DE880135C - Process for the production of malonitriles - Google Patents

Description

The invention relates to the production of malonitriles.

The inventive method for preparing the malonitrile is that an aliphatic Nitrile is heated with cyanogen halide to a temperature of at least 6oo °.

The reaction is conducted at a temperature in the range of 6oo to 700 ^0, preferably 650 to 700 carried out ^{the 0th} It is also possible to use higher temperatures, but the yields are reduced. In most cases, optimal yields are obtained at an average temperature of about 675 °. When carrying out the process according to the invention, the reaction components are passed in the vapor phase through a hot reaction tube, specifically at a rate which is sufficiently low to permit a reaction. However, the rate must not be so slow that the reactants have an opportunity to decompose. It has been found that generally a residence time of at least ^{1 to} ₂ seconds at the reaction temperature is necessary, and a residence time of 5 to 15 seconds is preferred.

The ratio of the reactants is not critical and it just becomes something less reaction product is formed even if the molar ratio varies widely. Since the cyanogen halide however, it is generally more expensive than the aliphatic nitrile, so it is from an economic standpoint preferable to use the cyanogen halide in a stoichiometric deficit. The reaction is

preferably carried out at atmospheric pressure; if desired, superatmospheric pressure can also be used Pressures are used.

The following example, in which acetonitrile and cyanogen chloride as reaction components for the production of malonitrile are used to explain the invention in more detail.

example

CH ₃ CN + ClCN

HCl

I ₃ ^ m -η- v ^ i ^ rx> - CH ₂ (CN) ₂

Acetonitrile vapor (3.14 moles) and cyanogen chloride vapor (1.36 moles) were passed through a refractory glass tube which was heated in an electric furnace. The reaction tube was maintained at an average temperature of 658 ⁰ and the contact time was six seconds. Acetonitrile and malonitrile were condensed out of the resulting vapor mixture in a container which was kept at a temperature of 75 ^{0, while}

ao the by-product hydrogen chloride and unconverted cyanogen chloride remained in the vapor phase. The latter gases were withdrawn from the top of the container through an alkaline receiver which was in contact with the atmosphere. In this reaction, 0.46 mol of hydrogen chloride were absorbed as a by-product in the alkaline receiver. The crude malonitrile together with unreacted acetonitrile was passed into a fractionation column, where the acetonitrile was separated off and recovered for reuse. The crude malonitrile was withdrawn from the bottom of the column for refractionation. In this operation, 2.54 mol of unreacted acetonitrile and recovered slightly less than 0.25 mole of malononitrile were, which is less than 18 ° / ₀ corresponds to a conversion of cyanogen chloride inserted into the nitrile of something.

Any reaction tube that is resistant to the relatively high reaction temperatures, is suitable for the implementation, i.a. Nickel, quartz, the alloy known as Inconel etc. At lower temperatures (such as below °), refractory glass can be used will. Instead of a hot container to hold the hydrogen chloride and cyanogen chloride To use in the vapor phase, all gaseous products can if desired be condensed and then distilled to obtain the nitrile. If desired, the reaction liquid can also be washed with alkali to be dissolved To remove hydrogen chloride and dissolved cyanogen chloride, and can then be fractionated to obtain the to separate unreacted acetonitrile and the malonitrile from one another.

Cyanogen bromide can just as well be used in place of cyanogen chloride.

Claims (4)

Patent claims: 1. A process for the preparation of malonitriles, characterized in that an aliphatic Nitrile with cyanogen halide, e.g. B. chlorine or cyanogen bromide, to a temperature of at least 600 ° is heated. 2. The method according to claim 1, characterized in that that the reaction is carried out at a temperature in the range from 650 to 700 °. 3. The method according to claim 1 or 2, characterized in that the reaction components are passed in the vapor phase through a heated reaction zone such that the residence time in the same at the reaction ^{temperature is at least 1} J ₉ seconds and preferably 5 to 15 seconds. 4. The method according to any one of the preceding claims, characterized in that the Cyanogen halide is used in a stoichiometric deficit. © 5204 6.