HK1048109A - Process for producing carbonic acid diaryl ester - Google Patents

Description

Process for producing diaryl carbonate

Technical Field

The present invention relates to a process for producing diaryl carbonates by reacting monophenols with phosgene in inert solvents in the presence of a base and a nitrogen base in an interfacial process at low reaction temperatures.

Summary of The Invention

An improvement to the interfacial boundary process for the production of diaryl carbonates is disclosed. In the two-step process of reacting phosgene and a monohydric phenol in an inert solvent in the presence of a base and a nitrogen base catalyst, the improvement comprising maintaining a temperature of < 50 ℃ in the first and second steps.

Background

The production of diaryl carbonates by the phase interface process is known in principle from the literature, see chemical and physical properties of polycarbonates by H.Schnell, reviews on polymers (Polymer reviews), volume 9, John Wiley and Sons, Inc. (1964), pages 50/51. U.S. Pat. No. 4016190 describes a process for the production of diaryl carbonates which is carried out at temperatures > 65 ℃ and in which a nitrogen base is used as catalyst.

In carrying out these processes, the aryl dialkyl urethanes are generally formed as by-products either as a result of the reaction of phosgene with the tertiary amine used as a catalyst to form carbamoyl chlorides which are subsequently reacted with the phenol present to form urethane (1), or as a result of the reaction of the aryl chloroformate formed between phenol and phosgene with the tertiary amine (2) according to the following general reaction scheme:wherein R is a group according to formula (I) (see below) and R ', R ", and R'" are typically organic groups.

In particular in the diphenyl carbonate cycle, these compounds interfere with the melt transesterification process of the polycarbonate and are concentrated. It is therefore particularly important to suppress the formation of these aryl dialkyl urethanes and to remove them from the diaryl carbonates.

However, some processes known from the state of the art, based on monohydric phenols and phosgene in a solvent and using a nitrogen base as catalyst, are unsatisfactory in terms of the purity of the product obtained, in particular in terms of the chlorine and urethane content of the product. For this reason, the products obtained by these processes must be subjected to further purification processes.

Detailed Description

It is therefore an object of the present invention, starting from the state of the art, to provide a process for producing diaryl carbonates having a low chlorine content, in particular a low content of by-products, in particular a low content of urethane.

It has now been surprisingly found that when reacting a monohydric phenol and phosgene in an inert solvent by a phase interface process in the presence of a base using a nitrogen-based catalyst to produce diaryl carbonate, low reaction temperatures are required in order to obtain a high purity diaryl carbonate product and to avoid the aforementioned side reactions.

In the process according to the invention, catalysts which can be used are tertiary amines, N-alkylpiperidines, or onium salts. Tributylamine, triethylamine, and N-ethylpiperidine are preferably used. N-ethylpiperidine is most preferred. The catalyst concentration is from 0.0001 mol% to 0.1 mol%, preferably from 0.01 mol% to 0.075 mol%, calculated on the phenol employed.

In the process according to the invention, suitable bases include alkali solutions (hydroxides of Na, K, Li and Ca), preferably sodium hydroxide solutions, preferably in the range from 20 to 55% by weight, particularly preferably in the range from 30 to 50% by weight.

Phosgene may be used in the form of a liquid or gas, or dissolved in an inert solvent.

In the process according to the invention, monohydric phenols which are suitable for use include phenols of the general formula (I):wherein R is hydrogen, tert-butyl, halogen, or branched or unbranched C₈And/or C₉An alkyl group.

Thus, there may be employed phenols themselves, alkylphenols such as cresol, p-tert-butylphenol, p-cumylphenol, p-n-octylphenol, p-isooctylphenol, p-n-nonylphenol and p-isononylphenol, and halogenated phenols such as p-chlorophenol, 2, 4-dichlorophenol, p-bromophenol and 2, 4, 6-tribromophenol. Phenol is preferred.

In the process according to the invention, inert organic solvents such as dichloromethane, toluene, the various dichloroethane and chloropropane compounds, chlorobenzene and chlorotoluene can be employed, dichloromethane being preferably employed.

The reaction can be carried out batchwise (batchwise) or continuously, preferably in plug flow without significant back-mixing. For example, the reaction may be carried out in a tubular reactor. The two phases (aqueous and organic) can be thoroughly mixed by a septum fitting, a static mixer, and/or a pump.

The reaction is initiated by mixing phosgene, inert solvent and phenol, preferably using only inert solvent as solvent for the phosgene and preferably dissolving the phenol in the alkaline solution beforehand. In the process according to the invention, the pH of the first step is generally adjusted, preferably by means of the ratio lye/phenol/phosgene, in such a way that the pH is adjusted to 11.0 to 12.0, preferably 11.2 to 11.8.

The reaction temperature is maintained by cooling at < 50 ℃, preferably < 40 ℃ and most preferably < 35 ℃. In the case of a continuous process according to the invention, the residence time of the first step is from 2 to 300 seconds, preferably from 4 to 200 seconds.

In the second step of the process according to the invention, the reaction is completed to form diaryl carbonate. Preferably, a catalyst is provided at this step. In the process according to the invention, the reaction mixture is cooled immediately after the addition of the catalyst or immediately during the addition of the catalyst. The reaction temperature is maintained by cooling at < 50 ℃, preferably < 40 ℃ and most preferably < 35 ℃. In the second stage of the process, the catalyst is advantageously added in a plurality of portions, preferably in two portions.

In the process according to the invention, the aryl chloroformate content in the diaryl carbonate obtained is < 2ppm, preferably < 0.5 ppm.

With the process according to the invention, the content of arylpiperidylurethane in the diaryl carbonate obtained is < 100ppm, preferably < 75ppm, most preferably < 50 ppm.

In the second step of the process according to the invention, the pH is preferably controlled by measuring the pH, preferably in-line by a continuous process, and by suitably adjusting the pH by adding lye. The amount of lye added is adjusted so that the pH in the second step of the process is adjusted to 7.5-10.5, preferably 8-9.

In the process according to the invention, phosgene is added in a proportion of 1.01 to 1.15 mol%, preferably 1.05 to 1.12 mol%, calculated on the phenol. The solvent is added so that the diphenyl carbonate solution after the reaction has a concentration of 5 to 60% and preferably 20 to 45%.

After the reaction, the organic phase comprising the diaryl carbonate is generally washed with an aqueous liquid and, after each washing process, is separated as far as possible from the aqueous phase. The washing is preferably carried out with deionized water. After washing and separation of the wash liquor, the diaryl carbonate solution is generally opaque. Using aqueous liquids, e.g. HCl or H₃PO₄The catalyst is separated with dilute mineral acid and further purified with completely ion-free water. HCl or H in the wash₃PO₄The concentration of (B) may be, for example, 0.5 to 1.0% by weight. The organic phase is preferably washed twice using the method of the examples.

It is possible to use basically known separation vessels, phase separators, centrifuges or coalescers, and also combinations of these as phase separation means for separating the wash liquid from the organic phase.

The solvent will be evaporated to obtain a high purity diaryl carbonate. The evaporation may be carried out using a multi-stage evaporator. For example by means of one or more successive distillation columns in which the solvent is separated from the diaryl carbonate.

This or these purification stages can be carried out, for example, continuously, in such a way that the temperature of the reservoir during the distillation is > 150 to 310 ℃, preferably > 160 to 230 ℃. The pressure required for carrying out these distillations is from 1 to 1000mbar, preferably from 5 to 100 mbar.

The carbonic acid diesters obtained are distinguished by a very high purity, a GC purity (cooling by the column method) of > 99.99%, preferably 99.9925%, most preferably > 99.995%, and by an extremely good transesterification behavior, so that polycarbonates of good quality can be produced using this.

Methods for the production of aromatic oligo/polycarbonates by the melt transesterification process are known from the literature, for example in Encyclopedia of Polymer Science, Vol.10 (1969); chemical and physical characterization of polycarbonates by Schnell, Polymer review, Vol.9, John Wiley and Sons, Inc. (1964); or as described in us patent 5340905.

Examples

Example 1

In a cooled tubular reactor, a mixture of 117kg/h of completely ion-free water with 48kg/h of 50% NaOH, and 54.9kg/h of phenol was mixed continuously with a solution of 98kg/h of methylene chloride and 31.2kg/h of phosgene (8 mol% excess, calculated as phenol). After an average residence time of 15 seconds, in the second step of the process, 6.5kg/h of 50% NaOH were again added to the reaction mixture, 1.1kg/h (0.9% in dichloromethane) of N-ethylpiperidine catalyst were then added immediately, and the reaction mixture was cooled to 30 ℃. The reaction mixture was then continuously mixed by passing through a tube equipped with a constriction. The organic phase is subsequently separated from the aqueous phase. After washing with 0.6% HCl and water and final phase separation, the dichloromethane was evaporated to give 99.996% (determined by GC method, cooled by column method) of diphenyl carbonate. The content of phenyl piperidyl urethane was 40ppm and the content of phenyl chloroformate was < 0.5 ppm. Comparative example 1

The same as in example 1, except that the reaction temperature was not cooled after the addition of the catalyst, the temperature was 55 ℃. After washing with 0.6% HCl and water and final phase separation, the methylene chloride was evaporated to give 99.97% (determined by GC method, cooled by column method) of diphenyl carbonate. The content of phenyl piperidyl urethane was 300ppm and the content of phenyl chloroformate was < 0.1 ppm.

Example 2

The same as in example 1, except that 0.55kg/h of N-ethylpiperidine (0.9% in dichloromethane) was added after 15 seconds, the reaction solution was immediately cooled to 30 ℃ and 0.55kg/h of N-ethylpiperidine (0.9% in dichloromethane) was added after a residence time of 1 minute, and the reaction mixture was continuously mixed by being transported through a tube equipped with a constriction. The mixture was then cooled to 30 ℃. The organic phase is then separated from the aqueous phase. After washing with 0.6% HCl and water and final phase separation, the dichloromethane was evaporated to give 99.998% (determined by GC method, cooled by column method) of diphenyl carbonate. The content of phenyl piperidyl urethane was 20ppm and the content of phenyl chloroformate was < 0.5 ppm.

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims (8)

1. In an interfacial boundary process for the production of diaryl carbonates from phosgene and monohydric phenol in an inert solvent in the presence of an alkaline solution and a nitrogen base catalyst, the process comprising a first step in which phosgene, inert solvent, and phenol are combined in solution to form a material system having a pH of from 11.0 to 12.0 and a second step in which a diaryl carbonate formation reaction is completed, the improvement comprising maintaining a temperature of < 50 ℃ in said first and second steps.

2. The method of claim 1, wherein the temperature is < 40 ℃.

3. The method of claim 1, wherein the temperature is < 35 ℃.

4. A diaryl carbonate prepared by the process of claim 1.

5. A carbonate according to claim 4 wherein the urethane content is < 100 ppm.

6. A method of using the diaryl carbonate of claim 4, comprising producing a polycarbonate.

7. The process of claim 1 wherein the nitrogen base is ethylpiperidine.

8. A carbonate according to claim 4 wherein the arylurethane content is < 100 ppm.