MXPA01007428A - Method of producing dimethyl sulfite - Google Patents

Abstract

The invention relates to a method of producing dimethyl sulfite by reacting a cyclic alkylene sulfite having at least 2 carbon atoms with methanol, optionally in the presence of a catalyst. The inventive method is carried out in a continuous manner in a column.

Description

"METHOD OF PRODUCING SULPHITE FROM DIMETILQ" The present invention relates to a process for the preparation of dimethyl sulfite of a dialkyl sulphite higher or a cyclic alkylene sulphite and methanol. A conventional process for the preparation of dialkyl sulphites, in particular of dimethyl sulphite, is the reaction of thionyl chloride with an alcohol, in the case of dimethyl sulfite, with methanol. The preparation of dimethyl sulfite by a reaction is described, for example, in W. Voss et al., Justus Liebigs Ann. Chem. 485 (1931), 258-283. However, the reaction with thionyl chloride has the disadvantage that large amounts of hydrogen chloride are formed in the reaction, which means that the materials used have to meet specific requirements with respect to to corrosion. If the hydrogen chloride is not removed sufficiently quickly from the reaction mixture, it undergoes a secondary reaction with the dialkyl sulphite formed to provide alkyl chloride, alcohol and sulfur dioxide. It is also known that dialkyl sulphites and cyclic alkylene sulfites can undergo, with the alcohols, transesterification reactions in which transesterified alkyl sulfites corresponding to the alcohols used are formed. This transesterification reaction is an equilibrium reaction. It is catalyzed by acids and bases but is carried out at elevated temperatures even without a catalyst. R. Riemschneider et al., Z. Naturforschung 15 b (1960), 552-554, describe the preparation of a cyclic sulfite, of 2-buten-l, 4-diol, by reacting the dimethyl sulfite with the corresponding diol. To displace the equilibrium of the reaction towards the desired product, the methanol formed is continuously removed by distillation. H. F. van Oerden, Chem. Rev. 93 (1963), 557-571, describes the transesferification of dimethyl sulfite with ethylene glycol to provide ethylene sulfite and methanol without a catalyst. To obtain the ethylene sulfite in good yields, the methanol formed is continuously stirred to displace the resulting equilibrium towards the product. This procedure is possible only when the formation of the alcohol has a lower boiling temperature than the alcohol used. In the preparation of the dimethyl sulfite by reacting the cyclic alkylene sulfites, the alcohol used is methanol. The formation of alcohol therefore always has a higher boiling temperature than the methanol used. In the case of equilibrium displacement by means of distillation, as described in the literature, the methanol will first be removed and in this way the reverse reaction will be activated towards the starting materials, instead of the equilibrium shift towards the product. An object of the present invention is to provide a process for the preparation of dimethyl sulfite - starting from sulphite to cyclic alkyl - wherein dimethyl sulfite can be obtained in good yields and in high purity. We have found that this object is achieved by a process for the preparation of dimethyl sulfite by transesterification of a cyclic alkylene sulfite of at least 2 carbon atoms with methanol, in the presence or absence of a catalyst. The novel process is carried out continuously in a column. The novel process has the advantage that the hydrogen chloride which can attack the materials used and can react with the formed product is not formed, in contrast to the chloride reaction of thionyl with alcohols. The resulting alcohol can also be used for different applications.

The novel process of preference can be carried out by the countercurrent method, methanol being added at the bottom of the column and flowing countercurrent to the cyclic alkylene sulfite added at the top of the column. Higher alcohol released and corresponding in the transesterification to the used cyclic alkylene sulfite, it is continuously extracted through the bottom of the column, and the resulting dimethyl sulphite is continuously extracted, together with the unconverted methanol, through the top of the column. The cyclic alkylene sulfite is referred to below as the starting sulfite. The alcohols released are diols. The column in which the transesterification is carried out can be either a column of the tray or a packed column. Preferably, the column is a tray column, for example a bubble tray column. The starting sulphite is usually supplied in a regulated manner as a liquid at the top of the column. The novel process preferably is carried out in the presence of a catalyst in order to accelerate the trans-spherification. This catalyst is particularly soluble preferably in the starting sulfite used. Consequently, the catalyst can be added to the starting sulfite used and introduced together with sulfite into the column. A particularly preferred catalyst is methanesulfonic acid. With a sufficient residence time in the trays of the column, a catalyst can be dispensed with. For simple regulated delivery, the catalyst dissolves in the starting sulfite. The methanol used for transesterification is usually supplied in a regulated manner as a vapor in the lower part of the column. The starting sulfite and methanol are usually added to the column in a 1 to 1 molar ratio. minus 2. Methanol is preferably used in a stoichiometric excess of 5-20: 1, particularly preferably 10: 1. The unconverted methanol is then preferably recycled to the process. Essentially, the diol released from the corresponding starting sulfite after transesterification is present at the bottom of the column. In addition, the bottom product may contain small amounts of diol condensates, and any catalyst used.

The dimethyl sulphite (reaction product) is obtained in the upper part of the column together with the unconverted methanol, generally in gaseous form. The dimethyl sulphite obtained is preferably separated in a second column from the methanol obtained simultaneously. The product stream, which contains the dimethyl sulfite and the methanole, is transferred in liquid form or preferably in a gaseous form to the second column. The second column can be a tray column or a packed column. The second column is generally operated at a pressure higher than 100 mbar at 5 bar, preferably at 500 to 1000 mbar, particularly preferably at 800 mbar. The bottom temperature in the second column at 800 mbar is 100 to 110 ° C, and the reflux ratio is adjusted so that the upper temperature is 55 ° C to 60 ° C. The methanol is obtained in the upper part of the second column and is preferably recycled to the first column. The methanol is preferably recycled in vapor form in order to save energy. The first and second columns of preference are connected to each other through power lines.

In a particularly preferred embodiment, the novel process is carried out in a column system (see Figure 1), comprising: a first column (Kl) in which the novel transesterification is carried out, and a second column ( K2) in which the mixture of dimethyl sulfite and methanol, obtained in the upper part of the first column, is separated, wherein the first column has a feed for the starting sulfite and, if required, the catalyst (1). ), which leads to the top of the column, a feed for methanol (2), which leads to the bottom of the column, and an outlet for the diol, the catalyst and any of the condensed products of the diol (3). ) which are obtained at the bottom, and a connection is present from the top of the first column to the middle part of the second column, through which the mixture of dimethyl sulphite and methanol is fed to the second column. column, in d The second column has an outlet for the dimethyl sulphite (product) (4) obtained at the bottom, and a connection from the top of the second column to the bottom of the first column, through which the excess of methanol obtained in the upper part of the second column can be recycled to the first column. The regulated supply of the fresh methanol to the first column is preferably controlled by means of the temperature profile in the lower region of the second column. If the temperature in the lower region of the second column increases too much, this means that there is insufficient methanol in the column system and the amount of methanol must be adjusted accordingly. The cyclic alkylene sulphide used is preferably 2 to 6, particularly preferably 2 to 4, carbon atoms. Ethylene sulfite and propylene sulfite are used particularly preferably. Although other cyclic alkylene sulfites that can be used as the starting sulfite are able to obtain essentially by reacting the thionyl chloride and the corresponding alcohol, with the disadvantages mentioned at the beginning, the alkylene sulfites of the formula I.

O II they can be prepared, inter alia, starting from the corresponding epoxides II. and sulfur dioxide by processes known from the literature. In formulas I and II, R ^, R ^, R3 and R4 independently of each other, are each hydrogen, aryl or alkyl, preferably hydrogen or methyl. Ethylene sulfite and propylene sulfite are used particularly preferably. The diol formed in the novel reaction of alkylene sulfite and methanol can be used for other purposes after purification. For example, the ethylene glycol formed in the reaction of ethylene sulfite and methanol is widely used in the industira, for example as a component for the cooling of liquids, a heat transfer medium, a hydraulic fluid or a solvent or as a starting material for additional syntheses. In the attached drawing, Figure 1 shows a diagram of the process to carry out the novel process. In it: Kl: is a column to carry out the transesterification K2: it is a column to separate the methanol from a methanol / dimethyl sulfite 1: represents the starting sulphite (= higher dialkyl sulphite or alkylene sulfite) cyclic) and the catalyst, which can be dissolved in methanol 2: represents 3-methanol: represents the resulting alcohol (upper) or the diol 4: represents dimethyl sulfite The example given below further illustrates the invention.

Example A stream of 100 grams per hour of ethylene sulfite and 0.44 gram per hour of methanesulfonic acid was fed into the 40th tray of a bubbler tray column (60 trays, diameter 43 millimeters) (stream 1). A stream of 400 grams per hour of methanol vapor was supplied in a regulated manner to the bottom of the column under temperature control. Most of the methanol was recycled from the second column and supplemented with fresh or new methanol (60 grams per hour) under temperature control (stream 2). The bottom product of the column was heated to 192 ° C and pumped out with level control (stream 3). It comprised predominantly ethylene glycol in addition to a small amount of oligoethylene glycol and the catalyst. The vapors in the column were cooled to 75 ° C by means of a reflux condenser and fed to a second column (packed column, diameter of 43 millimeters, packaging of laboratory cloth 2 m, surface area of 1000 square centimeters / cubic centimeters). This was operated at a pressure higher than 800 mbar. The bottom product of the second column was heated to 105 ° C. It contained the dimethyl sulphite and was discharged with level control (stream 4). The reflux ratio was adjusted so that the temperature at the top of the column was 58 ° C.

Claims (8)

CLAIMS:

1. A process for the preparation of dimethyl sulfite by transesterification of a cyclic alkylene sulfite of at least 2 carbon atoms with methanol, in the presence or absence of a catalyst, wherein the process is carried out continuously in a column by means of the countercurrent method, wherein the methanol is added at the bottom of the column and flows countercurrent to the cyclic alkyl sulfite added at the top of the column.

2. A process according to claim 1, wherein a catalyst soluble in the cyclic alkylene sulfite is used.

3. A process according to claim 2, wherein the catalyst used is methanesulfonic acid.

4. A process according to any of claims 1 to 3, wherein the cyclic alkylene sulfite and methanol are added to the column in a ratio of 1 to at least 2.

5. A process in accordance with any of claims 1 to 4, wherein the dimethyl sulfite is separated in a second column from the unconverted methanol extracted together with the dimethyl sulfite thh the top of the column.

6. A process according to claim 5, wherein the first and second columns are connected to each other thh power lines.

7. A process according to any of claims 1 to 6, wherein the cyclic alkylene sulfite has from 2 to 6 carbon atoms.

8. A process according to claim 7, wherein the cyclic alkylene sulfite used is ethylene sulfite or propylene sulfite.