FLUORINATION PROCESS FOR THE PRODUCTION OF NUCLEAR FLUORINATED PHTHALOYL- AND TEREPHTHALOYL FLUORIDES

Abstract: Nuclear fluorinated phthaloyl and terephthaloyl fluorides, especially tetrafluoroterephthaloyl fluoride, are obtained by reacting a corresponding nuclear chlorinated acid halide with potassium fluoride in a polar aprotic solvent, preferably sulpholane, at a temperature of from 100 to 200°C, preferably 120 to 150°C. The products are useful chemical intermediates for the synthesis of pesticides.

Description: FLUORINATION PROCESS This invention relates to a process for the preparation of nuclear fluorinated phthaloyl and terephthaloyl fluorides which are useful chemical intermediates in the synthesis of pesticidal compounds. A process for the preparation of tetrafluorophthaloyl fluoride is reported in Chem.Abs. 1966, 64, 14125. It consists of heating tetrachlorophthaloyl chloride with potassium fluoride at 1600C for 12 hours and at 2700C for 8 hours in a steel autoclave to give tetrafluorophthaloyl fluoride in 20% yield. A similarly protracted, high temperature process for the corresponding terephthaloyl compound in which tetrachloroterephthaloyl chloride is heated in a stirred autoclave for 18 hours at 1400C and then for 34 hours at 2700C, is reported in Chem.Abs. 1966, 64, 6532. The product, presumably tetrafluoroterephthaloyl fluoride, is extracted with methanol and isolated as the dimethyl ester of tetrafluoroterephthalic acid. A process for the preparation of nuclear fluorinated benzoyl fluorides from corresponding nuclear chlorinated benzoyl halides is described in DE 3140634 Al. The process comprises reacting a nuclear chlorinated benzoyl halide with potassium fluoride in a diluent optionally in the presence of a catalyst and is characterised by operating at an elevated temperature and the boiling pressure of the reaction mixture and distilling off the nuclear fluorinated benzoyl fluoride during the reaction. As diluents, inert organic solvents having a lower vapour pressure than the product are mentioned. Tetramethylene sulphone is instanced for the fluorination of pentachlorobenzoyl chloride. Generally high temperatures in excess of 2000C are required and the desired product tends to be contaminated with partially fluorinated compounds. According to the present invention there is provided a process for the preparation of a compound of the formula (I): EMI2.1 in which n is an integer of from 1 to 4, which comprises reacting a compound of the formula (II): EMI2.2 in which X is halogen, with potassium fluoride in a polar aprotic solvent at a temperÅature of from 100 to 2000 C, preferably 120 to 1500 C. The invention also includes the compound (I) whenever obtained by this process. The carboxylic acid halide groups, which in compound (11) are conveniently carboxylic acid chloride groups, will normally be in positions on the benzene ring ortho or para to each other. The process of the invention is of particular value for the preparation of compounds of formula (I) in which n is 4 and especially for the preparation of tetrafluoroterephthaloyl fluoride from tetrachloroterephthaloyl chloride. However, it is envisaged that the degree of nuclear fluorination may be varied by careful process control, e.g. by adjustment of the quantity of potassium fluoride used, the choice of solvent and/or temperature, such that the integer n has values of 1, 2 or 3. Any polar aprotic solvent may be used, but some are better than others. For preparing tetrafluoroterephthaloyl fluoride from tetrachloroterephthaloyl chloride, sulpholane is much preferred in terms of yield and ease of recovery. Diphenyl sulphone is comparable as a reaction medium but, being a higher boiling solvent, recovery is more difficult. Nitrobenzene is satisfactory but dimethylacetamide, N-methyl pyrrolidone and benzonitrile are less effective. Dimethyl sulphoxide is not recommended as it can give explosive mixtures with acid halides. For preparing di- and tri-nuclear fluorinated products from tetrachloroterephthaloyl chloride, diglyme is preferred. A catalyst, particularly a phase transfer catalyst, such as a quaternary ammonium halide, or a crown ether, may increase product yield but should be used with caution. Tetrabutyl ammonium bromide, for example, tends to react with product. When used with diglyme, a phase transfer catalyst can substantially increase the amount of nuclear fluorination. The starting compounds, tetrachloroterephthaloyl chloride and tetrachlorophthaloyl chloride, are described in the chemical literature (Chem.Abs. 1965, 62, 470 and Chem.Abs. 1966, 64, 14125, respectively). The former is available commercially. Other halides which may be used as the starting compound (II), may be obtained from the tetrachlorobenzene dicarboxylic acid chlorides by techniques well known for converting acid chlorides to other acid halides. The preparation of, for example, tetrachloroterephthaloyl fluoride from tetrachloroterephthaloyl chloride is described in Chem.Abs. 1965, 62, 470. In carrying out the process of the invention, the potassium fluoride and solvent are preferably first dried by distilling off water with some of the solvent, or, if the boiling point of the solvent is too high, with a small added amount of a second solvent, such as toluene, which forms an azeotropic mixture with water. Conveniently, the compound (II) and optionally a catalyst are added to the potassium fluoride and heated together in an agitated reaction vessel. The temperature at which they are heated will depend on the degree of nuclear fluorination required. As a guide, one or two chlorine atoms will be replaced by fluorine atoms over a temperature range of from 100 to 1300 C, three chlorine atoms at temperatures above 1300C and four chlorine atoms at temperatures above 1400 C. Chemical degradation is apparent at temperatures above 2000C, sometimes even at lower temperatures above 1500 C. Typically, to replace four chlorine atoms by fluorine atoms, the ingredients are heated at 1200 to 150 C for several hours. After reaction, the product may be isolated as compound (I) by vacuum distillation or more conveniently, as a diester of compound (I), such as the dimethyl ester, by quenching the reaction mixture in the appropriate alcohol, filtering to remove inorganic material, evaporating the filtrates under reduced pressure to remove excess alcohol and drowning into water to precipitate the diester. The potassium fluoride may be used in stoichiometric amount or excess. No more than a 50% excess is necessary. Where all four nuclear-bound chlorine atoms are to be substituted by fluorine an excess of 30% or less is satisfactory. The addition of a small amount of caesium fluoride may prove beneficial. The nuclear fluorinated phthaloyl and terephthaloyl fluorides obtained by the present invention are valuable chemical intermediates for the synthesis of pesticides via, for example, the corresponding methyl tetrafluorobenzyl alcohol. This may be derived from compound (I) by reduction with sodium borohydride in diglyme at room temperature, such as described in UK Patent Specification No.2127013, followed by catalytic hydrogenation of the tetrafluoroxylyldialcohol so obtained. The invention is illustrated by the following Examples 1 to 9. Example 1 Preparation of tetrafluoroterephthaloyl fluoride (TFTF) and isolation as the dimethyl ester of tetrafluoroterephthalic acid Potassium fluoride (13g) was stirred and heated in sulpholane (30ml) to 2000C. Vacuum was applied to remove, by distillation, residual moisture and any other material present with a boiling point below 1500C at 15-20 mm Hg. The mixture was cooled to 20 to 30 C and tetrachloroterephthaloyl chloride (8.75g) added. The temperature was raised to 1500C and the mixture stirred for 2-3 hours at this temperature to complete the reaction. The product, which had been isolated in a previous similar preparation and identified as tetrafluoroterephthaloyl fluoride by comparison of its melting point and IR spectrum with those of an authentic sample, was isolated as the dimethyl ester by drowning the reaction mixture into methanol (200ml) and filtering it to remove the inorganic material. The filtrates were then evaporated under reduced pressure to remove the excess methanol, and the residual material drowned into water (200ml). The dimethyl ester precipitated as a grey solid and was collected by filtration. (Weight 4.2g). Example 2 Preparation of TFTF in sulpholane at 1300C Potassium fluoride (85.3g) and sulpholane (441g) were stirred and heated together under vacuum and 141g of sulpholane removed by distillation in order to dry the system. The mixture was cooled to below 80"C and tetrachloroterephthaloyl chloride (67.5g) added. The reaction temperature was raised to 1300C and maintained at this temperature for 12 hours. On completion of the reaction, the product, tetrafluoroterephthaloyl fluoride, was isolated by distillation under vacuum at 20mm of mercury. The fraction boiling between 110cm and 1400C was collected to give 46g of material of approximately 80% strength. Example 3 Preparation of a mixture of dichioro-difluoro-, monochloro-trifluoro- and TFTF in diglyme at 1500C Potassium fluoride (10.2g) and diglytne (50g) were stirred and heated together and 25g of diglyme distilled off to dry the system. The mixture was cooled to below 800C and tetrachloroterephthaloyl chloride (8.75g) added. The reaction was stirred at 150 C for 21 hours to give a mixture containing 72% of the dichloro-difluoro-terephthaloyl fluoride, 22% of the monochloro-trifluoro-terephthaloyl fluoride and 6X of the tetrafluoroterephthaloyl fluoride. Example 4 Repeat of Example 3 but using a phase transfer catalyst at 1200C The reaction in Example 3 was repeated in the presence of 0.5g of tetrabutyl ammonium bromide at 1200C. After 14 hours a mixture consisting of 78% of tetrafluoroterephthaloyl fluoride, 112 of monochlorotrifluoroterephthaloyl fluoride, and 11% of dichlorodifluoroterephthaloyl fluoride was obtained. Example 5 Preparation of TFTF in diphenyl suiphone at 1500C Potassium fluoride (10.2g), diphenyl suiphone (25g) and toluene (25g) were stirred and heated and the system dried by removing the toluene by distillation. The reaction mixture was cooled and tetrachloroterephthaloyl chloride (8.75g) added. The temperature was raised to 1500C and maintained at this temperature for 3 hours to complete the reaction. The product was isolated by distillation. Example 6 Preparation of TFTF in dimethylacetamide at 1200C Potassium fluoride (10.9g) and dimethylacetamide (45g) were stirred and heated. 15g of solvent were removed by distillation to dry the system. The mixture was cooled to below 100 and tetrachloroterephthaloyl chloride (9.35g) added. The reaction temperature was then raised to 120 C and maintained at this temperature for 6 hours. The mixture was stirred and cooled to 250C and methanol (30g) added. This was drowned into water (250g) and the solid collected by filtration to give 2.7g of tetrafluorodimethyl- terephthalate. Example 7 Preparation of TFTF in nitrobenzene at 130 C Potassium fluoride (10.9g) and nitrobenzene (45g) were stirred and heated, under vacuum. 15g of the solvent were removed by distillation at 50mum of Hg in order to dry the system. The mixture was cooled to below 809C and tetrachloroterephthaloyl chloride (9.53g) added followed by 0.9g of tetrabutylammonium bromide. The reaction temperature was raised to 1300C and maintained at this temperature for 20 hours to complete the reaction. The product was isolated as in Example 6 to give 3.8g of tetrafluorodimethylterephthalate. Example 8 Preparation of TFTF in N-methyl-2-pvrrolidone at 1200C 9.5g of potassium fluoride and 45g of N-methyl-2pyrrolidone were stirred and heated and 15g of the solvent removed by vacuum distillation to dry the system (NP 1200C at 50 mm of Hg). The mixture was cooled to below 60"C and 7.5g of the tetrachloroterephthaloyl chloride added. The reaction temperature was raised to 120"C and maintained at this temperature for 6 hours to complete the reaction. The reaction mixture was then cooled to 250C, 50g of methanol added, and the mixture filtered. The filtrates were drowned into an excess of water to precipitate the product. The product was collected by filtration and dried to give 1.3g of tetrafluorodimethylterephthalate. Example 9 Preparation of TFTF in benzonitrile at 1500C 9.5g of potassium fluoride and 45g of benzonitrile were stirred and heated and 15g of benzonitrile distilled from the reaction mixture under vacuum (BP 100 C at 50 mm of Hg) to dry the system. The mixture was cooled to below 600C and 7.5g of the tetrachloroterephthaloyl chloride added. The reaction temperature was raised to 1500C and maintained at this temperature for 5 hours. G.C. examination of the reaction showed that the product was then cooled to 120 C and 0.8g of tetrabutylammonium bromide added. The reaction temperature was then raised to 1400C and maintained at this temperature for 20 hours to complete the reaction. 1.9g of the required product was isolated as the dimethyl ester.

Claims: CLAIMS 1. A process for the preparation of a compound of the formula (I): EMI9.1 in which n is an integer of from 1 to 4, which comprises reacting a compound of the formula (II): EMI9.2 in which X is halogen, with potassium fluoride in a polar aprotic solvent at a temperature of from 100 to 2000C. 2. A process according to claim 1 in which the temperature is from 120 to 15O0C. 3. A process according to claims 1 or 2 in which the polar aprotic solvent is sulpholane. 4. A process according to any one of the preceding claims in which compound (I) is tetrafluoroterephthaloyl fluoride and compound (II) is tetrachloroterephthaloyl chloride.

Inventors: CLEARE, PETER JOHN VERNON, COSTELLO, ALAN THOMAS
Applicants: IMPERIAL CHEMICAL INDUSTRIES PLC
Application year: 1984
Main classification: C07C51
IPC codes: C07C67, C07C51, C07C63