PROCESS FOR PREPARING N,N'-(1,2-ETHYLENE)-BIS-TETRABROMOPHTHALIMIDE

Abstract: N, N′-(halo)hydrocarbon -bis-tetrabromophthalimides are prepared by brominating a compound of the formula Z-R-Z (wherein each Z is a phthalimido group and R is a (halo)hydrocarbon) in 40-80% oleum, with or without a catalyst such as silver nitrate or iron/iodine. The designations "(halo)" and "(cyclo)" permit optional halogenation and cyclic character respectively. In preferred embodiments of the invention, the N, N′-(halo) hydrocarbon-bis-phthalimide is an N, N′-(cyclo) alkylene-bis-phthalimide - most preferably N, N′-(1,2-ethylene) -bis-phthalimide, the brominating agent is bromine, and the ingredients are admixed in such amounts that the reaction mixture contains about 1-1.5 atoms of bromine and about 1-1.9 molecules of sulfur trioxide per available aromatic carbon atom in the N, N-(halo)hydrocarbon-bis-phthalimide.

Description: PROCESS FOR PREPARING N, N'-(HALO)HYDROCARBON-BIS TETRABROMOPHTHALIMIDES. This invention relates to a novel process for preparing N, N'- (halo) hydrocarbon-bis- tetrabromophthalimides and more particularly relates to a process for preparing such compounds by the bromination of the corresponding N, N'-(halo)hydrocarbon-bisphthalimides. The designation "(halo)hydrocarbon" indicates that the hydrocarbon may or may not be halogenated. As shown in U.S. patents 3,873,567 (Cyba) 4,087,441 (Lee), 4,092,345 (Wolford et al.), 4,125,535 (Wolford), and 4,140,862 (Dobson et al.), British patent 1,287,934 (Raychem), and in Sydney M. Spatz and Herman Stone, "Some N-Substltuted Tetrabromophthalimide Fire Retardant Additives", INDUSTRIAL AND ENGINEERING CHEMISTRY PRODUCT RESEARCH AND DEVELOPMENT, Volume 8, pp. 397-398 (1969), it is known that N, N'-(halo)hydrocarbonbis-tetrabromophthalimides can be prepared by reacting a tetrabromophthalic anhydride, acid, or half-ester with the appropriate diamine. Some of these processes are more economical than others, but all leave something to be desired from the economical standpoint. Another disadvantage of the processes is that most of them lead to the formation of a yellow product, and the few that produce a white product are not commercially attractive enough. It is also known that reasonably simple aromatic molecules, such as phthalic anhydride, can be brominated by various techniques. A particularly valuable technique involves the use of oleum, as disclosed in U.S patents 3,382,254 (Jenkner et al.) 3,567,739 (Sanger) and 3,875,186 (Hein et al.), British patent 1,084,375 (Kalk) , and German patents 1,039,052 (Guthke) and 1,125,415 (Hahn). However, it has not previously been suggested to apply these known bromination techniques to the bromination of relatively complex aromatic molecules, such as N, N'-(halo)hydrocarbon-bis-phthalimides, which would be expected to suffer degradation when subjected to bromination in oleum. An object of this invention is to provide an economical process for preparing N, N'-(halo)hydrocarbonbis-tetrabromophthalimides which involves the bromination of N, N'-(halo)hydrocarbon-bis-phthalimides. In order to achieve this economy, not least because the products are white, we brominate an N, N' (halo)hydrocarbon-bis-phthalimide in 40-80% oleum. Relatively mild conditions can be used and, contrary to what would have been expected, the bromination process of the invention results in the preparation of an N, N' (halo) hydrocarbon-bis-tetrabromophthalimide instead of degrading the N, N' (halo)hydrocarbon-bis-phthalimide. The process is particularly advantageous in that it is an economical means of preparing the desired product from readily available raw materials and in that it produces a white product instead of the yellow product obtained from most processes for preparing N, N'-(halo)hydrocarbon-bis tetrabromophthalimides. When a silver catalyst is employed, the process has the additional advantage of producing lower tetrahydrofuran solubles (i.e., fewer byproducts) than comparable processes utilizing different catalysts, and it permits better utilization of the sulfur trioxide and easier clean-up of the brominated product. The N, N'-(halo)hydrocarbon-bis-phthalimide which is brominated in accordance with the invention may be any compound corresponding to the formula Z-R-Z wherein each Z is a phthalimido group and R is a divalent hydrocarbon or halohydrocarbon group. However it is generally a compound in which R is a divalent hydrocarbon, bromohydrocarbon, or chlorohydrocarbon group containing 2-15 carbon atoms, and may be one in which R is an aromatic (halo) hydrocarbon group; but it is preferably such a compound in which R is (cyclo)alkylene - that is to say, it is an alkylene or cycloaklylene group. Most preferably it is a compound in which R is an alkylene group containing 2-6 carbon atoms. Exemplary of utilizable N, N'-(halo)hydrocarbon-bis-phthalimides are those compounds in which R is 1,2-ethylene, 1,2-dibromoethylene, 1,2-propylene, 1,3propylene, 1,4-butylene, l,4-(2,-dichlorobutylene) , 1,5pentylene, 1,6-hexylene, 1,2-cyclohexylene, 1,4-(2-bromocyclohexylene), 1,4-(2,3-dibromocyclohexylene), 1,4cyclohexylene, 1,12-dodecyclene, 4,4'-methylene-biscyclohexylene, cyclohexylene-bis-methylene, phenylene, bromophenylene, chlorophenylene, toluylene, bromotoluylene, xylyene, bromoxylylene, etc. When not commercially available, these imides can be prepared by reacting two molar proportions of phthalicanhydride with one molar proportion of the appropriate diamine. The appropriate diamine is usually one that contributes the (halo) hydrocarbon group desired in the final product. However, when the final (halo) hydrocarbon group is to be a brominated aromatic hydrocarbon group, it is not necessary to start with a brominated aromatic hydrocarbon group. It is within the scope of the invention to start with an unbrominated aromatic hydrocarbon group as the R and then brominate this group at the same time as the phthalimido groups to yield an N,N'-bromohydrocarbon-bis-tetrabromophthalimide as the final product. The brominating agent used in the process of the invention is usually bromine, although other brominating agents, such as bromine chloride, can be employed if desired. The amount of bromine used should be at least the amount theoretically required to achieve complete bromination of the aromatic rings of the starting material, i.e., an amount that provides one bromine atom for each available aromatic carbon atom. There is no maximum to the amount of bromine that can be used, but there is no advantage to using unnecessarily large amounts of bromine. Therefore, it is preferable to employ amounts of bromine that provide about 1-1.5, most preferably about 1.05-1.15, atoms of bromine per available aromatic carbon atom. In the case of the preferred N, N'-(cyclo)alkylene-bis-phthalimide starting materials, it is thus preferable to use about 4-6 mols, most preferably about 4.2-4.6 mols, of bromine per mol of N, N'- (cyclo) alkylene-bis-phthalimide. Excellent results are obtained by using bromine in an amount that is about 10% more than the amount theoretically required for complete bromination. The oleum used in the practice of the invention is a solution of 40-80% by weight of sulfur trioxide in concentrated sulfuric acid. Because of readier availability as well as effectiveness, a 60-70% oleum is preferred. The oleum is employed in an amount such as to provide at least one molecule of sulfur trioxide per available aromatic carbon atom and is preferably used in larger amounts, since the reaction rate increases with an increased concentration of sulfur trioxide in the reaction mixture. Ordinarily the oleum is utilized in an amount such as to provide about 1 to about 1.9, preferably about 1.25 to about 1.75, molecules of sulfur trioxide per available aromatic carbon atom. Thus, in the case of the preferred N, N'-(cyclo)alkylene-bis- phthalimide starting materials, it is preferable to use about 8 to about 15 mols, most preferably about 10 to about 14 mols, of sulfur trioxide per mol of N, N' (cyclo)alkylene-bis-phthalmide. Excellent results are obtained by using about 50% more sulfur trioxide than is theoretically required for complete sulfonation of the aromatic rings of the imide. When an oleum containing the desired amount of sulfur trioxide is not readily available, the desired concentration of sulfur trioxide can be attained by using additional sulfur trioxide with an oleum having a low sulfur trioxide content. In this reaction we find that the bromination of the N, N'-(halo)hydrocarbon-bis-phthalimide can be accomplished under relatively mild conditions, so it is not necessary to use very high temperatures or pressures in the practice of the invention. Ordinarily the desired bromination can be achieved by heating the reactants at about 35-60 C., preferably about 5soy., for at least about 3 hours, although it is sometimes desirable to use higher temperatures, e.g., about 70-90oC., to complete the bromination when the concentration of sulfur trioxide in the reaction mixture has been relatively low during the initial stage of the reaction. Such relatively low concentrations in the reaction mixture may occur, for example, if a whole charge of N,N'-(halo)hydrocarbon-bisphthalimide is initially present, as distinct to being added gradually to the oleum. The reaction may be conducted under atmospheric or superatmospheric pressure, with or without a catalyst. When pressure is employed, it is ordinarily only the slight pressure created by a back pressure device, although higher pressures may be used if desired. When a catalyst is employed, it may be any suitable bromination catalyst, e.g., sodium nitrate, nitrogen dioxide, aluminium, iron, an iron-iodine mixture, a silver catalyst, etc. Catalysts, when employed, are normally used in concentrations of about 0.1-2%, based on the weight of the N, N'-(halo)hydrocarbon-bis-phthalimide. Particularly good results are obtained when the catalyst is a 50:50 mixture of iron and iodine, and even better results are obtained when the catalyst is a silver catalyst, e.g., silver or any inorganic or organometallic silver compound capable of catalyzing the bromination of aromatic carbons. Because of availability as well as effectiveness, the preferred silver catalysts are silver, silver nitrate, silver sulfate, silver carbonate, silver acetate, silver chloride, silver bromide, and mixtures thereof. Silver nitrate is particularly preferred. The manner of admixing the reactants is not critical, although the reaction is much more efficient when the reactants are admixed in such a manner as to maximize the concentration of sulfur trioxide at all times. One suitable method of conducting the raction is to dissolve the N, N'-(halo)hydrocarbon-bis-phthalimide and optional. catalyst in the oleum, heat the solution to about 35-60oC., add the brominating agent thereto over a period of about 3-10 hours, maintain the reaction mixture at about 35-6OoC. for an additional 0-5 hours, raise the reaction temperature to about 7Q-90OC., and maintain the reaction mixture at about 70-90sC. for about 1-3 hours. A preferred method of conducting the reaction is to charge optional catalyst and about 45-75% of the oleum to a reaction vessel, heat the oleum and optional catalyst to about 35-60oC., and simultaneously add the bromine and a solution of the N, N-(halo)hydrocarbon- bis-phthalimide in the remainder of the oleum over a period of about 3-5 hours. When the bromination has been completed, unreacted materials and by-products are removed by conventional techniques to isolate the N, N'-(halo)hydrocarbon-bis-tetrabromophthalimide product. Conveniently the product is isolated by raising the temperature to about 100-140oC. to distill off the excess bromine and sulfur trioxide, cooling to room temperature, filtering, washing with water until the product is free of acid, and drying. The following examples are given to illustrate the invention and are not a limitation thereof. Unless otherwise specified, quantities mentioned are quantities by weight. EXAMPLE I Charge a suitable reaction vessel with 40 parts of N, N'-(1, 2-ethylene)-bis-phthalimide, 0.25 parts of iodine, 0.25 parts of iron, and 100 parts of 30% oleum. Stir the mixture, cool it to 150C.. and add 144 parts of sulfur trioxide while stirring. Heat the reaction mixture to 50 C. and add 94 parts of bromine over a period of seven hours. After completing addition of the bromine, heat the reaction mixture to 100oC. and maintain this temperature for one hour. Then cool the reaction mixture to 40 C., and set up a Dean Stark trap to distill off sulfur trioxide, and heat the reaction mixture to 1200C. while collecting sulfur trioxide with the Dean Stark trap. Cool the reaction mixture to 250C., filter, wash the solid product three times with 100 parts of water, and dry overnight at l00oC. in a vacuum oven. The process results in a 91% yield of a white product having a melting point of 458-461oC., a bromine content of 66.05%, and an IR spectrum consistent for N, N'-(1,2- ethylene)-bis-tetrabromophthalimide. EXAMPLE II Charge 35 parts of N, N'-(1,2-ethylene)-bis- phthalimide and 244 parts of 65% oleum to a suitable reaction vessel equipped with a back pressure system including a check valve. Heat the reaction mixture to 550C. and add 80.5 parts of bromine over a period of six hours and ten minutes. Maintain the reaction temperature at 550C. for an additional 40 minutes, heat to 70 C., maintain the temperature at 700C. for one hour, heat- to lOOoC., maintain the temperature at lO0oC. for one hour, and cool to 80or. Place a Dean Stark trap in the system and heat to 140or. while removing excess sulfur trioxide. Then cool the reaction mixture to 20or., filter, wash the solid product twice with 200 parts of water, and dry at 100or, in a vacuum oven. The process results in an 88% yield of white N, N'-(1,2-ethylene)-bis-tetrabromo- phthalimide having a tetrahydrofuran solubles content of 0.3% and a melting point of 466-472oC. EXAMPLE III Charge 35 parts of N, N'-(1,2-ethylene)-bis- phthalimide, 0.035 parts of sodium nitrate, and 244 parts of 65% oleum to a suitable reaction vessel equipped with a back pressure system including a check valve. Heat the reaction mixture to 55or. and add 80.5 parts of bromine over a period of five hours. Maintain the reaction mixture at 55 C. for an additional two hours, heat to 700C., maintain the temperature at 70 C. for three hours, heat to 100oC. maintain the temperature at l00oC. for one hour, and cool to 80 C. Place a Dean Stark trap into the system and heat to 140 C. while removing excess sulfur trioxide. Then cool the reaction mixture to 20 C., filter, wash the solid product twice with 200 parts of water, and dry at 100or, in a vacuum oven. The process results in an 85% yield of white N, N'-(1,2- ethylene)-bis-tetrabromophthalimide having a tetrahydrofuran solubles content of 0.3% and a melting point of 466-4720C. EXAMPLE IV Charge 40 parts of N, N'-(1,2-ethylene)-bisphthalimide, 0.04 part of iodine, o.04 part of iron, and 244 parts of 65% oleum to a suitable reaction vessel equipped with a back pressure system including a check valve and cold trap. Heat the reaction mixture to 550C. and add 92 parts of bromine over a period of six hours. Maintain the reaction temperature at 550C. for an additional 30 minutes, heat to 70or., maintain the temperature at 70roc. for three hours, heat to 100or., maintain the temperature at 100oC. for one hour, and cool to 8OoC. Place a Dean Stark trap into the system and heat to 140or in stages while removing excess bromine and sulfur trioxide. Then cool the reaction mixture to 20or., filter, wash the solid product twice with 200 parts of water, and dry in a vacuum oven at 100oC. The process results in a 96% yield of white N, N'-(1,2ethylene)-bis-phthalimide having a tetrahydrofuran solubles content of 0.2% and a melting point of 471 476or. EXAMPLE V Charge 40 parts of N, N'-(1,2-ethylene)-bisphthalimide, 0.08 part of silver acetate, and 244 parts of 65% oleum to a suitable reaction vessel equipped with a back pressure system. Heat the reaction mixture to 55oC. and add 92 parts of bromine over a period of six hours. Maintain the reaction temperature at 55 C. for an additional 45 minutes, heat to 70 C., maintain the temperature at 70 C. for three hours, heat at 97 C. for another hour, and cool to 70 C. Place a Dean Stark trap into the system and heat to 140 C. while removing excess bromine and sulfur trioxide. Then cool the reaction mixture to 20 C., filter, wash the solid product twice with 200 parts of water, and dry. The process results in an 86% yield of white N, N'-(1,2-ethylene)-bis-tetrabromophthalimide having a tetrahydrofuran solubles content of 0.05% and a melting point of 470-4720C. EXAMPLE VI Charge 40 warts of N, N'-(1,2-ethylene)-bis- phthalimide, 0.04 part of silver nitrate, and 244 parts of 65% oleum to a suitable reaction vessel equipped with a back pressure system. Heat the reaction mixture to 55or. and add 92 parts of bromine over a period of five hours. Maintain the reaction temperature at 55or. for an additional 20 minutes, heat to 70or., maintain at 70or. for three hours, heat at 100oC. for one hour, and cool to 80 C. Place a Dean Stark trap into the system and heat to 140 C. while removing excess sulfur trioxide. Then cool the reaction mixture to 20 C., filter, wash the solid product twice with 200 parts of water, and dry. The process results in a 95% yield of white N, N-(1,2 ethylene)-bis-tetrabromophthalimide having a tetrahydrofuran solubles content of 0.05% and a melting point of 477-482oC. The process also leads to the recovery of 90.4% of the unreacted sulfur trioxide. EXAMPLE VII Charge 35 parts of N, N'-(1,2-ethylene)-bis- phthalimide and 244 parts of 65% oleum to a suitable reaction vessel equipped with a back pressure system. Heat the reaction mixture to 55 C. and add 80.5 parts of bromine over a period of six hours and ten minutes. Maintain the reaction temperature at 55 C. for an additional 40 minutes, heat to 70 C., maintain the temperature at 70oC. for one hour, heat to 100oC., maintain the temperature at 100oC for one hour, and cool to 800C. Place a Dean Stark trap in the system and heat to 140 C. while removing excess sulfur trioxide. Then cool the reaction mixture to 20oC., filter, wash the solid product twice with 200 parts of water, and dry. The process results in an 88% yield of white N, N'-(1,2 ethylene)-bis-tetrabromophthalimide having a tetrahydro furan solubles content of 0.3% and a melting point of 466-472OC. Only 40% of the unreacted sulfur trioxide is recovered. EXAMPLE VIII Charge 35 parts of N, N'-(1.2-ethylene)-bisphthalimide, 0.035 part of sodium nitrate, and 244 parts of 65% oleum to a suitable reaction vessel equipped with a back pressure system. Heat the reaction mixture to 55or. and add 80.5 parts of bromine over a period of five hours. Maintain the reaction mixture at 55or. for an additional two hours, heat to 70or., maintain the temperature at 70 C. for three hours, heat to 100oC., maintain the temperature at lO0oC. for one hour, and cool to SOoC. Place a Dean Stark trap into the system and heat to l40oC. while removing excess sulfur trioxide. Then cool the reaction mixture to 20 C., filter, wash the solid product twice with 200 parts of water, and dry. The process results in an 85% yield of white N, N'-(1,2 ethylene) -bis-tetrabromophthalimide having a tetrahydrofuran solubles content of 0.3% and a melting point of 466-472OC. Only 52% of the unreacted sulfur trioxide is recovered. EXAMPLE IX Charge 40 parts of N, N'-(1,2-ethylene)-bis- phthalimide, 0.04 part of iodine, 0.04 part of iron, and 244 parts of 65% oleum to a suitable reaction vessel equipped with a back pressure system. Heat the reaction mixture to 55 or. and add 92 parts of bromine over a period of six hours. Maintain the reaction temperature at 550C. for an additional 30 minutes, heat to 70 C., maintain the temperature at 70 C. for three hours, heat to 100OC., maintain the temperature at l00oC. for one hour, and cool to SOOC. Place a Dean Stark trap into the system and heat to 140or. while removing excess bromine and sulfur trioxide. Then cool the reaction mixture to 20or., filter, wash the solid product twice with 200 parts of water, and dry. The process results in a 96% yield of white N, N'-(1,2-ethylene)-bis-tetrabromo- phthalimide having a tetrahydrofuran solubles content of 0.2% and a melting point of 471-476OC. The process also leads to the recovery of 90% of the unreacted sulfur trioxide. Similar results are observed when the Examples are repeated except that (1) the ingredients are replaced by materials taught to be their equivalents in this specification or (2) the reaction conditions are varied as indicated in this specification.

Claims: CLAIMS 1. A process for preparing an N, N'-(halo)hydrocarbon-bis-tetrabromophthalimide characterized in brominating a compound of the formula Z-R-Z, in which each Z is a phthalimido group and R is a (halo)hydrocarbon group, in 40-808 oleum. 2. A process according to claim 1, wherein 60-70% oleum is used. 3. A process according to claim 1 or claim 2, wherein R is a (halo)-hydrocarbon group containing 2-15 carbon atoms. 4. A process according to claim 3, wherein R is a (cyclo) alkylene group. 5. A process according to claim 3, wherein R is an alkylene group containing 2-6 carbon atoms. 6. A process according to claim 5, wherein R is an ethylene group. 7. A process according to claim 3, wherein R is an aromatic (halo) hydrocarbon group. 8. A process according to any one of the preceding claims, wherein the reaction mixture contains about 1 to about 1.5 atoms of bromine and about 1 to about 1.9 molecules of sulfur trioxide per available aromatic carbon atom in the compound Z-R-Z. 9. A process according to claim 8, wherein the reaction mixture contains about 1.05 to about 1.15 atoms of bromine and about 1.25 to about 1.75 molecules of sulfur trioxide per available aromatic carbon atom in the compound Z-R-Z. 10. A process according to any one of claims 1 to 7, wherein about 4-6 molar proportions of bromine are reacted with one molar proportion of an N, N'-(cyclo)alkylene-bis-phthalimide in an amount of the oleum containing about 8-15 molar proportions of sulfur trioxide by heating about 45-75% of the oleum to a temperature of about 35-60oC., then simultaneously adding thereto over a period of about 3-5 hours the bromine and a solution of the N, N'-(cyclo)alkylene-bis-phthalimide in the remainder of the oleum, and removing unreacted materials and by-products to isolate the resultant N, N' (cyclo) alkylene-bis-tetrabromophthalimide. 11. A process according to any one of the preceding claims, wherein the bromination is conducted in the presence of a silver or an iron/iodine catalyst. 12. A process according to claim 11, wherein the catalyst is silver nitrate.

Inventors: DOTSON, ANDERSON O., LEE, CHIEN YUNG, WADSWORTH, FRANCIS T., WOLFORD, LIONEL T.
Applicants: ETHYL CORPORATION
Application year: 1980
Main classification: C07D209
IPC codes: C07D209