THE PREPARATION OF SUBSTITUTED 3'-BROMODIPHENYLETHERS

Abstract: 3'-Carboxydiphenylether salts can be halode­ carboxylated using diacyl peroxides, molecular bromine, moderate temperature, an inert atmosphere and atmospheric pressure to afford 2-chloro-4-trifluoro­ methyl-3'-bromo-4'-nitrodiphenylether.

Description: This invention is concerned with the preparation of 2-chloro-4-trifluoromethyl-3'-bromo-4'-nitrodi­ phenylether. The preparation of certain diphenylethers is known to be accomplished by reacting a suitably substituted phenol or alkali metal salt thereof with a suitably substituted halobenzene in the presence of an alkaline agent in a polar aprotic solvent and optionally in the presence of a catalyst; see for example U.S.-A-3,966,453; 3,950,435; 4,046,798; 4,093,446 and 4,358,308 and Canadian Patent 1,079,303. Diphenylethers prepared by the above techniques are also generally reported to be used as precursors in preparing certain other diphenylether derivatives. For example, the 4'-halo or 4'-nitro derivatives are prepared by halogenating or nitrating an otherwise suitably substituted diphenylether. Further, 3'-hydroxydiphenylethers can be converted to alpha-­ oxymethylene carboxylic esters by condensation with alpha-halo esters in the presence of bases such as potassium carbonate or hydroxide. These alpha-­ oxymethylene carboxylic esters can then be converted to the corresponding carboxylic acids, acid chlorides or amides. Furthermore, 3'-alkoxydiphenylethers can be made by reacting the corresponding 3'-halodiphenyl­ ether prepared by the above described techniques with a carbinol in an inert nonpolar solvent in the presence of base. We have now found a process which can be carried out at about atmospheric pressure, in a substantially inert atmosphere, at moderate temperatures, using molecular bromine and a suitable diacyl peroxide. Unless otherwise stated in this specification, "equivalents" should be understood as meaning on a molar basis. This invention provides a process for the preparation of 2-chloro-4-trifluoromethyl-3'-bromo-4'-­ nitrodiphenylether which comprises halodecarboxylating diphenylether having the formula where R¹ is an alkali metal or alkaline earth metal in a polar aprotic solvent in a substantially inert atmosphere, preferably at a temperature from 65°C to 150°C, preferably at about atmospheric pressure and optionally in the presence of light, in the presence of diacyl peroxide having the formula R²--O-O--R³ (II) where R² and R³ may be the same or different and are aliphatic, aromatic or alkylaromatic groups, and in the presence of molecular bromine. In the above process, typically suitable polar aprotic solvents include ethers such as diethyl ether, tetrahydrofuran (THF) and glyme (ethylene glycol dimethyl ether); acetonitrile; dimethylformamide (DMF). Acetonitrile is the preferred solvent. Generally, from about one to about five equivalents, preferably about three, of diacyl peroxide of Formula II is utilized for each equivalent of phenylether of Formula I. The amount of molecular bromine (Br₂) utilized generally is from about one to about 5, preferably about 2, equivalents for each equivalent of phenylether of Formula I. The presence of a source of light may optionally be utilized in the process. When employed, the light should have a power rating of at least about 25 watts, and preferably at least about 75 watts. Preferred temperatures utilized for the process are from about 75°C to about 110°C. The process should be carried out in a substantially inert atmosphere such as nitrogen or argon. The alkali metal or alkaline earth metal salts of Formula I can be prepared by known standard techniques such as those described above or by the process disclosed in U.S.-A-4,485,254. For example, the alkali metal salts such as sodium, potassium and lithium, and the alkaline earth metal salts such as magnesium and calcium, can be prepared by treating the carboxylic acid with an alkali metal hydroxide or hydride, or an alkaline earth metal hydroxide or hydride, such as sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium hydride or magnesium hydride in an inert or substantially inert solvent. Examples of suitable diacyl peroxides of Formula II include diacetyl peroxide, dibenzoyl peroxide, di- n -­ octanoyl peroxide, di-heptafluoro- n -propionyl peroxide, acetyl benzoyl peroxide, di- p -chlorobenzoyl peroxide and phthaloyl peroxide. The diaromatic diacyl peroxides are preferred and dibenzoyl peroxide is most preferred. The 2-chloro-4-trifluoromethyl-3'-bromo-4'-­ nitrodiphenylether prepared by the process of this invention can be used as a herbicide or as an intermediate in the preparation of other herbicidal diphenylethers by known techniques. The following examples further illustrate the process of this invention. Percentages are by weight unless noted otherwise. EXAMPLE 1 - Preparation of 2-chloro-4-trifluoromethyl-­ 3'-bromo-4'-nitrodiphenylether with Irradiation A 100 ml, three-necked round-bottomed flask was fitted with a thermometer, condenser, nitrogen inlet adapter and stir bar. The apparatus was flushed with nitrogen while drying with a heat gun. Potassium 2-chloro-4-trifluoromethyl-3'-carboxy-4'-nitrodiphenyl­ ether (0.20 g) was added to the flask and dissolved in acetonitrile (20 ml). Bromine (0.12 g, 1.5 equivalents) dissolved in acetonitrile (10 ml) was added to the flask and the mixture heated to reflux (80°C). When reflux was achieved benzoyl peroxide (0.12 g, 1 equivalent) was added in one portion and reflux continued for 4 hours under nitrogen with constant irradiation. The equipment had been wrapped in aluminum foil with a portion of the foil opened to allow a 100-watt light bulb to shine into the reaction mixture. Thin-layer chromatographic analysis on silica gel using 25/75 v/v EtOAc/hexane solvent indicated the presence of the 3'-bromo compound by comparison with a known standard. EXAMPLE 2 - Preparation of 2-chloro-4-trifluoromethyl-­ 3'-bromo-4'-nitrodiphenylether without Irradiation The potassium salt of 2-chloro-4-trifluoro­ methyl-3'-carboxy-4'-nitrodiphenylether (2.0 g), benzoyl peroxide (1.2 g, 1 equivalent) and bromine (1.2 g, 1.5 equivalents) were refluxed in acetonitrile for 15 hours under nitrogen. Additional quantities of benzoyl peroxide (total 2.0 extra equivalents) were added periodically during the reflux period when thin-layer chromatographic analysis indicated that the benzoyl peroxide was gone. An additional quantity of bromine (0.5 equivalent) was also added during this period. After the reflux period, the reaction was cooled to room temperature and the solvent was removed under vacuum. The residue was dissolved in methylene chloride, and the resulting solution was washed with aqueous sodium bisulfite, aqueous sodium bicarbonate, dried over anhydrous magnesium sulfate and concentrated under vacuum to a brown oil (2.7 g). Thin-layer chromatographic analsysis of this product indicated the presence of 2-chloro-4-trifluoromethyl-3'-bromo-4'-­ nitrodiphenylether by comparison with a known standard using silica gel and 20/80 v/v EtOAc/hexane eluent. The aqueous layer was acidified and extracted with methylene chloride. Concentration under vacuum of the methylene chloride extract provided an off-white solid (1.3 g). High-pressure liquid chromatographic analysis of this solid indicated that the solid contained about 50% 2-chloro-4-trifluoromethyl-3'-­ carboxy-4'-nitrodiphenylether (in the acid form) by comparison of its retention time with that of a known standard. EXAMPLE 3 - Preparation of 2-chloro-4-trifluoromethyl-­ 3'-bromo-4'-nitrodiphenylether without Irradiation A 500 ml, three-necked round-bottomed flask was fitted with a thermometer, condenser, nitrogen inlet adapter and stir bar. The apparatus was flushed with nitrogen while drying with a heat gun. The potassium salt of 2-chloro-4-trifluoromethyl-3'-carboxy-4'-­ nitrodiphenylether (10.0 g) was added to acetonitrile (150 ml). Bromine (6.0 g, 1.5 equivalents) in acetonitrile (50 ml) was added and the solution was heated to 60°C (heating mantle). At this time, a portion of benzoyl peroxide (3.0 g, 0.5 equivalents) was added and the reaction mixture was heated to reflux at 80°C. Additional benzoyl peroxide (total 18.0 g, 3.0 equivalents) was added in 3.0 g portions every few hours. After refluxing for 15 hours, the mixture was cooled to room temperature and the acetonitrile was removed under vacuum. The residue was taken up in methylene chloride and the resulting solution washed with sodium bisulfite solution (aqueous 5% w/w), sodium hydroxide solution (aqueous 1M), dried over magnesium sulfate and concentrated under vacuum to give a brown-­ yellow oil (7.8 g). A portion of this product (6.0 g) was purified by chromatography on a 35.6 cm (14 inch) long, 5.1 cm (2 inch) diameter silica gel (70-230 mesh) column using 10/90 v/v EtOAc/hexane. From the resulting fraction was isolated the pure 3'-bromo compound (2.5 g, corresponds to 34% yield based on 2-chloro-4-trifluoromethyl-3'-bromo-4'-nitrodiphenyl­ ether potassium salt, m.p. 56-59°C). NMR and infrared spectroscopic data are consistent with the proposed structure of the 3'-bromo compound. The combustion analysis of this product corresponded to 2-chloro-3'-­ bromo-4'-nitro-4-trifluoromethyldiphenylether, C₁₃H₆BrClF₃NO₃.

Claims: 1. A process for preparing 2-chloro-4-trifluoro­ methyl-3'-bromo-4'-nitrodiphenylether which comprises reacting a diphenylether having the formula: where R¹ is an alkali metal or alkaline earth metal ion with a diacyl peroxide having the formula: R²--O-O--R³ (II) where R² and R³ are the same or different aliphatic, aromatic or alkylaromatic radicals; and molecular bromine in a polar aprotic solvent, at about atmospheric pressure, in a substantially inert atmosphere at temperatures from about 65°C to about 150°C and optionally in the presence of light. 2. A process as claimed in claim 1 carried out at a temperature of 65°C to 150°C. 3. A process as claimed in claim 1 or 2 carried out at substantially atmospheric pressure. 4. A process as claimed in any preceding claim wherein from about one to about five, preferably about 3, equivalents of diacyl peroxide II are utilized for each equivalent of diphenylether I. 5. A process as claimed in any preceding claim wherein the diacyl peroxide comprises diaromatic diacyl peroxide. 6. A process as claimed in claim 4 wherein said diacyl peroxide is dibenzoyl peroxide. 7. The process as claimed in any preceding claim wherein from one to five, preferably about 2, equivalents of molecular bromine are utilized per equivalent of diphenyl ether II. 8. A process as claimed in any preceding claim carried out at a temperature of 75°C to 110°C. 9. A process as claimed in any preceding claim carried out under the influence of at least 25-watts of light. 10. A process as claimed in claim 9 wherein the power rating of the light is at least 75-watts.

Inventors: LANGE, BARRY CLIFFORD, SZAPACS, EDWARD MICHAEL
Applicants: ROHM AND HAAS COMPANY
Application year: 1986
Main classification: C07C201
IPC codes: C07C201, C07C67, C07C205