HK1144191A - Process for preparing diaryl carbonates - Google Patents

Description

Process for preparing diaryl carbonates

This application claims the benefit of german patent application 102008050828.4 filed on 8/10/2008, which is incorporated herein by reference in its entirety for all useful purposes.

Technical Field

The invention relates to a process for preparing diaryl carbonates, which comprises reacting aromatic monohydroxy compounds with phosgene or aryl chloroformates in the presence of mixed hydroxides of elements of groups 2 to 14 of the periodic Table (IUPAC, New) as heterogeneous catalysts, with elimination of hydrogen chloride.

Background

Diaryl carbonates are suitable for the preparation of Polycarbonates by the melt transesterification process (see, for example, Chemistry and Physics of Polycarbonates, Polymer Reviews, H.Schnell, Vol.9, John Wiley and Sons, Inc. (1964)) or for the preparation of phenylcarbamates (phenylurethanes) or as precursors to active ingredients in the field of pharmaceuticals and crop protection.

It is known that diaryl carbonates can be obtained by phase boundary phosgenation of aromatic hydroxy compounds (Schotten-Baumann reaction). In this process, the use of solvents and sodium hydroxide solutions has an adverse effect, since aqueous bases can lead to partial hydrolysis of phosgene or chloroformates. In each case, a large amount of sodium chloride is obtained as a by-product. In addition, care must be taken to recover the solvent.

Thus, it has been proposed to carry out the condensation reaction in the presence of tetramethylammonium halide as A catalyst without using A solvent and A sodium hydroxide solution (U.S. Pat. No. 3, 2837555). However, the amount of catalyst required is relatively large. In order to obtain economically viable reaction rates, it is generally necessary, depending on the amount of phenol used, to have from 5 to 7% by weight of catalyst; reaction temperatures of 180 ℃ to 215 ℃ also carry the additional risk of decomposition of thermally unstable tetramethylammonium halides. In addition, the catalyst must be removed by washing with water, which significantly complicates recovery. In addition, much more phosgene is consumed than is stoichiometrically necessary.

In another method (U.S. Pat. No. 3, 3234263), diaryl carbonates are obtained by heating aryl chloroformates in the presence of large amounts of alkali/alkaline earth metal compounds using A tertiary nitrogen base as catalyst. However, this process has the disadvantage that high temperatures have to be used in order to achieve an even marginally acceptable reaction time, and that the catalyst (e.g.alkali/alkaline earth metal compound) has to be partially dissolved. In this process, CO is used₂Half of the phosgene initially used was lost formally. In addition, chloroformates need to be synthesized in a separate prior process step.

According to U.S. Pat. No. 3, 2362865, diaryl carbonates are obtained by phosgenating monophenols in the presence of the metals titanium, iron, zinc and tin or in the form of their soluble salts, in particular chlorides and phenolates. Even with good yields, it is difficult to separate the catalyst from the product. Even in the case of distillation, some volatility of these compounds is expected and these compounds thermally decompose, which leads to contamination, reduced quality and loss of yield.

It therefore appears reasonable to use heterogeneous insoluble catalysts, which substantially simplifies the work-up of the reaction mixture. Proposals have also been made for this purpose. For example, the teaching of EP-A-516355 proposes in particular the use of aluminum trifluoride, which is optionally applied to ｃA support, such as an aluminosilicate. However, the synthesis of aluminum trifluoride is complicated and expensive due to the handling of fluorine or hydrofluoric acid. In addition, WO91/06526 describes metal salts on porous supports as catalysts for the conversion according to the invention. It is clear from the test examples that a completely continuous phosgenation of phenol on these catalysts is only possible in the gas phase, which however requires relatively high reaction temperatures and carries the risk of the decomposition of sensitive phenyl chloroformates. It is obviously not possible to phosgenation of phenol in the liquid phase with these catalysts, since the hot liquid phenol washes out the active catalyst components.

Disclosure of Invention

It is therefore an object of the present invention to develop an efficient heterogeneous catalyst which is readily available.

It has now been found that mixed hydroxides of elements of groups 2 to 14 of the periodic table (IUPAC, new) (e.g. hydrotalcites) are suitable catalysts for the reaction of phosgene or aryl chloroformates with monophenols to give diaryl carbonates, and that the hydrogen chloride formed can be reused as reactant or oxidized to chlorine in other processes.

The process of the present invention has the great advantage of obtaining very high selectivity and excellent phenol conversion, and thus high purity product. In addition, the catalyst can be easily removed and is therefore substantially easier to work up.

Modes for carrying out the invention

One embodiment of the present invention is a method for preparing diaryl carbonates, said method comprising reacting a monohydric phenol with phosgene or an aryl chloroformate, wherein said reaction is carried out in the presence of a compound of formula (III) as a heterogeneous catalyst

[M(II)_1-x M(III)_x M(IV)_y(OH)₂]A^n- _z/n·m H₂O (III)

Wherein

M (II) is a divalent metal cation;

m (III) is a trivalent metal cation;

m (IV) is a tetravalent metal cation;

x is a number from 0.1 to 0.5;

y is a number from 0 to 0.5;

z is 1+ y;

m is an integer of 0 to 32;

a is an anion; and is

n is 1 or 2.

Another embodiment of the present invention is the above process, wherein the anion is selected from the group consisting of CO₃ ^2-、OH^-、SO₄ ^2-、NO₃ ^-、CrO₄ ^2-And Cl^-。

Another embodiment of the present invention is the above process, wherein the reaction is carried out at a temperature of 50 to 450 ℃ and a pressure of 0.05 to 20 bar.

Another embodiment of the present invention is the above process, wherein the heterogeneous catalyst has a BET method of 0.1 to 400m²Per g of surface area and is used in an amount of from 0.5 to 100% by weight, based on the amount of monohydric phenol, in a non-completely continuous manner, or in a space velocity of from 0.1 to 20g monohydric phenol per g of catalyst per hour in a completely continuous manner.

Another embodiment of the present invention is the above method, wherein the divalent metal cation m (ii) is Mg, Ni or Zn, the trivalent metal cation m (iii) is Al, and the tetravalent metal cation m (iv) is Ti or Zr.

Another embodiment of the present invention is the above process, wherein the diaryl carbonate is prepared continuously.

Another embodiment of the present invention is the above process, wherein said process is carried out at a temperature of 100 to 350 ℃ and a pressure of 0.05 to 20 bar.

Another embodiment of the present invention is the above process, wherein the reaction is carried out in the gas phase.

Another embodiment of the present invention is the above process, wherein the reaction is carried out in trickle-phase countercurrent.

Another embodiment of the present invention is the above process, wherein the heterogeneous catalyst consists of a supported active phase of the compound of formula (III).

Another embodiment of the present invention is the diaryl carbonate obtained by the above process.

Detailed Description

The present invention accordingly provides a process for preparing diaryl carbonates by reacting monophenols with phosgene or aryl chloroformates, characterized in that the process is carried out in the presence of mixed hydroxides of elements of groups 2 to 14 of the periodic Table (IUPAC, new) as heterogeneous catalysts.

The monohydric phenol used in the process of the present invention is a compound of the formula

Ar-OH (I)

Wherein

Ar is phenyl, naphthyl, anthracenyl, phenanthrenyl, indanyl, tetrahydronaphthyl or a radical of a 5-or 6-membered aromatic heterocycle having 1 or 2 heteroatoms from the group consisting of N, O and S, where these carbocyclic and heterocyclic radicals may be substituted by 1 or 2 substituents, such as straight-chain or branched C₁-C₄Alkyl, straight or branched C₁-C₄Alkoxy, straight or branched C₁-C₄Alkoxycarbonyl, these substituents being substituted by phenyl, cyano and halogen (for example F, Cl, Br), and heterocyclic groups being additionally bonded to the fused benzene ring.

Examples of monophenols of the formula (I) are phenol, o-, m-and p-cresol, o-, m-and p-isopropylphenol, the corresponding halogenated or alkoxyphenols (such as p-chlorophenol or p-methoxyphenol), methyl salicylate, ethyl salicylate, monohydroxy compounds of naphthalene, anthracene and phenanthrene, and also 4-hydroxypyridine and hydroxyquinoline. Preference is given to using phenol and optionally substituted phenols, particular preference being given to using phenol itself.

The process of the present invention can be carried out with phosgene or with aryl chloroformates. In the case of phosgene, aryl chloroformates are first formed and then reacted with additional monohydric phenol present in the reaction mixture to give diaryl carbonates.

When the starting materials are aryl chloroformates and monophenols, symmetrical or unsymmetrical diaryl carbonates are obtained.

Suitable aryl chloroformates for use in the method of the present invention are compounds of formula (II)

Ar-OCOCl (II)

Wherein Ar is as defined for formula (I).

Suitable mixed hydroxides for use in the present invention are compounds of the general formula (III)

[M(II)_1-x M(III)_x M(IV)_y(OH)₂]A^n- _z/n·m H₂O (III)

Wherein

M (II) is a divalent metal cation; and is

M (III) is a trivalent metal cation; and is

M (IV) is a tetravalent metal cation; and is

x is 0.1 to 0.5; and is

y is 0 to 0.5;

z is 1+ y; and is

m is 0 to 32;

a is an anion, e.g. CO₃ ^2-、OH^-、SO₄ ^2-、NO₃ ^-、CrO₄ ^2-Or Cl^-Preferably CO₃ ^2-、OH^-、SO₄ ^2-；

n is 1 or 2.

Examples of metal cations m (ii) include:

divalent metal cations, such as Be, Mg, Ca, Zn, Fe, Mn, Co, Ni, Cu, Cd, preferably Mg, Ni, Zn and Fe, particularly preferably Mg, Ni and Zn.

Examples of metal cations m (iii) include:

trivalent metal cations such as Al, Ga, Ni, Co, Fe, Mn, Al, Cr, Fe, Sn, V, preferably Al, Cr, Fe, particularly preferably Al.

Examples of metal cations M (IV) include tetravalent metal cations, such as Ti, Zr and Hf, preferably Ti and Zr, particularly preferably Ti is used.

In the mixed hydroxide, a plurality of different metal cations M (II) or metal cations M (III) or metal cations M (II) or metal cations M (III) of the same element with different valences can also coexist with one another.

The mixed hydroxides used according to the invention can have a layered structure composed of polycations and polyanions, for example hydrotalcite, or have different structures, for example glauberite.

The mixed hydroxides used are of natural origin, i.e. different minerals, e.g.

Hydrotalcite Mg₆Al₂(OH)₁₆CO₃·4H₂O

Brucite Mg6Al₂(OH)₁₆CO₃·4H₂O

Lepidocrocite Mg₆Fe₂(OH)₁₆CO₃·4.5H₂O

Brucite Mg6Fe₂(OH)₁₆CO₃·4.5H₂O

Chrome scale magnesium ore Mg₆Cr₂(OH)₁₆CO₃·4H₂O

Brucite Mg₆Cr₂(OH)₁₆CO₃·4H₂O

Nissan Ni₆Al₂(OH)₁₆CO₃·OH·4H₂O

Siderite nickel Ni₆Fe₂(OH)₁₆CO₃·4H₂O

Magnesium manganese carbonate Mg₆Mn₂(OH)₁₆CO₃·4H₂O

Hydrocalumite [ Ca ]₂Al(OH)₆]OH·6H₂O

Magnesium plus aluminum [ Mg)₁₀Al₅(OH)₃₁](SO₄)₂·mH₂O

Aluminium [ Ca ]₆Al₂(OH)₁₂](SO₄)₃·26H₂O，

Mixed hydroxides, also from synthesis, are generally prepared by precipitation from a solution of a precursor (e.g., a metal salt or metal oxide) and a base.

Such mixed hydroxides and sources or methods of preparation of such compounds are described, for example, in Clays and Clay Minerals25(1977)14，23(1975)369，Catalysis Today 11(1991)173，Chimia24(1970)99 and EP-A749941, EP-A421677, EP-A684872, EP-A0749941, DE-A2024281 and WO 95/17246.

Particularly suitable heterogeneous catalysts are mixed hydroxides having a hydrotalcite structure, for example mixed hydroxides of magnesium, zinc, nickel, aluminum, cobalt, tin and titanium.

The mixed hydroxides of the present invention may exist in crystalline forms of various polymorphs. They may be completely or partially amorphous and may be dried or partially dried or used as hydrates.

The reaction of mixing metal salts in the presence of a base at a temperature of 80 to 100 ℃ first produces a basic carbonate, which is subsequently converted to an anhydrous mixed hydroxide at relatively high calcination temperatures by decarboxylation and progressive dehydration. For example, hydrotalcite Mg in the case of calcination at above 500 ℃₆Al₂(OH)₁₆CO₃·4H₂Conversion of O to Mg₆Al₂O₅(OH)₂. Depending on the type of starting hydroxide or basic carbonate, the calcination may be carried out through various polymorphs of the mixed hydroxides described above.

Preferred mixed hydroxides have a particle size of from 0.1 to 500m²G, more preferably from 0.5 to 450m²G, most preferably 1 to 300m²BET surface area in g.

The catalyst can be used, for example, in the form of a powder or shaped body and can be removed again after the reaction, for example by filtration, sedimentation or centrifugation. In the case of an arrangement as a fixed bed, the metalate is preferably used in the form of shaped bodies, such as spheres, cylinders, rods, hollow cylinders, rings, etc.

When carried out with a suspended catalyst, the mixed hydroxide catalyst is used in an amount of 0.5 to 100% by weight, preferably 5 to 100% by weight, more preferably 5 to 50% by weight, based on the amount of monohydric phenol used, in a stirred vessel or bubble column.

In the case of countercurrent or cocurrent or in trickle phase or in continuous mode in the gas phase over a fixed bed catalyst, catalyst hourly space velocities of from 0.1 to 20g of monohydric phenol per g of catalyst hour, preferably from 0.2 to 10g, are used^-1·h^-1More preferably 0.2 to 5 g.g^-1·h^-1。

The mixed hydroxide used in the batch experiment can be reused without purification, assuming the starting materials are the same. In the case of a change of starting materials, the mixed hydroxides are suitably purified by extraction with inert solvents, which are specified, for example, downwards as reaction medium, or by purification with alcohols, such as methanol, ethanol, isopropanol or butanol, or by purification with esters or amides of acetic acid, or by treatment with superheated steam or air.

In the continuous mode, the mixed hydroxide used can be retained in the reactor for a long time. Regeneration can be carried out if appropriate, for example by superheated steam at from 150 to 800 ℃ and, if appropriate, addition of small amounts of air (for example from 0.1 to 20% by weight, based on the amount of steam used), or by dilution gases containing oxygen, such as nitrogen or carbon dioxide, from 0.01 to 20% by weight, or by carbon dioxide alone at from 200 to 800 ℃. Preferred regeneration temperatures are from 150 ℃ to 700 ℃, more preferably from 200 ℃ to 600 ℃.

The process of the invention is carried out at from 50 ℃ to 450 ℃, preferably from 100 ℃ to 400 ℃, more preferably from 100 ℃ to 350 ℃. During the performance of the process of the invention, the temperature may vary within a specified range, preferably increasing.

The process of the invention is carried out at a pressure of from 0.05 to 20bar, preferably from 1 to 5 bar.

The process of the invention can optionally be carried out with a solvent, for example aliphatic and aromatic hydrocarbons, such as hexane, octane, benzene, the isomeric xylenes, diethylbenzenes, alkylnaphthalenes, biphenyls or halogenated hydrocarbons, such as dichloromethane and trichloroethylene.

The process of the present invention may be carried out in the gas phase or in the liquid phase.

The process of the invention is preferably carried out in the melt, for example by mixing a suspension of the hydroxide by introducing phosgene or an aryl chloroformate of the formula (II) into a monophenol melt of the formula (I), and removing the catalyst after the reaction has ended, for example by filtration or centrifugation.

The process of the invention can be carried out in the gas phase by evaporating phosgene and monophenol and passing the mixture through a catalyst bed arranged in the form of a sheet in a tube.

Another preferred embodiment of the synthesis is to bubble the monophenol melt of the formula (I) with the mixed hydroxide catalyst suspended therein, with phosgene or a phosgene-hydrogen chloride mixture or with the aryl chloroformate of the formula (II) in a continuous bubble column or a cascade of bubble columns.

Another preferred embodiment is a co-current process, in which a monohydric phenol of the formula (I) and phosgene or an aryl chloroformate of the formula (II) are applied co-currently, for example from the top, to a catalyst bed arranged in a tube, and hydrogen chloride and phosgenation products are withdrawn at the bottom of the tube.

Another preferred embodiment is to carry out the reaction according to the invention in trickle-phase countercurrent, in which case the monophenol of the formula (I) is introduced as a melt or in solution at the top of the mixed hydroxide bed and a stream of phosgene or aryl chloroformate is fed back to this liquid stream from below. Where appropriate, this embodiment is carried out in a vertical coarse reactor, which may also comprise intermediate trays for better distribution of the gas and liquid streams.

Another preferred embodiment is a gas phase process wherein the temperature is from 150 to 450 ℃, preferably from 200 to 350 ℃ and the pressure is from 0.05 to 20bar, preferably from 0.1 to 4bar, more preferably from 0.1 to 3 bar.

In this process, the pressure varies with temperature so that the components remain in the gas phase without condensing on the catalyst bed.

The molar ratio of the monophenol reactant of formula (I) to the phosgene reactant is from 0.5 to 8: 1, preferably from 1.5 to 3: 1. In this case, the equivalent molar ratio is 2: 1.

In a corresponding manner, the monophenol is reacted with the aryl chloroformate in a molar ratio of 0.25 to 4: 1, preferably 0.8 to 1.5: 1. In this case, the molar ratio is 1: 1.

The crude diaryl carbonates obtained by heterogeneous catalysis according to the invention are generally already very pure and can be used in this form for a large number of applications after degassing to remove residual hydrogen chloride or other volatile substances. For more demanding applications, the diaryl carbonate can optionally be further purified by known methods, such as distillation or crystallization.

The invention further provides a process for preparing diaryl carbonates using the supported catalyst. Suitable heterogeneous catalysts in this case are, in particular, compounds of the formula (III) on support materials which may also be doped

[M(II)_1-x M(III)_x M(IV)_y(OH)₂]A^n- _z/n·m H₂O (III)。

The compounds of the formula (III) may also be mixed with further substances as constituents of the catalyst formulation, in order to possibly produce synergistic effects. Suitable examples for this purpose are silicon dioxide, graphite, titanium dioxide with rutile or anatase structure, zirconium dioxide, aluminum oxide, silicon carbide or mixtures thereof, preferably titanium dioxide, zirconium dioxide, aluminum oxide or mixtures thereof.

The reaction to give the diaryl carbonate can be carried out in a plurality of stages. It can be carried out batchwise, preferably continuously as a fluidized bed or fixed bed process, preferably as a fixed bed process, more preferably in a tube bundle reactor over a heterogeneous catalyst.

A preferred embodiment consists in using a structured catalyst bed in which the catalyst activity increases in the flow direction. Such a structure of the catalyst bed can be achieved by differential impregnation of the catalyst support with active substances or differential dilution of the catalyst with inert substances.

The heat of reaction can be utilized in an advantageous manner by increasing the pressure of the steam.

All references mentioned above are incorporated herein by reference in their entirety for all useful purposes.

While certain specific structures embodying the invention have been shown and described, it will be apparent to those skilled in the art that various modifications and adaptations of the parts may be made without departing from the spirit and scope of the inventive concept set forth below, and these should not be limited to the specific forms set forth and described herein.

Examples

The catalysts used are commercially available products or are prepared by known methods (see catalysis today)11(1991)173、EP-A 421677、EP-A 749941、WO 95/17248、EP-A684872、DE-A2024282)。

Example 1

141g (1.50mol) of phenol were bubbled continuously in a flat-plate flanged drum with baffles, a bubble stirrer and a reflux condenser, using 0.75mol/h phosgene and in the presence of 14.1g (10% by weight based on phenol) of pulverulent hydrotalcite (Mg/Al molar ratio 2: 1) at 140 ℃. After about 2h of reaction time, the conversion of phenol was 29.8% and only diphenyl carbonate (57.6g) was formed. The selectivity to carbonate was > 99.7%.

Example 2

Example 1 was repeated at 140 ℃ with 14.1g of powdered zinc-aluminium hydroxide (Zn/Al molar ratio 2: 1). After a reaction time of 2h, the conversion of phenol was 15.2%, yielding 0.03g of phenyl chloroformate and 23.9g of diphenyl carbonate. The carbonate selectivity was about 90%.

Example 3

Example 1 was repeated at 140 ℃ with 14.1g of pulverulent nickel (II) aluminum hydroxide (Ni/Al molar ratio 2: 1). After a reaction time of 2h, the conversion of phenol was 11.2%, yielding 0.6g of phenyl chloroformate and 17.4g of diphenyl carbonate. The carbonate selectivity was about 99%.

Example 4

Example 1 was repeated at 140 ℃ with 14.1g of pulverulent hydrotalcite from Condea (Mg/Al molar ratio 7: 3). After a reaction time of 2h, the conversion of phenol was 24.4% and 39.0g of diphenyl carbonate were formed. The carbonate selectivity was > 99%.

Example 5

Example 1 was repeated at 140 ℃ with 14.1g of powdered magnesium tin (II) hydroxide (Mg/Sn molar ratio 1.0/0.034). After a reaction time of 2h, the conversion of phenol was 24.6% and 39.2g of diphenyl carbonate were formed. The selectivity to carbonate is greater than 99%.

Example 6

Example 1 was repeated at 140 ℃ with 14.1g of powdered magnesium titanium (IV) hydroxide (Mg/Ti molar ratio 1.0/0.050). After 2h of reaction time, the conversion of phenol was 26.6% and 42.4g of diphenyl carbonate were formed. The carbonate selectivity was > 99%.

Example 7

Example 1 was repeated at 140 ℃ with 14.1g of pulverulent hydrotalcite from Condea (Mg/Al molar ratio 7: 3). After a reaction time of 2h, the conversion of phenol was 24.4% and 39.0g of diphenyl carbonate were formed. The carbonate selectivity was > 99%.

Example 8

Example 1 was repeated at 140 ℃ with 14.1g of powdered nickel (II) magnesium aluminum hydroxide (Ni/Mg/Al molar ratio 0.14/2.34/1.0). After 2h of reaction time, the conversion of phenol was 19.9% and 31.0g of diphenyl carbonate were formed. The carbonate selectivity was about 97%.

Example 9

Example 1 was repeated at 140 ℃ with 1.41g of powdered titanium (IV) magnesium aluminum hydroxide (Ti/Mg/Al molar ratio 0.26/2.63/1.0). After 2h of reaction time, the conversion of phenol was 22.8% and 36.5g of diphenyl carbonate were formed. The selectivity to carbonate was > 99%.

Example 10

In a three-necked flask with thermometer and reflux condenser, a mixture of 9.4g (0.10mol) of phenol and 15.7g (0.10mol) of phenyl chloroformate was heated to 140 ℃ in the presence of 0.94g (10% by weight based on phenol) of pulverulent hydrotalcite (Mg/Al molar ratio 2: 1). After 5h reaction time, 90.7% of the phenol had been converted to diphenyl carbonate.

Example 11

Example 10 was repeated at 140 ℃ with 0.94g of powdered zinc-aluminium hydroxide (molar ratio 2: 1). After 1h of reaction time, the conversion of phenol to diphenyl carbonate was 99.8%. The carbonate selectivity was > 99%.

Example 12

Example 10 was repeated at 140 ℃ with 0.94g of nickel (II) aluminum hydroxide (molar ratio 2: 1). After 3h of reaction time, the conversion of phenol to diphenyl carbonate was 97.5%. The carbonate selectivity was > 99%.

Example 13

Example 10 was repeated at 140 ℃ with 0.94g of powdered magnesium tin hydroxide (molar ratio 1.0/0.034). After a reaction time of 2h, the conversion of phenol to diphenyl carbonate was 49.7%. The selectivity to carbonate was > 99%.

Example 14

Example 10 was repeated at 140 ℃ with 0.94g of powdered magnesium titanium (IV) hydroxide (molar ratio 1.0/0.050). After a reaction time of 2h, the conversion of phenol to diphenyl carbonate was 86.1%. The carbonate selectivity was > 99%.

Example 15

Example 10 was repeated at 140 ℃ with 0.94g of pulverulent hydrotalcite from Condea (Mg/Al molar ratio 7: 3). After a reaction time of 1h, the conversion of phenol to diphenyl carbonate was 98.8%. The selectivity to carbonate was > 99%.

Practice ofExample 16

Example 10 was repeated with 0.94g of powdered titanium (IV) magnesium aluminum hydroxide (molar ratio 0.26/2.63/1.0). After 1h of reaction time, the conversion of phenol to diphenyl carbonate was 98.6%. The selectivity to carbonate was > 99%.

Comparative example 1

Example 1 was repeated at 140 ℃ without adding mixed hydroxide. After 2h reaction time, the phenol conversion was less than 0.2%.

Comparative example 2

Example 1 was repeated at 140 ℃ in the presence of powdered alumina 507-C-I. After 2h reaction time, the phenol conversion was 41% and the carbonate selectivity was > 99.5%.

Comparative example 3

Example 11 was repeated at 140 ℃ in the presence of powdered alumina 507-C-I. After 2h reaction time, the phenol conversion was 90% and the carbonate selectivity was > 99%.

Claims (11)

1. A method for preparing diaryl carbonates, said method comprising reacting a monohydric phenol with phosgene or aryl chloroformate, wherein said reaction is carried out in the presence of a compound of formula (III) as heterogeneous catalyst

[M(II)_1-x M(III)_x M(IV)_y(OH)₂]A^n- _z/n·m H₂O (III)

Wherein

M (II) is a divalent metal cation;

m (III) is a trivalent metal cation;

m (IV) is a tetravalent metal cation;

x is a number from 0.1 to 0.5;

y is a number from 0 to 0.5;

z is 1+ y;

m is an integer of 0 to 32;

a is an anion; and is

n is 1 or 2.

2. The method of claim 1, wherein the anion is selected from the group consisting of CO₃ ^2-、OH^-、SO₄ ^2-、NO₃ ^-、CrO₄ ^2-And Cl^-。

3. The process of claim 1, wherein the reaction is carried out at a temperature of from 50 to 450 ℃ and a pressure of from 0.05 to 20 bar.

4. The process of claim 1, wherein the heterogeneous catalyst has a particle size of 0.1 to 400m as determined by BET method²Per g of surface area and is used in an amount of from 0.5 to 100% by weight, based on the amount of monohydric phenol, in a non-completely continuous manner, or in a space velocity of from 0.1 to 20g monohydric phenol per g of catalyst per hour in a completely continuous manner.

5. The method of claim 1, wherein the divalent metal cation m (ii) is Mg, Ni, or Zn, the trivalent metal cation m (iii) is Al, and the tetravalent metal cation m (iv) is Ti or Zr.

6. The process of claim 1, wherein the diaryl carbonate is prepared continuously.

7. The process of claim 1, wherein the process is carried out at a temperature of from 100 to 350 ℃ and a pressure of from 0.05 to 20 bar.

8. The process of claim 1, wherein the reaction is carried out in the gas phase.

9. The process of claim 1, wherein the reaction is carried out in trickle-phase countercurrent.

10. The process of claim 1, wherein the heterogeneous catalyst consists of a supported active phase of the compound of formula (III).

11. A diaryl carbonate obtained by the process of claim 1.