ESTERS OF ALPHA-CYANOACRYLIC ACID AND PROCESS FOR THE MANUFACTURE THEREOF

United States Patent Office 3,254,111 Patented May 31, 1966 1 3,254,111 ESTERS OF ALPHA-CYANOACRYLIC ACID AND PROCESS FOR THE MANUFACTURE THEREOF Gary F. Hawkins and Hartsell F. McCurry, Kingsport, Tet-.n., assignors to Eastman Kodak Company, Roches- ter, N.Y., a corporation of New Jersey No Drawing. Filed Dec. 9, 1960, Ser. No. 74,748 11 Claims. (Cl. 260-4654) This invention relates to the preparation of esters of oc-cyanoacrylic acid and more particularly to the prepara- tion of monomeric ac-cyanoacrylates useful in adhesive compositions. The monomeric form of an a-cyanoacrylate has in the past usually been prepared by depolymerization of a poly- mer thereof which is formed by reacting a cyanoacetate’ with formaldehyde or a polymer of formaldehyde in the presence of a basic condensation catalyst. Heretofore, the reaction between the cyanoacetate and the formalde- hyde was effected in aqueous medium, usually by em- ploying an aqueous solution of formaldehyde. ' A method of this kind was disclosed in Ardis, U.S. Patent 2,467,927. The monomeric oc-cyanoacrylates are readily polymer- izable without the use of either heat or a catalyst, and it has -consequently been diflicult to store the monomer without premature polymerization. This is particularly true of the monomeric or-cyanoacrylates prepared from polymer made in aqueous medium, since the presence of even small amounts of water catalyzes the polymerization reaction and contributes to the instability of the monomer. It has been dificult to reduce the moisture content of the polymeric cc-cyanoacrylates to a sufiiciently low level prior to depolymerization to -give monomers having good sta- bility at room temperature in bulk. Furthermore, the presence of even small amounts of moisture has made the depolymerization reaction diflicult to perform. Recently an improved method has been developed for producing monomeric oc—cyanvo-aoryl:a.tes which insures the formation of «substantially anhydrous polymeric oc-cyano- acrylates without the necessity of subjecting the polymer to prolonged drying periods. In this improved method, equimolar quantities of formaldehyde and cyanoacetate are reacted in the presence of a basic condensation "cata- lyst in solution with a nonaqueous organic solvent, such as a lower alkyl .monohydric alcohol, which distills at a temperature below the depolymerization temperature of the polymer formed by the reaction. After the chemical reaction has been completed at least part of the solvent is removed by distillation. Then an organic solvent such as benzene, which is -capable of forming an azeotrope with water, is added to the -polymeric reaction mixture. The reaction solvent, water, and the azeotrope-forming solvent tare distilled off as a ternary azeotrope -and the water content of the polymer is reduced to a very low level. A substantially anhydrous, viscous, crude polymer is ob- tained as a ‘residue. The polymer can be readily de- polymerized by heating in the presence of a polymeriza- tion inhibit-or without the necessity of further drying. The monomeric vapor evolved from the polymer is con- densed and recovered as the oz-cyanoacrylate product. This monomer has »a low water content and, therefore, good stability against polymerization. The recently developed process is a marked improve- ment over prior-processes in yielding a product of low moisture content. However, we have now made a further improvement. In accordance with the present invention, We employ more than 1 mol and less than 2 mols of cyanoacetate per mol of formaldehyde in preparing the cyanoacrylate. We obtain a polymeric intermediate re- action product having an average composition of relative- ly low molecular weight -and we subject the intermediate product to depolymerization under conditions such that 10 15 20 25 30 40 50 55 60 65 70 2 the depolymerization product consists essentially of oz- cyanoacrylate and oc,oc’-dicyanoglutarate. The latter is not decomposed to substantial extent. In the preferred embodiment it is recycled -to the initial polymerization stage. The chemical reaction occurring in our process is il- lustrated by the following over-all reaction equation: 0 II 4H—O ——H + 5NEC—C 112-0 0 OR ———> Forrna1- Cyanoacetate dehyde C N C N C N C N C N I I I I I H-0 -0 H2—C —c 152-0 -0 112-0 —c Hg—C H + 41120 —_+ I I I I COOR COOR COOR COOR $0013’. ON ON ON 3CHz=C—CI}OOR + ROOC~—éH——CH2—-éH——COOR a-Cyauo- a,a’-Dicyauoglutarate acrylate where R: alkyl, alkenyl, cyclohexyl or aryl. A number of important advantages are obtained by our new procedure. One unexpected result is that the in- termediate polymeric product is much less viscous than the intermediate -obtained in the prior processes. In our process the intermediate product is sufliciently fluid to eliminate the need for heat transfer agents or solvents other than an azeotrope-forming solvent such as benzene. Thus, our process does not require the use of an alcohol- type reaction -solvent for the polymerization reaction nor the addition of a diluent such as tricresyl phosphate to. the polymeric intermediate product. Our intermediate product is sufficiently fluid that there is no difliculty of agitation or of heat transfer. A uniform temperature can readily be maintained throughout the reaction mix- ture with the result that the uniformity or purity of the ultimate product is improved. Furthermore, a consistent yield" and quality of product can be obtained in different runs. The time required to carry out the process is re- duced. Still further, by eliminating the inert solvents previously required we obtain a higher production of de- sired product for a reaction vessel of given size. The use of a mol ratio of less than two mols of cyano- acetate per mol of formaldehyde also leads to an im- portant advantage in our new process. As we have in- dicated, the productsobtained by depolymerizing the intermediate polymeric product of our process comprise the desired cyanoacrylate monomer and =a higher boiling material consisting essentially of oc,oc’-dicyanoglutarate. The latter -boils sufficiently higher than the desired mono- meric product that the monomer can be recovered in high purity by subatmospheri-c distillation. This provides an important -advantage over the type of process in which cyanoacetate is reacted with formaldehyde in a 2:1 mol ratio. The latter type of process produces an intermediate product that consists essentially of dicyanoglutarate, in- stead of the characteristic polymeric intermediate product ofour process. When the intermediate product consists entirely of the glutarate, the glutarate must be decom- posed in order to obtain the desired monomeric cyano- acrylate. However, decomposition of the glutarate to obtain the desired ac-cyanoacrylate produces one mol of -cyanoacryalte and one mole of cyanoacetate. Because of their close boiling points it is difficult to separate the cyanoacrylate in high purity from the cyanoacetate by distillation. In contrast, in our process we avoid the de- composition of the oc,u’-dicyanoglutarate and conse- quently high purity cyanoacry-late monomer can be re- covered by rdistilrlation of the depolymerization product. The novel procedure of our invention that produces the described advantages, in general, comprises reacting a cyanoacetate with formaldehyde in a molar ratio of more than one mol but less than two mols of cyanoacetate per 3,254,111 3 mol of formaldehyde in solution with a nonaqueous or- ganic solvent such as benzene that forms an azeotrope with water and in the presence of a basic condensation catalyst. Water is azeotropically distilled from the re- action mixture and a polymeric intermediate reaction product is obtained. The polymeric product is then sub- jected to depolymerization conditions and the -resulting depolymerization product is distilled to recover an over- head product comprising the desired on-cyanoacrylate. The residue comprises u,oc’-dicyanoglutarate. In the pre- ferred embodiment of the invention, the latter is recycled to the initial polymerization stage. The reaction equation above demonstrates the preferred embodiment of our process in which we react 4 mols of formaldehyde with 5 mols of alkyl cyanoacetate to ob- tain an intermediate polymeric product that depolymerizes to 3 mols of oz-cyanoacrylate and 1 mol of oc,oc’-dicyano- glutarate. An essential feature of our process is that more than one mol but less than two molsof cyanoacetate is ‘ employed per mol of formaldehyde. This makes possi- ble the formation of our characteristic polymeric inter- mediate, which is a copolymer of one molecule of oc,oc’- dicyanoglutarate with one or more molecules of an oc-Cy- anoacrylate, and avoids formation of a long chain viscous homopolymer of oc-cyanoacrylate. To obtain the copoly- mer of the glutarate with the cyanoacrylate, it is neces- sary to react “n+1” molecules of the cyanoacetate with “)1” molecules of formaldehyde, being at least 2. The copolymer can then be decomposed to yield one mol of dicyanoglutarate ‘and “n—1” mols of cyanoacrylate. For example, 5 molecules of cyanoacetate react with 4 molecules of formaldehyde to yield a polymer that de- composes to 3 mols of cyanoacetate and 1 mol of glu- tarate; 3 molecules of cyanoacetate react with 2,mols of formaldehyde to yield a copolymer that decomposes to 1 mol of cyanoacrylate and 1 mol of cyanoglutarate; 6 mols of cyanoacetate react with 5 mols, of formaldehyde to yield a copolymer that decomposes to 4 mols of cyano- acrylate and 1 mol of cyanoglutarate; etc. Thus, to ob- tain the desired intermediate with minimum yield of other products the mol ratio of alkyl cyanoacetate to formalde- hyde is greater than 1:1 but no greater than 1.521. If the molar ratio of cyanoacetate to formaldehyde ex- ceeds 1.5:1, stoichiometrici considerations indicate that the intermediate reaction product will be a mixture of the dicyanoglutarate and the copolymer of the cyano- acrylate with. the glutarate. Although the copolymer in the mixture can be depolymerized to yield cyanoacrylate -that can be separated by distillation from the undecom- posed glutarate, the yield of cyanoacrylate in relation to the yield of glutarate is too low. In other words the re- 4 the range of 1.221 to 1.5:1. Most preferably the ratio is 1.25:1, which is obtained by the use of 5 mols of cy- . anoacetate with 4 mols of formaldehyde. 5 10 30 35 40 45 50 actants are not used as eflficiently as possible for produc- , ing the desired product. Therefore, while the scope of our invention extends to the use of molar ratios higher than 1.5 :1 (but less than 2: 1) the preferred embodiment of our process, and that in which the greatest benefits of the invention are obtained, employs a molar ratio of alkyl cyanoacetate to formaldehyde no greater than 1.5 :1. The molar ratio of the reactants should not -approach too closely to 1:1 or the proportion of on-‘cyanoacrylate in the intermediate copolymer with the glutarate -will be excessive, the chain will be too long and an excessively viscous intermediate will be obtained, as in the prior equimolar process. We prefer to form an intermediate that is a copolymer of 1 molecule of the dicyanoglutarate 60 65 with 3 molecules of the cyanoacrylate although an inter- . mediate of somewhat longer chain, e.g., a copolymer of 1 molecule of the glutarate with 4 molecules of the acry- late is satisfactory, but a polymer of chain length greater than this may be excessively viscous. Thus, we have found that an undesirably viscous intermediate is obtained in reacting 5 mols of cyanoacetate with 4% mols of form- aldehyde (1.175 :1 mol ratio). Therefore, the molar ratio of cyanoacetate to formaldehyde is preferably in 70 75 In a preferred embodiment of our -process the u,oc’-di- cyanoglutarate recovered from the depolymerization prod- uct is recycled to the initial polymerization stage. In determining the mol ratio of reactants for the initial stage in the recycle operations, the glutarate should be con- sidered as the equivalent of 2 mols of cyanoacetate and 1 mol of formaldehyde. Thus, for obtaining the equiv- alent of the preferred ratio of 5 mols of cyanoacetate to 4 mols of formaldehyde when 1 mol of dicyanoglutarate is recycled to the initial reaction stage, the actual propor- tion of‘ reactants should be: 1 mol of dicyanoglutarate, 3 mols of cyanoacetate, and 3 mols of formaldehyde. Throughout the specification and claims we intend that any specified mol ratio of cyanoacetate to formaldehyde be construed as coveringpthe equivalent ratio obtainable by substituting 1 mol of the corresponding dicyanoglu- tarate for 2 mols of the cyanoacetate and 1 mol of form- aldehyde. An important feature of our process is that the oc,oc’-di- cyanoglutarate obtained by depolymerization of the in- termediate product is not substantially decomposed and, in the preferred embodiment of the process, is recycled to the initial polymerization stage. Another procedure within the scope of the invention is to react the glutarate with formaldehyde alone or with cyanoacetate and form- aldehyde in a reaction zone apart from the initial polym- erization reaction zone. In these reactions, the molar ratio of reactants should also be such as to yield an intermediate product thatiis a copolymer of one mole- cule of the dicyanoglutarate with one or more molecules (preferably no more- than four) of the or-cyanoacrylate. The process of the invention is applicable for preparing many of the low ‘molecular weight esters of oc-cyano- acrylic acid. Thus any low molecular weight cyanoace- tate can be used for the reaction. The on-cyanoacrylates which‘ are of greatest utility, particularly for use as ad- hesive compositions, are those which are alkyl, alkenyl, cyclohexyl, or phenyl esters of oucyanoacrylic acid. Con- sequently, the process preferably employs an alkyl cyano- acetate, an alkenyl cyanoacetate, a cyclohexyl cyanoace- tate, or a phenyl cyanoacetate. The alkyl esters are de- sirably those in which the alkyl group contains from 1 to about 8 carbon atoms, with the lower alkyl esters con- taining from 1 to 4 carbon atoms being preferred. Thus, for example, the cyanoacetate is preferably methyl cyano- acetate, ethyl cyanoacetate, propyl cyanoacetate, butyl cyanoacetate, vinyl cyanoacetate, allyl cyanoacetate, cyclo- hexyl cyanoacetate, or phenyl cyanoacetate. The cyano- acetate is reacted with formaldehyde, and in this applica- tion the term “formaldehyde” is intended to include form- aldehyde itself, as well as the polymer thereof such as p-formaldehyde or the like, but is not intended to include aqueous solutions of formaldehyde as typified by Formalin. The reaction between the cyanoacetate and the formal- dehyde to form a polymeric on-cyanoacrylate is readily effected by. heating the reaction mixture to -a temperature of about 50 to 90° C. in the presence of a basic catalyst. Many basic condensation catalysts are known, and any of such materials can be used to catalyze the reaction. Thus the catalyst can be any basic material, including the inorganic bases such as sodium or potassium hydroxide, ammonia, or ammonium hydroxide, the organic bases such as quinoline, piperidine, isoquinoline, dialkyl amines such as diethyl amine, alkali metal alkoxides such as sodium or potassium methoxide or ethoxide, or similar well known basic material. The -amount of catalyst is not critical and can be varied if desired. Ordinarily, a very small amount of the basic material such as about 0.001 to 0.5 percent by weight is adequate, however,. larger amounts can be used but are not usually advantageous. The initial reaction between the cyanoacetate and for- Amaldehyde is carried out in the presence of a nonaqueous 3,254,111 5 organic solvent which is capable of forming an azeotrope with water. It is necessary that the azeotrope solvent distill -at a temperature below the depolymerization tem- perature of the intermediate polymeric product. A num- ber of volatile organic solvents are suitable therefore be- cause depolymerization is usually effected by heating the polymeric product at a temperature of the order of 100 to 185° C. under a vacuum of the order of 1-3 mm. Hg. Benzene is greatly preferred as the azeotrope-forming solvent because it provides a suitable temperature of dis- tillation. Other suitable solvents include toluene and heptane. _ The polymeric intermediate product obtained in the first stage of our process is substantially anhydrous. De- polymerization is effected by heating the polymer at low pressure and in the presence of a polymerization inhibitor. Because of the inherent polymerization reactivity of the monomeric a-cyanoacrylates, it is desirable to depolymer- ize the intermediate product in the presence of a polymeri- zation inhibitor, even though the low water content of the polymer results in a monomer of greater stability than that produced by reaction in an aqueous medium. We preferably employ inhibitors both for ionic and free-radical polymerization. However, the more im- portant of the two types of inhibitors are the acidic sub- stances that inhibit ionic polymerization. Various suit- able inhibitors include polyphosphoric acid, phosphorous pentoxide, antimony pentoxide, picric acid, hydroquinone, t-butyl catechol, metaphosphoric acid, maleic anhydride, ferric chloride, and the like. A particularly desirable group of polymerization inhibitors are the acidic gaseous inhibitors such as sulfur dioxide, nitric oxide, hydrogen fluoride, and the like. Usually it is desirable to include a nonvolatile inhibitor in the vessel and also to collect the depolymerization vapors in a receiving vessel also con- taining a nonvolatile polymerization inhibitor. During depolymerization and redistillation it is also preferred to introduce in to the system a stream of gaseous inhibitor which mixes with the monomeric vapors evolved and dis- solves in the monomeric product, at least to some extent, when the vapor is condensed. Phosphorous pentoxide and polyphosphoric acid are the preferred nonvolatile inhibitors for the depolymerization stage, and sulfur di- oxide is the preferred gaseous inhibitor. A particularly stable monomeric product is obtained when the receiving vessel contains a small amount of hydroquinone, whereby the monomer product obtained contains a mixture of sulfur dioxide and hydroquinone, The monomeric on-cyanoacrylic esters prepared in ac- cordance with this invention are excellent adhesive com- positions for bonding almost any type of material to it- self or to a dissimilar material. The adhesive composi- tions are readily employed by merely spreading them in a thin film on the surface to be bonded. Polymerization occurs within. a few seconds without the use of either heat or a polymerization catalyst, and the bonds which are obtained are of very high strength. A further understanding of our invention will be had heat or a polymerization catalyst, and the bonds which are set forth to illustrate certain preferred embodiments. Example I To 332 parts (2.65 moles) of allyl cyanoacetate, 250 parts of benzene, 1 part piperidine and 1 part of a 50% solution of sodium hydroxide in a 1-liter, stirred flask, fitted with a Dean-Stark tube, was added 65 parts (2.16 moles) of para-formaldehyde in 4 portions while reflux- ing to remove the water formed. After substantially all of the water of reaction had been removed the major por- tion of the benzene was distilled out. About 30 parts of a mixture of equal parts of 85% phosphoric acid and phosphorus pentoxide along with 1 part of hydroquinone were then added. The remainder of the benzene was distilled out under subatmospheric pressure. A good vacuum was applied and the flask was heated further 10 15 20 CO U! 40 50 55 60 70 75 6 causing the depolymerization products to distill into a flask containing a little hydroquinone and P205. Most of the product distilled at 170—180° C. at a pressure of 5 to 6 mm. of mercury. The distillate was redistilled in a stream of S02 at a pot temperature of 70° C. at a pressure of 1 to 2 mm. of mercury. Distillation was dis- continued when the pot temperature started to rise in order to prevent the distillation of diallyl oc,oc’-dicyano- glutarate. There was obtained 135 parts of allyl cyano- acrylate having good stability and adhesive properties. The following example indicates yields obtainable in preparing methyl or-cyanoacrylate according to one modi- fication of the process of our invention, the polymeriza- tion reaction being carried out at the reflux temperature of benzene, i.e., about 80 to 90° C. Example 2 To 495 parts (5 mols) of methyl cyanoacetate, 100 parts of benzene, 0.2 part of piperidine and 5.5 parts of 9% sodium hydroxide contained in a 1-liter, stirred flask, fitted with a Dean-Stark tube was added 120 parts (4 mols) of paraformaldehyde in 4 portions while refluxing to remove the water formed. After all the water of re- action was removed, 5 parts of 85% phosphoric acid, 10 parts of phosphorus pentoxide and 10 parts of hydro- quinone were added. The benzene was then distilled out, vacuum was applied and product was distilled in a stream of S02 into a flask containing a little hydroquinone and P205. Distillation was continued until a pot temperature of about 175° C. was reached. The distillate was redis- tilled in a stream of S02, the first cut coming over at 39—44° C. and a pressure of about 1 mm. of mercury, giving 270 parts of methyl ac-cyanoacrylate. The second cut boiled at 155—165° C./1-2 mm., giving 110 parts of this material, which was essentially dimethyl oa,oc’-dicyano- glutarate. The yield of 270 parts of methyl u-cyano- acrylate amounted to approximately 2.45 mols. The the- oretical yield by reaction of 5 mols of methyl cyanoacetate with 4 mols of formaldehyde is 3 mols of methyl o:-cyano- acrylate plus 1 mol of dimethyl oc,u’-dicyanoglutarate. Therefore, the actual yield of the desired monomer was about 81% of theory. The methyl u-cyanoacrylate ob- tained in the run was very active as an adhesive. ' We have indicated that the dicyanoglutarate obtained by depolymerization of the intermediate reaction, product can be recycled to the initial reaction zone for reaction with cyanoacetate and formaldehyde or can be reacted with formaldehyde alone to yield again a copolymer of cyanoacrylate with the glutarate, which is then depolym- erized to obtain the cyanoacrylate. The following example describes a run in which the dicyanoglutarate was reacted with paraformaldehyde to obtain the cc-cyanoacrylate. Example 3 348 parts of high boiler obtained from runs such as Example 2, which consisted essentially of dimethyl oc,oc’- cyanoglutarate (1% mols), and 30 parts of paraformalde- hyde (1 mol of formaldehyde) were placed in a 1-liter flask with 0.2 part piperidine, 5.5 parts of 9% NaOH, and 100 parts of benzene. The mixture was refluxed until all of the water was removed. Then the distillation of benzene, the depolymerization of the intermediate prod- uct, and redistillation were carried out substantially as described in Example 2 to obtain 181.7 parts of methyl cyanoacrylate. The reaction of 12/3 mols of dimethyl oc,oc’-dicyanoglutarate with 1 (mol of formaldehyde is pro- portionally equivalent to the reaction of 5 mols of methyl cyanoacetate with 4 mols of formaldehyde, and theoret- ically will yield 2 mols of methyl on-cyanoacrylate and 2/3 mol of dicyanoglutarate. Consequently, the yield of 181.7 parts of methyl cc-cyanoacrylate (1.64 mols) was about 82% of theory. The following example describes results obtained in a 3,254,111 7 run carried out by adding a slurry of feed mixture to the reaction mixture in the reaction vessel as in Example 1. Example 4 To 594 parts (6 mols) of methyl cyanoacetate, 200 parts of benzene and 1 part of piperidine contained in a 2-liter flask and heated to 75° C. was added _slowly a slurry -composed of 396 parts (4 mols) of methyl cyano- acetate and 247 parts (8 mols) of paraformaldehyde. The dropping funnel through which the slurry was added was washed with 200 parts of benzene. The reaction mix- ture was refluxed until all of the water was removed as the azeotrope. Fifteen parts of P205 and 10 parts of hydroquinone were then added and the reaction mixture worked up as in Example 2. The yield of monomeric methyl oc-cyanoacrylate was 620 parts (5.6 mols). Theo- retical yield for reaction of 10 mols of cyanoacetate with 8 mols of formaldehyde is 6 mols of cc-cyanoacrylate plus 2 mols of dicyanoglutarate. Therefore, the actual yield of cc-cyanoacrylate was about 93% of theory. The yield of high boiler, consisting essentially of dimethyl oc,oc’-di- cyanoglutarate, was 330.5 parts or 79%. p The following example describes a run in which the residual reaction product of the process, .ie., the di- cyanoglutarate, is reacted with methyl cyanoacetate and formaldehyde to obtain the desired cyanoacrylate. Example 5 To 210 parts of high boiler (1 mol of dimethyl oc,oc’- dicyanoglutarate) from previous runs, 100 parts (1 mol) of methyl cyanoacetate, 100 parts of benzene and 0.25 part of piperidine in a 1-liter flask was slowly added at reflux a slurry composed of 90 parts of paraformaldehyde and 197 parts (2 mols) of methyl cyanoacetate. After all of the water had been azeotroped off, 10 parts of P205 and 5 parts of hydroquinone were added. The re- action mixture was worked up as in Example 2 to pro- duce 329.6 parts (2.97 mols) of methyl or-cyanoacrylate product. The reaction of 1 mol of dicyanoglutarate with 3 molsof cyanoacetate and 3 mols of formaldehyde is equivalent to a 5:4 mol ratio of cyanoacetate:formalde- hyde and gives a theoretical yield of three mols of oz- cyanoacrylate. Therefore, the actual yield in this run was about 99% of theoretical and demonstrates the ef- ficacy of recycling the glutarate to the reaction of the cyanoacetate with formaldehyde. , The following example describes a run according to the invention which employed another cyanoacetate of the preferred class of cyanoacetates, i.e., the lower alkyl cyanvoacetates of which the alkyl groups have from 1 to 4 carbon atoms. Example 6 To a mixture of 405 parts (2.9 mols) of isobutyl cyanoacetate, 200 parts of benzene, 0.5 part piperidine, and 5 parts of 10% sodium hydroxide solution, at reflux, was added a slurry of 123.5 parts (4 mols) of paraform- aldehyde in 300 parts (2.1 mols) of isobutyl cyanoacetate. The residue from the slurry was washed into the flask with 100 parts of benzene. Refluxing was continued until all of the water came off as an azeotrope. The reaction mix- ture was cooled slightly and 3 parts of 85% phosphoric acid, 15 parts of phosphorous pentoxide and 10 parts of hydroquinone were added. The benzene was removed and the reaction mixture was distilled to produce 675 parts of crude product. This crude material was re- distilled, with fractionation, in the presence of sulfur dioxide and phosphorus pentoxide to produce 250 parts of isobutyl oc-cyanoacrylate product and 398 parts of high boiler. The invention has been described in considerable detail with particular reference to certain preferred embodi- ments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims. 10 15 20 30 40 C?! C?! 60 65 70 . 8 We claim: 1. Allyl ac-‘cyanoacrylate. 2. The process for preparing a monomeric oc-cyano- acrylate of the formula, (‘IN CHz=C—CO0R which comprises reacting a cyanoacetate of the formula, NCCH2COOR with formaldehyde in a molar ratio of more than one but less than two mols of cyanoacetate per mol of formaldehyde, obtaining an intermediate prod- uct that is a copolymer of said cc-cyanoacrylate and the corresponding a,oc-divcysanwoglutarate of the formula, ‘EN ?N ROOCCHCEHCHCOOR heating said intermediate product to a temperature suffi- ciently high to depolymerize said‘ copolymer to a mix- ture of said oc-cyanoacrylate and said glutarate and recover- ing said ac-cyanoacrylate from said mixture without sub- stantially decomposing said glutarate, wherein R is selected from the group consisting of alkyl of 1 to 8 carbon atoms, lower alkenyl, cyclohexyl and phenyl. 3. The process according to claim 2 in which the molar ratio of cyanoacetate to formaldehyde is in the range of 1.2:1 to 1.5:1. 4. The process for preparing a monomeric oc-cyano- acrylate of the formula, ?N CH2=C—COOR which comprises reacting a cyanoacetate of the formula, NCCHZCOOR, with formaldehyde in a molar ratio of more than one but less than two mols of cyanoacetate per mol of formaldehyde at a temperature of 15 0° to 90° C. and in the presence of a basic condensation catalyst and a nonaqueous organic solvent that forms an azeotrope with water, azeotropically distilling water of reaction and said organic solvent from the reaction mixture to obtain a substantially anhydrous intermediate polymeric reaction product, heating said intermediate product in the presence of a polymerization inhibitor to a temperature sufliciently high to depolymerize said intermediate product to a mix- ture of said wcyanoacrylate and u,oc’-dicyanoglutarate of the formula, W ‘EN ROOCCHCH2(JHCOOR and separating said ac-cyanoacrylate from said glutarate by distillation, wherein R is selected from the group consisting of alkyl of 1 to 8 carbon atoms, lower alkenyl, cyclohexyl and phenyl. _ 5. The process of claim 4 in which the ratio of cyano- acetate to -formaldehyde is in the range 1.2:1 to 1.5 :1. 6. The process for preparing a monomeric u-cyano- acrylate of the formula, ON CH2=C‘J -0 0 OR which comprises in an initial reaction stage reacting a cyanoacetate of the formula, NCCH2COOR, with form- aldehyde in a molar ratio of cyanoacetate to formalde- hyde in the range of 1.2:1 to 1.5 to 1 at a temperature of 50 to 90° C. and in the presence of a basic condensa- tion catalyst and a nonaqueous organic solvent from the group consisting of benzene, toluene and heptane, azeo- tropically distilling water of reaction and said solvent from the reaction mixture and recovering a substantially anhydrous intermediate product that is a copolymer of saicil cc-cyanoacrylate and u,a’-dicyanoglutrate of the for- mu a, (EN CIIN ROOCCHCH2CHCO0R heating. said intermediate product in the presence of an acidic polymerization inhibitor to a temperature sulfi- 3,254,111 9 ciently high to depolymerize said interrnedaite product to a mixture of said on-cyanoacrylate and said oc,oc’-dicyano- glutarate, without substantially decomposing said gluta- rate, and distilling from the reaction zone a ‘mixture of said on-cyanoacrylate and said ec,oc’-dicyanoglutarate, re- distilling said latter mixture recovered as distillate from said latter distillation step, recovering said monomeric on-cyanoacrylate as the overhead product without sub- stantially decomposing said oc,oc’-dicyanoglutarate and re- cycling said a,a’-dicyanoglutarate to the initial reaction stage, wherein R is lower alkyl. 7. The process for preparing monomeric methyl cyano- acrylate which comprises reacting methyl cyanoacetate with formaldehyde in a molar ratio of about 1.25 mols of on-cyanoacetate per mol of formaldehyde at a tempera- ture of 80 to 90° C. and in the presence of a basic con- densation catalyst and benzene, azeotropically distilling water of the reaction and benzene from the reaction mixture at atmospheric pressure to obtain a substantially anhydrous intermediate product that is copolymer of methyl on-cyanoacrylate with dimethyl a,oc’-dicyanoglu- tarate, heating said intermediate product in the presence of an acidic polymerization inhibitor to a temperature sufficiently high to depolymerize said intermediate product to a mixture -of methyl on-cyanoacrylate and dimethyl a,a’- dicyanoglutarate, distilling said mixture from the reaction zone at subatmospheric pressure, redistilling said mix- ture recovered as distillate from said latter distillation step without decomposing said dimethyl a,oc’-dicyanoglu- tarate, recovering as the overhead product monomeric methyl on-cyanoacrylate, and thereafter reacting said di- methyl oc,oc-dicyanoglutrate with a reactant selected from the group consisting of formaldehyde and a mixture of formaldehyde and said methyl cyanoacetate to form said copolymer intermediate reaction product. 8- The process of claim 7 in which the dimethyl oc,ot’- dicyanoglutarate is recycled to the initial reaction stage. 9. The process of claim 7 in which the dimethyl o:,oc’- 10 15 20 25 30 35 10 dicyanoglutarate is thereafter reacted with formaldehyde to form said copolymer intermediate reaction product. 10. The process of claim 7 in which the dimethyl oc,ot’- dicyanoglutarate is thereafter reacted with a mixture of formaldehyde and said methyl cyanoacetate to form said copolymer" intermediate reaction product. 11. The process for preparing an ac-cyanoacrylate of the formula, ON I C H2=C—-C 0 OR which comprises reacting an oc,a’-dicyanoglutarate of the formula, — 9” 0:“ ROOCCHCH2CI-ICOOR with a reactant selected from the group consisting of formaldehyde and a mixture of formaldehyde and cyano- acetate of the formula, NCCHgCOOR, to obtain, an inter- mediate product that is a copolymer of the oz-cyanoacrylate with the a,oc’-dicyanoglutarate, heating said copolymer in" the presence of a polymerization inhibitor at a tem- perature sufliciently high to depolymerize said copolymer, and separating said on-cyanoacrylate from the depolym- erization product without substantially decomposing the oc,a’-dicyanoglutarate, wherein R is lower alkyl. References Cited by the Examiner UNITED STATES PATENTS 2,338,834 1/1944 Britton et a1 ______ __ 260-465.4 2,467,927 4/ 1949 Ardis ___________ __ 260—465.4 2,624,751 ‘ 1/1953 Mowry. 2,628,164 2/1953 Mowry et al ____ __ 260—465.4 X 2,721,858 10/1955 Joyner et al .... __ 260-46.5.4 X 2,776,232 1/1957 Shearer et al. _;_ 260—465.4 X 3,036,066 5/1962 Sims _________ __ 260—465.4 X CHARLES B. PARKER, Primary Examiner.