Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
1999-12-20
2001-10-30
Nazario-Gonzalez, Porfirio (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C502S171000, C556S108000, C558S270000, C558S271000, C558S274000
Reexamination Certificate
active
06310229
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the preparation of diaryl carbonates by carbonylation. More particularly, it relates to the improvement of diaryl carbonate yield and selectivity in the carbonylation reaction.
Diaryl carbonates are valuable intermediates for the preparation of polycarbonates by transesterification with bisphenols in the melt. This method of polycarbonate preparation has environmental advantages over methods that employ phosgene, a toxic gas, as a reagent and environmentally detrimental chlorinated aliphatic hydrocarbons such as methylene chloride as solvents.
Various methods for the preparation of diaryl carbonates by an oxidative carbonylation (hereinafter sometimes simply “carbonylation” for brevity) reaction of hydroxyaromatic compounds with carbon monoxide and oxygen have been disclosed. In general, the carbonylation reaction requires a rather complex catalyst. Reference is made, for example, to U.S. Pat. No. 4,187,242, in which the catalyst is a heavy Group VIII metal; i.e., a Group VIII metal having an atomic number of at least 44, said metals consisting of ruthenium, rhodium, palladium, osmium, iridium and platinum, or a complex thereof.
The production of carbonates may frequently be improved by including a lead-containing cocatalyst along with the heavy Group VIII metal catalyst. Suitable lead-containing cocatalysts have been described broadly in various patents and publications, particularly in U.S. Pat. No. 5,498,789. Also preferred in general is the use of various halides, as illustrated by tetra-n-butylammonium bromide, as part of the catalyst package. Compounds characterized as inert solvents, such as toluene, diethyl ether, diphenyl ether and acetonitrile, can also be present.
Lead-containing systems of this type have, however, certain disadvantages. In the first place, selectivity of the reaction (i.e., the amount of diphenyl carbonate produced as a percentage of total reaction products derived from phenol) is poor, with various by-products such as biphenols and bromophenols being formed in addition to the desired diaryl carbonates. In the second place, sediments are often formed when lead compounds such as lead(II) oxide are added to other components of the catalyst package, and their presence can result in poor reproducibility of reaction results. In the third place, water is frequently formed by the reaction of lead(II) oxide with the other catalyst components and may adversely affect the activity of the catalyst.
It is of interest, therefore, to develop lead-containing catalyst systems that do not adversely affect catalyst activity.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that lead(II) oxide reacts with hydroxyaromatic compounds such as phenol in the presence of halide salts, forming lead halophenoxides (including lead oxyhalophenoxides) which form homogeneous mixtures with other carbonylation catalyst constituents. Said lead halophenoxides, when present in the catalyst system, afford diaryl carbonate with improved selectivity and in high yield.
In one of its aspects, an embodiment of the invention is directed to lead halophenoxides of the formula
Pb
n
O
m
(OA)
(2−z)(n−m)
X
z(n−m)
, (I)
wherein A is an aromatic radical, X is chlorine or bromine, n has a value in the range of 1-3, m has a value in the range of 0-1 and z has a value in the range of 0.1-2.0, with the proviso that the values of n and m cannot be the same.
A further aspect of the invention is directed to a method for preparing a lead halophenoxide. An embodiment of the method comprises contacting lead(II) oxide with at least one bromide or chloride salt and at least one hydroxyaromatic compound, the molar ratio of lead to bromide or chloride being at least 2:1.
A further aspect is directed to a method for preparing a diaryl carbonate. An embodiment of the method comprises contacting at least one hydroxyaromatic compound with oxygen and carbon monoxide in the presence of an amount effective for carbonylation of a catalyst composition comprising the following and any reaction products thereof:
(A) a Group VIII metal having an atomic number of at least 44 or a compound thereof,
(B) at least one bromide or chloride salt, and
(C) at least one lead halophenoxide, particularly one of formula I.
A still further aspect is directed to catalyst compositions comprising components A, B and C as described above, and any reaction products thereof.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In formula I, A may be any aromatic radical, unsubstituted or substituted. In general, A corresponds to the diaryl carbonate to be formed in the carbonylation reaction. Therefore, it is usually unsubstituted phenyl. X may be bromide or chloride and is preferably bromide.
The values of n, m and z are as described hereinabove. Most often, n is 2.5-3 and m is 0.8-1.
The method of the invention for the preparation of the lead halophenoxides involves bringing the designated reagents into contact, usually at a temperature in the range of about 20-120° C. Suitable bromide and chloride salts include alkali metal and alkaline earth metal bromides and chlorides and tetraalkylammonium, tetraalkylphosphonium and hexaalkylguanidinium bromides and chlorides. The bromides are preferred. When the bromide or chloride salt is an inorganic salt such as sodium bromide, the reaction is preferably facilitated by the presence of an electron-donating compound, especially a nitrile such as acetonitrile or a polyether such as diethylene glycol dimethyl ether (diglyme) or tetraethylene glycol dimethyl ether (tetraglyme).
The molar ratio of lead to halide in the reaction mixture should be at least 2:1, since at lower molar ratios the principal products are the lead(II) halides and hydroxyhalides. In general, molar ratios in the range of about 2-20:1 are preferred. It should be noted, however, that the molar ratio of lead to halide in the product is not necessarily at least 2:1. Rather, the method of the invention involves this minimum since it permits isolation of the lead halophenoxide.
Hydroxyaromatic compound is most often present in excess and is preferably employed as a solvent for the reaction. The electron-donating compound, when employed, may also be present in molar excess with respect to halide salt, typically in a molar ratio in the range of about 50-200:1. Under such conditions, the lead halophenoxide forms a separate phase, which may be isolated by conventional methods including such operations as filtration and drying.
Any hydroxyaromatic compound may be employed in the diaryl carbonate preparation method of the present invention. Monohydroxyaromatic compounds, such as phenol, the cresols, the xylenols and p-cumylphenol, are generally preferred with phenol being most preferred. The invention may, however, also be employed with dihydroxyaromatic compounds such as resorcinol, hydroquinone and 2,2-bis(4-hydroxyphenyl)propane or “bisphenol A”, whereupon the products are polycarbonate oligomers.
Other reagents in the diaryl carbonate preparation method of the invention are oxygen and carbon monoxide, which react with the phenol to form the desired diaryl carbonate. They may be employed in high purity form or diluted with another gas such as nitrogen, argon or carbon dioxide, which has no negative effect on the reaction.
For the sake of brevity, the constituents of the catalyst system of the invention are defined as “components” irrespective of whether a reaction between said constituents occurs before or during the carbonylation reaction. Thus, the catalyst system may include said components and any reaction products thereof.
Component A of the catalyst system is one of the heavy Group VIII metals, preferably palladium, or a compound thereof. Thus, useful palladium materials include elemental palladium-containing entities such as palladium black, palladiun/carbon, palladium/alumina and palladium/silica; palladium compounds such as palladium chloride, palladium bromide, palladium iodide, palladium sulfate, palladium nitrate, palladium acetate
Ofori John Yaw
Patel Ben Purushatom
Soloveichik Grigorii Lev
Cabou Christian G.
General Electric Company
Johnson Noreen C.
Nazario-Gonzalez Porfirio
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