Patented July 11, 1950 ‘i 7 2,514,387 ES PATENT 1' 2,514,387 - ~ . a __ .. PREPARATION-0F LI-DICYANO ETHYLENE ;:BY ‘THE PYROLYSIS OF 1,1,3,3-TETRA CYANO PROPANE “ Harry Gilbert, Cuyahoga Falls, Ohio, asslgnor to vThe B. F. Goodrich Company, New York, N.,Y., . - . _ _v a corporation of New York ~ - 7 ‘No Drawing. Application March 4. 1949, ., ’ _ Serial No. 79,712 a _ Y ' j ‘p - (01. 260-4658) 11 Claims. This invention relates to a method for the preparation of 1,1-dicyano ethylene. which meth therefore desirable that reduced pressures "or higher temperatures, preferably both, be “em ployed, whereupon the thermal decomposition of the 1,1,3,3 -tetraoyano‘propane proceeds quite od involves the thermal decomposition of 1,13,3 tetracyano propane. In copending applications of 'Alan E. Ardis, rapidly. In this connection it has beenpfound that pressures‘ of approximately 2;to,;50 mm. of mercury are preferably used while temperatures of from 150° C. to;250° C. are especially preferred. Serial Nos. 785,520,'?led November 7, 1947 now Patent Number 2,476,270, and 63,434, ?led Decem ber 3, ‘1948 now ,Patent Number 2,502,412, two ,novel'methods'i'or the preparation of ,1,1-dicyano 'jethylene'j‘are disclosed. Tha?rst. method in _:'volves, the pyrolysis of l-acetoxy-Ll-dicyano The thermal decomposition reaction maybe carried out in any one of a number-of di?ferent manners. For. examplerone preferred-method ethane to give 1,1-‘dicyano, ethylene and acetic consists simply in heating the 1,1,3,3-tetracy_ano acid, and the second method involves the pyrolysis _', of compoundsof the general formula propane, a white solid, in a distillation apparatus whereupon vapors of 1,1-‘dicyano ethylene) are formed, and collecting and condensing itheji/re suiting vapors in a suitable receiver, preferably provided with external cooling means. _ Alterna Qwh'ereinX and "Y are selected from the class con-, sisting of ,-_—'CN and‘—CONHz groups to give 1,1 dicyanoethylene' and butadiene. _‘ ' ' ' I have now discovered that 1,1-dicyano'ethyl ‘tively, however, the reaction may be, carried out by passing the 1,l,3,3-'tetracyano propane through 20 a heated metal or glass pyrolysis tube and con densing the eiiluent vapors or by other methods - of thermal decomposition. When the thermal de composition is accomplished in the above manner the product which collects in thereceiver is a mix 1,1,3,3-,~._ .25 ture of 1,1-dicyano ethylene, malononitrile, and in ene may also be readily prepared in excellent ,yields by the thermal decompositionof tetracyan'o propane. In addition to l,l-dicyan_o ethylene, some malononitrile is alsov formed, the '_ pyrolysis’ ‘reaction proceeding substantially as fol lows: _. ' some instances; small quantities of 1,1,3,3-tetr-a cyano propane. The l,l-dicyano ethylene is then separated from the mixture ‘by utilizing any. of several methods of separation. For example; one . p30 method of separating the 1,1,-dicyano' ethylene consists in utilizing the tendencyof monomeric I,1-dicyano ethyleneto polymerize on standing or on heating, and allowing “it to polymerize,.;or -' even adding'water to hasten the'polymerization. i reactionprovides a valuable‘ and economi-ii 35 An alcohol such as ethyl, propyl or butylalcohol. or the like, is then added to the mixture to dis solve the malononitrile and any 1,1,3B-tetra cal method for the preparation of 1,1-dicyano ethylene since the starting material, 1,l,3,3-tetra ’ cyano propane which might be present and'the cyano propane, is easily prepared by the reaction of malon'onitrile and .formaldehyde in aqueous ~solution. ' ' ' ‘ " ‘ ‘ ' ' The precise ‘conditions under which the'thermal I.‘ decomposition, reaction is carried out are‘not strictly critical provided, of course, that the heat insoluble polymer is removed by ?ltering.’ vThe . polymerized 1,1-dicyano ethylene ' can then be depolymerizedi by pyrolysis, preferably at term ' peratures of 170° C. to 250° C., to obtain very pure monomeric‘ 1,1-dicyano ethy1en'e,- a process dis‘ closed ‘in a cope'nding application, Serial -_No. : ing'of the‘1,1,3,3-tetracyano propane be su‘?icient " > '- 1 - 5 ‘to cause ‘the'evolution of vapors.‘ The tetra 45 79.713, ?led Mar. 4, 1949. "A second and the preferred method consists icyanoi propane is‘! itself thermally unstable and simply in fractionating the mixture from there does not exist in the gaseous formii Vapors con ceiver in an efficient column, and ‘preferably at taining the desired 1,1edicyano iethylene are evolved when l,l,3,3‘-tetracyano propane is heated “reduced pressures. "l,l-'-dicyano ‘ethylene 'distills at 47° C. at 2 mm. and malononitrile 'atf90°'C2.at under atmospheric pressure, towa temperature just above its melting point, thatis, just above 2mm‘. A third . useful . i method of separation > involves I 137° C., and accordingly these conditions are op treating the reaction mixture with a conjugated erative. However,- the reaction proceeds very slowly at atmospheric pressures when tempera .d-iole?n such as '"butadiener' or :cyclopentadiene tures belowabout 150° C-uare utilized and it is 55 which‘ reacts- with the > 1,1-dicyano - ethylene, to 2,514,887 3 temperature of 150° C. 44.7 parts (93%) or sub stantially pure monomeric 1,1-dicyano ethylene form a solid substituted cyclohexane which can be separated from the malononitrile and impuri ties and pyrolyzed again at temperatures in ex cess of 400° C. to give monomeric 1,1-dicyano (M. P. 8° C.) are obtained. Example III 60 parts of 1,1,3,3-tetracyano propane are ethylene and the conjugated diolefln. When using either of the latter two methods, it is desirable that the 1,1-dicyano ethylene be stabilized against polymerization from the time that it is formed. This may beaccomplished pyrolyzed at a pressure of 2 mm. and a tempera ture of 180° C. through a plug of phosphorus pentoxide into a receiver maintained at a tem by using a suitable LI-dicyanqethylene stabilizer * X perature of 770" C. until all the material is pyrolyzed. The mixture in the receiver is then fractionated ‘into a ?ask containing phosphorus (that is, a polymerization inhibitor) which‘ may be mixed with the l,l,3,3-tetracyano propane prior to pyrolysis or placed in the receiver for the pyrolysis product. Such a stabilizer is also pentoxide whereupon 20 parts of monomeric 1,1 dicyano ethylene (M. P. 8° C.) are obtained. vii'mample IV preferably present in the receiver used to col- - Li lect the 1,1-dicyano ethylene when it is separated by distillation and when it is" desired to obtain, the monomer by pyrolysis of the polymer or the conjugated diole?n product. suitablestabilizers include phosphorus pentoxide and phosphorus .12 ‘parts of 1,l,3,3-tetracyano propane are ' heated at a temperature of 180° C. and a pressure - of 2 mm. in a distillation ?ask and the vapors conducted into a receiver maintained at -70° C. 1.9 parts of monomeric LL-dicyano ethylene and vpentasul?de, which are preferred, as well as cer 7.7 parts of polymeric 1,1-dicyano ethylene are obtained. 1 part of malononitrile is also ob tained. The polymer thus obtained is converted to substantially pure monomer by depolymeriza tion at temperatures of 170° -C. to 250° C. Example V 10 parts of 1,1,,3,3-tetracyano propane are tain phenolic materials such as vpicric acid, trini trobenzene and pyrogallol,' or the stabilization may be accomplished simply by passing a cur rent of sulfur dioxide through the pyrolysis sys tem, the oxides of sulfur in general being excellent stabilizers for the monomer. The stabilizer may be present in any desired amount but in gen eral as little as 0.5 to 3% based on, the amount heated at a temperature of 200° C. and a pressure of monomer is suiiicient to prevent polymeriza 30 of 50 mm. in, a distillation ?ask connected to a tion for extended periods of time. > i receiver containing para-isopropyl toluene (para— In addition to the methods disclosed herein above, still another useful method for collecting cymene). The vapors formed are introduced into the receiver below the surface of the para and separating the 1,1-dicyano ethylene exists. iscpropyl toluene. The monomeric 1,1-dicyano This method comprises directing the pyrolysis 35 ethylene and the maloncnitrile formed are solu vapors ‘into a receiver containing a liquid hydro ble in the para-isopropyl toluene while the small carbon such as toluene, isopropyl toluene (p amount of 1,1,3,3-tetracyano propane which is cymene) and the like. 1,1-dicyano ethylene and formed by the reversibility of the thermal decom malononitrile are soluble in such hydrocarbons while any 1,1,3,3-tetracyano propane present is 40 position reaction is insoluble and is removed by ?ltering. The ?ltrate is fractionated and 2 parts insoluble and can ‘be removed simply by ?ltering. of monomeric 1,1_-dicyano ethylene .(M. P. 'Z°—8° Upon fractionation of the ?ltrate, ‘monomeric C.) are obtained. 17,1-dicyano ethylene is obtained in a very pure Example VI form. Alternatively, the 1,1-dicyano ethylene can be recovered from the liquid mixture by cool ing; to a temperature below about »i~.20° C. where (5 upon the monomer crystallizes and can be re moved by ?ltering. ' ' 10 parts of l,1',3,_3-tetracy_.ano, propane are heated to a temperature of 170° C. and at a, pres sure of 2 mm. in a distillation ?ask connected to a receiver. A current of sulfur dioxide is con ‘ The following speci?c examples are. intended tinuously passed through the entire apparatus to illustrate the preparation of 1,1-dicyano 50 to inhibit the polymerization of the 1,1-dicyano ethylene ‘by, the method of this invention, .but ethylene. The contents of the receiver are frac are not intended to be construed as limiting the tionated in a 12 inch column packed with glass scope thereof, for there are, of course, numerous helices and 4 parts of substantially pure mono possible variations and modi?cations. In the meric 1,1-dicyano ethylene (M. P. 6°-8° C.) are examples all parts are by weight. obtained. 3% parts of malononitrile are also obtained. Example I Example ‘VII 190 parts (1.32 moles) of l,l,3,3-tetracyano propane are placed in a distilling ?ask which is connected to a receiver. The receiver is cooled to -5' C. and is lined with phosphorus pentoxide 10 parts of 1,1,3,3!tetracyano propane main tained in a pyrolysis ?ask are heated to a tem perature of 200° C. at 1 mm. pressure and the re sulting vapors condensed in a receiver cooled to ‘to inhibit the polymerization. of the 1,1-dicyano ethylene. The LLSB-tetracyano propane is then 0° C. ‘Polymeric Ll-dioyano ethylene is, recov ered from the mixture the receiver by adding ethyl alcohol to the mixture and filtering off the heated to a temperature of 180° C‘. and at a pres sure of 2 mm. until all the starting material is thermally decomposed. ‘The contents of the re ceiver are then fractionated’ through a 12 inch insoluble polymer. The polymer thus obtained gives the following analysis: column packed with glass helices. 82.5 parts 680%) of monomeric Ll-dicyano ethylene (Np2o 1.442, M; P. 8° C., B. P. 47° (1/2 mm.) are ob tained. '70 parts of malononitrile are also, ob tained. -' Example If 70 ‘ - Calculated Found C, 51.55% H, 2.58% C, 60.03% H, 2.99%.‘ N.e,5.e0%, N, 36.58% 7 '90' parts (.65 mole) of 1,1,3,3-tetracyano pro pane are pyrolyzed as in Example I, utilizing a 75 When the above examples are repeated utiliz 2,514,887 5 ing atmospheric pressures and/or temperatures monomeric 1,1-dicyano ethylene from the result in excess of 250° C., 1,1-dicyano ethylene is again obtained in good yield although the yields are ing condensate. not as high as those obtained when the preferred tetracyano propane at a temperature in excess of 150° C., at a reduced pressure, andin the pres— ‘ 7. The method which comprises heating 1,13,3 conditions are utilized. 1,1-dicyano ethylene prepared by the method ence of phosphorus pentoxide whereupon vapors are evolved, condensing the e?iuent vapors, and of this invention is very valuable for the prepara tion of polymers and copolymers suitable as syn separating monomeric 1,1-dicyano ethylene from thetic rubbers, synthetic resins and plastics. the resulting condensate. Furthermore, the polymers of 1,1-dicyano ethyl-l 10 8. The method which comprises heating 1,l,3,3 ene are extremely useful in the preparation of spinning solutions from which can be spun ?bers and ?laments possessing many valuable proper tetracyano propane at a temperature in excess of 150° C., at a pressure below 100 mm., and in ties including great tensile strength and resist vapors are evolved, condensing the effluent vapors, the presence of phosphorus pentoxide whereupon ance to abrasion and chemical action. 15 and separating monomeric 1,1-dicyano ethylene This application is a continuation-in-part of from the resulting condensate. and a replacement for my application, Serial No. 9. The method which comprises heating 1,1,33 775,149, ?led September 19, 1947, now abandoned. tetracyano propane at a temperature in excess of Numerous variations and modifications in the 150° 0., at a reduced pressure whereupon vapors above procedure will be apparent to those skilled 20 are evolved, collecting said vapors in a receiver‘ in the art and are included within the scope of containing para-isopropyltoluene, and separat the invention as de?ned in the appended claims. ing 1,1-dicyano ethylene from the resulting mix I claim: ' ture. 1. The method which comprises heating 1,1,33 ‘ 10. The method which comprises heating 1,1,3,3-tetracyano propane at a temperature in tetracyano propane at a temperature and pres sure such that vapors are evolved, condensing the excess of 150° 0., at a reduced pressure, and in the presence of sulfur dioxide whereupon vapors are evolved, condensing the eiiluent vapors‘, and eilluent vapors, and separating 1,1-dicyano ethyl~ ene from ,the resulting condensate. 2. The method which comprises heating 1,1,13,3 separating monomeric 1,1-dicyano ethylene from tetracyan’o propane at a temperature in excess of 30 the resulting condensate. 150° C. whereupon vapors are evolved, condens 11. The method which comprises heating ing the ef?uent vapors, and separating 1,1-di 1,1,3,3-tetracyano propane at a temperature and cyano ethylene from the resulting condensate. pressure such that decomposition occurs to form 3. The method which comprises heating 1,1,3,3 vapors of 1,1-dicyano ethylene and malononitrile tetracyano propane at a temperature of 150° to 35 and separating the 1,.1-dicyano ethylene from the 250° C. whereupon vapors are evolved, condensing malononitrile. the eilluent vapors, and separating 1,1-dicyano HARRY GILBERT. ethylene from the resulting condensate. 4. The method which comprises heating 1,1,3,3~ REFERENCES CITED tetraoyano propane at a temperature in excess 40 The following references are of record in the of 150° C. and at a reduced pressure whereupon ?le of this patent: vapors are evolved, condensing the e?luent vapors, UNITED STATES PATENTS and separating 1,1-dicyano ethylene from the re Number Name Date sulting condensate. 5. The method which comprises heating 1,1,3,3~ 45 tetracyano propane at a temperature in excess of 150° C. and at a pressure below 100 mm. where upon vapors are evolved, condensing the e?luent 2,467,378 2,476,270 Gilbert __________ __ Apr. 19, 1949. Ardis ____________ __ July 19, 1949 OTHER REFERENCES vapors and separating 1,1-dicyano ethylene from. the resulting condensate. 6. The method which comprises heating 1,1,3,3 Ostling: Chem. Abstracts, vol. 15, p. 2829 (1921). Diels et al.: Ber. Deut. Chem., vol. 55, pp. tetracyano. propane at a temperature in excess 3445-3446 (1922). of 150° C. and in the presence of phosphorus pentoxide whereupon vapors are evolved, con Conn et al,: Ber. Deut. Chem., vol. 56, 2076 2080 (1923). densing the e?iuent vapors, and separating '