Preparation of ethylbenzene hydroperoxide

Ethylbenzene hydroperoxide is prepared by the oxidation of ethylbenzene with molecular oxygen in the presence of a minute amount of solid barium oxide.

FIELD OF THE INVENTION 
This invention relates to ethylbenzene hydroperoxide and more particularly 
it relates to the preparation of ethylbenzene hydroperoxide by the 
oxidation of ethylbenzene using molecular oxygen in the presence of a 
catalyst. 
DESCRIPTION OF THE PRIOR ART 
U.S. Pat. No. 2,867,666 describes the preparation of ethylbenzene 
hydroperoxide from ethylbenzene by oxidation of the ethylbenzene with 
molecular oxygen. The specification states that it is essential that a 
basic substance be employed in the reaction mixture because practically no 
oxidation occurs in its absence. A suitable quantity of the basic 
substance is specified to be in the range of 0.5 to 10 weight percent and 
barium oxide is listed as one of the suitable basic substances. 
SUMMARY OF THE INVENTION 
We have discovered a catalyzed process for the preparation of ethylbenzene 
hydroperoxide by the oxidation of ethylbenzene with molecular oxygen in 
which the yield of ethylbenzene hydroperoxide as well as the selectivity 
to ethylbenzene hydroperoxide is substantially increased. More 
particularly, we have discovered that these benefits result when 
ethylbenzene is oxidized in the presence of a minute amount of barium 
oxide. 
Certain hydrocarbons can be oxidized to the hydroperoxide by direct 
oxidation using molecular oxygen. In particular, hydrocarbons having a 
hydrogen atom on a tertiary carbon atom are relatively easy to oxidize to 
a hydroperoxide in good yield. Other hydrocarbons are more difficult to 
oxidize to the hydroperoxide and the resulting hydroperoxide is itself 
quite unstable. Cumene which contains both a tertiary carbon atom and an 
aromatic ring is comparatively easy to oxidize and can be directly 
oxidized to concentrations as high as 50 percent and higher. Furthermore, 
according to Lloyd in Methods in Free Radical Chemistry, Vol. 4, edited by 
Huyser (1973), cumene hydroperoxide decomposes at a temperature above 
80.degree. C. As a result of this stability, cumene hydroperoxide is the 
only aromatic hydroperoxide which has been commercially available. 
In striking contrast with cumene and cumene hydroperoxide, ethylbenzene and 
ethylbenzene hydroperoxide exhibit substantial differences in chemical 
properties. For example, ethylbenzene is difficult to oxidize with 
molecular oxygen and is oxidized to a relatively low concentration of 
ethylbenzene hydroperoxide. Furthermore, the resulting ethylbenzene 
hydroperoxide has a low degree of stability. For example, ethylbenzene 
hydroperoxide concentrated by distillation to a concentration of 40 
percent in ethylbenzene is unstable at room temperature 
(20.degree.-25.degree. C.). As a result of this relative instability, 
solutions containing a desirable concentration of ethylbenzene 
hydroperoxide generally include significant quantities of co-products, 
such as 1-phenylethanol and acetophenone. 
In Pat. No. 2,867,666 barium oxide has been included in a list of basic 
substances stated to be essential for the oxidation of ethylbenzene to 
ethylbenzene hydroperoxide. We have, in fact, ascertained that barium 
oxide, when used in moderate amounts, does increase the production of 
ethylbenzene hydroperoxide and in even larger amounts decreases the amount 
of ethylbenzene hydroperoxide as compared with the amount resulting in the 
absence of barium oxide. But in addition we have surprisingly discovered 
that barium oxide actively catalyzes the decomposition of ethylbenzene 
hydroperoxide. In view of this discovery, we have more surprisingly made 
the further discovery that optimum selectivity to ethylbenzene 
hydroperoxide occurs in the presence of a minute amount of barium oxide, 
and not in its absence. 
When ethylbenzene is oxidized to ethylbenzene hydroperoxide, the primary 
aromatic by-products are acetophenone and 1-phenylethanol. Although these 
by-products can theoretically be converted to ethylbenzene for recycle, 
the economics of this recovery operation would, in general, prohibit its 
use in commercial scale. Therefore, these aromatic by-products represent a 
process loss. Additionally, the nonaromatic by-products and also the total 
oxidation to carbon dioxide and water represents a process loss. 
Generally, the fuel value of these organic by-products represents their 
true value in the process. Therefore, in carrying out the oxidation 
reaction of ethylbenzene, it is most desirable to reduce the losses, if 
possible, without reducing the yield of the desired ethylbenzene 
hydroperoxide. By our invention we have unexpectedly discovered that 
maximum yield and maximum selectivity to ethylbenzene hydroperoxide can be 
concurrently induced when a minute amount of barium oxide, that is a 
minimum amount of about 0.005 weight percent and a maximum amount of about 
0.15 weight percent, is present during the oxidation reaction. It is 
highly unexpected that barium oxide is a catalyst for the desired reaction 
in these minute amounts while it functions overall as a decomposition 
catalyst in the larger amounts. Furthermore, this is unexpected because it 
is contrary to general experience to find selectivity and yield in a 
chemical reaction concurrently reaching a maximum at the same reaction 
conditions. It is additionally unexpected in view of U.S. Pat. No. 
2,867,666 because this patent specifies a range of 0.5 to 10 weight 
percent of the base such as barium oxide as being suitable. 
In our procedure for preparing ethylbenzene hydroperoxide with barium oxide 
catalyst, the barium oxide is preferably introduced into the reactor as a 
finely divided powder in order to accelerate its dispersion throughout the 
liquid and hasten its availability as a catalyst. Therefore, it is 
preferred that the initial particle size be small enough to stay in 
suspension in the liquid phase. However, larger sized particles of barium 
oxide even including pellet size can be used since the stirring or 
agitation of the reactor contents will gradually break down and disperse 
the barium oxide, including this larger sized barium oxide, throughout the 
solution. Therefore, the initial particle size of the barium oxide can 
broadly range from about 20 microns to about 5 millimeters in diameter and 
preferably a particle size ranging between about 50 and about 1,000 
microns is used. 
When the solution containing the powdered barium oxide is heated up under 
agitation, a fairly rapid, distinct change in appearance occurs at about 
120.degree.-125.degree. C. This change can be described as a transition 
from a powdery appearance to a milky appearance. This transition to a 
milky solution is followed by the oxidation reaction, indicative of some 
type of interaction, probably physical, between the barium oxide and the 
organic phase to form a more intimate association. We believe that this 
transition is related to the unexpected catalytic effect exhibited by 
barium oxide. The experimental data suggests to us that a minute amount of 
the barium oxide is involved in this transition and that it is this barium 
oxide that is responsible for the positive catalytic effect and the 
concomitant increased selectivity. The experimental data further suggests 
that more than a minute amount of barium oxide is not involved in this 
transition but remains in solid particulate form and that it is this solid 
barium oxide that is responsible for the negative, decomposition effect. 
This transition to a milky solution upon heating this organic solution 
containing dispersed barium oxide and these catalytic effects are believed 
to be unique with barium oxide since they are not observed with 
conventional bases, such as solid sodium hydroxide which does not exhibit 
a significant catalytic effect. When the stirring of this milky solution 
is stopped while the elevated temperature is maintained, the solution 
retains its milky appearance. When the unstirred solution is cooled to 
room temperature, it reverts to its powdery appearance and the barium 
oxide precipitates out, resulting in a clear solution. The oxidation 
reaction is carried out under anhydrous conditions since the presence of 
water results in lowered selectivity as well as a reduced rate of 
oxidation. 
In order to obtain beneficial results in accordance with our invention, a 
minute amount of barium oxide is used for the oxidation of ethylbenzene to 
ethylbenzene hydroperoxide. Significant improvement in yield and 
selectivity to ethylbenzene hydroperoxide results when barium oxide is 
used in an amount as low as about 0.0005 weight percent based on the 
ethylbenzene, but we prefer that at least about 0.001 percent barium oxide 
be used for a more significant improvement and we most prefer that at 
least about 0.002 be used. The maximum amount of barium oxide to obtain 
the desired catalytic effect of this invention should not exceed about 
0.15 weight percent although higher amounts can be used, if desired, at 
reduced selectivity and yield. We prefer that the maximum amount of barium 
oxide does not exceed about 0.1 weight percent and most prefer that it not 
exceed 0.04. Since the barium oxide catalyzes the decomposition of the 
ethylbenzene hydroperoxide, it is desirable to remove the barium oxide 
from the ethylbenzene hydroperoxide following its preparation. 
In the oxidation of ethylbenzene to ethylbenzene hydroperoxide, both the 
reaction rate and the product stability are a function of temperature. The 
temperature of the reactant ethylbenzene solution can conveniently be as 
low as 120.degree. C., but we prefer that it be at least about 125.degree. 
C. for a suitable rate of reaction. The maximum temperature should not 
exceed about 150.degree. C. because of the greatly increasing instability 
of the product ethylbenzene hydroperoxide at the higher temperatures. We 
prefer that the reaction temperature not exceed about 140.degree. C. 
The oxidation of the ethylbenzene by our procedure can conveniently be 
carried out in a batch reaction in which the molecular oxygen is bubbled 
through the ethylbenzene solution at an appropriate elevated temperature 
and pressure. A suitable elevated pressure is required, sufficient to 
maintain the ethylbenzene in solution at the temperature of reaction. Any 
suitable source of molecular oxygen, such as air or pure oxygen, can be 
used. When the oxygen is mixed with diluent gas, it is important that the 
diluent be free of any reactive contaminant gas, such as a nitrogen oxide 
or an oxide of sulfur, which would adversely react with one or more of the 
components in the reaction vessel. The partial pressure of oxygen in the 
reaction vessel is not critical. We prefer that the partial pressure of 
oxygen in the reaction zone be at least about 10 psia (68.9 kPa) but a 
partial pressure of oxygen as low as about 5 psia (34.5 kPa) is useful. 
The partial pressure of oxygen can be as high as about 200 psia (1,376 
kPa) or even higher, but we prefer that the partial pressure be no greater 
than about 50 psia (344 kPa). 
It is desirable that a minor amount of a hydrocarbon hydroperoxide be 
initially present in the ethylbenzene to eliminate the substantial 
induction time required to initiate the oxidation reaction and therefore 
to substantially increase the rate of oxidation in the early phase of the 
oxidation reaction. This hydroperoxide is desirably used in an amount up 
to about 5 weight percent based on the ethylbenzene used. Higher amounts 
can be present but do not exert an additional beneficial effect. It is 
preferred to use at least about 0.5 weight percent of the initiator 
hydroperoxide. Most preferably the hydroperoxide initiator is the same 
hydroperoxide that is produced in the reaction, namely, ethylbenzene 
hydroperoxide, however, any suitable hydrocarbon hydroperoxide can be used 
including both aromatic and paraffinic hydroperoxides. Suitable 
hydroperoxide initiators include cumene hydroperoxide, isobutane 
hydroperoxide, isopentane hydroperoxide, and the like. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
In the following examples the ethylbenzene contained no reactive impurities 
and a maximum of 1.0 weight percent inert hydrocarbon isomers. The barium 
oxide, BaO, was 97.5 percent pure with barium carbonate and strontium 
oxide comprising the major impurities and was used as a 60-80 mesh powder. 
The air was dried to remove water and treated to remove carbon dioxide. 
The isobutane hydroperoxide used as an initiator contained 70 percent of 
the hydroperoxide in t-butanol. A 300 milliliter glass reactor with 
stirrer and heating jacket was used for these experiments. The initial and 
product samples were analyzed for hydroperoxide concentration by standard 
iodometric titration. The initial finite hydroperoxide measurement 
resulted from the hydroperoxide initiator plus a minor amount of oxidation 
that occured before analysis could be accomplished. 
Analysis of the by-products was carried out in a gas-liquid chromatograph 
using a carbowax column or in a high performance liquid chromatograph. In 
the gas-liquid chromatograph analysis all of the ethylbenzene 
hydroperoxide was pyrolyzed to acetophenone and 1-phenylethanol. The 
analysis determined ethylbenzene, acetophenone and 1-phenylethanol. The 
by-product, acetophenone and 1-phenylethanol, was determined by difference 
in conjunction with the titration analysis for ethylbenzene hydroperoxide. 
The high performance chromatograph analysis did not decompose the 
ethylbenzene hydroperoxide since it was carried out at room temperature 
(20.degree.-25.degree. C.), therefore, it gave a direct analysis of the 
by-products.

EXAMPLES 1-4 
Ethylbenzene hydroperoxide was prepared in a series of experiments. In the 
first experiment 100 ml. ethylbenzene were heated to 135.degree. C. in a 
reactor. Five ml. of isobutane hydroperoxide initiator were added. Air was 
then bubbled through the reaction at a rate of 100 cc./per minute and a 
pressure of 140 psig. (965 kPa). The concentration of ethylbenzene 
hydroperoxide (EBHP) was determined at 30 minute intervals. This procedure 
was repeated several times except that 0.5 g. of sodium hydroxide, barium 
hydroxide or barium oxide was used under anhydrous conditions. The results 
of these experiments are set out in Table I. 
Table I 
______________________________________ 
Ethylbenzene Hydroperoxide Conc. % 
Example 1 2 3 4 
Time, hrs. 
No Base NaOH Ba(OH).sub.2 
BaO 
______________________________________ 
0 3.1 3.2 3.1 3.0 
0.5 6.9 5.3 7.4 7.1 
1.0 9.1 7.7 10.1 11.4 
1.5 10.4 9.5 12.1 14.3 
2.0 11.0 10.5 13.5 16.0 
2.5 10.8 10.7 14.5 16.9 
3.0 10.8 10.8 14.4 17.2 
______________________________________ 
EXAMPLE 5 
The effect of barium oxide on ethylbenzene hydroperoxide was studied at 
room temperature. Ethylbenzene was oxidized to a reaction product 
containing ethylbenzene hydroperoxide. Pure ethylbenzene hydroperoxide was 
obtained by extracting this reaction product with 10 percent aqueous 
sodium hydroxide. The aqueous solution containing the sodium salt of 
ethylbenzene hydroperoxide was reacted with gaseous carbon dioxide until 
the pH went below 9.0 to liberate pure ethylbenzene hydroperoxide. 
Analysis of the purified ethylbenzene hydroperoxide by high performance 
liquid chromatography indicated that a trace of acetophenone was the only 
remaining impurity. 
The purified ethylbenzene hydroperoxide was made up into a 3.5 percent 
solution in ethylbenzene and 100 ml. of this solution was charged to a 
glass reactor. A small sample from the reactor was titrated iodometrically 
to determine the initial concentration of ethylbenzene hydroperoxide. The 
desired quantity of powdered barium oxide was added and the reactor was 
pressured to 50 psi. (0.34 MPa) with nitrogen. After stirring for five 
minutes at room temperature, the solution was titrated to determine the 
final concentration of ethylbenzene hydroperoxide (EBHP). The results from 
a series of experiments are tabulated in Table II. 
Table II 
______________________________________ 
EBHP, % EBHP, % % EBHP 
BaO, % initial final decomposed 
______________________________________ 
0 3.45 3.45 0 
0.010 3.51 3.43 2.3 
0.033 3.65 3.60 1.4 
0.1 3.65 3.52 3.6 
0.2 3.64 3.40 6.6 
0.67 3.45 3.03 12.2 
1.67 3.60 2.97 17.5 
5.0 3.34 0.71 78.7 
______________________________________ 
EXAMPLE 6 
The oxidation of ethylbenzene to produce ethylbenzene hydroperoxide was 
studied using various amounts of barium oxide. The oxidation reaction was 
carried out in a 300 ml. glass reactor maintained in a constant 
temperature bath equipped with a magnetic stirrer, a gas bubbling tube and 
a dip tube for sampling. In each experiment 100 ml. of ethylbenzene, five 
ml. of 70 percent isobutane hydroperoxide and a desired amount of finely 
divided barium oxide catalyst were charged to the reactor. Air was then 
bubbled through the reaction mixture at a rate of 100 cc. per minute and a 
pressure of 140 psi. (965 kPa). The stirrer was started and the reactor 
was heated to 135.degree. C. for three hours. 
The reaction product was analyzed by iodometric titration and by gas-liquid 
chromatograph. The analysis of the experiment using 0.1 percent barium 
oxide is set forth as typical. Iodometric titration of the reaction 
product disclosed 18.75 percent ethylbenzene hydroperoxide. Since most of 
the isobutane hydroperoxide initiator is decomposed during the reaction, 
the analysis for ethylbenzene hydroperoxide will include only a trace of 
isobutane hydroperoxide. The gas-liquid chromatograph analysis resulted in 
78.89 percent ethylbenzene, 12.78 percent acetophenone, 5.58 percent 
1-phenylethanol and 2.78 percent other products comprising primarily 
t-butanol from the decomposition of the isobutane hydroperoxide initiator. 
These analyses indicated a conversion of 21.1 percent and a selectivity to 
ethylbenzene hydroperoxide of 88.9 percent. When pure ethylbenzene 
hydroperoxide was pyrolyzed in the gas-liquid chromatograph, the analysis 
showed 56 percent acetophenone, 21 percent 1-phenylethanol with the 
balance assumed to be oxygen and water which were not determined. With 
this data the selectivity to acetophenone and 1-phenylethanol was 
determined to be 5.7 percent and 5.4 percent, respectively. The results of 
these analyses are set out in Table III which lists the yield of 
ethylbenzene hydroperoxide (EBHP), the conversion of ethylbenzene and the 
selectivity to ethylbenzene hydroperoxide, acetophenone (AP) and 
1-phenylethanol (PE). 
Table III 
______________________________________ 
Selectivity, % 
BaO, % EBHP, % Conv. % EBHP AP PE 
______________________________________ 
0.sup.1 
11.41 13.72 83.4 8.2 6.0 
0.0013.sup.1 
19.28 21.03 91.7 4.8 4.0 
0.0033.sup.2 
19.2 19.62 97.9 .sup.3 
.sup.3 
0.0067.sup.1 
20.1 21.08 95.4 .sup.3 
.sup.3 
0.010 18.01 19.68 91.5 .sup.3 
.sup.3 
0.020 19.17 20.25 94.7 .sup.3 
.sup.3 
0.033 18.98 20.93 90.7 5.2 4.0 
0.10 18.75 21.10 88.9 5.7 5.4 
0.20 17.32 21.11 82.2 14.0 3.5 
0.67 16.56 24.8 66.7 24.0 8.9 
1.67 9.43 21.0 45.0 45.4 9.6 
5.0 0.34 9.0 3.8 60.3 35.9 
______________________________________ 
.sup.1 average of two experiments 
.sup.2 average of three experiments 
.sup.3 too small to be determined accurately. 
According to the data in Table III the conversion of ethylbenzene 
substantially diminishes in the presence of large amounts of barium oxide. 
We believe that this is the result of a diminished amount of hydroperoxide 
initiator which is decomposed by the excess barium oxide as shown in 
Example 5. This conclusion is suggested, in particular by the last 
experiment using five percent barium oxide in which about 3.5 percent 
hydroperoxide is introduced as an initiator and less than one percent 
hydroperoxide is present in the reaction product. 
Even though the oxidation of ethylbenzene to ethylbenzene hydroperoxide in 
the presence of barium oxide is carried out under substantially anhydrous 
conditions preferably including the use of dried air and predried 
ethylbenzene, it is recognized that very low concentrations of water will 
result when minor amounts of co-product acetophenone are produced. It is 
believed that most of this water of reaction leaves the system but some of 
this water of reaction may react with the barium oxide to form a minor 
amount of barium hydroxide. Since barium hydroxide is an inferior catalyst 
for the oxidation of ethylbenzene to ethylbenzene hydroperoxide, its 
presence is not desired. Advantageously, the present procedure of using a 
minute amount of barium oxide to obtain maximum selectivity results in 
less by-product water and therefore less of the inferior barium hydroxide 
in the reactor. As used herein, the expression "substantially anhydrous 
barium oxide" contemplates barium hydroxide as a possible minor component, 
while "substantially anhydrous conditions" refers to the substantial 
absence of free water. 
It is to be understood that the above disclosure is by way of specific 
example and that numerous modifications and variations are available to 
those of ordinary skill in the art without departing from the true spirit 
and scope of the invention.