DE875349C - Process for the production of vinylidenecyanide (1,1-dicyanaethylene) - Google Patents

Description

Process for the production of vinylidenecyanide (1,1-dicyanethylene) The invention relates to a process for the production of vinylidene dicyanide by Pyrolysis of i -: @ cetoxy-i, i-dicyanethane.

According to the present invention, i-acetoxyi, i-dicy anethane is used a temperature of q.oo to; 5o 'pyrolyzed and the vinylidenecyanide from the reaction mixture removed. It is expedient to work under reduced pressure and in the presence of a Catalvsators like chlorides of metals of the 2nd group of the periodic table.

The pyrolysis proceeds essentially as follows This reaction is a valuable and economical process for the production of vinylidenecyanide, since i-acetoxy-i, i-dicyanethane can easily be produced by dimerization of acetyl cyanide, which in turn is made from aetanhydride and sodium cyanide or from ketene and hydrogen cyanide is available.

The temperature at which. the pyrolysis is carried out can go far to be changed. Temperatures from 40o to 750 ° can be used, preferably from 600 to 65o °.

.Increased yields of vinylidenecyanide are achieved if a catalyst is used. Particularly suitable as such are chlorides of the metals of the 2nd Group of the Periodic Table, including Beryllium, Magnesium, Calcium, Zinc, Strontium, cadmium and barium, with zinc chloride being the preferred catalyst. The amount of catalyst is not critical and can be varied considerably will. It can e.g. B. Amounts of catalyst in the ratio i part by weight to 8 parts by weight or even more i-acetoxy-i, i-dieyanethane or i: i can be used.

Pyrolysis can be carried out in several ways. With the preferred one Process are vapors of i-acetoxy-i, i-dicyanethane (F. == 7o °) through a metal pipe, preferably made of brass, which is connected to a collecting vessel that is preferably provided with an external coolant. Instead of a metal pipe A glass tube can also be used or the starting material can be placed over a hot resistance wire be pyrolyzed. The pyrolysis is preferably carried out at reduced pressure, in particular carried out from 2 to 50 mm, although a pressure up to atmospheric pressure or even still a higher one can be applied.

The liquid product in the collecting vessel is a mixture of unreacted i-Acetoxy-i, i-dicyanethane, acetic acid and vinylidenecyanide. The vinylidencyanide is then recovered from the mixture by some sort of separation process. A procedure to separate the vinylidenecyanide consists, for example, of the monomeric vinylidenecyanide, how it is formed, to allow it to polymerize, or to pour the liquid product in water to accelerate the polymerization. The solid, polymeric vinylidenecyanide can easily be separated from the liquids by filtration or decanting will. The polymerized vinylidenecyanide is then depolymerized by pyrolysis, preferably at temperatures from # 170 to 250 ° to form monomeric vinylidenecyanide.

A second useful method is the vinylidenecyanide from the liquid solution by using a solvent, preferably one to extract those from which the vinylidenecyanide crystallizes. this will z. B. carried out in that the liquid product and dry toluene or a similar aromatic hydrocarbon, preferably in equal volumes, mixed and the mixture is cooled to a temperature of -2o ° or below, whereupon monomeric vinylidenecyanide precipitates out of the solution in crystalline form, the separated by filtration. The toluene layer is then decanted off and the liquid floating above is distilled to produce the non-crystallized monomer to win. This process results in high yields of very pure monomers achieved.

In a third method, the liquid product is conjugated with a Diolefin, such as butadiene or cyclopentadiene, is treated with vinylidenecyanide to a solid, substituted cyclohexene converts that of acetic acid and others Impurities can be separated and again at temperatures above 400 ° is pyrolyzed to yield monomeric vinylidenecyanide and diolefin.

A fourth method is the distillation of the liquid product, preferably under reduced pressure.

When using any of the above three methods, it is desirable that the vinylidenecyanide be stabilized against polymerization from the time it is formed. This can be done by using a suitable stabilizer, ie a polymerization inhibitor which can be added to the i-acetoxy-i, i-dicyanethane before the pyrolysis or introduced into the collecting vessel for the liquid pyrolysis product. Such a stabilizer is also added when the vinylidenecyanide is obtained by distillation or by pyrolysis of the polymer or the diolefin adduct. Suitable stabilizers are phosphorus pentoxide, phosphorus pentasulphide, antimony pentoxide, concentrated sulfuric acid and others. The stabilizer is "based on the weight of the monomer generally used in an amount of 0.5 to 3.0 0 /.

The following examples explain the preparation of vinylidenecyanide. The parts given are parts by weight. Example i 8o parts of i-acetoxy-i, i-dicyanethane and ten parts of zinc chloride are heated until evaporated, and the vapors at 5 mm pressure through a brass tube heated to 56o °. 67 parts of the liquid product are in a collecting vessel cooled with acetone dry ice caught. The liquid product is then distilled at a pressure of 5 mm, whereby 18.5 parts (4 °; o yield) vinylidenecyanide in partially polymeric form can be obtained.

If the process is repeated in the absence of the zinc chloride, a yield of vinylidenecyanide will be up to 250i. obtain. Yields of about 20 to 50% are also possible when using other metal chlorides, such as beryllium chloride, which evaporates under the pyrolysis conditions. Example 2 80 parts of i-acetoxy-i, i-dicyanethane and 10 parts of zinc chloride are heated and the vapors are passed through a brass pipe connected to an ice-cooled collecting vessel. The pyrolysis is carried out at a temperature of 675 ° and a pressure of 7 mm; 54 parts of liquid product are obtained, which is then poured into water, whereupon the vinylidenecyanide polymerizes. The solid polymer is separated off by filtration. 15 parts (550 / o) vinylidenecyanide are obtained. The polymer can be converted quantitatively into the monomer by heating to 200 °.

Example 3 40 parts of i-acetoxy, i-dicyanethane and 40 parts of zinc chloride are heated and the vapors are passed through a brass tube that also has a brass chain wrap contains. The tube is connected to an ice-cold collecting vessel. One temperature of 67o ° and a pressure of 9 mm is maintained during the reaction time. 34 parts of liquid product are collected in the collecting vessel. The liquid product is then fractionally distilled at a reflux ratio of i: i, wherein 23 parts of a fraction consisting of impure vinylidenecyanide are obtained. The vinylidenecyanide is collected in monomeric form, but polymerizes on standing quickly to a hard, clear fabric.

By distilling 80 parts, 24 parts of an intermediate fraction are obtained 0 "D - 1.43o) mixed with an equal volume of dry toluene. This mixture is cooled to -25 °, whereby monomeric vinylidenecyanide separates in crystalline form, which is filtered off. The filtrate is made by distillation 15 parts of the non-crystallized vinylidenecyanide obtained. Example 4 io parts i-Acetoxy-i, i-dicyanethane and io parts of zinc chloride are red-hot Nickel wire pyrolyzed at a temperature of 600 ° and a pressure of 10 mm. 6 parts are collected in the collecting vessel, which is cooled with dry ice. That Liquid product is then heated, turning the vinylidenecyanide into a solid is polymerized and separated by filtration. When further heating the solid It depolymerizes polymers at 2oo ° in the presence of phosphorus pentoxide, and it 4 parts of inonomeric vinylidenecyanide with a melting point of 8 "are obtained. Example 5 80 parts of i-acetoxy-i, i-dicyanethane, 20 parts of zinc chloride and 3 parts of phosphorus pentoxide are heated to a temperature of 46o ° and a pressure of 7 mm. It will 28 parts of liquid product are obtained, which is then treated with 20 parts of butadiene for 20 hours lets stand in a sealed tube at room temperature. The content is at Distilled 45o ° in a vessel filled with phosphorus pentoxide, 10 parts being monomeric Vinylidenecyanide (melting point S '; xD = 1.4440) can be obtained. Example 6 8o parts i-Acetoxy-i, i-dicyanethane and 40 parts of zinc chloride are heated and the vapors passed through a glass tube filled with ceramic packing and on a Maintained temperature of 51o "and a pressure of 15 mm. 5o parts liquid Product are received. 28 parts of it are then treated as in example e, and a vinylidenecyanide yield of 40% is achieved.

Example 40 parts of i-acetoxy-i, i-dicyanethane and 50 parts of zinc chloride are heated and the vapors at a temperature of 67o ° and a pressure of 9 mm passed through a brass tube containing a brass chain packing, with 34 parts of liquid product are obtained. This is then poured into water, wherein the vinylidenecyanide polymerizes to a solid. The water solution is then distilled to the acetic acid and unreacted i-acetoxy-i, i-dicyanethane to be separated: 23 parts of polymerized vinylidenecyanide, which contains some impurities included are won.

Vinylidenecyanide made by the process of this invention is used for the production of polymers and mixed polymers, for synthetic rubber, synthetic resins and plastic compounds. Polymeric vinylidenecyanide can also be used and their copolymers with other polymerizable compounds to form synthetic ones Fibers are spun that have great tensile strength, flexibility and chemical resistance to have.

Claims (7)

PATENT CLAIMS: i. Process for the preparation of vinylidenecyanide (i, i-Dicyanäthylen), characterized in that i-acetoxy-i, i-dicyanethane in a temperature of 400 to 750 °, suitably pyrolyzed under reduced pressure and the resulting vinylidenecyanide from the reaction mixture obtained in a suitable manner Way is separated. 2. The method according to claim i, characterized in that pyrolysis in the presence of a catalyst, preferably of chlorides of metals of the 2nd group of the Periodic Table and optionally in the presence of polymerization-preventing Substances. 3. The method according to claim 2, characterized in that that the pyrolysis at a pressure of 2 to 5o mm Hg and at a temperature of 600 to 65o ° is carried out in the presence of zinc chloride. 4. Procedure after a of the preceding claims, characterized in that the reaction mixture with Phosphorus pentoxide is stabilized. 5. The method according to claim i to 4, characterized characterized in that the vinylidenecyanide formed from the condensation of the The liquid reaction mixture obtained from pyrolysis vapors is separated off in that this is preferably distilled under reduced pressure. 6. The method according to claim i to 4, characterized in that the separation of the reaction product takes place in that it is polymerized by mixing with water, the solid polymer is separated and depolymerized by heating to 170 to #; "5o °. 7th The method according to claim i to 4, characterized in that the liquid reaction mixture extracted with suitable solvents and the vinylidenecyanide from the extract is deposited by freezing or evaporation of the solvent. B. Procedure according to claims i to q., characterized in that the reaction product is used for purification by condensation with diolefins with conjugated double bonds into solid cyclohexene derivatives transferred, this separated and then by pyrolysis at temperatures above 40o ° converted back into vinylidenecyanide.