CH493475A - Process for purifying malononitrile - Google Patents

Description

  

  
 



  Process for purifying malononitrile The invention relates to a process for purifying malononitrile by removing from the reaction mixture the fumaric acid and maleic acid dinitrile obtained in the production of malononitrile from acetonitrile and cyanogen chloride.



   It is known that malononitrile can be prepared by reacting acetonitrile and cyanogen chloride at elevated temperatures, optionally in the presence of gaseous chlorine as a catalyst. In this reaction, large amounts of fumaric and maleic acid dinitrile are produced as by-products. The removal of these by-products from the reaction mixture is associated with considerable difficulties due to the similarity of the physical constants.



   The invention is based on the object of separating the fumaric acid and maleic acid dinitrile from malonic acid dinitrile in a simple manner.



   According to the invention, this is achieved by converting the maleic acid and fumaric acid dinitrile present in the reaction mixture into the corresponding Diels-Alder addition compounds by a Diels-Alder reaction and separating the latter from the malonic acid dinitrile.



   Compounds with conjugated double bonds can be used as reaction components for the Diels-Alder reaction. Such are, for example, butadiene, isoprene, dimethylbutadiene, piperylenes, anthracene, perylene, furan, sorbic acid. Butadiene and anthracene are preferably used.



   Depending on the Diels-Alder reaction components, addition compounds are formed which, at temperatures above the melting point of malononitrile, represent solid or liquid products. Are solid addition products produced, such as If anthracene or perylene is used, the Diels-Alder addition compounds can be separated off by simple filtration or centrifugation at temperatures above the melting point of the malononitrile, advantageously at temperatures of 35-40 ° C.



   If there are liquid addition products, e.g. If butadiene is used, the separation can be carried out by simply distilling off the malononitrile in vacuo.



   The Diels-Alder reaction is carried out in a reaction mixture obtained in the reaction of acetonitrile and cyanogen chloride and optionally subsequently enriched in malonitrile. Preferred reaction temperatures are from 40 to 1500 ° C., the reaction being carried out in an autoclave under certain circumstances. However, it is advantageous to first remove unreacted starting product by distillation and then to subject the reaction mixture to a vacuum distillation at 5 to 30 mm Hg before the Diels-Alder reaction in order to remove other impurities present in small amounts, such as e.g. p-chloropropionitrile.



   The process of the invention can be carried out either batchwise or continuously.



  In the latter case, it is advisable to carry out the reaction in a tubular reactor with an appropriate residence time.



   Examples
1. 100 g of a reaction mixture consisting of 97 g of malonic acid dinitrile, 2 g of maleic acid dinitrile and 1 g of fumaric acid dinitrile were mixed with 7 g of anthracene while stirring in a reaction vessel and kept at 1400 ° C. for two hours. It was then cooled to 350 ° C. and the Diels-Alder addition compound was filtered off at this temperature.

 

  The filtrate was distilled again at 12 mm Hg.



  92 g of malononitrile resulted in a purity of over 99%. The yield was 95%.



   2. Starting material (acetonitrile) still present was removed from a reaction mixture obtained through the conversion of acetonitrile and cyanogen chloride by distillation, then by-products (e.g. 8-chloropropionitrile) still present were removed in vacuo (13 mm Hg). 80 g of this reaction mixture, which now contained 96% malononitrile, were mixed with 4 g of butadiene in an autoclave and heated at 100-110 ° C. for 10 hours. It was then distilled (13 mm Hg). In this way 74.7 g of pure malononitrile (99.8%) were obtained, corresponding to a yield of 97%.

 

Claims (1)

PATENT CLAIM Process for purifying malononitrile by removing the maleic acid and fumaric acid dinitrile obtained in the production of malonic acid dinitrile from acetonitrile and cyanogen chloride, characterized in that the maleic acid and fumaric acid dinitrile is converted into the corresponding Diels-Alder addition compounds by a Diels-Alder reaction and the latter separated from the malononitrile. SUBCLAIMS 1. The method according to claim, characterized in that the Diels-Alder reaction is carried out with the aid of anthracene as a reaction component. 2. The method according to claim, characterized in that the Diels-Alder reaction is carried out with the aid of butadiene as a reaction component. 3. The method according to claim and dependent claim 1, characterized in that the resulting Diels-Alder addition product is separated off by filtration or centrifugation at temperatures above the melting point of the malonitrile. 4. The method according to claim and the dependent claims 1 and 2, characterized in that the malonitrile is separated from the Diels Alder adduct by distillation in vacuo.