Process for producing carbonic acid ester

Abstract: Disclosed herein is a process for producing a carbonic acid ester by reacting alcohol, carbon monoxide, and oxygen with one another in the presence of a copper compound alone or together with a platinum metal compound and reaction accelerator, characterized in that the reaction is carried out with a nitrile compound or amide compound.

Description: The present invention relates to a process for producing a carbonic acid ester. A carbonic acid ester is an industrially important compound as an intermediate and solvent for the production of polymers and drugs and agricultural chemicals. A carbonic acid ester is industrially produced by the reaction of alcohol with phosgene. This process, however, has the disadvantage that phosgene is highly toxic and the reaction of alcohol with phosgene produces highly corrosive hydrochloric acid as a by-product. There is a process for producing a carbonic acid ester without using phosgene. According to this method, alcohol, carbon monoxide, and oxygen are reacted with each other in the presence of a copper compound alone or together with a platinum metal compound and a basic compound. (See Japanese Patent Publication Nos. 11129/1970 and 8816/1986 and Japanese Patent Laid-open No. 185542/1983.) This process also has the disadvantage that the catalyst, especially the copper component, is poor in solubility and the formation of the carbonic acid ester is rather slow. It has the additional disadvantage that a large amount of carbon dioxide as a by-product is formed as the result of combustion of carbon monoxide and the decomposition of carbonic acid ester. It is the object of the present invention to provide a process for producing a carbonic acid ester with a minimum of carbon dioxide formed as a by-product and which does not have the disadvantages of poor solubility and low reaction rate. Said object is achieved by a process for producing a carbonic acid ester by reacting an alcohol, carbon monoxide and oxygen in the presence of a copper compound alone or together with a platinum metal compound and a solvent, characterized in that said solvent is a nitrile compound or amide compound. The materials used in the process of the present invention are described in detail in the following. The platinum metal compound includes halides, acetates, and nitrates of ruthenium, rhodium, and palladium. Of these platinum metal compounds, a palladium compound is most desirable. Usually the platinum metal compound is used in an amount of 0.1 to 1000 mmol, preferably 1 to 100 mmol, per 1 liter of alcohol. The copper compound includes cuprous and cupric halides, acetates, and nitrates. Usually these copper compounds are used in an amount of more than 1 mol, preferably more than 3 mol, per 1 mol of the platinum metal compound. The alcohol as a reactant in the process of the invention includes saturated aliphatic alcohols such as methanol and ethanol; unsaturated aliphatic alcohols such as allyl alcohol; aromatic alcohols such as phenol; and diols and polyols. Alcohols having 1 to 20 carbon atoms are preferred. Particularly preferred is methanol. The carbon monoxide and oxygen may be used in pure form or in diluted form. A diluent in the latter case may be argon or carbon dioxide which is inert in the reaction. Air may be used as the oxygen. The reaction is carried out under normal pressure or appropriate pressure. Carbon monoxide and oxygen are introduced into the reaction system such that their partial pressures are 10.1 - 3040 kPa (0.1 - 30 atm) and 5.1 - 1013 kPa (0.05 - 10 atm), respectively. According to the process of the present invention, a nitrile compound or amide compound is used as a solvent. The nitrile compound includes benzonitrile and isobutyronitrile, and the amide compound includes N,N-dimethylformamide and N,N-dimethylacetamide. These solvents may be used individually or in combination. In addition, the solvents should preferably have a boiling point higher than that of water and the carbonic acid ester to be produced. Such solvents make it possible to recycle the catalyst in the form of a liquid or a slurry to the reaction system in the step (such as flash vaporization) of separating the catalyst from the resulting carbonic acid ester and water. The total amount of the solvent in the reaction liquid should be 5-80% by volume, preferably 10-50% by volume. With an amount in excess of 80% by volume, the concentration of the reactant is low so that the reaction rate is slow. With an amount of less than 5% by volume, the reactants are not dissolved completely. The nitrile compound or amide compound used as the solvent increases the efficiency of the copper compound and hence increases the production rate of the carbonic acid ester. The following examples illustrate the invention. Comparative Example 1 In a 500 ml jacketed flask equipped with a stirrer and condenser were placed 221 ml of methanol, 3.76 mmol of palladium bromide, 16.4 mmol of cuprous bromide. 7.51 mmol of potassium bromide, and 22.5 mmol of potassium acetate. The reaction was carried out at 60°C for 2 h while carbon monoxide and oxygen were introduced into the flask under normal pressure at a flow rate of 8.0 l/h and 4.0 l/h, respectively. The analysis by gas chromatography of the liquid product indicated that dimethyl carbonate (DMC) formed at a rate of 285 mmol/l.h (r DMC ). Examples 1 to 4 The same procedure as in Comparative Example 1 was repeated except that a nitrile compound as a solvent was used and the amount of methanol was changed as shown in Table 1. Dimethyl carbonate was formed at a rate (r' DMC ) which is 1.74 times or more greater than (r DMC ) in Comparative Example 1. Example Amount of methanol (ml) Amount of solvent (ml) r' DMC (mmol/l.h) r' DMC /r DMC 1 110.5 benzonitrile 110.5 495 1.74 2 166 benzonitrile 55 495 1.74 3 199 benzonitrile 22 505 1.77 4 110.5 isobutyronitrile 110.5 508 1.78 It is noted from Table 1 that the nitrile solvent greatly increases the rate at which DMC is formed. Examples 5 and 6 The same procedure as in Comparative Example 1 was repeated except that an amide compound as a solvent was used and the amount of methanol was changed as shown in Table 2. Dimethyl carbonate was formed at a rate (r' DMC ) which is 1.46 times or more greater than (r DMC ) in Comparative Example 1. Example Amount of methanol (ml) Amount of solvent (ml) r' DMC (mmol/l.h) r' DMC /r DMC 5 199 dimethylformamide 22 417 1.46 6 199 dimethylacetamide 22 430 1.51 It is noted from Table 2 that the amide solvent greatly increases the rate at which DMC is formed. Comparative Example 2 The same procedure as in Example 6 was repeated except that the solvent was replaced by 22 ml of xylene, which is disclosed in Japanese Patent Publication No. 8816/1986. Dimethyl carbonate was formed at a rate of 348 mmol/l.h. This is 1.22 times higher than that in Comparative Example 1. This result suggests that xylene is less effective than nitrile compounds and amide compounds in increasing the rate at which DMC is formed.

Claims: A process for producing a carbonic acid ester by reacting an alcohol, carbon monoxide and oxygen in the presence of a copper compound alone or together with a platinum metal compound and a solvent, characterized in that said solvent is a nitrile compound or amide compound. The process of claim 1, in which the platinum metal compound is a palladium compound. The process of claim 1, in which the alcohol has 1 to 20 carbon atoms. The process of claim 1, in which the alcohol is methanol.

Inventors: KOJIMA HIDETAKA, KOYAMA HIROSHI, YOKOTA SHIGERU, KOJIMA, HIDETAKA, KOYAMA, HIROSHI, YOKOTA, SHIGERU
Applicants: DAICEL CHEM, DAICEL CHEMICAL INDUSTRIES, LTD.
Application year: 1987
Main classification: C07C68
IPC codes: B01J31, C07C68