relative Reactivity 
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CH.sub.2 .dbd.CH.sub.2 
1 
C.sub.6 H.sub.5 CH.sub.2 --CH.dbd.CH.sub.2 
11 
R--CH.dbd.CH.sub.2 
25 
Ar--CH.dbd.CH--Ar 
27 
Ar--CH.dbd.CH.sub.2 
60 
Ar--CH.dbd.CH--R 
240 
(Ar).sub.2 C.dbd.CH.sub.2 
250 
R--CH.dbd.CH--R 500 
(R).sub.2 C.dbd.CH.sub.2 
500 
Cyclohexene 675 
Cycloheptene 900 
Cyclopentene 1000 
(R).sub.2 C.dbd.CH--R 
6500 
(R).sub.2 C.dbd.CH(R).sub.2 
&gt;&gt;6500 
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In the above table, Ar and R represent aryl and alkyl, respectively. 
In order to solve the above-mentioned problems involved in the preparation 
of styrene oxide by the reaction of styrene and hydrogen peroxide, there 
has heretofore been proposed the use of a specific catalyst. 
For example, according to J. Org. Chem., 53, 1553, (1988), styrene oxide is 
obtained in 74% yield (based on hydrogen peroxide) if a quaternary 
ammonium salt of phosphotungstic acid is used as a hydrogen peroxide 
epoxidizing catalyst. Although this reported process is greatly improved 
in the yield of styrene oxide as compared with other conventional 
processes, it is difficult to adopt it on an industrial scale because the 
quaternary ammonium salt (an interphase transfer catalyst) used as a 
catalyst component is every expensive. 
In Japanese Patent Laid Open No. 129276/1980 there is proposed a process 
wherein styrene and hydrogen peroxide are reacted in the presence of 
arsenic oxide and 3,5-di-tertbutyl-4-hydroxytoluene. However, a combined 
use of arsenic oxide with aqueous hydrogen peroxide involves such 
drawbacks as rapid decomposition of hydrogen peroxide and a low 
epoxidizing speed. Further, since arsenic compounds are strong in 
toxicity, it is necessary to pay close attention to the manufacturing 
equipment to prevent poisoning during production and also during use of 
the resulting products with the arsenic compounds incorporated therein. 
In U.S. Pat. No. 3,806,467 there is proposed a process wherein an olefin 
and hydrogen peroxide are reacted in the presence of a 
bis(tri-n-methyltinoxy)molybdic acid catalyst to prepare an epoxide. 
However, as long as the working Examples thereof are reviewed, the yield 
of styrene oxide is a little lower than 3% (based on hydrogen peroxide) 
and thus this proposed process cannot be considered preferable as a 
styrene oxide preparing process although the yield of cyclohexene epoxide 
is high and the process in question is effective as a cyclohexene epoxide 
preparing process. It is presumed that the low yield of styrene oxide in 
the said process is because the resulting styrene oxide cleaves 
oxidatively and byproduces benzaldehyde and further benzoic acid. 
The bis(tri-n-methyltinoxy)molybdic acid catalyst described in the above 
U.S. Pat. No. 3,806,467 is inexpensive and easily available industrially 
and can be fixed to active carbon and also to organic adsorbent resins, 
thus permitting the reaction to be carried out in a heterogeneous catalyst 
system and thereby permitting easy separation of the catalyst from the 
reaction system. 
It is the object of the present invention to solve the above-mentioned 
problems of the process proposed in the foregoing U.S. Pat. No. 3,806,467 
and provide an improved process capable of suppressing the formation of 
byproducts and affording styrene oxide in high yield under application of 
the process proposed in the said U.S. patent to the preparation of styrene 
oxide from styrene. 
SUMMARY OF THE INVENTION 
The present invention resides in a process of preparing, styrene oxide by 
the reaction of styrene and hydrogen peroxide in the presence of alkyltin 
oxide - molybdic acid catalyst, wherein an inorganic anion is made present 
as a promotor in the reaction and the reaction is carried out in a 
heterogeneous system. 
The process of the present invention can afford the desired styrene oxide 
in high activity and high selectivity at a low temperature.

DETAILED DESCRIPTION OF THE INVENTION 
The hydrogen peroxide used in the present invention may be a commonly-used 
one. An aqueous solution containing 5 to 90 wt % of hydrogen peroxide is 
employable, but it is desirable to use a 10-70 wt % aqueous solution 
thereof which is available easily. 
In the reaction of styrene and hydrogen peroxide, both may be used in an 
equimolar amount. But either of the two may be used in a too small or too 
large amount. 
For example, usually 0.1 to 3.0 moles of hydrogen peroxide is employable, 
but preferably 0.3 to 2.0 moles of hydrogen peroxide is used, per mole of 
styrene. 
The alkyltin oxide - molybdic acid catalyst used in the present invention 
can be prepared easily by a known process. There may be used an addition 
product prepared from ammonium molybdate and alkyltin oxide which are 
catalyst components, or the catalyst components may be added separately 
into the reaction system and the reaction may be allowed to take place in 
situ. 
As alkyltin oxides employable in the invention there are dialkyltin oxides 
and trialkyltin oxides. Preferred alkyl groups are those having 1 to 18 
carbon atoms, particularly n-alkyl groups having 1 to 8 carbon atoms. 
Examples of such alkyltin oxides include di-n-methyltin oxide, 
di-n-ethyltin oxide, di-n-propyltin oxide, di-n-butyltin oxide, 
di-n-octyltin oxide, tri-n-memthyltin oxide, tri-n-ethyltin oxide, 
tri-n-propyltin oxide, tri-n-butyltin oxide, and tri-n-octyltin oxide. 
The amount of the catalyst to be used is usually larger than 0.0001 mole, 
preferably larger than 0.001 mole. The upper limit thereof is not 
specially limited, but usually it is less than 0.1 mole, preferably less 
than 0.01 mole. 
As examples of the inorganic anion used as a promotor there are mentioned 
sulfate ion and nitrate ion. The amount of the inorganic anion is usually 
in the range of 0.1 to 6.0 moles, preferably 0.3 to 2.0 moles, per mole of 
the molybdic acid catalyst. The inorganic anion can be foremed by the 
addition of a salt thereof, e.g. sodium sulfate, sodium nitrate, or 
potassium sulfate. 
The epoxidation reaction in the present invention is conducted in a 
heterogeneous system, which is formed using an organic solvent immiscible 
with water. More particularly, the starting styrene and styrene oxide as 
an oxidation product are present in a dissolved state in the 
water-immiscible organic solvent, while hydrogen peroxide is present in 
the aqueous phase, and thus there are formed two phases which are the 
organic solvent phase and the aqueous phase. 
By using an organic solvent immisible with water it is made possible to 
avoid the contact between styrene oxide as an oxidation product and water. 
The organic solvent employable in the invention is not specially limited if 
only it is inert to the reaction and immiscible with water. Examples 
thereof include monochloromethane, dichloromethane, chloroform, carbon 
tetrachloride, dichloroethane, trichloroethane, tetrachloroethane, 
dichloroethylene, trichloroethylene, tetrachloroethylene, 
monochlorobenzene, dichlorobenzene, benzene, toluene, xylene, and 
mesitylene. 
The reaction can be performed at a relatively low temperature because the 
catalyst used in the present invention is very high in activity as 
compared with conventional catalysts. The reaction temperature is usually 
in the range of 0.degree. to 70.degree. C., preferably 10.degree. to 
40.degree. C. 
The following examples are given to illustrate the present invention in 
more detail, but the invention is not limited thereto at all. 
EXAMPLE 1 
5 ml (43.7 mmol) of styrene, 5 ml of monochloromethane, 0.07 mmol of 
ammonium molybdate [(NH.sub.4).sub.6 MO.sub.7. 4H.sub.2 O], 1 mmol of 
di-n-octyltin oxide and 0.6 mmol of sodium sulfate were charged into an 
Erlenmeyer flask having a capacity of 50 ml, then stirred together with 1 
ml of water at room temperature for 20 minutes. After the ammonium 
molybdate and the di-n-octyltin oxide had been dissolved, 3 ml (43.7 mmol) 
of 60% hydrogen peroxide was added at a time, followed by immersion in a 
constant temperature bath with shaking apparatus held at 
29.degree.-30.degree. C., and reaction was allowed to proceed for 24 
hours. 
Styrene and styrene oxide were analyzed by gas chromatographyy, while the 
amount of residual hydrogen peroxide was determined by iodometric 
titration. The results obtained are as shown in Table 1. 
EXAMPLE 2 
Reaction was performed in the same way as in Example 1 except that 0.6 mmol 
of sodium nitrate was used in place of sodium sulfate. The results 
obtained are as shown in Table 1. 
COMATIVE EXAMPLE-1 
Reaction was performed in the same way as in Example-1 except that there 
was used no inorganic anion. The results obtained are as set forth in 
Table 1. 
TABLE 1 
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(on hydrogen peroxide basis) 
Conversion 
Yield Selectivity 
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Comparative Example-1 
77% 34% 45% 
Comparative Example-1 
69% 59% 86% 
Comparative Example-2 
62% 62% 100% 
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