Method for making organic carbonates

A method is provided for making an organic carbonate such as, a diaryl carbonate by heating a mixture under elevated conditions of temperature and pressure comprising an arylhydroxy compound, such as phenol, carbon monoxide and oxygen in the presence of a palladium catalyst and carbon dioxide as a desiccant.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for making organic carbonates 
such as diphenyl carbonate by effecting reaction of an organic hydroxy 
compound, such as phenol, with carbon monoxide and oxygen in the presence 
of an effective amount of a palladium catalyst and carbon dioxide as a 
desiccant. More particularly, the present invention relates to a 
continuous or batch method for making organic carbonates at elevated 
temperatures and pressures under neat conditions in the absence of a solid 
desiccant. 
Prior to the present invention, aromatic carbonates, such as diphenyl 
carbonate were made by effecting reaction between phenol, carbon monoxide, 
an oxidant and a Group VIII element or catalyst. Aromatic carbonates are 
of interest to thermoplastic manufacturers, since they offer an 
alternative non-phosgene route to aromatic polycarbonates by melt 
transesterification. A procedure for making aromatic carbonates using an 
organic solvent, such as, methylene chloride, is shown by Chalk, U.S. Pat. 
No. 4,187,242. Additional procedures for making organic carbonates are 
shown by Hallgren, U.S. Pat. Nos. 4,361,519 and 4,410,464, utilizing a 
molecular sieve as a drying agent for the water formed during the 
reaction. Further procedures for making aromatic carbonates by catalytic 
carbonylation of aromatic hydroxy compounds, are shown by Japanese patent 
No. 01,165,551. Reference also is made to copending applications Ser. No. 
17,248, filed Jul. 11, 1988, and Ser. No. 217,257, filed Jul. 11, 1988, 
utilizing a divalent or trivalent manganese salt or cobalt (II) salt and 
hydroquinone in combination with a palladium catalyst to catalyze the 
conversion of an organic hydroxy compound to an organic carbonate. 
Although the aforementioned methods for making organic carbonates provide 
effective results in particular instances, the yields of the product are 
often less than 10%. In addition organic solvents are generally employed 
as well as solid drying agents which can interfere with the recovery of 
catalyst values. 
SUMMARY OF THE INVENTION 
The present invention is based on the discovery that if carbon dioxide is 
initially charged under ambient conditions to the reactor along with the 
key ingredients used in organic carbonate production, namely the organic 
hydroxy compound, carbon monoxide, oxygen or air and a palladium catalyst, 
substantially higher yields of the organic carbonate can be obtained. 
Those skilled in the art know, for example, that carbon dioxide is often 
produced as a side product resulting from the direct combustion between 
carbon monoxide and oxygen during organic carbonate formation, sometimes 
referred to as the "burn reaction". However, as provided by the present 
invention, carbon dioxide can function as a desiccant if added to the 
reactor along with the reactants under ambient conditions, in amounts such 
as about 0.01 to 50 moles of carbon dioxide per mole of organic hydroxy 
compound. The carbon dioxide can react with the water of reaction to form 
carbonic acid and also minimize the burn reaction. There is also provided 
by the present invention the advantage of being able to introduce make-up 
oxygen and carbon monoxide into the reactor after they have been initially 
consumed, to simulate continuous conditions and achieve superior yields of 
organic carbonate, as compared to organic carbonate yields obtained when 
make-up reactants are used in methods of the prior art. 
STATEMENT OF THE INVENTION 
There is provided by the present invention, a method for making an organic 
carbonate which comprises, 
(1) charging a reaction vessel under ambient conditions with a mixture 
comprising organic hydroxy compound, carbon monoxide, an oxygen-containing 
gas, a catalytic amount of a palladium material, and a desiccant amount of 
carbon dioxide, 
(2) agitating the mixture of (1) at a temperature of from about 50.degree. 
C. to about 170.degree. C. and a pressure of from about 100 psi to 300 
psi, and 
(3) recovering organic carbonate from the mixture of (2). 
The organic hydroxy compound used in the practice of the invention can be 
selected from aliphatic, alicyclic and aromatic mono or polyhydroxy 
compounds, such as methanol, ethanol, butanol, cyclohexanol, phenol, 
cresol, xylenol, ethylene glycol, propyleneglycol, resorcinol, 
hydroquinone, and bisphenol A. Aromatic hydroxy compounds are particularly 
preferred, with phenol being the most preferred. 
The palladium material or catalyst can be used in elemental form or it can 
be employed as a palladium compound. Accordingly, palladium black or 
elemental palladium deposited on carbon can be used as well as palladium 
compounds, such as halides, nitrates, carboxylates, and complexes 
involving such compounds such as carbon monoxide, amines, phosphines or 
olefins. The preferred palladium compounds are palladium (II) salts of 
organic acids including carboxylates with C.sub.2-6 aliphatic acids. 
Palladium (II) acetate is particularly preferred. There also can be used 
in combination with palladium catalyst, tetraalkylammonium halide, such as 
the chlorides and bromides and particularly the bromides. Alkyl groups of 
the alkyl ammonium halides are primary and secondary alkyl groups 
containing about 1-8 carbon atoms. Tetra-n-butylammonium bromide is 
particularly preferred. There also can be used in combination with the 
palladium catalyst and the tetraalkylammonium halide at least one quinone 
and aromatic diol formed by the reduction of said quinone or a mixture of 
thereof. 1,4-quinone, 1,4-benzoquinone and hydroquinone are preferred. In 
addition, compounds such as 1,2-quinone and catechol, anthraquinone and 
9,10-dihydroxyanthracene, tetramethyldiquinone and phenanthrenequinone 
also can be used. 
In instances where the formation of aromatic carbonates, such as diphenyl 
carbonate, is desired, manganese or cobalt cocatalysts also can be used. 
For example, cobalt or manganese compounds such as a divalent or trivalent 
compounds, for example, salts such as halides and carboxylates and 
complexes with amines, diketones and carbon monoxide have been found 
effective. Cobalt (II) acetate is particularly preferred. It has been 
found that optimum selectivity, i.e., optimizing the formation of aromatic 
carbonate and minimizing the formation of aromatic salicylate is achieved 
using the cobalt (II) catalyst. 
An effective amount of the palladium catalyst is, for example, an amount 
sufficient to provide about 1 gramatom of palladium, per 800-10,000 and 
preferably 5,000-10,000 moles of organic hydroxy compound. The other 
components of the palladium catalyst are, for example, per gram-atom of 
palladium, about 0.1-5.0, preferably about 0.5-1.5 gramatoms of manganese 
or cobalt and about 10 to 100 and preferably about 40-80 moles of the 
tetraalkylammonium halide and about 10-60 and preferably about 25-40 moles 
of quinone and/or reduction product thereof. 
In the practice of the present invention, the reactants such as, the 
organic hydroxy compound, carbon monoxide, an oxygen-containing gas, the 
carbon dioxide desiccant and the palladium catalyst are initially 
introduced into the reactor. The resulting mixture can then be heated 
under sealed conditions while being agitated. The conditions of 
temperature and pressure have been previously cited in the Statement of 
the Invention. Of course, under continuous reaction conditions, any or all 
of the components can be further recycled depending upon the point at 
which the organic carbonate is recovered. 
In order that those skilled in the art will be better able to practice the 
present invention, the following examples are given by way of illustration 
and not by way of limitation. All parts are by weight unless otherwise 
indicated.

EXAMPLE 1 
There was added to a Parr stirred pressure reactor, 76.06 grams of phenol, 
1.896 grams of diphenyl ether, 0.33 gram benzoquinone, 0.042 gram 
palladium diacetate, 0.035 gram of anhydrous cobalt diacetate, and 2.49 
grams of tetrabutylammonium bromide. The reactor vessel was sealed, purged 
4 times with CO.sub.2 at 400 psi and then charged with 0.278 mole of 
carbon dioxide, 0.209 mole of oxygen and 0.417 mole of carbon monoxide at 
room temperature. The resulting partial pressures of carbon dioxide were 
400 psi, oxygen 300 psi, and carbon monoxide 600 psi. The mixture was 
heated to 100.degree. C. while it was stirred rapidly to ensure efficient 
aeration of the solution phase. After 2 hours, 7.3 grams of diphenyl 
carbonate (8.4% yield based on phenol) had been produced. A total internal 
pressure drop of 195 psi was also observed during the first 2 hours. The 
reactor was exhausted to 1000 psi and then recharged with 300 psi of 
oxygen and 620 psi of carbon monoxide. An aliquot of the mixture was 
removed after 3 hours following the initiation of the reaction and it was 
found that 9.25 grams of diphenyl carbonate (10.7% yield) had formed based 
on GC. At the termination of the reaction which lasted 5 hours, a total of 
13.2 grams of diphenyl carbonate (15.2% yield) had been formed. Recovery 
of the diphenyl carbonate is readily achieved by stripping the mixture to 
dryness at about 19 torr and 150.degree.-190.degree. C. followed by 
distillation at about 15 torr and 200.degree. C. 
EXAMPLE 2 
The procedure of Example 1 was repeated except there was utilized 50.5 gram 
of phenol, 4.46 grams of diphenylether, 0.275 grams of benzoquinone. 1.5 
grams of tetrabutylammonium bromide, 0.062 gram of palladium diacetate, 
and 0.042 gram of cobalt diacetate. The reactor vessel was then again 
sealed and purged with 4 times 600 psi of carbon dioxide. The reaction 
vessel was then charged with 620 psi of carbon dioxide (0.431 mole), 380 
psi of oxygen and 800 of psi of carbon monoxide, to provide a total 
pressure at room temperature of about 1800 psi. The reactor was then 
heated to 100.degree. C. After one hour, the reactor was depressurized to 
1000 psi and then recharged with 380 psi of oxygen and 760 psi of carbon 
monoxide to produce a total pressure of 2140 psi. After 2 hours of 
reaction, the reaction vessel was exhausted to 900 psi then repressurized 
with 450 psi of oxygen and 700 psi of carbon monoxide to provide a total 
pressure at 100.degree. C. of 2050 psi. The reactor was then allowed to 
cool to room temperature after 3 hours of reaction. There was obtained 
10.9 grams of diphenyl carbonate or a 19% yield. 
EXAMPLE 3 
Procedure of Example 1 was repeated except there was utilized 50.1 grams of 
phenol, 6.281 grams of diphenyl ether, 1.955 grams of benzoquinone, 1.5 
gram of tetraabutylammonium bromide, 0.060 of palladium (II) acetate and 
0.032 gram of cobalt (II) acetate. The reactor was sealed and pressurized 
with 400 psi of oxygen, 450 psi of carbon dioxide, and 800 psi of carbon 
monoxide to provide a total pressure of 1650 psi at room temperature. The 
reactor was heated to 100.degree. C. At 0.5 hours, the pressure of the 
reactor was reduced to 1200 psi and then repressurized with 400 psi of 
oxygen and 600 psi of carbon monoxide. After 1 hour, the pressure of the 
reactor was reduced to 1000 psi, then repressurized with 350 psi of oxygen 
and 700 psi of carbon monoxide. The aforementioned repressurizing 
procedure was repeated after 2 hours had elapsed. At this time, a sample 
of the reaction mixture showed that it contained 22% yield of diphenyl 
carbonate based on GC. After the reaction had been running for 5 hours the 
mixture showed that it contained 14.85 grams or a 26.1% yield of diphenyl 
carbonate. 
The above procedure was repeated except that carbon dioxide was not 
included in the reactor when it was initially charged with oxygen and 
carbon monoxide. At the termination of the reaction, it was found that 
there was 9.79 grams of diphenyl carbonate, or a 17.2% yield based on GPC 
analysis. 
These results show that the presence of carbon dioxide during the initial 
stages of the reaction period can substantially enhance the yield of 
diphenyl carbonate. 
Although the above results are directed to only a few of the vary many 
variables which can be used in the practice of the method of the present 
invention, it should be understood that the present invention is directed 
to a method for making a much broader variety of organic carbonates 
utilizing ingredients as set forth in the description preceding these 
examples.