METHOD OF REDUCING RING CHLORINATION IN THE MANUFACTURE OF A TRICHLOROMETHOXYBENZENE

Abstract: Disclosed is a method of making a trichloromethoxybenzene from a methoxybenzene or partially chlorinated methoxybenzene, such as anisole or p-chloroanisole, that contains at least 20 ppm phenol. The phenol concentration is reduced to less than 20 ppm and a mixture is prepared of the methoxybenzene and a source of chlorine free radicals, such as chlorine or sulfuryl chloride. The reaction is performed in a solvent, which can be either benzotrifluoride, orthochlorobenzotrifluoride, metachlorobenzotrifluoride, parachlorobenzotrifluoride, or a dichlorobenzotrifluoride. The mixture is exposed to actinic radiation, such as ultraviolet light, which generates the chlorine free radicals.

Description: METHOD OF REDUCING RING CHLORINATION IN THE MANUFACTURE OF A TRICHLOROMETHOXYBENZENE This invention relates to a method of making a trichloromethoxybenzene by reacting a methoxybenzene, such as anisole or p-chloroanisole, with chlorine free radicals in a benzotrifiuoride (BTF) solvent to produce a trichloromethoxybenzene, such as α,α,α-trichloromethoxybenzene (TCMB) or α,α,α-trichloromethoxy-p-chlorobenzene (TCMCB), respectively. In particular, it relates to the use of a trichloromethoxybenzene that contains phenol as an impurity and to the removal of that phenol prior to this reaction. U.S. Patent No. 5,773,668 discloses a process for making TCMB by reacting anisole with gaseous chlorine in the presence of ultraviolet light in a BTF based solvent. While that reaction works well, the product can sometimes contain small quantities of ring chlorinated TCMB, chlorinated phenols, dioxins, and furans. We have discovered that the presence of a small amount of phenol in a methoxybenzene results in ring chlorination and dioxin formation, and that ring chlorination and dioxin formation can be very significantly reduced if the phenol is removed first. While we do not wish to be bound by any theories, we believe that the phenol is chlorinated first, and that the chlorinated phenol then ring chlorinates the methoxybenzene. We have found that a methoxybenzene can be photochlorinated in a BTF based solvent without significant chlorination of the aromatic ring and without the formation of significant amounts of dioxin if a methoxybenzene that contains phenol is first purified to reduce the amount of phenol to below 20 ppm. While in the prior process it was preferable to use 20% anisole and meter in the anisole in order to avoid ring chlorination, we have found that if the anisole is first purified of phenol, ring chlorination is avoided even when the anisole is not metered in and is used at 50 wt%. As a result, throughput is substantially higher and the process is more efficient and economical. Capital costs are also lower. Thus according to one aspect of this invention there is provided a method of making a trichloromethoxybenzene selected from the group consisting of α,α,α-trichloromethoxybenezene, α,α,α-trichloromethoxy-p-chlorobenzene, or a mixture thereof comprising (A) taking a methoxybenzene having the general formula Cl m where m is 0 or 1 and n is 1 , 2, or 3, that contains more than 20 ppm phenol and removing sufficient phenol to reduce the phenol concentration therein to less than 20 ppm; (B) preparing a mixture of said methoxybenezene from step A and a source of chlorine free radicals in a solvent selected from the group consisting of benzotrifiuoride, orthochlorobenzotrifluoride, metachlorobenzotrifluoride, parachlorobenzotrifluoride, and dichlorobenzotrifluoride; (C) heating said mixture; and (D) generating said chlorine free radicals in said mixture. Preferably said mixture is heated to the reflux temperature of said solvent. Conveniently said source of chlorine free radicals is chlorine gas. The solvent may be benzotrifiuoride and preferably is parachlorobenzotrifluoride. Conveniently the methoxybenzene is anisole. Preferably the method includes the additional last step of reacting said trichloromethoxybenzene with hydrogen fluoride to produce a trifluoromethoxybenzxene. Advantageously said source of chlorine free radicals is added to a mixture of said methoxybenzene and said solvent. In an alternative method said methoxybenezene and said source of chlorine free radicals are added separately to said solvent. Conveniently a small amount of said methoxybenzene is first mixed with said solvent. Preferably the amount of said methoxybenzene is about 10 to about 60 wt% of the total weight of methoxybenzene and solvent. Conveniently said process is performed in contact with metal and about 5 to about 500 ppm of a metal scavenger is added to said mixture. Advantageously the method comprises the step of irradiating said mixture with actinic radiation of an energy sufficient to form chlorine free radicals. The invention also provides A method of making α,α,α trichloromethoxybenzene comprising (A) removing sufficient phenol from anisole that contains more than 1000 ppm phenol to reduce the phenol concentration therein to less than 5 ppm; (B) preparing a mixture of (1 ) about 30 to about 50 wt% of said anisole from step A; (2) about 50 to about 70 wt% benzotrifiuoride or parachlorobenzotrifluoride; and (3) at least a stoichiometric amount of chlorine gas; (C) heating said mixture to reflux; and (D) irradiating said mixture with actinic radiation of an energy sufficient to form chlorine free radicals. Conveniently the actinic radiation is ultraviolet light. Again the solvent may be benzotrifiuoride, preferably parachlorobenzotrifluoride. Advantageously said anisole and said chlorine gas are added separately to said solvent. Preferably a small amount of said solvent is first mixed with said anisole. The invention also provides A method of making α,α,α- trichloromethoxybenzene comprising (A) removing sufficient phenol from anisole that contains more than 1000 ppm phenol to reduce the phenol concentration therein to less than 5 ppm; (B) continuously separately adding anisole and chlorine gas to a moving stream of benzotrifiuoride or parachlorobenzotrifluoride heated to reflux, where the concentration of anisole in said stream is about 30 to about 50 wt% and said chlorine gas is about 1 to about 5 mole% in excess of stoichiometric; (C) exposing said moving stream to ultraviolet light. The solvent may be benzotrifiuoride or parachlorobenzotrifluoride. Anisole can be made by reacting phenol with dimethyl sulfate or with a base and methyl chloride. When anisole is made by either process, some unreacted phenol remains in the product. Other methods of making anisole and p-chloroanisole also result in a product that contains some phenol. This invention applies to methoxybenzenes (i.e., anisole, p-chloroanisole, and mixtures thereof), including partially α-chlorinated methoxybenzenes (e.g., α- chloromethoxybenzene), that contain at least 20 ppm of phenol. Preferably, the methoxybenzene contains at least 1000 ppm of phenol as those grades are less expensive and work as well. In the first step of the process of this invention, the phenol content of the methoxybenzene feed is reduced to less than 20 ppm and preferably to less than 5 ppm. Methods that can be used for accomplishing this are known in the art. For example, the methoxybenzene can be passed through a bed of basic alumina, clay, or zeolite. Purification can also be accomplished by distillation. In the second step of the method of this invention, the methoxybenzene is reacted with chlorine free radicals in a BTF based solvent to produce a trichloromethoxybenzene. If chlorine is used, the reaction with anisole is: Anisole TCMB The methoxybenzenes are liquids which can be mixed with the BTF based solvent in order to control undesireable side reactions. At least about 10 wt% methoxybenzene (based on total solvent plus methoxybenzene weight) should be used for an economical process, and if the weight % of methoxybenzene is greater than about 60, ring chlorination may begin to occur. Preferably, the concentration of methoxybenzene is about 30 to about 50 wt%. Examples of BTF based solvents that can be used in this invention include BTF, orthochlorobenzotrifluoride, metachlorobenzotrifluoride, parachlorobenzotrifluoride (PCBTF), and dichlorobenzotrifluoride. BTF and PCBTF are preferred. The use of these solvents is essential to reducing ring chlorination. The source of chlorine free radicals can be, for example, elemental gaseous or liquefied chlorine or liquid sulfuryl chloride (SO 2 CI 2 ). Gaseous chlorine is preferred as it results in fewer byproducts, it is inexpensive, and it works well. At least a stoichiometric amount of the source of chlorine free radicals is needed (i.e., 3 moles Cl 2 per mole of the methoxybenzene), but a slight (1 to 5 mole%) excess is preferred to insure a complete reaction and reduce ring chlorination. The methoxybenzene, solvent, and chlorine free radical source can be mixed together in any fashion such as, for example, adding the chlorine free radical source to a mixture of the methoxybenezene and the solvent, adding the methoxybenezene and the chlorine free radical source separately to the solvent, or mixing some of the solvent with the methoxybenezene first, then adding that mixture and the chlorine free radical source separately to a solvent. It has been found that if the methoxybenezene and the chlorine free radical source are kept apart until they are mixed with the solvent, ring chlorination is reduced. It has also been found that ring chlorination increases at lower temperatures and therefore it is preferable to perform the reaction at as high a temperature as is practical. Generally, therefore, it is preferable to reflux the solvent during the reaction; this reduces ring chlorination by removing hydrogen chloride. Chlorine free radicals can be produced by exposing the source of chlorine free radicals to actinic radiation of an energy sufficient to form chlorine free radicals, such as by the reaction Examples of actinic radiation include, for example, ultraviolet light, radio frequency, or x-rays. Free radical initiators can also be used to generate chlorine free radicals, but ultraviolet light is preferred as it is convenient and easy to use. An ultraviolet wavelength of about 320 to about 340 nm is preferred. Since the light does not penetrate deeply into the mixture, the light source should be placed as close to the mixture as possible. This can be accomplished, for example, by placing the light in a well which is inside the reactor. The mixture should be stirred to expose all portions of the mixture to the light to ensure continuous generation of chlorine free radicals. If the reaction mixture is in contact with a metal, it may be desirable to add about 5 to about 500 ppm (based on mixture weight) of a metal scavenger to the mixture to prevent the metal ions from catalyzing the production of byproducts. Examples of suitable metal scavengers include N,N-dialkyl amides (sold as "Hallcomid" by the OP. Hall company) and ethylenediaminetetraacetic acid (EDTA). The reaction can be performed as a batch, continuous, or semi- continuous process, but a continuous process is preferred as it is more efficient and is more likely to result in less ring chlorination. It is also possible to partially chlorinate the methoxybenzene to a mixture of mono-, di- and trichloromethoxybenzenes in a continuous process, and then transfer the mixture to a batch reactor to finish off the chlorination. In a preferred continuous process, the methoxybenezene and the chlorinating agent are added separately to a stream moving past a source of ultraviolet light. The rate of addition to the stream in a continuous process should be selected to optimize the reaction. The TCMB product is useful as a chemical intermediate. For example, it can be reacted with hydrogen fluoride to make trifluoromethoxybenzene, which can be used to make herbicides and pesticides. The TCMCB product is useful as an agricultural intermediate. The following examples further illustrate this invention. Example 1 - Comparative Into a 500 ml photochlorination vessel equipped with a 100 watt medium pressure Hanovia light (air cooled), a reflux condenser, and an inlet for chlorine was placed 81 g of anisole and 325 g of BTF. The anisole contained 1200 ppm of phenol as a by-product of the manufacturing process. The UV light was turned on, and the unit was heated to reflux (108°C) by means of a heat tape wrapped around the vessel. Once the unit was at reflux, chlorine flow was started at a rate of 250 cc/min for 140 minutes, then decreased to 225 cc/min for the remainder of the reaction. Chlorine flow was stopped when approximately 2.9 equivalents of chlorine had been added to the unit. A total of 460 g of solvent and chlorinated anisoles were recovered. Analysis by gas chromatography (GC) showed 23.6 wt% α,α- dichloromethoxybenzene, 44.9 wt% TCMB, and 29.2 wt% of various ring chlorinated methoxybenzenes. Example 2 Example 1 was repeated with 326 g of benzotrifiuoride and 81 g of anisole made by a process that resulted in the anisole containing less than 20 ppm of phenol. The UV light was turned on, and the unit was heated to reflux (108°C) before chlorine flow was started. Chlorine was added at a rate of 275 cc/min for approximately 3 hours. Chlorine flow was stopped when approximately 3.1 equivalents of chlorine had been added to the unit. A total of 457 g of solvent and chlorinated anisoles were recovered. Analysis by GC showed 87.8 wt% TCMB and 5.4 wt% of various ring chlorinated methoxybenzenes. Example 3 - Comparative Example 2 was repeated with 82 g of the anisole that contained less than 20 ppm of phenol, 328 g BTF, and 0.101 g of added phenol for a total phenol content of 1200 ppm. The UV light was turned on, and the unit was heated to reflux (109°C), before chlorine flow was started. Chlorine was added at a rate of 275 cc/min for approximately 3 hours. Chlorine flow was stopped when approximately 2.9 equivalents of chlorine had been added to the unit. A total of 461 g of solvent and chlorinated anisoles were recovered. Analysis by GC showed 24.8 wt% α,α- dichloromethoxybenzene, 48.3 wt% TCMB, and 26.2 wt% of various ring chlorinated methoxybenzenes. Example 4 - Comparative Example 2 was repeated with 82 g of the anisole that contained less than 20 ppm of phenol, 324 g BTF, and 0.097 g of added phenol for a total phenol content of 1180 ppm. The UV light was turned on, and the unit was heated to reflux (109°C) before the chlorine flow was started. Chlorine was added at a rate of 275 cc/min for approximately 3 hours. Chlorine flow was stopped when approximately 2.9 equivalents of chlorine had been added to the unit. A total of 434 g of solvent and chlorinated anisoles were recovered. Analysis by GC showed 26.2 wt% α,α- dichloromethoxybenzene, 47.5 wt% TCMB, and 25.2 wt% of various ring chlorinated methoxybenzenes. Example 5 Anisole containing 1200 ppm phenol, which was used in Example 1 , was passed through a column containing 80 to 325 mesh activated basic alumina. Analysis after treatment indicated less than 20 ppm phenol. As in Example 1 , 82 g of the purified anisole was charged to the reactor along with 328 g of BTF. The UV light was turned on, and the unit was heated to reflux (109°C) before chlorine flow was started. Chlorine was added at a rate of 275 cc/min for approximately 3 hours. Chlorine flow was stopped when approximately 2.9 equivalents of chlorine had been added to the unit. A total of 464 g of solvent and chlorinated anisoles were recovered. Analysis by GC showed 11.6 wt% α,α-dichloromethoxybenzene, 80.3 wt% TCMB, and 5.7 wt% of various ring chlorinated methoxybenzenes.

Claims: WE CLAIM: 1. A method of making a trichloromethoxybenzene selected from the group consisting of α,α,α-trichloromethoxybenezene, α,α,α-trichloromethoxy-p- chlorobenzene, or a mixture thereof comprising (A) taking a methoxybenzene having the general formula where m is 0 or 1 and n is 1 , 2, or 3, that contains more than 20 ppm phenol and removing sufficient phenol to reduce the phenol concentration therein to less than 20 ppm; (B)preparing a mixture of said methoxybenezene from step A and a source of chlorine free radicals in a solvent selected from the group consisting of benzotrifiuoride, orthochlorobenzotrifluoride, metachlorobenzotrifluoride, parachlorobenzotrifluoride, and dichlorobenzotrifluoride; (C) heating said mixture; and (D) generating said chlorine free radicals in said mixture. 2. A method according to Claim 1 wherein said mixture is heated to the reflux temperature of said solvent. 3. A method according to Claim 1 or 2 wherein said source of chlorine free radicals is chlorine gas. 4. A method according to Claim 1 , 2 or 3 wherein said solvent is benzotrifiuoride. 5. A method according to Claim 1 , 2 or 3 wherein said solvent is parachlorobenzotrifluoride. 6. A method according to any one of the preceding Claims wherein methoxybenzene is anisole. 7. A method according to any one of the preceding Claims including the additional last step of reacting said trichloromethoxybenzene with hydrogen fluoride to produce a trifluoromethoxybenzene. 8. A method according to any one of the preceding Claims wherein said source of chlorine free radicals is added to a mixture of said methoxybenzene and said solvent. 9. A method according to any one of Claims 1 to 7 wherein said methoxybenezene and said source of chlorine free radicals are added separately to said solvent. 10. A method according to Claim 9 wherein a small amount of said methoxybenzene is first mixed with said solvent. 11. A method according to any one of the preceding Claims wherein the amount of said methoxybenzene is about 10 to about 60 wt% of the total weight of methoxybenzene and solvent. 12. A method according to any one of the preceding Claims wherein said process is performed in contact with metal and about 5 to about 500 ppm of a metal scavenger is added to said mixture. 13. A method according to any one of the preceding Claims comprising the step of irradiating said mixture with actinic radiation of an energy sufficient to form chlorine free radicals. 14. A method of making α,α,α-trichloromethoxybenzene comprising (A) removing sufficient phenol from anisole that contains more than 1000 ppm phenol to reduce the phenol concentration therein to less than 5 ppm; (B) preparing a mixture of (1 ) about 30 to about 50 wt% of said anisole from step A; (2) about 50 to about 70 wt% benzotrifiuoride or parachlorobenzotrifluoride; and (3) at least a stoichiometric amount of chlorine gas; (C) heating said mixture to reflux; and (D) irradiating said mixture with actinic radiation of an energy sufficient to form chlorine free radicals. 15. A method according to Claim 13 or Claim 14 wherein the actinic radiation is ultraviolet light. 16. A method according to Claim 14 or Claim 15 dependent thereon wherein said solvent is benzotrifiuoride. 17. A method according to Claim 14 or Claim 15 dependent thereon wherein said solvent is parachlorobenzotrifluoride. 18. A method according to Claim 14, 15 as dependent thereon 16 or 17 wherein said anisole and said chlorine gas are added separately to said solvent. 19. A method according to Claim 18 wherein a small amount of said solvent is first mixed with said anisole. 20. A method of making α,α,α-trichloromethoxybenzene comprising (A) removing sufficient phenol from anisole that contains more than 1000 ppm phenol to reduce the phenol concentration therein to less than 5 ppm; (B) continuously separately adding anisole and chlorine gas to a moving stream of benzotrifiuoride or parachlorobenzotrifluoride heated to reflux, where the concentration of anisole in said stream is about 30 to about 50 wt% and said chlorine gas is about 1 to about 5 mole% in excess of stoichiometric; (C) exposing said moving stream to ultraviolet light. 21. A method according to Claim 20 wherein said solvent is benzotrifiuoride. 22. A method according to Claim 20 wherein said solvent is parachlorobenzotrifluoride.

Inventors: BENSON KEVIN R, FIFOLT MICHAEL J, HICKEY JOHN, MANDAL SANJAY, BENSON, KEVIN, R., FIFOLT, MICHAEL, J., HICKEY, JOHN, MANDAL, SANJAY
Applicants: OCCIDENTAL CHEM CO, STEPHENS DINAH, OCCIDENTAL CHEMICAL CORPORATION, STEPHENS, DINAH
Application year: 1999
Main classification: C07C43
IPC codes: C07C41, C07C43