PROCESS FOR THE PREPARATION OF TRIFLUOROETHOXYARENECARBOXYLIC ACIDS

Abstract: A process for producing trifluoroethoxyarenecarboxylic acids or salts thereof by reaction of haloarenecarboxylic acids or salts thereof with 2,2,2-trifluoroethanol in the presence of a strong base and copper containing materials. The compounds obtained by the process of the present invention are used as synthetic intermediates in the pharmaceutical industry.

Description: PROCESS FOR THE PREPARATION OF TRIFLUOROETHOXYARENECARBOXYLIC ACIDS FIELD OF THE INVENTION The present invention relates to a process for the preparation of trifluoroethoxyarenecarboxylic acids of the general formula [ I ] or salts thereof [il wherein Ar represents a monocyclic or polycyclic aromatic nucleus; n is 1, 2 or 3; R is a substituent selected from alkyl, alkoxy, alk lthio, halogen, haloalkyl, haloalkoxy, haloalkylthio, phenyl, phenoxy, benzoyl, haloalkoxybenzoyl, haloalkoxynaphthyl, nitro, alkoxycarbonyl, cyano, carboxamido, N-substituted carboxamido and carboxy and when m > 1 the R substituents may be the same or different; and m is 0, 1, 2, 3, 4 or 5. BACKGROUND OF THE INVENTION Trifluoroethoxyarenecarboxylic acids of the formula [ I ] above are useful as intermediates in the pharmaceutical industry. For example, 2,5-bis(2,2,2-trifluoroethoxy)benzoic acid [ ϋl ] is the key intermediate for the synthesis of the antiarrhythmic drug Flecainide [ IV ] and pharmaceutically acceptable salts thereof [ in ] [ IV ] (Banitt, E.H. et al, J. Med. Chem. 18:1130 (1975) and 20:821 (1977); Leir, CM. GB 2 045 760A, (1980) and The Merck Index, 12 th Edition, 4136). It is known that the acids [ I ] can be obtained by the reaction of hydroxyarenecarboxylic acids of the general formula [ V ] with trifluoroethyl esters [ VI ] according to Scheme 1 (Banitt, E.H. et al, J. Med. Chem. 18: 1130 (1975) and 20:821 (1977)). Scheme 1 where Ar, R, m and n are as defined above and Rl = F, Cl, CF 3 , CCI 3 , Ar. alkyl. This method requires the use of trifluoroethyl esters [ VI ] which are costly and not easily available commercially. Another method involves the oxidation of the acetyl group of trifluoroethoxyacetylarenes as shown in Scheme 2 (Lair, CM., GB 2045 760A): Scheme 2 [VTI ] [m ] The starting materials used in this method are not commercially available which makes this synthetic route difficult for commercial production of the tnfluoroethoxyarenecarboxylic acids [ I ]. THE OBJECT OF THE INVENTION It is the object of the present invention to overcome the above disadvantages of the known processes and to provide a comparatively simple, one-step process for preparing trifluoroethoxyarenecarboxylic acids [ I ] in good yields ' , employing commercially available and relatively inexpensive compounds. DETAILED DESCRIPTION OF THE INVENTION The above object is attained by the present invention which provides a process for the preparation of trifluoroethoxyarenecarboxylic acids of the formula [ I ] or salts thereof [IJ wherein Ar represents a monocyclic or polycyclic aromatic nucleus; n is 1, 2 or 3; R is a substituent selected from alkyl, alkoxy, alkylthio, halogen, haloalkyl, haloalkoxy, haloalkylthio, phenyl, phenoxy, benzoyl, haloalkoxybenzoyl, haloalkoxynaphthyl, nitro, alkoxycarbonyl, cyano, carboxamido, N-substituted carboxamido and carboxy and when m > 1 the R substituents may be the same or different; and m is 0, 1, 2, 3, 4 or 5; which process comprises reacting a haloarenecarboxylic acid or a salt thereof of the formula [ II ] wherein R, m and n are as defined above, and M is hydrogen or a metal, ammonium or phosphonium cation; and X is Cl, Br or I, and when n >1 the X substituents may be the same or different; with 2,2,2-trifluoroethanol in the presence of a strong base and a copper containing material; if desired, followed by acidification. Trifluoroethoxyarenecarboxylic acids [I] or salts thereof obtained in accordance with the process of the present invention may contain one or more aromatic rings and one or more trifluoroethoxy groups. Additionally, other substituents R as defined above may be present on an aromatic ring. As defined herein, the term "haloarenecarboxylic acid" includes monocyclic and polycyclic arenecarboxyhc acids containing one or more halogen atoms and optionally additional substituents as defined for R above, other than halogen. According to a preferred embodiment of the present invention a chloro-, bromo- or iodo-arenecarboxylic acid is reacted with trifluoroethanolate in the presence of copper iodide or bromide in an aprotic solvent, such as N.N-dimethylformamide, N-methylpyrrolidone, N,N-dimethylacetamide, pyridine, collidine or their mixtures. The reaction is preferably carried out at a temperature in the range of from ambient temperature to 170 °C. In the process of the invention, preferably at least one mole of 2,2,2-trifluoroethanol is used per each halogen atom of the haloarenecarboxylic acid [ II ] which it is desired to replace by a trifluoroethoxy group. However, a large molar excess of 2,2,2-trifTuoroethanol can be used in which cases this reactant may also serve as a solvent. At least one mole of 2,2,2-trifluoroethanol per mole of the strong base should be used and the mole ratio of the copper containing, compound to the haloarenecarboxylic acid [ π ] can be in the range of 0.01 to 2: 1. Suitable copper contaning materials are for example: copper salts, copper oxides, metallic copper, copper alloys, etc. The present invention will be described in more detail with the aid of the following examples, which are merely representative and should not serve to limit the scope of the invention. EXAMPLE 1 Synthesis of 2,5-bis(2',2',2'-trifluoroethoxy)benzoic acid [ in ] from 2,5-dibromobenzoic acid, sodium salt [VHI-a] Scheme 3 [ VHI-a ] [ III ] A 50-mL round-bottomed flask equipped with a magnetic stirrer, a thermometer pocket and a reflux condenser, was charged with 0.60 g of a 60% strength suspension of sodium hydride in mineral oil (equivalent to a total of 0.36 g (15.0 mmole) of pure NaH) and 10 mL of anhydrous N,N-dimethylformamide. The mixture was cooled in an ice-water bath and 2.25 g (22.5 mmole) of anhydrous 2,2,2-trifluoroethanol was added dropwise through a pressure equalisation arm dropping funnel during the period of 10 min. The, mixture was cooled to room temperature and 0.48 g (2.5 mmole) of anhydrous copper iodide and 1.51 g (5.0 mmole) 2,5-dibromobenzoic acid sodium salt [ VHI-a] dried in vaccuo were added. The black mixture obtained was heated to about 110 - 115 °C and maintained at this temperature for 2 hours. The reaction mixture was cooled to room temperature and poured into a mixture of crushed ice and cone, hydrochloric acid. The mixture was vigorously stirred for 1 hour, the black precipitate was filtered off and washed at once with water. The obtained solid was suspended at room temperature in 5% aqueous KOH under vigorous stirring for 15 min, followed by filtration through a celite modified filter and washing with 5 % aqueous KOH. The transparent clear alkaline solution was thrice extracted with dichloromethane. The alkaline solution was added dropwise under vigorous stirring to a mixture of ice and cone, hydrochloric acid, at a temperature not higher than 0 °C and a pH 1. The mixture was stirred for 0.5 hours at these conditions. The obtained precipitate was filtered off, washed with water, collected and dried in vacuum to constant weight to give 1.32 g of crude product. After recrystallisation from ethanol-water system, 1.03 g (65 % yield) of 2,5-bis(2',2',2'-trifluoroethoxy)benzoic acid [ HI ], mp. 118.5 - 120 °C was obtained. EXAMPLE 2 Synthesis of 2,5-bJs(2,2,2-trfflBQroethosy)benzoic acid [ -m ] from 5-bro o-2-cMorobe3izoic acid [ VUI ] and 2,2,2- riiluoroetlιanoL Scheme 4 [VE23 [ ] A I L round-bottomed flask equipped with a magnetic stirrer, a thermometer pocket, dropping funnel and a reflux condenser, was charged with 51.0 g of a 60 % strength suspension of sodium hydride in mineral oil (equivalent to a total of 30.6 g (1.28 mole) of pure NaH) and 570 mL of anhydrous N,N-dimethylformamide. The mixture was cooled to room temperature in an ice-water bath and 189.5 g (1.90 mole) of anhydrous 2,2,2-trifluoroethanol were added dropwise during 40 minutes. The mixture was cooled to room temperature and 24.8 g (0.13 mole) of anhydrous copper iodide and 59.5 g (0.25 mole) of 5-bromo-2-chlorobenzoic acid were added. The black reaction mixture was heated to about 110 - 115 °C and kept at this temperature for 2 hours. The reaction mixture was cooled to room temperature and poured into a mixture of crushed ice (3 kg) and cone, hydrochloric acid (0.78 L). The mixture was vigorously stirred for 1 hour, the black precipitate was filtered off and washed at once with 200 mL of water. The obtained solid was suspended at room temperature in 1 L of 5 % aqueous KOH under vigorous stirring for 15 min, followed by filtration through a Celite modified filter and washing with 100 mL of 5 % aqueous KOH. The transparent clear alkaline solution was thrice extracted with 150 mL of dichloromethane. The alkaline solution was added dropwise under vigorous stirring to mixture of 0.6 kg of ice and 0.2 L of cone, hydrochloric acid, at a temperature not higher than 0°C and a pH 1. The mixture was stirred .for 0.5 hours at these conditions. The obtained precipitate was filtered off, washed with water, collected and dried under vacuum to a constant weight. Yield: 64.7 g (81.4%) of crude 2,5-bis(2',2 , ,2 , -trifluoroethoxy)benzoic acid, m.p. 116 -118°C After recrystallisaiton from an ethanol/water system, a product with m.p. 120- 121°C was obtained. EXAMPLES 3 TO 21 Syntheses of (2',2',2'-trifluoroethoxy)arenecarboxylic acids of the general formula [ X ] by condensation of sodium trifluoroethanolate with corresponding haloarenecarboxylic acids and salts thereof [ IX ] identified in Table 1 in the presence of copper salts identified in Table 1. The procedures set forth in Example 1 (in cases were M is different from H) or in Example 2 (in cases were M = H) were followed with the exceptions apparent from Table 1. Sodium trifluoroethanolate was prepared in situ by the action of sodium hydride in trifluoroethanol. The synthesis is described by the following Scheme 5: Scheme 5 [IX] [X] The results and the conditions are summarised in Table 1. Table 1. [IX] [X] (/> c m <n H H C H m rπ m H ι c m- I Table 1 (continued) CO c σ w H H C H m m m H 3 c m to o * The following abbreviations were used in the Table TOE - 2,2,2-Trifluoroethanol DMF - N,N-Dimethylformamide; CLN - Collidine N P - N-Methylpyπolidone PRD - Pyiidine DMA - N,N-Dl ethylacetamide EXAPMLE 22 Synthesis of 6-methoxy-5-(2',2',2'-trifluoroethoxy)-2-naphthalene carboxylic acid [ XII ] from 5-bromo-6-methoxy-2-naphthalene carboxylic acid [ XI ] and 2,2,2-trifluoroethanol Scheme 6 [ XI ] [ XII ] The same procedure as set forth in Example 2 was used, but 3 mole equivalents of NaH with respect to the halonaphthalenecarboxylic acid [ XI ] were added and 6-methoxy-5-(2',2',2'-trifluoroethoxy)-2-naphth- alene-carboxylic acid [ XII ] was obtained. EXAMPLE 23 Synthesis of 3,4,5-tris(2',2',2'-trifluoroethoxy)benzoic acid [ XIV ] from 3,4,5-tribromobenzoic acid [ XIII ] and 2,2,2-trifluoroethanol Scheme 7 [ XIII ] [ XIV ] The same procedure as set forth in Example 2 was used, but 5 mole equivalents of NaH with respect to the halobenzoic acid [ XIII ] were added and 3,4,5-tris(2',2',2'-trifluoroethoxy)benzoic acid [ XIV ] was obtained. EXAMPLE 24 Synthesis of 2-(2',2',2'-trifluoroethoxy)benzoic acid [ XV ] from 2-iodobenzoic acid [ XVI ] and 2,2,2-trifluoroethanoI Scheme 8 [ XVI ] [ XV ] A 50-mL round-bottomed flask equipped with a magnetic stirrer, a thermometer pocket and a reflux condenser, was charged with 3.37 g (30.0 mmole) of potassium tert-butoxide. Anhydrous 2,2,2-trifluoroethanol (10 mL) was added dropwise through the pressure equalisation arm dropping funnel. The mixture was cooled to room temperature and 0.95 g (5 mmole) ..of anhydrous copper iodide and 2.48 g (10.0 mmole) of 2-iodobenzoic acid dried under vacuum [ XVI ] were added. The black mixture obtained was refluxed for 6 hours. After cooling, the reaction mixture was poured into 50 mL of distilled water and filtered. The filtrate was extracted with 3 x 10 mL methylenechloride, cooled to 0 - 5 °C and acidified with 32 % hydrochloric acid to pH ~ 2 and the water layer was extracted with 3 x 10 mL methylenechloride. The combined organic layers were dried over anhydrous sodium sulphate, filtered and concentrated under reduced pressure to obtain 2-(2',2',2'-trifluoroethoxy)-benzoic acid [ XV ].

Claims: CLAIMS: 1. A process for the preparation of trifluoroethoxyarenecarboxylic acids of the formula [ I ] or salts thereof f i] wherein Ar represents a monocyclic or polycyclic aromatic nucleus; n is 1, 2 or 3; R is a substituent selected from alkyl, alkoxy, alkylthio, halogen, haloalkyl, haloalkoxy, haloalkylthio, phenyl, phenoxy, benzoyl, haloalkoxybenzoyl, haloalkoxynaphthyl, nitro, alkoxycarbonyl, cyano, carboxamido, N-substituted carboxamido and carboxy and when m > 1 the R substituents may be the same or different; and m is 0, 1, 2, 3, 4 or 5; which process comprises reacting a haloarenecarboxylic acid or a salt thereof of the formula [ II ] in wherein R, m and n are as defined above; M is hydrogen or a metal, ammonium or phosphonium cation; and X is Cl, Br or I, and when n >1 the X substituents may be the same or different; with 2,2,2-trifluoroethanol in the presence of a strong base and a copper containing material; if desired, followed by acidification. 2. The process of claim 1, wherein the reaction is carried out in the presence of copper iodide and/or copper bromide. 3. The process of claim 1 wherein the 2,2,2-trifluoroethanol is reacted in a first step with a strong base to form a 2,2,2-trifluroethanolate and, which is reacted in a second step with a haloarenecarboxylic acid or salt thereof of formula [ II ] in the presence of the copper containing material. 4. The process of claim 1 wherein the reaction is conducted in an aprotic solvent. 5. The process of claim 4 wherein said aprotic solvent is a dipolar aprotic solvent or an N-containing heterocycle or a mixtures thereof. 6. The process of claim 5 wherein the dipolar aprotic solvent is selected from N-N-dimethylformamide, N-methylpyrrolidone, N,N-dimethyl- acetamide, DMSO, hexamethylphosphoramide or mixtures thereof. 7. The process of claim 5 wherein the N-containing heterocycle is selected from pyridine, picolines, lutidines, collidines, methylethylpyridine (MEP), other substituted pyridines, quinoline and substituted quinolines. 8. The process of claim 1 wherein the strong base is selected from Na, NaH, NaNH2, Na- and K-alcoholates, NaOH, KOH, fully N-substituted amidines, guanidines and tetraalkylammonium hydroxides and alcoholates. 9. The process for the preparation of 2,5-bis(2,2,2-trifluoroethoxy) benzoic acid [ III ] or salt thereof, which comprises reacting a halobenzoic acid of the formula [ XVII ] with 2,2,2-trifluoroethanol in the presence of a strong base and a copper containing material: [ XVII ] [ HI ] wherein: X 3 is Br or I, X 4 is Cl, Br or I, or one of X 3 and X 4 may also be CF 3 CH 2 0-; if desired, followed by acidification.

Inventors: GUTMAN ARIE L, NISNEVICH GENADY, SHKOLNIK ELEONORA, TISHIN BORIS, ZALTZMAN IGOR, GUTMAN, ARIE, L., NISNEVICH, GENADY, SHKOLNIK, ELEONORA, TISHIN, BORIS, ZALTZMAN, IGOR
Applicants: FINETECH LTD, GUTMAN ARIE L, NISNEVICH GENADY, SHKOLNIK ELEONORA, TISHIN BORIS, ZALTZMAN IGOR, FINETECH LTD., GUTMAN, ARIE, L., NISNEVICH, GENADY, SHKOLNIK, ELEONORA, TISHIN, BORIS, ZALTZMAN, IGOR
Application year: 1998
Main classification: C07C51
IPC codes: B01J27, C07B61, C07C51, C07C65