ISOCYANATE COMPOUNDS AND THEIR PRODUCTION

Abstract: A process for preparing alkenoyl isocyanates of the formula: wherein R is a hydrogen atom or a lower alkyl group which comprises subjecting an oxazolinedione hydrohalide of the formula: wherein X is a halogen atom and R is as defined above to decomposition under an ordinary pressure, in the presence of a hydrogen halide-eliminating agent and/or in a liquid medium having a dielectric constant of not more than 4.

Description: The present invention relates to the production of alkenoyl isocyanates of the formula CH₂=CR-CO-NCO (I) wherein R is H or C₁₋₅ alkyl, from corresponding oxazolinedione hydrohalides of the formula wherein X is a halogen atom. In general, compounds having an isocyanate group are widely used in the field of polymer chemistry because of their excellent reactivity. Compounds having both a polymerisable double bond and an isocyanate group in the molecule are expected to have great usefulness, because the double bond and the isocyanate group can respectively participate in various reactions depending upon different reaction mechanisms. Specific examples are vinyl isocyanate (Angew. Chem., Int. Ed., 18 , 319 (1979)), isocyanatoethyl methacrylate (Japanese Patent Publn. (unexamined) No. 5921/79), acryloyl isocyanate (Chem. Ber., 84 , 4 (1951)), methacryloyl isocyanate (Chem. Ber., 84 , 4 (1951)), etc. Among them, the alkenoyl isocyanates (I) such as acryloyl isocyanate (I: R = hydrogen) and methacryloyl isocyanate (I: R = methyl) are particularly interesting in that the reactivities of the polymerizable double bond and the isocyanate group are enhanced by the carbonyl group present between them. The alkenoyl isocyanates (I) can thus undertake various reactions such as radical polymerization, anion polymerization, dimerization, trimerization, polar addition and addition of active hydrogen based on the partial structure (A) (i.e. conjugated double bond structure) and/or on the partial structure (B) (i.e. acylisocyanate structure) as set forth below and may be used as the industrial starting materials in various chemical fields: The alkenoyl isocyanates (I) were originally prepared by reacting the corresponding alkenoyl chlorides with silver isocyanate (Chem. Ber., 84 , 4 (1951)). Apparently, this process is industrially disadvantageous in using an expensive reagent such as silver isocyanate. There is also known the process wherein isocyanic acid is used in place of silver isocyanate (U.S. patent 3,155,700). In this process, however, isocyanic acid is produced by heat decomposition of its trimer, i.e. isocyanuric acid, at such a high temperature as 620°C. In addition, isocyanic acid is a gaseous material. Accordingly, a special apparatus is needed, and handling of the gaseous material is troublesome. In 1962 to 1965, Speziale et al developed a process for production of acyl isocyanates from amides by reacting the latter with oxalyl chloride (J. Org. Chem., 27 , 3742 (1962); ibid., 23 , 1805 (1963); ibid., 30 , 4306 (1965)). By application of this process, Urano et al recently provided the industrial production of the alkenoyl isocyanates (I) from acrylamide or methacrylamide and an oxalyl halide (EP-A-0143613). While the process as provided by Urano et al affords the alkenoyl isocyanates (I) in relatively good yields, by-production of the corresponding haloalkanoyl isocyanates of the formula: wherein R and X are each as defined above to a certain extent is unavoidable so that the application of a troublesome purification procedure to the reaction mixture is needed. Diefenbach et al reported that the reaction of methacrylamide with oxalyl chloride at such a low temperature as -50°C gives 2-isopropenyloxazoline-4,5-dione hydrochloride (III: R=CH₃; X=Cl), in a yield of 76% (Die Makromolekulare Chemie, 131 , 247 (1970)). They also report that, when the 2-isopropenyloxazoline-4,5-dione hydrochloride is heated at 100°C under a reduced pressure of 15 Torr, α-methyl-β-chloropropionyl isocyanate (II: R=CH₃; X=Cl) is obtained. At page 251 of the article, it is stated that pyrolysis of the α-methyl-β-chloropropionyl isocyanate in a mass spectrometer gives methacryloyl isocyanate (I: R=CH₃). It has been found that, when acrylamide is reacted with oxalyl chloride, the corresponding oxazolinedione hydrochloride (III: R=H; X=Cl) is not obtained even at such a low temperature as -50°C. Instead, β-chloropropionyl isocyanate (II: R=H, X=Cl) is obtained. According to the present invention, a process for producing an alkenoyl isocyanate of formula I comprises subjecting an oxazolinedione hydrohalide of formula III, wherein X is a halogen atom and R is H or C₁₋₅ alkyl, to decomposition in a liquid medium, under ambient pressure, and recovering the product. R is preferably C₁₋₃ alkyl (e.g. methyl, ethyl or propyl) and more preferably methyl. "Halogen" includes chlorine, bromine, iodine and fluorine; chlorine and bromine, particularly chlorine, are preferred. Whereas the alkenoyl isocyanate (I) is normally liquid and quite sensitive to moisture, the oxazolinedione hydrohalide (III) is usually solid and relatively stable to moisture. Thus, the oxazolinedione hydrohalide (III) is suitable for storage on an industrial scale. Further, the oxazolinedione hydrohalide (III) can be readily separated from impurities such as unreacted oxalyl halide, so that the alkenoyl isocyanate (I) can be obtained in high purity and good yield. The oxazolinedione hydrohalides (III) wherein R is H are novel. They can be used as monomers, for the production of polymeric materials. The oxazolinedione hydrohalide (III) may be prepared by any process, but is preferably produced by reaction between an alkenylamide of the formula CH₂=CR-CONH₂ (IV) wherein R is as defined above and an oxalyl halide of the formula (COX)₂ (V) wherein X is as defined above, the reaction being carried out by adding the alkenylamide portionwise to the oxalyl halide charged in a reactor. Surprisingly, the mere change of the charging order of the reagents into a reactor overcomes the given defects in the analogous process described by Diefenbach et al . Thus, charging the oxalyl halide (V) first into a reactor, and subsequent addition of the alkenylamide (IV), according to this invention, makes it possible to carry out the reaction at room temperature, to give the oxazolinedione hydrohalide (III) in yield of 85% or more. The procedure according to this invention makes it possible to obtain the oxazolinedione hydrohalide (III) even when acrylamide (IV: R=H) is used as the starting material. In the process of the invention, the alkenylamide (IV) is added portionwise, continuously or intermittently. The molar ratio of the alkenylamide (IV) to the oxalyl halide (V) is usually 1:1-3, preferably 1:1-1.5. No reaction medium is required, but its use is normally preferred for uniform and smooth processing of the reaction. Examples of the reaction medium are inert solvents such as hydrocarbons (e.g. benzene, toluene, hexane), ethers (e.g. diethyl ether, dioxane, tetrahydrofuran) and esters (e.g. methyl acetate, ethyl acetate). Particularly preferred are halogenated hydrocarbons, of which specific examples are carbon tetrachloride, chloroform, dichloromethane, 1,1-dichloroethane, 1,2-dichloroethane, 1,6-dichlorohexane, 1,5-dichloropentane, 1,2-dichloropropane, 1,3-dichloropropane, 2,2-dichloropropane, 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, 1,4-dichlorobutane, 2,3-dichlorobutane, 1-chlorobutane, 2-chlorobutane, chlorobenzene, chlorocyclohexane, ethylene tetrachloride, trichloroethylene, pentachloroethane, chloropropane, 1,2-dichloroethylene, o-, m- or p-dichlorobenzene, o-, m-or p-chlorotoluene, 1,2,4-trichlorobenzene, bromobenzene, bromoethane, 1- or 2-bromopropane, 1- or 2-bromobutane, 1- or 2-bromopentane, o-, m- or p-bromotoluene, bromocyclohexane, bromochloroethane and 1-bromohexane. When these inert solvents are used, either one or both of the alkenylamide (IV) and the oxalyl halide (V) may be previously dissolved or suspended therein. The reaction temperature is ordinarily from -50°C to the decomposition temperature of the oxazolinedione hydrohalide (III), and preferably from 0 to 40°C. From the industrial viewpoint, the reaction is preferably conducted at room temperature or under ice-cooling. For separation of the oxazolinedione hydrohalide (III) from the reaction mixture, any conventional separation procedure may be used, such as filtration or distillation under reduced pressure. Addition of seed crystals of the oxazolinedione hydrohalide (III) to the reaction mixture may sometimes help to accelerate the precipitation of the oxazolinedione hydrohalide (III). However, separation of the oxazolinedione hydrohalide (III) from the reaction mixture is not necessarily required, provided that the oxazolinedione hydrohalide (III) is present in the reaction mixture. According to the primary process of the invention, the oxazolinedione hydrohalide (III) is then subjected to decomposition, to give the alkenoyl isocyanate (I), while suppressing by-production of the haloalkanoyl isocyanate (II). The reaction is conducted under ambient pressure (atmospheric or autogenic). As stated above, Diefenbach et al carried out the decomposition of the oxazolinedione hydrohalide (III) at about 100°C under reduced pressure. Because decomposition was considered to give first the alkenoyl isocyanate (I), which would then react with by-produced hydrogen halide to give the haloalkanoyl isocyanate (II), reduced pressure was reasonably considered to be effective in eliminating the by-produced hydrogen halide. Contrary to this expectation, it has been found that ambient, not reduced, pressure is effective in such suppression. Decomposition can take place at as low a temperature as 40°C. The temperature is usually 40 to 150°C, preferably 60 to 120°C. The liquid medium may be any inert solvent, e.g. as exemplified above. The use of halogenated hydrocarbons as exemplified above is particularly preferred. The liquid medium preferably has a dielectric constant of not more than 4. Examples of such inert solvents are aliphatic or alicyclic hydrocarbons (e.g. pentane, hexane, heptane, octane, decalin, cyclohexane), aromatic hydrocarbons (e.g. benzene, toluene, xylene, naphthalene), ethers (e.g. propyl ether, butyl ether, dioxane, isopropyl ether), esters and halogenated hydrocarbons (e.g. carbon tetrachloride). A dielectric constant of not more than 4 may be attained by the use of a single solvent or by the use of two or more solvents in combination. The decomposition is preferably conducted in the presence of a hydrogen halide-eliminating agent, preferably an agent not having an active hydrogen atom or not giving an active hydrogen atom on reaction with a hydrogen halide. Amines (which are in general the most popular hydrogen halide-eliminating agents) are not suitable for use in the process of this invention. Preferred hydrogen halide-eliminating agents are metal complex compounds (e.g. Ph₃P)₂Ru(CO)₃, (Ph₃P)₃Pt), metal halides (e.g. lithium chloride, titanium tetrachloride, aluminium chloride, cuprous chloride) and synthetic zeolite (e.g. molecular sieve, microporous glass). The hydrogen halide-eliminating agent is used normally in an amount of 0.1 to 100 mol, preferably of 0.1 to 10 mol. The decomposition may be effected by keeping the oxazolinedione hydrohalide (III) in the presence of the hydrogen halide-eliminating agent at a temperature of -50 to 200°C, preferably from 0 to 150°C. Recovery of the alkenoyl isocyanate (I) from the reaction mixture may be accomplished by a per se conventional separation procedure such as filtration or distillation under atmospheric or reduced pressure. In any of the above reactions and the post-treatments, a small amount of a polymerisation inhibitor may be incorporated into the reaction mixture, to prevent unnecessary polymerisation of the double bond. Examples of the polymerization inhibitor are hydroquinone, p-methoxyphenol, 2,6-di-t-butyl-4-methylphenol, 4-t-butylcatechol, bisdihydroxybenzylbenzene, 2,2'-methylene-bis(6-t-butyl-3-methylphenol), 4,4'-butylidene-bis(6-t-butyl-3-methylphenol), 4'4'-thiobis(6-t-butyl-3-methylphenol), p-nitrosophenol, diisopropylxanthogenesulfide, N-nitrosophenylhydroxylamine ammonium salt, 1,1-diphenyl-2-picrylhydrazil, 1,3,5-triphenylpheldazyl, 2,6-di-t-butyl-alpha-(3,5-di-t-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-trioxy, 2,2,6,6-tetramethyl-4-piperidone-1-oxil, dithiobenzoyl sulfide, p,p'-ditolyl trisulfide, p,p'-ditolyl tetrasulfide, dibenzyl tetrasulfide, tetraethylthiuram disulfide, etc. The alkenoyl isocyanates (I) are, in general, obtained in a liquid stable at room temperature and therefore can be handled with ease. They are soluble in various organic solvents and can be used in their solution form. When allowed to stand in the air, they are readily reacted with moisture in the air to give the corresponding amides. This property is meritorious from the viewpoint of environmental pollution. Their double bond is very reactive and can be readily reacted with other compounds to give isocyanate derivatives. Further, for instance, the alkenoyl isocyanates (I) exert a strong antimicrobial activity in their gaseous state and therefore are useful as antimicrobial agents. Furthermore, the alkenoyl isocyanates (I) can participate in various chemical reactions due to the functional groups present therein and therefore can be used for production of starting materials and intermediates in the fields of pharmaceuticals, agro-chemicals, dyestuffs, etc. Moreover, they have a wide use as monomers for production of various polymers. For instance, their copolymerization with styrene, alkyl acrylate, alkyl methacrylate or the like affords varnish resin. Further, for instance, their copolymerization with other monomers affords polymers useful as dyestuffs, adhesives, dipping agents, foaming agents, fiber treating agents, etc. In general, the alkenoyl isocyanates (I) wherein R is lower alkyl are more stable than the one wherin R is hydrogen particularly when heated. Practical and presently preferred embodiments of the invention are illustratively shown in the following Examples wherein part(s) and % are by weight unless otherwise indicated. Example 1 Preparation of 2-vinyloxazoline-4,5-dione hydrochloride (III: R = H; X = Cl):- Oxalyl chloride (130 g; 1.02 mol) was charged in a reactor, and a warm solution of acrylamide (71 g; 1.0 mol) in dichloroethane (250 ml) was dropwise added thereto (reaction temperature, 10 to 30°C). After completion of the dropwise addition, the solvent and excess of the oxalyl chloride were removed by distillation under reduced pressure to obtain 2-vinyloxazoline-4,5-dione hydrochloride (161 g) as a yellow oil. Viscosity, 100,000 cp. Yield, 100 %. Examples 2 to 7 Preparation of 2-isopropenyloxazoline-4,5-dione hydrochloride (III: R = CH₃; X = Cl):- Oxalyl chloride was charged in a reactor, and methacrylamide or its organic solvent solution was dropwise added thereto in about 1 to 2 hours. After completion of the dropwise addition, 2-isopropenyloxazoline-4,5-dione hydrochloride was recovered from the reaction mixture by a per se conventional separation procedure. Decomposition point, 102 to 103°C. In Example 2, a warm solution of methacrylamide in dichloroethane was dropwise added to oxaly chloride kept at room temperature (20°C) while stirring. The resultant mixture was cooled with water to room temperature. The produced 2-isopropenyloxazoline-4,5-dione hydrochloride was collected by filtration under suction, washed with hexane and dried under reduced pressure. In Example 3, a warm solution of methacrylamide in dichloroethane was dropwise added to oxalyl chloride under cooling with water while stirring. The produced 2-isopropenyloxazoline-4,5-dione hydrochloride was collected by filtration under suction and dried under reduced pressure. In Example 4, methacrylamide was added portionwise to oxalyl chloride while stirring, whereby the reaction proceeded with generation of heat. At the stage that addition of 10 g of methacrylamide was completed, the reaction mixture was solidified. Dichloroethane (100 ml) was added thereto. The produced crystals were collected by filtration, washed and dried under reduced pressure to give 2-isopropenyloxazoline-4,5-dione hydrochloride. Examples 5 to 7 were carried out in the same manner as in Example 2. Comparative Example 1 Preparation of 2-isopropenyloxazoline-4,5-dione hydrochloride (III: R = CH₃; X = Cl):- Methacrylamide was charged in a reactor, and while stirring, oxalyl chloride was dropwise added thereto in about 1 to 2 hours. With the progress of the dropwise addition, the reaction mixture changed to a brown, transparent resin. The resin was dissolved in dichloroethane (90 ml) and allowed to stand at room temperature, whereby 2-isopropenyloxazoline-4,5-dione hydrochloride was precipitated. The precipitate was collected by filtration and dried under reduced pressure. The reaction conditions and the yields in Examples 2 to 7 and Comparative Example 1 of the objective oxazolinedione hydrochloride are shown in Table 1. Example 8 To 2-isopropenyloxazoline-4,5-dione hydrochloride (200 g; 1.14 mol), o-dichlorobenzene (800 g) was added, and the resultant mixture was heated to 140°C while stirring for about 40 minutes. After cooling with water, the reaction mixture was distilled under reduced pressure to give methacryloyl isocyanate (70.9 g) and alpha-methyl-beta-chloropropionyl isocyanate (48.7 g). Example 9 To 2-isopropenyloxazoline-4,5-dione hydrochloride (200 g; 1.14 mol), dichloroethane (800 g) was added, and the resultant mixture was heated to 60 - 65°C while stirring for about 5.5 hours. After cooling with water, the reaction mixture was distilled under reduced pressure to give methacryloyl isocyanate (25.3 g) and alpha-methyl-beta-chloropropionyl isocyanate (80.7 g). Example 10 To 2-vinyloxazoline-4,5-dione hydrochloride (100 g; 0.62 mol), o-dichlorobenzene (400 g) was added, and the resultant mixture was heated at 110 to 120°C while stirring for about 30 minutes. After cooling with ice, the reaction mixture was distilled under reduced pressure to give acryloyl isocyanate (8.9 g) and beta-chloropropionyl isocyanate (56.4 g). Examples 11 to 16 2-Isopropenyloxazoline-4,5-dione hydrochloride (8.775 g; 50 mmol) was dissolved in dichloroethane (44 ml), and molecular sieve was added thereto. The resultant mixture was heated at 80°C for 1 hour while stirring. A portion of the reaction mixture was sampled, deuterated chloroform was added thereto, and NMR spectrum was measured. From the ratio of the absorption area of the methyl group (δCH₃: 1.87 ppm) in methacryloyl isocyanate to that of the methyl group (δCH₃: 1.32 ppm) in alpha-methyl-beta-chloropropionyl isocyanate, the molar ratio of methacryloyl isocyanate to alpha-methyl-beta-chloropropionyl isocyanate was determined. The results are shown in Table 2. Comparative Example 2 In the same manner as in Example 11 except that molecular sieve was not used, the operation was carried out. As the result, the molar ratio of methacryloyl isocyanate to alpha-methyl-beta-chloropropionyl isocyanate in the reaction mixture was 1.8 : 1. Example 17 In the same manner as in Example 11 except that cuprous chloride (4.950 g; 50 mmol) was used in place of molecular sieve, the operation was carried out. As the result, the molar ratio of methacryloyl isocyanate to alpha-methyl-beta-chloropropionyl isocyanate in the reaction mixture was 3.2 : 1. Example 18 Oxalyl chloride (139.6 g; 1.1 mol) and o-dichlorobenzene (400 g; dielectric constant, 9.88] were mixed together and cooled to a temperature of 0 to 10°C. Methacrylamide (85.1 g; 1.0 mol) was portionwise added thereto in 40 minutes, followed by stirring at 35 to 40°C for 2 hours. A small amount of seed crystals of 2-isopropenyloxazoline-4,5-dione hydrochloride was added thereto, and the resultant mixture was allowed to stand whereby 2-isopropenyloxazoline-4,5-dione hydrochloride was crystallized out. To the above mixture comprising crystals of 2-isopropenyloxazoline-4,5-dione hydrochloride, hexane (600 g; dielectric constant, 1.88) was added so that the dielectric constant of the solvent mixture was made to 3.45. Stirring was continued at a temperature of 70 to 75°C for 1.5 hours. Distillation of the reaction mixture gave methacryloyl isocyanate (55.9 g). Yield, 88.4 %. Examples 19 to 23 In the same manner as in Example 18, except that the reaction conditions were changed as shown in Table 3, the operation was carried out. The results are shown in Table 3. Example 24 Oxalyl chloride (139.6 g; 1.1 mol) and o-dichlorobenzene (400 g; dielectric constant, 9.88) were mixed together and cooled to a temperature of 0 to 10°C. Methacrylamide (85.1 g; 1.0 mol) was portionwise added thereto in 40 minutes. A small amount of seed crystals of 2-isopropenyloxazoline-4-5-dione hydrochloride was added thereto, and the resultant mixture was allowed to stand whereby 2-isopropenyloxazoline-4,5-dione hydrochloride was crystallized out. Hexane (600 g; dielectric constant, 1.88) was added thereto. Precipitated crystals were collected by filtration to obtain 2-isopropenyloxazoline-4,5-dione hydrochloride in a yield of 98.6 %. 2-Isopropenyloxazoline-4,5-dione hydrochloride as obtained above (100 g) was suspended in a mixture of hexane (240 g) and o-dichlorobenzene (160 g), the dielectric constant of the solvent mixture being 3.45. The suspension was heated at a temperature of 70 to 75°C under reflux for 1.5 hours. Distillation of the reaction mixture gave methacryloyl isocyanate (49 g; yield, 89.9 %) and alpha-methyl-beta-chloropropionyl isocyanate (1.4 g; yield, 1.7 %). Examples 25 to 27 2-Isopropenyloxazoline-4,5-dione hydrochloride as obtained in Example 24 was subjected to decomposition under the conditions as shown in Table 4. The results are shown in Table 4. Examples 28 and 29 and Comparative Examples 3 and 4 In the same manner as in Example 18 but using the the conditions as shown in Table 5, the operation was carried out. The results are shown in Table 5.

Claims: A process for producing an alkenoyl isocyanate of the formula wherein R is H or C₁₋₅ alkyl, which comprises subjecting an oxazolinedione hydrohalide of the formula wherein X is a halogen atom and R is as defined above, to decomposition in a liquid medium, under ambient pressure, and recovering the product. A process according to claim 1, wherein R is methyl and X is Cl. A process according to claim 1, wherein R is H and X is Cl. A process according to any preceding claim, wherein the decomposition is conducted in the presence of a hydrogen halide-eliminating agent. A process according to any preceding claim, wherein the liquid medium has a dielectric constant of not more than 4. A process according to any preceding claim, which additionally comprises producing the oxazolinedione hydrohalide by charging an oxalyl halide of the formula (COX)₂ wherein X is as defined in claim 1, into a reactor, and adding portionwise an acrylamide of the formula wherein R is as defined in claim 1. A process according to claim 6, wherein the oxalyl halide is charged into the reactor with an inert solvent, the acrylamide is added at 0 to 25°C, seed crystals of the oxazolinedione hydrohalide are added to the reaction mixture, to crystallise out the oxazolidinedione hydrohalide which is produced, and the oxazolinedione hydrohalide as crystallised out is subjected to decomposition in a liquid medium having a dielectric constant of not more than 4, at 40 to 150°C, under ambient pressure. A process according to claim 7, wherein the oxazolidinedione hydrohalide as crystallised out is collected once from the reaction mixture, prior to decomposition. An oxazolinedione hydrohalide of the formula wherein X is a halogen atom.

Inventors: AOKI, KEI, MATSUMURA, AKIRA, MIZUGUCHI, RYUZO, SUZUKI, YUJI, TSUBONIWA, NORIYUKI, URANO, SATOSHI
Applicants: NIPPON PAINT CO., LTD.
Application year: 1986
Main classification: C07C265
IPC codes: C07C265, C07C263, C07D263