This invention provides a process for photochemical epoxidation of olefins with molecular oxygen in a liquid phase with irradiation in the presence of a combination of 1,2-diketone photosensitizers. Propylene can be converted to propylene oxide by reaction with molecular oxygen in an ortho-dichlorobenzene reaction medium in the presence of 2,3-butanedione and 1-phenyl-1,2-propanedione photosensitizers, at a space time yield rate of at least 15 grams per liter hour.

BACKGROUND OF THE INVENTION 
Epoxides are important chemical commodities which are employed as starting 
materials for the preparation of antifreeze compositions, humectants, 
pharmaceutical preparations, cosmetic formulations, as monomers for the 
preparation of polymers, and the like. 
Epoxides such as ethylene oxide and propylene oxide currently are prepared 
by a vapor phase catalytic method and by the two-step chlorohydrin route, 
respectively. The vapor phase process in industrial production of epoxides 
is confined to the preparation of ethylene oxide. Higher olefins are not 
amenable to a vapor phase catalytic process to provide economic production 
of the corresponding epoxide. 
The older chlorohydrin route is the principal industrial process which 
supplies the largest quantities of propylene oxide for commerce. This 
process is suitable for conversion of ethylene and propylene to their 
corresponding epoxides, but higher olefins are not particularly adaptable 
to the chlorohydrin route. 
Another process for preparation of epoxides is that involving organic 
peroxide or hydroperoxide oxidation of olefins. This process appears to 
have wider application insofar as olefin structure is concerned than do 
the first two methods described. Highly substituted ethylenes such as 
tetramethylethylene and trimethylethylene react smoothly and rapidly with 
a peroxy compound to give the corresponding epoxides. However, ethylenic 
compounds having much lower degrees of substitution about the carbon to 
carbon double bond (e.g., ethylene and propylene) react sluggishly with 
peroxy compounds and the rate of formation of the corresponding epoxides 
is very slow. 
Each of the above described processes has inherent disadvantages. For 
example, vapor phase catalytic oxidation of ethylene to ethylene oxide 
requires large volume equipment and the handling of large quantities of 
potentially explosive mixtures of ethylene and oxygen. The chlorohydrin 
route to propylene oxide essentially involves a two-step process and in 
addition, chlorinated byproducts are produced. The process involving 
hydroperoxide oxidation of olefins is potentially hazardous if relatively 
large quantities of peroxy compound are to be handled. 
Other prior art processes which are more pertinent for purposes of the 
present invention involve liquid phase olefin epoxidation with molecular 
oxygen. These prior art processes propose a variety of approaches to an 
improved balance of reaction variables such as specific oxidation 
catalysts or catalyst-solvent systems, the presence of polymerization 
inhibitors, the use of neutralizing agents such as metal hydroxides, the 
control of oxygen pressure, and the like. These prior art processes are 
disclosed in U.S. Patents which include U.S. Pat. Nos. 2,279,470; 
2,366,724; 2,530,509; 2,650,927; 2,741,623; 2,780,634; 2,780,635; 
2,837,424; 2,838,524; 2,879,276; 2,942,007; 2,974,161; 2,977,374; 
2,985,668; 3,153,058; 3,210,380; 3,228,967; 3,228,968; 3,232,957; 
3,238,229; 3,275,662; 3,281,433; 3,428,658; 3,674,813; 3,980,676; and 
references cited therein. 
Among the more recent developments are liquid phase reactions in which 
olefins are converted to epoxides by a photooxidation mechanism. For 
example, Japanese Pat. No. 80/09,004 [C.A. 92, 164507 (1980)] describes 
the epoxidation of propylene with oxygen in a polar solvent in the 
presence of sulfur dioxide under irradiation with light of at least 2600 
angstroms wavelength. 
In J. Am. Chem. Soc., 98(14), 4193 (1976), N. Shimizu and P. D. Bartlett 
report the results of photooxidation of olefins sensitized by 
.alpha.-diketones and by benzophenone. Epoxides are produced, as well as 
allylic hydroperoxides and oxetanes. 
There is continuing effort to develop improved and more efficient processes 
for the production of epoxides from olefins. 
Accordingly, it is a main object of this invention to provide an improved 
liquid phase process for converting olefins to epoxides with molecular 
oxygen. 
It is another object of this invention to provide a photochemical process 
for efficient epoxidation of olefins in liquid phase with molecular 
oxygen. 
It is a further object of this invention to provide a liquid phase 
photochemical process for converting propylene to propylene oxide with 
molecular oxygen at a space time yield (STY) rate of at least 15 grams per 
liter hour. 
Other objects and advantages of the present invention shall become apparent 
from the accompanying description and examples. 
DESCRIPTION OF THE INVENTION 
One or more objects of the present invention are accomplished by the 
provision of a process for the photochemical epoxidation of olefins which 
comprises oxidizing an alkene compound with molecular oxygen in liquid 
phase with irradiation in the presence of at least two 1,2-diketone 
photosensitizers which absorb light in a range between about 3700-4600 
angstroms. 
The term "alkene" is meant to include acyclic and cyclic alkenes. 
Illustrative of suitable alkenes are those containing between about 3-12 
carbon atoms such as propylene, 2-methylpropene, butene, 1,3-butadiene, 
pentene, hexene, heptene, decene, cyclopentene, cyclohexene, 
4-methylhexene, cycloheptene, norbornene, and the like. The alkene can be 
a constituent contained in a light hydrocarbon stream from a petroleum 
refinery cracking operation. 
The term "1,2-diketone" as employed herein refers to 1,2-diketone 
photosensitizer compounds in which the two vicinal carbonyl groups are 
freely rotatable around the connective bond with respect to each other. 
Excluded from the definition are 1,2-diketone compounds such as 
9,10-phenanthrene quinone and ortho-chloranil. Included in the definition 
are 1,2-diketone photosensitizers which have freely rotatable ketone 
groups and which absorb electromagnetic radiation in the wavelength range 
between about 3700-4600 angstroms, such as 2,3-butanedione (biacetyl), 
1-phenyl-1,2-propanedione, benzil, 4,4'-dimethoxybenzil, 
4,4'-dimethylbenzil, 4,4'-dichlorobenzil, 1,4-dibromo-2,3-butanedione, 
4-nitrobenzil, 1,3-bis(phenylglyoxylyl)benzene, 
1,4-bis(phenylglyoxylyl)benzene, 4,4'-dibenzilylether, 
4,4'-dibenzilylsulfone, and the like. 
The molecular oxygen which is employed can be either in pure form or 
present as a component of a gasiform stream such as air. 
The invention can be conducted either batchwise or continuously in 
equipment which provides adequate exposure of the liquid reaction medium 
to an electromagnetic radiation source. Either glassware is employed, or 
alternatively metal equipment is used which has transparent sections or 
ports. 
The control of the temperature and other reaction conditions of the 
exothermic reaction are facilitated when the liquid phase in the reaction 
zone comprises the alkene and molecular oxygen reactants dissolved in an 
aprotic solvent. The preferred solvent is one that is oxidatively stable 
and not susceptible to an environment of free radicals initiated by 
electromagnetic radiation input. 
Alkyl substituted aromatic hydrocarbons such as toluene and xylene are not 
desirable solvents for the practice of the invention process, since they 
are sensitive to free radical attack and tend to form phenolic and 
quinonoid type of byproducts in the presence of molecular oxygen. 
Illustrative of oxidatively stable solvents are acetonitrile, 
tetrahydrofuran, dimethylformamide, 1,2,4-trichlorobenzene, 
o-dichlorobenzene, monochlorobenzene, benzene, carbon tetrachloride, 
1,1,2-trichlorofluoroethane, ethyl acetate, ethyleneglycol diacetate, 
cyclohexane, and the like. 
The choice of solvent medium appears to affect the overall rate of alkene 
conversion and selectivity to the desired epoxide product. Superior 
results are obtained with acetonitrile or o-dichlorobenzene as the solvent 
medium. It is preferred that the solvent constitute at least 50 percent by 
volume of the liquid phase. 
The electromagnetic radiation can be supplied by any conventional type of 
lamp which has an emission spectrum that includes a 3700-4600 angstroms 
wavelength range, e.g., an Hanovia 450 W medium-pressure mercury lamp. It 
is preferred to exclude ultraviolet light below about 3700 angstroms from 
the epoxidation reaction zone, since the higher energy radiation tends to 
cause cleavage and loss of 1,2-diketone photosensitizers. Light filters 
can be employed as necessary to restrict the radiation to the desired 
3700-4600 angstroms wavelength range. If the radiation is being 
transmitted through a Pyrex glass reactor vessel, the Pyrex glass filters 
out most of the undesirable ultraviolet wavelength radiation. 
In the practice of the process, the liquid phase reaction medium is 
maintained at a temperature in the range between about -10.degree. C. and 
150.degree. C., and preferably in the range between about 
10.degree.-50.degree. C. 
The pressure in the reaction system can be varied in the range between 
about 15-1500 psi, and preferably in the range between about 90-200 psi. 
In the case of a normally gaseous alkene such as propylene, it is highly 
advantageous to provide a sufficiently high pressure at a given reaction 
zone temperature to cause the said gaseous alkene to be at least partially 
liquefied during the course of the epoxidation reaction. A higher pressure 
increases the dissolution of both alkene and molecular oxygen in a liquid 
phase solvent medium, and promotes the efficiency of the epoxidation 
reaction. 
The molecular oxygen is consumed at a rapid rate under the epoxidation 
conditions. Hence, the amount of molecular oxygen is fed into the reaction 
system in a quantity that does not permit the formation of potentially 
hazardous explosive mixtures of molecular oxygen and organic materials. 
Further, conducting the epoxidation reaction under oxygen-starved 
conditions serves to prevent degradation of the epoxide product which is 
produced. 
The rate of alkene conversion and the selectivity to epoxide product are 
increased when the photosensitizer component in the reaction system 
consists of at least two 1,2-diketones. Unexpectedly it has been found 
that the efficiency of the epoxidation reaction is increased when two or 
more 1,2-diketone photosensitizers are employed rather than the equivalent 
quantity of only one 1,2-diketone compound. 
The said combination of two or more 1,2-diketone photosensitizers usually 
is employed in a quantity between about 0.1-40 weight percent, based on 
the weight of alkene reactant which is present in the liquid phase 
reaction zone. As between any two 1,2-diketone photosensitizers being 
employed, the said photosensitizers can be present in a weight ratio 
between about 1-10:1-10 relative to each other. 
Under optimum conditions, an alkene such as propylene in a solvent medium 
such as o-dichlorobenzene, and in the presence of a photosensitizer 
combination such as 1-phenyl-1,2-propanedione/biacetyl (3.5:1), can be 
converted to propylene oxide at a space time yield rate of at least 15 
grams per liter hour. A lower rate is obtained if only one 1,2-diketone 
photosensitizer is employed, or if a 1,2-diketone photosensitizer is 
employed which is not freely rotatable about around the 1,2-diketone 
connecting bond, e.g., ortho-chloranil. 
In the practice of the process the intimate contact between the alkene and 
molecular oxygen reactants in the liquid phase medium is established by 
stirring, sparging, shaking, spraying or other such means of vigorous 
agitation. The agitation of the reaction medium also facilitates removal 
of heat of reaction to heat exchangers. 
The admixture and contact of the reactants can be accomplished in several 
ways. For example, the alkene and molecular oxygen can be premixed with a 
solvent and introduced into the reaction zone; or the reaction zone may be 
charged with solvent, and the alkene and molecular oxygen introduced 
simultaneously through separate feed lines. 
In one embodiment, a mixture of alkene and molecular oxygen is added to a 
solvent solution of 1,2-diketone photosensitizers in a continuously 
strired reactor under selected conditions of temperature and pressure. The 
oxygen input is controlled at a rate which keeps the oxygen concentration 
in the off-gas at less than about one percent. 
After completion of the epoxidation reaction (e.g., after a reaction period 
of about 1-5 hours), in a batch type operation the entire reaction product 
mixture is removed from the reactor system, and then conventional 
techniques such as distillation are employed for separation of the epoxide 
product, and recycle of recovered fractions such as alkene and solvent. 
In a continuous type operation, the gaseous and liquid effluent is 
continuously withdrawn from the reaction zone and subjected to extraction 
and/or distillation and the like means to separate and recover the epoxide 
product, solvent, unreacted alkene and oxidation byproducts. 
An important advantage of the invention process is the high selectivity of 
the epoxidation reaction over a broad range of processing conditions. A 
propylene conversion to propylene oxide with a selectivity in the range of 
about 90-100 percent is readily achieved. 
The following examples are further illustrative of the present invention. 
The reactants and other specific ingredients are presented as being 
typical, and various modifications can be derived in view of the foregoing 
disclosure within the scope of the invention. 
Examples I-IV demonstrate typical results obtained when propylene was 
epoxidized in the presence of one 1,2-diketone and the results obtained in 
the presence of two 1,2-diketones. In Example IV the propylene oxide was 
produced at the rate of 6.7 mmole per hour. 
Examples V-IX demonstrate a comparison of propylene epoxidation reactions 
involving a 2:1 molar ratio of 1-phenyl-1,2-propanedione/biacetyl mixture 
with reactions involving equal quantities of the individual 
photosensitizers. The results obtained are summarized in Table I. 
Example X, when compared to Examples VII and IX, demonstrates the increased 
propylene oxide rate of formation which is obtained when a combination of 
two photosensitizers is employed in a quantity which is substantially the 
molar equivalent of either photosensitizer employed individually. 
Examples XI-XIV demonstrate the effect of high propylene concentration and 
elevated pressure on the relative epoxidation rate during propylene 
conversion. The results obtained are summarized in Table II. 
It was observed that the rate of epoxidation is dependent both on the 
particular ratio of the 1,2-diketone photosensitizers employed and on the 
total concentration of the photosensitizer mixture. 
It was also found that the quantum efficiency of epoxidation under pressure 
conditions is at least about 75 percent of the available absorbable light 
efficiency. The quantum energy increases proportionally as the pressure 
increases.

EXAMPLE I 
A solution of 2.75 grams of biacetyl (0.13M) in 250 milliliters of 
o-dichlorobenzene was placed in a cylindrical photochemical reactor 
equipped with a water-cooled Pyrex lamp immersion well and a Dry Ice 
condenser. The path length through the annular reaction space was 0.5 cm. 
The system was purged with oxygen introduced through a fritted glass disc 
in the bottom of the reactor. The solution was saturated with propylene 
(approx. 0.1 mole), introduced through the same fritted glass disc. 
The oxygen sparge was reestablished and the solution was irradiated with a 
450 Watt high pressure mercury lamp for 180 minutes. The reaction 
temperature was maintained at 15.degree.-25.degree. C. with the 
water-cooled immersion well and the return of condensed propylene from the 
Dry ice condenser. Analysis of the reaction mixture by gas chromatography 
indicated the formation of 15 mmoles of propylene oxide (5 mmoles/hr.) and 
1.0 mmole of acetone (sensitizer decomposition product). 
EXAMPLE II 
A solution of 4.5 grams of benzil (0.086M) in 250 milliliters of 
o-dichlorobenzene was placed in the apparatus described in Example I. The 
system was purged with oxygen and saturated with propylene, then 
irradiated (450 Watt high pressure mercury lamp) with oxygen sparging for 
120 minutes. Irradiation under these conditions produced 7.0 mmoles of 
propylene oxide (3.5 mmoles/hr.) as the only product. 
EXAMPLE III 
A solution of 3.5 grams of 1-phenyl-1,2-propanedione (0.095M) in 250 
milliliters of o-dichlorobenzene was charged to the apparatus described in 
Example I. The system was purged with oxygen and saturated with propylene. 
Irradiation of the solution (1000 Watt tungsten lamp) with oxygen sparging 
for 250 minutes produced 19.0 mmoles of propylene oxide (4.6 mmoles/hr.) 
and 1.0 mmole of acetone. 
EXAMPLE IV 
A solution of 0.52 gram of biacetyl (0.024M) and 1.90 grams of 
1-phenyl-1,2-propanedione (0.051M) in 250 milliliters of o-dichlorobenzene 
was charged to the apparatus described in Example I. The system was purged 
with oxygen and saturated with propylene. Irradiation of the solution 
(1000 Watt tungsten lamp) with oxygen sparging for 150 minutes produced 
16.7 mmoles of propylene oxide (6.7 mmoles/hr.) and 0.7 mmole of acetone. 
EXAMPLE V 
A solution of 0.75 gram of biacetyl (0.035M) and 2.7 grams of 
1-phenyl-1,2-propanedione (0.073M) in 250 milliliters of o-dichlorobenzene 
was charged to the apparatus described in Example I. The system was purged 
with oxygen and saturated with propylene. Irradiation (1000 Watt tungsten 
lamp) with oxygen sparging for 150 minutes produced 10.9 mmoles of 
propylene oxide (4.4 mmoles/hr.) and a trace amount of acetone. 
EXAMPLE VI 
A solution of 0.75 gram of biacetyl (0.035M) in 250 milliliters of 
o-dichlorobenzene was charged to the apparatus described in Example I. The 
system was purged with oxygen and saturated with propylene. Irradiation of 
this mixture (1000 Watt tungsten lamp) for 70 minutes while sparging with 
oxygen produced 2.0 mmoles of propylene oxide (1.7 mmoles/hr.) as the only 
detectable product. 
EXAMPLE VII 
A solution of 2.25 grams of biacetyl (0.104M) in 250 milliliters of 
o-dichlorobenzene was charged to the apparatus described in Example I. The 
system was purged with oxygen and saturated with propylene. Irradiation of 
this mixture (1000 Watt tungsten lamp) for 70 minutes with oxygen sparging 
produced 4.0 mmoles of propylene oxide (3.4 mmoles/hr.) as the only 
detectable product. 
EXAMPLE VIII 
A solution of 2.7 grams of 1-phenyl-1,2-propanedione (0.073M) in 250 
milliliters of o-dichlorobenzene was charged to the apparatus described in 
Example I. The system was purged with oxygen and saturated with propylene. 
Irradiation (1000 Watt tungsten lamp) of the mixture with oxygen sparging 
for 70 minutes produced 2.8 mmoles of propylene oxide (2.4 mmoles/hr.) and 
a trace amount of acetone. 
EXAMPLE IX 
A solution of 4.05 grams of 1-phenyl-1,2-propanedione (0.109M) in 250 
milliliters of o-dichlorobenzene was charged to the apparatus described in 
Example I. The system was purged with oxygen and saturated with propylene. 
Irradiation (1000 Watt tungsten lamp) of the mixture with oxygen sparging 
for 70 minutes produced 3.7 mmoles of propylene oxide (3.2 mmoles/hr.) and 
a trace amount of acetone. 
EXAMPLE X 
A solution of 1.12 grams biacetyl (0.052M) and 2.02 grams 
1-phenyl-1,2-propanedione (0.054M) in 250 milliliters o-dichlorobenzene 
was charged to the apparatus described in Example I. The system was purged 
with oxygen, then saturated with propylene. Irradiation (1000 Watt 
tungsten lamp) of this mixture for 70 minutes with oxygen sparging 
produced 4.8 mmoles of propylene oxide (4.1 mmoles/hr.) as the only 
detectable product. 
The quantities of biacetyl and 1-phenyl-1,2-propanedione employed were 
one-half the respective quantities used in Examples VII and IX. Propylene 
oxide formation rates in Examples VII and IX were 3.4 and 3.2 mmoles/hr., 
respectively. The rate of 4.1 mmoles/hr. observed in this Example 
demonstrated that propylene oxide formation rates may be increased by 
using a multiple sensitizer system in accordance with the present 
invention. 
EXAMPLE XI 
Pressurized reactions were conducted in a stirred pressure reactor 
consisting of a 750 milliliter glass bowl (1/4" flint glass) bolted by a 
flange to a stainless steel cover. A solution of 0.5 gram of biacetyl 
(0.017M) and 1.8 grams of 1-phenyl-1,2-propanedione (0.035M) in 350 
milliliters o-dichlorobenzene was placed in the reactor. The solution was 
saturated with propylene and the headspace of the reactor was purged with 
oxygen. 
The reactor was sealed and irradiated for 120 minutes with an externally 
placed 450 Watt high pressure mercury lamp. The temperature was maintained 
at 15.degree.-20.degree. C. by a water flow through the reactor cooling 
coil. The pressure during the reaction was 15-20 psia. Analysis by gas 
chromatography indicated formation of 2.1 mmoles of propylene oxide (1.05 
mmoles/hr.) as the only product. 
EXAMPLE XII 
A solution of 0.4 gram of biacetyl (0.012M) and 1.4 grams of 
1-phenyl-1,2-propanedione (0.024M) in 300 milliliters o-dichlorobenzene 
was charged to the Example X pressure reactor. Condensed propylene (46.7 
grams, 2.84M) was added, increasing the pressure of 70 psia. The pressure 
was increased to 98 psia with oxygen and the solution was vigorously 
stirred. Irradiation (450 Watt high pressure mercury lamp) for 90 minutes 
produced 9.3 mmoles of propylene oxide (6.2 mmoles/hr.) as the only 
product. 
EXAMPLE XIII 
A solution of 0.4 gram of biacetyl (0.014M) and 1.4 grams of 
1-phenyl-1,2-propanedione (0.028M) in 250 milliliters of o-dichlorobenzene 
was charged to the pressure reactor. Condensed propylene (45.6 grams, 
3.20M) was added increasing the pressure to 80 psia. Nitrogen was added to 
bring the pressure to 150 psia, and oxygen was added to a pressure of 169 
psia. Irradiation (450 Watt high pressure mercury lamp) of the vigorously 
stirred solution for 90 minutes produced 11.2 mmoles of propylene oxide 
(7.5 mmoles/hr.) as the only product. 
EXAMPLE XIV 
Biacetyl (0.28 gram, 0.014M) and 1-phenyl-1,2-propanedione (1.0 gram, 
0.029M) were charged to the pressure reactor. Condensed propylene (118.0 
grams, 12.2M) was placed in the reactor, increasing the pressure to 144 
psia. Nitrogen (21 psi) and oxygen (20 psi) were added to bring the 
pressure to 185 psia. Irradiation (450 Watt high pressure mercury lamp) 
for 90 minutes produced 3.05 mmoles of propylene oxide (2.0 mmoles/hr.) as 
well as 7.15 mmoles of acetaldehyde (4.7 mmoles/hr.) and a detectable 
quantity of formaldehyde. 
TABLE I 
______________________________________ 
Comparison of Propylene Oxide Formation Rates 
Using Single Sensitizer And Multiple Sensitizers 
Total Rate, 
1-Phenyl-1,2- 
Sensitizer, 
mmoles 
Example 
Biacetyl, M 
Propanedione, M 
M PO/hr. 
______________________________________ 
5 0.035 0.073 0.108 4.4 
6 0.035 -- 0.035 1.7 
7 0.104 -- 0.104 3.4 
8 -- 0.073 0.073 2.4 
9 -- 0.109 0.109 3.2 
______________________________________ 
TABLE II 
______________________________________ 
Effect Of Propylene Concentration On Epoxidation Rate 
Pressure, 
Example 
Propylene, M 
Atmosphere psia Rel. Rate.sup.(a) 
______________________________________ 
11 0.38 O.sub.2 15-20 1.00 
12 2.84 O.sub.2 98 5.90 
13 3.20 Air 169 7.10 
14 12.2.sup.(b) 
50% N.sub.2, 
185 1.90.sup.(c) 
50% O.sub.2 
______________________________________ 
.sup.(a) Rates relative to 1.05 mmoles PO/hr for saturated propylene 
(0.38M) at 1 atm. 
.sup.(b) Condensed propylene. 
.sup.(c) Selectivity to PO = 30%; acetaldehyde and formaldehyde also 
formed.