Organic compounds -- part of the class 532-570 series – Organic compounds – Carbonate esters
Reexamination Certificate
2001-06-19
2002-10-22
Lambkin, Deborah C. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbonate esters
Reexamination Certificate
active
06469191
ABSTRACT:
It is known to produce organic carbonates by oxidative reaction of an aromatic hydroxy compound with carbon monoxide in the presence of a noble metal catalyst (DE-OS 27 38 437). Palladium is preferably used as the noble metal. A co-catalyst (for example manganese or cobalt salts), a base, a quaternary salt, various quinones or hydroquinones and desiccants may additionally be used. The process may be performed in a solvent, preferably methylene chloride.
When reacting aromatic dihydroxy compounds with carbon monoxide and oxygen, one mole of water is liberated per mole of carbonate units formed. If this water remains in the reaction system, organic carbonate which has already been formed may be hydrolysed, such that the space-time yields which may be achieved without effective water separation are only low; the catalyst system may moreover be deactivated by water. However, reactivation of the deactivated catalyst entails considerable technical effort. Replacing the deactivated catalyst with fresh catalyst is very costly. Effective removal of water is consequently essential for economic use of this process.
DE-OS 27 38 437 proposes using molecular sieve for separating water. However, using molecular sieve makes industrial use of the process unattractive as effective separation of the water from the liquid phase entails using large quantities of molecular sieve (100-500% excess) which must be regenerated in a technically elaborate manner.
U.S. Pat. No. 5,498,724 discloses a process in which the water formed during the reaction is removed by stripping with excess reaction gas. The reaction gas may contain 0 to 30vol. % of an inert gas which forms an azeotrope with water. The reaction mixture may also contain inert organic solvents. However, large quantities of gas must be used in this process in order to remove the water completely; the minimum achievable water content is above 500 ppm. When the water is removed, relatively large quantities of aromatic hydroxy compound are also discharged, which must be separated from the gas stream.
It has now surprisingly been found that adding inert organic solvents to the reaction mixture, which solvents form an azeotrope with water under the reaction conditions, and removing this azeotrope from the reaction mixture, makes it possible to adjust the water content in the reaction mixture to distinctly below 500 ppm, preferably even below 250 ppm. Substantially smaller quantities of reaction gas may additionally be used than when performing pure stripping with reaction gas (DE-OS 44 03 075). Considerable cost savings may accordingly be made when implementing the process on a large industrial scale.
The present invention accordingly provides a process for the production of an aromatic carbonate of the formula
R—O—CO—O—R (I),
in which
R means a substituted or unsubstituted C
6
-C
12
aryl, preferably substituted or unsubstituted phenyl, particularly preferably unsubstituted phenyl,
by reacting an aromatic hydroxy compound of the formula
R—O—H (II),
in which R has the above-stated meaning,
with carbon monoxide and oxygen in the presence of a platinum group metal catalyst, a co-catalyst, a base, and optionally a quaternary salt as well as an inert organic solvent, wherein, under the reaction conditions, the inert organic solvent forms an azeotrope with the water arising during the reaction, and this azeotrope is removed from the reaction mixture.
In a preferred embodiment, removal of the water from the reaction mixture as an azeotrope with the solvent is promoted by stripping with excess reaction gas. It is crucial in this process that more than 5 vol. % of the solvent are removed from the reaction mixture as an azeotrope. In a preferred embodiment, removal of the azeotrope from the reaction mixture is promoted by excess reaction gas. Distinctly lower conversions are achieved under pure stripping conditions (DE-OS 44 03 075), i.e. without formation of an azeotrope with the inert, organic solvent and simultaneous removal of the azeotrope from the reaction mixture.
The process according to the invention for forming carbonate is performed at a reaction temperature of 30 to 200° C., preferably of 50 to 150° C., particularly preferably of 60 to 130° C., and at a reaction pressure of 1 to 100 bar, preferably of 1 to 50 bar, particularly preferably of 1 to 10 bar. The temperature and total pressure should be selected such that the azeotrope may be formed under the reaction conditions and partially removed from the reaction mixture.
Halogenated hydrocarbons and aromatic solvents which boil at a suitable temperature and form azeotropes with water, such as chlorobenzene, dichlorobenzene, fluorobenzene, benzene, anisole, methylene chloride or 1,2-dichloroethane, optionally also mixtures thereof, may be used as the inert organic solvent. Chlorobenzene is particularly preferably used. The inert solvent may be present in the reaction mixture in a proportion of 1-99%, preferably of 20-98%, particularly preferably of 40-98%.
By means of a separating unit, such as for example a dephlegmator, a distillation column with plates or packing and other apparatus known to the person skilled in the art, located in the exhaust gas stream containing the azeotrope, the majority of the solvent entrained during dewatering may be separated from the water and passed into the return stream to the reactor. Separation or breaking of the separated azeotrope may be achieved in accordance with the prior art, for example by extraction, freezing or distillation.
In a preferred embodiment, the fraction of dissolved gases driven off with the azeotrope may be returned, once separated, to the circulating reactor gas. Entrained educts (for example phenol), solvents, products and water are separated from the gas mixture to be recycled, which is optionally compressed before separation, using prior art methods, for example by adsorption, absorption or preferably by condensation. The reaction gas required for the reaction, consisting of carbon monoxide, oxygen and an inert gas, is introduced to this end in a quantity of 1 to 10000 Nl per liter of reaction solution, preferably of 5 to 5000 Nl per liter of reaction solution and particularly preferably of 10 to 1000 N1 per liter of reaction solution. The gas mixture to be recycled originating from dewatering is included in the stated volume with regard to its content of CO and O
2
.
The composition of the reaction gases carbon monoxide and oxygen may be varied within wide concentration limits, but a CO:O
2
molar ratio (standardised to CO) of 1:(0.001-1.0), preferably of 1:(0.01-0.5) and particularly preferably of 1:(0.02-0.3) is conveniently established. At these molar ratios, the oxygen partial pressure is sufficiently high to be able to achieve elevated space-time yields, while simultaneously avoiding explosive carbon monoxide/oxygen gas mixtures.
All the starting compounds may be contaminated with impurities from the production and storage thereof, but for the purposes of purity of the final product it is desirable to use the cleanest possible chemicals. No particular purity requirements apply to the reaction gases either. Synthesis gas may accordingly be used as the CO source and air as the O
2
medium, but care must be taken not to introduce any catalyst poisons such as for example sulfur or the compounds thereof. Pure CO and pure oxygen are used in the preferred embodiment of the process according to the invention.
Aromatic hydroxy compounds which may be reacted according to the invention comprise, for example, phenol, o-, m- or p-cresol, o-, m- or p-chlorophenol, o-, mor p-ethylphenol, o-, m- or p-propylphenol, o-, m- or p-methoxyphenol, 2,6-dimethylphenol, 2,4-dimethylphenol, 3,4-dimethylphenol, 1-naphthol, 2-naphthol and bisphenol A, preferably phenol. In general, any substitution of the aromatic hydroxy compound comprises 1 or 2 substituents of the meaning C
1
-C
4
alkyl, C
1
-C
4
alkoxy, fluorine, chlorine or bromine.
Bases usable in the process according to the invention comprise alkali metal hydroxides, alkali meta
Eek Rob
Jansen Ursula
Rechner Johann
Reisinger Claus-Peter
Bayer Aktiengesellschaft
Gil Joseph C.
Lambkin Deborah C.
Preis Aron
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