Method for making aromatic carbonates

A method is provided for making diphenyl carbonate by the direct carbonylation of phenol utilizing a palladium catalyst in combination with an inorganic cocatalyst in the form of a cobalt pentadentate complex.

CROSS REFERENCE TO RELATED APPLICATIONS 
Reference is made to copending applications Ser. Nos. 07/929,862, 
07/929,861 and 07/929,860 filed on Aug. 17, 1992 filed concurrently 
herewith, and copending application Ser. No. 07/906,681, filed Jul. 7, 
1992. 
BACKGROUND OF THE INVENTION 
The present invention relates to a method for making aromatic organic 
carbonates such as diphenyl carbonate by effecting reaction between an 
aromatic organic hydroxy compound, such as phenol, and carbon monoxide and 
oxygen in the presence of an effective amount of a palladium carbonylation 
catalyst. More particularly, the present invention relates to the 
carbonylation of an aromatic organic hydroxy compound utilizing an 
inorganic cocatalyst, such as a cobalt complex containing a pentadentate 
Schiff base in combination with the palladium catalyst. 
Procedures for making diorganic 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. An additional 
carbonylation method for making diorganic carbonates is shown by Japanese 
patent 01,165,551. Aromatic organic carbonates are of particular interest 
to thermoplastic manufacturers, since they offer an alternative 
non-phosgene route to aromatic polycarbonates by melt transesterification. 
A procedure for making aromatic organic carbonates using an organic 
solvent, such as methylene chloride, is shown by Chalk, U.S. Pat. No. 
4,187,242. Reference also is made to T. C. Chang in copending application 
Ser. No. 217,248, filed Jul. 11, 1988, and EP350-700-A, 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 
aromatic organic hydroxy compound, such as phenol, to an aromatic organic 
carbonate. U.S. Pat. No. 4,218,391, Romano et al employs a copper salt to 
prepare organic esters of carbonic acid. Attempts to use such catalyst 
with aromatic organic hydroxy compounds, such as phenol, under constant 
flow conditions have been found to provide unsatisfactory results with 
respect to % carbonate yields and % carbonate selectivity as compared to 
the use of aliphatic hydroxy compounds, such as methanol, in preparing 
aliphatic carbonates under substantially the same conditions. 
In application EP350-700-A and copending application Ser. No. 07/906,681, 
carbonylation of aromatic organic hydroxy compound was achieved utilizing 
a divalent or trivalent manganese salt or cobalt (II) salts and organic 
cocatalysts such as hydroquinone or benzoquinone in combination with a 
palladium catalyst. Although the aforementioned cocatalyst system provided 
improved yields of aromatic organic carbonate as a result of the 
carbonylation of aromatic organic hydroxy compounds, using inorganic 
cocatalyst, such as cobalt (II) salts, methods for achieving higher rates 
of aromatic organic carbonate production are constantly being evaluated. 
In addition, it is also known that a variety of organic cocatalysts can 
sometimes degrade after being used at elevated pressures and temperatures 
in a carbonylation reaction and then exposed to ambient conditions of 
pressure and temperature. Color bodies also can be formed in the reaction 
mixture. 
SUMMARY OF THE INVENTION 
The present invention is based on the discovery that certain cobalt 
complexes containing pentadentate Schiff base ligands can be substituted 
for cobalt (II) salts, and trivalent manganese salts as inorganic 
carbonylation cocatalyst. The resulting palladium carbonylation catalysts 
have been found to substantially enhance the rate of aromatic organic 
carbonate production. In addition, aromatic organic carbonate having 
reduced color bodies can be obtained using the cobalt complex containing a 
pentadentate Schiff base ligand as a palladium cocatalyst, since the 
resulting palladium carbonylation catalyst does not require the addition 
of an organic cocatalyst.

STATEMENT OF THE INVENTION 
There is provided by the present invention, a method for making aromatic 
organic carbonate comprising effecting reaction at a temperature of about 
60.degree. C. to about 150.degree. C., between aromatic organic hydroxy 
compound, carbon monoxide and oxygen in the presence of an effective 
amount of a palladium carbonylation catalyst comprising, 
(a) catalytically active palladium in the metallic or chemically combined 
state, 
(b) an inorganic catalyst in the form of a cobalt complex of a cobalt (II) 
salt and a material capable of forming a pentadentate ligand with the 
cobalt (II) salt, which material is a member selected from the class 
consisting of aromatic amines, aliphatic amines, aromatic ethers, 
aliphatic ethers, aromatic or aliphatic amine ethers, and Schiff bases, 
and 
(c) quaternary ammonium or phosphonium halide. 
The palladium material useful as a catalyst can be 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, oxides and complexes 
involving such compounds such as carbon monoxide, amines, phosphines or 
olefins. The preferred palladium compounds are palladium (II) salts or 
organic acids including carboxylates with C.sub.(2-6) aliphatic acids. 
Palladium (II) acetate is particularly preferred. The quaternary ammonium 
halide which is used in combination with palladium catalyst include 
tetraalkylammonium halide or tetraalkylphosphonium 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. 
Cobalt (II) salts which can be used in making the inorganic cocatalyst 
employed in the practice of the present invention are for example, 
halides, and carboxylates, for example, Cobalt (II) chloride or Cobalt 
(II) acetate. Cobalt (II) acetate is preferred. Materials which are 
capable of forming pentadentate ligand with the cobalt (II) salt are for 
example, aromatic amines, such as bipyridines, pyridines, terpyridines, 
quinolines, isoquinolines and biquinolines; aliphatic amines, such as 
ethylene diamine and tetraalkylethylenediamine; aromatic ethers, such as 
crown ethers; aromatic or aliphatic amine ethers, such as cryptanes; and 
Schiff bases, such as di-(salicylal)-3,3'-diamino-N-methyldipropylamine. 
Schiff bases are the preferred material for making the pentadentate ligand 
to form the inorganic cocatalyst of the present invention. The procedure 
of R. S. Drago et al, J. Am. Chem. Soc. 1985, 107, 2903 and Drago et al 
"Coordination Chemistry Review", 79 (1987) 321 can be used. 
If desired, organic cocatalyst can be used in combination with the 
inorganic cobalt (II) cobalt complex. These organic cocatalysts are for 
example, quinones and aromatic diols formed by the reduction of said 
quinones, or a mixture thereof. 1,4-benzoquinone and hydroquinone have 
been found to be effective. In addition, compounds, such as 1,2-quinone 
and catechol, anthroquinone, 9,10-dihydroxy anthracene, phenanthroquinone 
also can be used. 
Aromatic organic amines are the preferred organic cocatalyst which can be 
utilized in the practice of the present invention and are selected from 
the class consisting of terpyridines, phenanthrolines, and quinolines. 
More particularly there can be used terpyridine compounds, such as 
2,2':6',2"-terpyridine, 2,2':6',2"-4'-thiomethylterpyridine and 
2,2':6',2"-4-terpyridine-N-oxide. In addition to terpyridine compounds, 
phenanthrolines also can be used such as, 1,10-phenanthrolines, 
2,4,7,8-tetramethyl-1,10-phenanthroline, 4,7-diphenyl-1,10-phenanthroline 
and 3,4,7,8-tetramethyl-1,10-phenanthroline. 
An effective amount of the palladium catalyst is, for example, an amount 
sufficient to provide about 1 gram-atom of palladium, per 800-10,000 and 
preferably 2,000-5,000 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 gram-atoms of cobalt, 
and about 5 to 150 and preferably about 20-50 moles of the 
tetraalkylammonium halide and about 0.1-3 and preferably about 0.3-1 moles 
of organic cocatalyst and/or reduction product thereof. 
Solid drying agents, such as molecular sieves, can be used to improve 
yields. In some instances, carbon dioxide also can be used as a dessicant 
as taught in copending application Ser. No. 07/503,404, filed Apr. 2, 
1990. 
In order that those skilled in the art will be better able to practice a 
preferred form of the present invention, reference is made to the drawing. 
The drawing shows a schematic of a gas flow reactor system for preparing 
aromatic organic carbonate capable of delivering in a continuous manner, 
flow rate of about 50 ml to 1,000 ml, and preferably about 300 ml to 600 
ml, a mixture of carbon monoxide and oxygen maintained at a substantially 
constant molar ratio and partial pressures. 
More particularly, there is shown at 10 a carbon monoxide gas inlet and at 
11, an oxygen inlet. 12 is a manifold vent, and 13 is an optional inlet 
for a gas, such as carbon dioxide. The reaction mixture can be fed into a 
low pressure reservoir at 20, or a high pressure reservoir at 21 which can 
be operated at a higher pressure than the reactor for the duration of the 
run. At 22 there is shown a reservoir outlet and at 23 an reservoir inlet. 
The gas feed pressure can be adjusted to about 50 psi over the desired 
reactor pressure at a reducing pressure regulator at 30. The gas can be 
further purified in scrubber 31 and then fed into a mass flow controller 
at 32 to allow for flow rates of from 1 to 1000 ml/min STP. The reactor 
feed gas can be heated in an oil bath at 33 having appropriate conduit 
means prior to being introduced to the reactor at 40. The reactor pressure 
can be controlled through manipulation of a back pressure regulator at 41. 
The reactor gas effluent may be either sampled for further analysis at 42 
or vented to the atmosphere at 50. The reactor liquid can be sampled at 
43. 45 is a condenser. An additional vent at 44 can allow for further 
system control, but is typically closed during the gas flow reaction. 
In the practice of one form of the invention, the palladium catalyst, 
cocatalyst package, and organohydroxy compound are charged to the reactor. 
The reactor is sealed. Carbon monoxide and oxygen are introduced into an 
appropriate reservoir within proportions previously defined, until a 
suitable pressure such as 2800 psi is achieved. 
Circulation of condenser water is initiated and the oil bath temperature 
can be raised to 100.degree. C. Conduit between the oil bath and the 
reactor can be heated to a suitable temperature such as 100.degree. C. The 
mass flow bypass can be opened and an appropriate accumulator valve can be 
opened and the reducing pressure regulator can be used to adjust the 
pressure. The reactor pressure can be further adjusted by the back 
pressure regulator. The mass flow bypass can be closed and the flow can be 
adjusted using the mass flow controller. Agitation of the reaction 
ingredients can be initiated once the reactor temperature is raised 
sufficiently to minimize the presence of solids such as phenol. Upon 
reaching a desirable reactor temperature, such as 100.degree. C., aliquots 
can be taken to monitor the reaction. 
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 into a 300 ml 316 SS Parr autoclave, 36.41 g (600 mmol) of 
phenol, 1.16118 g (5 mmol) of tetrabutylammonium bromide, 26.8 mg (0.12 
mmol or 203 ppm of palladium) of palladium diacetate, 9.6 mg (0.04 mmol) 
of terpyridine, 24.6 mg (0.06 mmol) of "CoSMDPT" or cobalt 
di-(salicylal)-3,3'-diamino-N-methyldipropylamine and 5.01 g (30 mmol) of 
diphenyl ether as an internal standard for determination of diphenyl 
carbonate production by GC analysis. The reactor was sealed and flushed 
three times with carbon monoxide at 400 psi. The reactor vessel was then 
charged with oxygen (110 psi) and carbon monoxide (590 psi) at 30.degree. 
C. The vessel was heated to 115.degree. C. with rapid stirring of the 
solution (500 rpm) over the course of the reaction, during heat-up and 
cool-down. Aliquots were taken at predetermined times for GC analysis to 
access the amount of diphenyl carbonate which had been produced. 
The same procedure was repeated except that in place of the CoSMDPT, there 
was utilized 0.06 mmol of cobalt diacetate. 
After a 31/2 hour reaction period, the following results were obtained 
where CoSMDPT is the cobalt pentadentate catalyst: 
TABLE 1 
______________________________________ 
% DPC moles DPC/liter-hr 
Inorganic Co-Catalyst 
3.5 hr 3.5 hr 
______________________________________ 
Co(OAc).sub.2 13.4 0.17 
CoSMDPT* 23.6 0.35 
______________________________________ 
*CoSMDPT = Cobalt di(salicylal)3,3'-diamino-N-methyldipropylamine (4) 
The above results show that the cobalt pentadentate organic cocatalyst 
provides a faster diphenyl carbonate production rate as compared to the 
use of the cobalt diacetate catalyst. 
EXAMPLE 2 
A series of reactions utilizing the constant composition gas flow reactor 
shown by the drawing were performed to further evaluate the effectiveness 
of the cobalt complex containing the pentadentate Schiff base as an 
inorganic cocatalyst for palladium in the direct carbonylation of phenol. 
There was added to the flow reactor, 60.9900 g (648 mmol) of phenol, 
4.0700 g (12.62 mmol) of tetrabutylammonium bromide, 0.1218 g (0.2967 
mmol) of CoSMDPT, and 0.0660 g (2940 mmol; 479 ppmpd) of palladium 
diacetate. There was also introduced into the reactor 26.07 g of molecular 
sieves (4 Angstrom) which had been activated overnight at 300.degree. C. 
The molecular sieves were contained in a perforated Teflon resin basket 
mounted to the stir shaft above the liquid level of the reaction mixture 
and were used as a dessicant. The reaction vessel was sealed. The constant 
flow reactor system was then charged to a total pressure 2800 psi 
including 2600 psi of carbon monoxide (7.1% oxygen in carbon monoxide) and 
200 psi of oxygen. The reactor was then heated to a temperature of 
115.degree. C. and the pressure was set to 1650 psi. The gas reservoir was 
then opened to the reactor solution followed by opening the reactor outlet 
to permit gas flow through the reactor solution. The reactor pressure was 
adjusted to 1600 psi and there was introduced a flow of 350 ml/min STP of 
the mixture of oxygen and carbon monoxide. Stirring was initiated at 
570-620 rpm as soon as the reactor temperature reached 40.degree. C. Upon 
reaching the reacted temperature of 115.degree. C., aliquots were taken 
periodically for GC analysis to quantify the amount of diphenyl carbonate 
produced. 
At 0.0 hr, the yield of diphenyl carbonate was 0.336 g (4.83%). At 1.00 hr, 
the yield of diphenyl was 13.4 g (19.25%). At 2.00 hr, the yield of 
diphenyl carbonate was 20.3 g (29.24%). At 7.00 hr, the yield of diphenyl 
carbonate was 28.7 g (41.28%). 
The same procedure was repeated except that in one instance 0.0354 g 
(0.1517 mmol) of 2,2':2',6"-terpyridine was added to the mixture as an 
organic cocatalyst. An additional reaction was run following the same 
procedure except that 0.0564 g (0.3186 mmol) of cobalt diacetate was 
substituted for the CoSMDPT along with 2,2':2',6"-terpyridine (0.0354 g, 
0.1517 mmol) was as an organic cocatalyst. The following results were 
obtained after a 2 hour reaction run: 
TABLE 2 
______________________________________ 
Inorganic 
Organic % DPC moles DPC/liter-hr 
Co-Catalyst 
Co-Catalyst 
2 Hr 2 Hr 
______________________________________ 
Co(OAc).sub.2 
None 6.2 0.17 
CoSMDPT* None 29.2 0.80 
Co(OAc).sub.2 
Terp** 23.5 0.61 
CoSMDPT* Terp** 45.0 1.19 
______________________________________ 
*CoSMDPT = Cobalt di(salicylal)-3,3'-diamino-N-methyldipropylamine (4) 
**Terp = 2,6',2' ,6"-terpyridine 
The above results Clearly demonstrate the beneficial use of cobalt 
pentadentate Schiff base complexes as inorganic cocatalyst in a direct 
carbonylation of phenol to diphenyl carbonate. Optimization of the 
reaction conditions outlined above and/or further refinement of the 
relative catalyst loadings concentrations would greatly improve both the 
yield and the rate of diphenyl carbonate production. It was further found 
that the selectivity between diphenyl carbonate and phenyl salicylate 
formation and selectivity between diphenyl carbonate and carbon dioxide 
formation was comparable to or better than that found with cobalt 
diacetate as an inorganic cocatalyst. 
Although the above examples are directed to only a few of the very many 
variables which can be utilized in the practice of the method of the 
present invention, it should be understood that the present invention is 
directed to the use of a much broader variety of materials capable of 
forming ligands with the cobalt (II) salts as well as organic cocatalyst 
which can be utilized in combination with such cobalt pentadentate 
complexes as set forth in the description preceding these examples.