PREPARATION OF NUCLEAR CHLORINATED AROMATIC COMPOUNDS

Abstract: Disclosed is a method of preparing an aromatic compound having general formula (I) where R is CF3, OCF3, OC2F5, CN, NCO, or COCl, m is 0, 1, or 2, n is 0, 1, or 2, q is 1 or 2, and q+m+n is an integer from 1 to 5. A vapor is prepared of a substrate having general formula (II) and a chlorinating agent. The mixture is reacted at a temperature above the boiling point of the substrate but below its decomposition temperature. The amount of chlorinating agent is about 0.5 to about 2 times the amount stoichiometrically required to replace the nitro groups on the substrate with chlorine. Unreacted substrate and partially reacted substrate are condensed from the product mixture and are recycled. The substrate is preferably in contact with the chlorinating agent before it is vaporized.

Description: 'PREPARATION OF NUCLEAR CHLORINATED AROMATIC COMPOUNDS" THIS INVENTION relates to a process for chlorodenitrating aromatic compounds. U.S. Patents 4,470,930 and 4,582,948 describe a process for the nuclear chlorination of aromatic compounds. In that process, an aromatic compound having nifto and other groups on the ring is heated in the presence of a chlorinating agent, which results in the replacement of the nifto groups by chlorine. To obtain a high yield, excess chlorine and higher temperatures are used. While the yield in the process described in those patents is good, the product also contains partially chlorinated intennediates, unreacted stalling material, and overchlorinated byproducts. Separation of the desired product from these undesirable byproducts and unreacted starting material by distillation can result in the decomposition of the partially chlorinated intermediates and the unreacted starting material. According to one aspect of this invention there is provided a method of making a chlorinated aromatic compound having the general formula comprising (A) preparing a vaporized mixture of a chlorinating agent and a substrate having the general formula where R is CF 3 , OCF 3 , OC 2 F 5 , CN, NCO, or COCl, m is 0, 1, or 2, n is 0, 1, or 2, q is 1 or 2, q + m + n is an integer from 1 to 5, and the amount of chlorinating agent in said mixture is about 0.5 to about 2 times the amount stoichiomeftically required to replace the nifto groups on said substrate with chlorine; (B) heating said vaporized mixture to a temperature above the boiling point of said substrate but below its decomposition temperature to produce a product mixture; (C) condensing said subsftate and partially reacted subsftate from said product mixture; and (D) recycling said condensed subsftate and said condensed partially reacted substrate to step (A). In this formula, R is preferably CF , m is preferably 0, n is preferably 1, and q is preferably 2 as those compounds are more important commercially. Preferably step (B) is performed in a reactor and steps (B), (C) and (D) are repeated until at least 95 wt% of the organic overhead from said reactor is said chlorinated aromatic compound. According to another aspect of this invention there is provided a method of making a chlorinated aromatic compound having the general formula comprising (A) vaporizing a substrate having the general formula where R is CF 3 , OCF , OC 2 F 5 , CN, NCO, or COCl, m is 0, 1, or 2, n is 0, 1, or 2, q is 1 or 2, q + + n is an integer from 1 to 5; (B) preparing a mixture of said vaporized subsftate and chlorine where the amount of chlorine in said mixture is about 0.8 to about 1.4 times the amount stoichiomeftically required to replace the nitro groups on said substrate; (C) heating said vaporized mixture in a reactor to about 290 to about 350°C to produce a product mixture; (D) condensing said subsftate and partially reacted subsftate from said product mixture; (E) recycling said condensed subsftate and said condensed partially reacted subsftate to step (A); (F) repeating steps (B), (C), (D) and (E) until at least 95 wt% of the organic overhead from said reactor is said chlorinated aromatic compound; and (G) isolating said chlorinated aromatic compound from said overhead. According to a further aspect of this invention there is provided a method of making 3,4,5-trichloiObenzotrifluoride comprising (A) preparing mixture of liquid 4-chloiO-3,5-dmiftObenzotrifluoride and about 0.8 to about 1.4 moles of chlorine gas per mole of said liquid 4-chloio-3,5-diniftObenzotrifluoride; (B) vaporizing said liquid 4-chloiO-3,5-diniftObenzotrifluoride in said mixture; (C) heating said mixture in a reactor to about 290 to about 350°C to produce a product mixture; (D) condensing aromatics that boil above about 180°C from said product mixture; (E) recycling said condensed aromatics to step (B): (F) repeating steps (C), (D), and (E) until at least 95 wt% of the organic overhead from said reactor is 3,4,5- trichlorobenzotrifluoride; and (G) condensing said 3,4,5-trichlorobenzotrifluoride from said overhead. We have found that the process described in U.S. Patents 4,470,930 and 4,582,948 can be improved upon by using very little excess chlorine, or even less than a stoichiomeftic amount of chlorine, and by heating at relatively low temperatures. While this initially results in a significantly lower yield of the desired product, the product mixture contains veiy little over-chlorinated byproduct. We have found that by condensing the unreacted starting material and the partially chlorinated starting material from the product mixture and repeatedly recycling them, the final product can be made in very high yield while, at the same time, significant quantities of over-chlorinated compounds are not produced. The preferred starting material for the access of the invention is 4- chloro-3,5-diniftObenzotrifluoride (CDN-BTF), as the product formed by the chlorodenitration of this substrate, 3,4,5-trichloiObenzotrifluoride, is used to make an agricultural intermediate for making a herbicide. Chlorinating agents that can be used for the process of this invention include chlorine gas, hydrogen chloride gas, thionyl chloride, sulfuryl chloride, sulfur chloride, phosgene, and phosphorous trichloride. However, the preferred chlorinating agent is chlorine gas as it is inexpensive and reacts well. The amount of chlorinating agent should be carefully controlled. About 0.5 to about 2 times the amount of chlorinating agent required to stoichiometrically replace the nifto groups on the aromatic compound should be used. If less than 0.5 times as much chlorinating agent is used, too much recycling will be required to bring the yield to high levels, and if more than 2 times the amount of chlorinating agent needed is used, more over-chlorinated byproducts will be produced. The preferred amount of chlorinating agent is about 0.8 to about 1.4 times the amount stoichiomeftically required. The chlorodenitration reaction is performed in the vapor phase, which requires the vaporization of the subsftate. Typically, the subsftate is a low melting point solid which is melted and charged into a vaporizer where it is heated to its boiling point. It is preferable to add the chlorinating agent before the subsftate is vaporized because if the subsftate is vaporized in the absence of the chlorinating agent it may decompose. Decomposed substrate does not react with the chlorinating agent and is therefore wasted. The vaporized reactants are preferably reacted in a vapor phase reactor that is separate from the vaporizer. It is preferable to use a packed column for this reactor as that facilitates heat and mass transfer and mixing of the reactants. The column can be packed with an inert material such as nickel metal, stainless steel, or various ceramics. It is preferable to use a thermally conductive packing material, such as a metal, for better heat transfer. Since the typical residence time in the vapor phase reactor is about a minute or two, the reactor volume should be selected to accommodate the volume of reactants. Preferably the condensing step is effected in a column packed with metallic nickel. The reaction temperature is above the boiling point of the substrate but below its decomposition temperature. A preferred temperature range is about 290 to about 350°C. At lower temperatures too little product is produced and at higher temperatures more over-chlorinated byproduct is produced. For example, if the subsftate is CDN-BTF, higher temperatures can result in the production of 2,3,4,5-tetxachloiObenzotrifluoride or even products such as 1,2,3,4,5-pentachlorobenzene or hexachlorobenzene. No catalyst is needed in this reaction. The desired product has the general formula: where R, m, n, and q were herein above defined. Examples of chloro-substituted benzotrifluorides that can be made by the process of this invention include 2-chloiObenzotrifluoride; 3-chlorobenzotrifluoride; 4-chlorobenzotrifluoride; 3- chloro-4-fluorobenzoftifluoride; 4-chloiO-3-fluoiObenzotrifluoride; 2-chloro-5- fluoiObenzoft'ifluoride; 5-chloiO-2-fluorobenzotrifIuoride; 2-chloro-4-fluoiO- benzotrifluoride; 4-chloiO-2-fluorobenzorrifluoride; 3-chloro-5 flurobenzotri- fluoride; 2,5-dichloiO-4-fluoiObenzotιifluoride; 4,5-dichlor-2-flurobenzotri- fluoride; 3,5-dichloro-4-fluoiObenzorrifluoride; 3,4-difluoro-5- chlorobenzoylftifluoride; 2,5-difluoiO-3-chloiObenzotrifluoride; 3,5-difluoro-4- chlorobenzotrifluoride; and 3,4-5-ftichloiObenzoftifluoride. Examples of chloro-substituted benzoyl chlorides that can be prepared include 2-chlorobenzoyl chloride; 3-chlorobenzoyl chloride; 4-chlorobenzoyl chloride; 4-chloιo-3-fluoiObenzoyl chloride; 3-chloro-4-fluoro-benzoyl chloride; 2-chloiO-4-fluorobenzoyl chloride; 4-chloiO-2-fluorobenzoyl chloride; 2-chloro-5-fluoiO-benzoyl chloride; 5-chloiO-2-fluorobenzoyl chloride; 3- chloro-5-fluorobenzoyl chloride; 2,5-dichloro-4-fluorobenzoyl chloride; 3,5- dichloro-4-fluorobenzoyl chloride; 4,5-dichloiO-2-fluorobenzoyl chloride; 3,4- difluoiO-5-chlorobenzoyl chloride; 3,5-difluoiO-4-chlorobenzoyl chloride; and 3,4,5-trichlorobenzoyl chloride. Examples of chloro-substituted trifluoromethoxybenzenes that can be prepared include 2-chloiOtrifluoiOinethoxybenzene; 3-chlorotι ifluoromethoxybenzene; 4-chloroftifluoromethoxy benzene; 3-chloiO-4-fluoiOtrifluoiOmethoxybenzene; 2-chloro-4-fiuoiOtrifluoromethoxybenzene; 4-chloro-2 fluiOftifluromethoxy- benzene; 2-chloiO-5-fluoiOftifluoiOmethoxybenzene; 5-chloro-2- fluorotrifluoromethoxybenzene; 3-chloro-5-fluorotrifluoiOmethoxybenzene; 2,5-dichloiO-4-fluoiOftifluoromethoxybenzene; 4,5-dichloiO-2-fluiOft * ifluoiO- methoxybenzene; 3,5-dichloiO-4-fluoromethoxybenzene; 3,4-difluoro-5- chloroftifluoromethoxybenzene; 2,5-difluoiO-3-chloiO-ftifluoromethoxy- benzene; 3,5-difluoro-4-chloiOtrifluoromethoxybenzene; and 3,4,5-trichloro- trifluoromethoxybenzene. Examples of chloro-substituted pentafluoroethoxybenzenes that can be prepared include 2-chloropentafluoroethoxybenzene; 3-chloropentafluoroethoxybenzene; 4-chloropentafluoroethoxybenzene; 2-chloiO-5-fluropentafluoiOethoxy- benzene; 5-chloiO-2-fluoropentafluoroethoxybenzene; 3-chloro-4- fluoiOpentafluoroethoxybenzene; 4-chloiO-3-fluoropentafluoiOethoxybenzene; 2-chloro-4-fluoropentafluoiOethoxybenzene; 4-chloiO-2-fluoropentafluro- ethoxybenzene; 3-chloiO-5-fluoropentafluoroethoxybenzene; 2,5-dichloro-4- fiuoropentafluoroethoxybenzene; 4,5-dichloiO-2-fluoropentafluoroehoxy- benzene; 3,5-dichloiO-4-fluoropentafluoiOethoxybenzene; 3,4-difluoro-5- chloropentafluoroethoxybenzene; 2,5-difluoiO-3-chloropentafluoiOethoxy- benzene; 3,5-difluoiO-4-chloiO-pentafluoroethoxybenzene; and 3,4,5-ftichloiOpentafluoroethoxybenzene. Examples of chloro-substituted benzonitriles that can be prepared include 2-chlorobenzonitrile; 3-chlorobenzonitrile; 4-chlorobenzonitrile; 2- chloro-5-fluorobenzonitrile; 5-chloiO-2-fluorobenzoniftile; 3-chloro-4- fluorobenzonitrile; 4-chloiO-3-fiuorobenzonitrile; 2-chloro-4-fluorobenzoni- trile; 4-chloiO-2-fluorobenzonitιile; 3-chloro-5-fluoiObenzonitrile; 2,5-dichloro- 4-fluorobenzonitrile; 4,5-dichloiO-2-fluorobenzoniftile; 3,5-dichloro-4- fluorobenzonitrile; 3,4-difluoiO-5-chlorobenzoniftile; 2,5-difluoro-3- chlorobenzonitrile; 3,5-difluoiO-4-chloiObenzonitrile; and 3,4,5-trichlorobenzonitιile. Examples of chloro-substituted phenyl isocyanates that may be prepared aie 2-chlorophenyl isocyanate; 3-chlorophenyl isocyanate; 4-chlorophenyl isocyanate; 2-chloro-5-fluoiOphenyl isocyanate; 5-chloro-2-fluorophenyl isocyanate; 3-chloro-4-fluoiOphenyl isocyanate; 4-chloro-3 -fluorophenyl isocyanate; 2-chloro-4-fluorophenyl isocyanate; 4-chloiO-2-fluorophenyl isocyanate; 3-chloro-5-fluorophenyl isocyanate; 2,5-dichloiO-4-fluorophenyl isocyanate; 4,5-dichloiO-2-fluorophenyl isocyanate; 3,5-dichloro-4- fluorophenyl isocyanate; 3,4-difluoiO-5-chlorophenyl isocyanate; 2,5-difluoro- 3-chlorophenyl isocyanate; 3,5-difluoiO-4-chlorophenyl isocyanate; and 3,4,5- trichlorophenyl isocyanate. The product mixture contains the desired product as well as unreacted substrate, partially reacted subsftate, and a small amount of over-chlorinated byproduct. The product mixture is sent to a partial condenser where aromatics that boil below the boiling point of the desired product are condensed. The partial condenser is preferably another heated column packed in the same manner as the reactor. Nonnally, the desired product will be the highest boiling aromatic. For example, if the desired product is 3,4,5- trichlorobenzotrifluoride, the condenser temperature is set at about 180 to about 200 °C so that the desired product does not condense but CDN-BTF, 3,4- dichloro-5-nitrobenzoftifluoride, 4,5-dichloiO-3-niftObenzotrifluoride, and overchlorinated byproducts do condense. The temperature of the partial condenser should be selected so that the substrate, partially reacted substrate, and possibly even part of the product are condensed, with the result that at least 95 wt% of the organic overhead from the partial condenser is the desired product. Preferably, the temperature of the partial condenser is selected so that at least 99 wt% of its organic overhead is the desired product. These condensed materials are then recycled to the vaporizer. Since any overchlorinated byproduct that is present will also be recycled with the subsftate and partially reacted subsftate, its concentration will eventually build up in the recycling loop. Over-chlorinated byproducts can be removed from the system periodically by, for example, filtration or other means. The desired product can be recovered from the partial condenser overhead by condensation. The chlorine and nitrogen dioxide gases that are present can be scrubbed with water or caustic or they can be treated by other means. The following examples further illustrates this invention. Example 1 Chlorine and CDN-BTF were continuously charged to a 2.54 cm (1- inch) tubular nickel reactor consisting of an unpacked vaporizer section, a reactor section packed with nickel mesh, and a partial condenser section also packed with nickel mesh. The chlorine ( 120 cc/min) and the CDN-BTF (1.46 g/min) were mixed, then fed into the vaporizer. The molar ratio of chlorine to CDN-BTF was 0.98. The vaporizer was heated to 315 to 320°C to totally vaporize the CDN- BTF. The mixed CDN-BTF and chlorine were fed to the packed reactor section, which was heated to 330°C. The reactor section was sized to allow a residence time for the chlorine/CDN-BTF mixture of 1 to 2 minutes. The resulting vapor reaction product mixture was fed to the partial condenser section, which was heated to 190°C, where unreacted CDN-BTF, reaction intermediate, and a portion of the desired product, 3,4,5- trichloiObenzotrifluoride, were condensed and collected. The remaining vapor, containing unreacted chlorine, nitrogen dioxide, 3,4,5-ftichlorobenzoftifluoride, and a small amount of reaction intermediate, was vented to a condenser, where the organic compounds were condensed and collected and the chlorine and nitrogen dioxide were scrubbed. The 3,4,5- trichloiObenzotrifluoride collected was 97% pure. The isolated yield of 3,4,5-trichlorobenzotrifluoride was 68%. When the recovered starting material, reaction inteπnediate, and product collected from the partial condenser were recycled, the yield increased to 96%. Example 2 - Comparative Example 1 was repeated except that no partial condenser was used. The 3,4,5-ftϊchloiObenzoftϊiiUθride collected was 75% pure. The isolated yield of 3,4,5-trichloiObenzotrifluoride was 78%. Distillation of the material to a higher purity was undesirable because the high concentration of high boiling nitro- and dinitro- compounds present would concentrate in the distillation bottoms. Example 3 - Comparative Example 2 was repeated except that the CDN-BTF was fed to the vaporizer and the chlorine was added to the vaporized CDN-BTF prior to introduction into the reactor section. The 3,4,5-ftϊchloiObenzotrifluoride collected was 75% pure. The isolated yield of 3,4,5-trichloiObenzotrifluoride was 67%. Distillation of the material to a higher purity was undesirable because the high concentration of high boiling nifto- and dinitro- compounds present would concentrate in the distillation bottoms. Inspection of the condenser after the reaction revealed that approximately 10% of the CDN-BTF charged had decomposed in the vaporizer and had deposited on the walls of the vaporizer. In the present specification "comprise" means "includes or consists of and "comprising" means "including or consisting of . The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims: AIM: A method of making a chlorinated aromatic compound having the general formula comprising (A) preparing a vaporized mixture of a chlorinating agent and a subsftate having the general fonnula where R is CF 3 , OCF 3 , OC 2 F 5 , CN, NCO, or COCl, m is 0, 1, or 2, n is 0, 1, or 2, q is 1 or 2, q + m + n is an integer from 1 to 5, and the amount of chlorinating agent in said mixture is about 0.5 to about 2 times the amount stoichiomeftically required to replace the nifto groups on said subsftate with chlorine; (B) heating said vaporized mixture to a temperature above the boiling point of said subsftate but below its decomposition temperature to produce a product mixture; (C) condensing said subsftate and partially reacted subsftate from said product mixture; and (D) recycling said condensed subsftate and said condensed partially reacted subsftate to step (A). 2. A method according to Claim 1 wherein R is CF 3 . 3. A method according to Claim 1 or Claim 2 wherein m is 0. 4. A method according to any one of Claims 1 to 3 wherein n is 1. 5. A method according to any one of the preceding Claims wherein q is 2. 6. A method according to Claim 1 wherein said substrate is 4-chloro-3,5- dinitro-benzoftifluoride. 7. A method according to any one of the preceding Claims wherein said subsftate is mixed with said chlorinating agent before it is vaporized. 8. A method according to any one of the preceding Claims wherein said chlorinating agent is chlorine. . A method according to any one of the preceding Claims wherein said mixture is reacted in a column packed with an inert material. 10. A method according to any one of the preceding Claims wherein said substrate is selected from the group consisting of chloro-substituted benzotrifluorides, chloro-substituted benzoyl chlorides, chloro- substituted trifluoromethoxybenzenes, chloro-substituted pentafluoroethoxybenzenes, chloro-substituted benzonitriles, and chloro- substituted phenyl isocyanates. 11. A method according to any one of the preceding Claims wherein said substrate and said partially reacted subsftate are condensed in a column packed with an inert material. 12. A method according to any one of the preceding Claims wherein the amount of said chlorinating agent is about 0.8 to about 1.4 times the amount needed to stoichiomeftically replace the nifto groups on said substrate. 13. A method according to any one of the preceding Claims wherein said vaporized mixture is heated to about 290 to about 350°C. 14. A method according to any one of the preceding Claims wherein step (B) is perfoπned in a reactor and steps (B), (C), and (D) are repeated until at least 95 wt% of the organic overhead from said reactor is said chlorinated aromatic compound. 15. A method of making a chlorinated aromatic compound having the general formula comprising (A) vaporizing a substrate having the general formula where R is CF 3 , OCF 3 , OC 2 F 5 , CN, NCO, or COCl, m is 0, 1, or 2, n is 0, 1, or 2, q is 1 or 2, q + m + n is an integer from 1 to 5; (B) preparing a mixture of said vaporized subsftate and chlorine where the amount of chlorine in said mixture is about 0.8 to about 1.4 times the amount stoichiomeftically required to replace the nifto groups on said subsftate; (C) heating said vaporized mixture in a reactor to about 290 to about 350°C to produce a product mixture; (D) condensing said subsftate and partially reacted substrate from said product mixture; (E) recycling said condensed subsftate and said condensed partially reacted substrate to step (A); (F) repeating steps (B), (C), (D) and (E) until at least 95 wt% of the organic overhead from said reactor is said chlorinated aromatic compound; and (G) isolating said chlorinated aromatic compound from said overhead. 16. A method according to Claim 15 wherein said subsftate is selected from the group consisting of chloro-substituted benzotrifluorides, chloro- substituted benzoyl chlorides, chloro-substituted trifluoromethoxy- benzenes, chloro-substituted pentafluoroethoxybenzenes, chloro- substituted benzoniftiles, and chloro-substituted phenyl isocyanates. 17. A method according to Claim 15 or Claim 16 wherein said subsftate is 4-chloiO-3,5-dinitiO-benzotrifluoride. 18. A method of making 3,4,5-ftichlorobenzoftifluoride comprising (A) preparing mixture of liquid 4-chloro-3,5-diniftObenzotrifluoride and about 0.8 to about 1.4 moles of chlorine gas per mole of said liquid 4-chloro-3,5-diniftObenzotrifluoride; (B) vaporizing said liquid 4-chloiO-3,5-diniftObenzotrifiuoride in said mixture; (C) heating said mixture in a reactor to about 290 to about 350°C to produce a product mixture; (D) condensing aromatics that boil above about 180°C from said product mixture; (E) recycling said condensed aromatics to step (B): (F) repeating steps (C), (D), and (E) until at least 95 wt% of the organic overhead from said reactor is 3,4,5- trichloiObenzotrifluoride; and (G) condensing said 3,4,5-ftichlorobenzotιifluoride from said overhead. 19. A method according to Claim 18 wherein said mixture is heated in a column packed with metallic nickel. 20. A method according to Claim 18 or Claim 19 wherein, in step (D), said aromatics are condensed in a column packed with metallic nickel.

Applicants: OCCIDENTAL CHEM CO, STEPHENS DINAH, OCCIDENTAL CHEMICAL CORPORATION, STEPHENS, DINAH
Application year: 1999
Main classification: C07B39
IPC codes: C07B39, C07C17, C07C41, C07C51, C07C253, C07C263