DE1949424A1 - Process for the preparation of chlorofluoropyridines - Google Patents

Description

Folder 2 207 6 ~ Dr,
Case MD »21388

IMPERIAL CHEMICAL IKDUSTRIEb LTD. London, UK

Process for the preparation of chlorofluoropyridines

Priority: 3O ₀ September 1968 - United Kingdom

The invention relates to the production of chlorofluoropyridines.

Eb is known (Finger, Starr, Dickerson, Gutowsky and Hamer, JoOrg.Chem., 1963, ££ ♦ 1666) that certain chlorine atoms in chlorine-substituted pyridines are replaced by fluorine atoms can if the chlorine-substituted pyridines are heated with potassium fluoride in a polar organic solvent » For example 3 »5-dichloro-2,6-difluoropyridine in a yield of 33% can be obtained if you use 2,3,5,6-tetrachloropyridine and converts potassium fluoride into dimethyl sulfone,

009817/1902

British Patent 1,059,987 describes a process for the preparation of fluoroderivatives of pentachloropyridine, which is carried out by heating penta- chloropyridine with anhydrous potassium fluoride in a liquid medium, pentafluoropyridine, 3-Cblor.otetrafluoropyridin and 3, 5-dichlorotrifluoropyridine isolated as products. In one example of said British patent specification anhydrous Knliumfluorid is with tentachloropyridin in N-methylpyrrolidone (which has been dried by distillation) was reacted for 24 hours at 200 ⁰ C, with a mixture of 3-Chlorotetrafluoropyridin and 3, 5-Dichlorotrifluoropyridin (mixing ratio 65: 35) is obtained, which means a 32% conversion of pentachloropyridine into chlorofluoropyridine "

It has now been found that chlorine substituted in chlorine Pyridines or in chlorofluoro-substituted pyridines can be replaced by fluorine, with chlorofluoro-substituted derivatives can be obtained in a high yield and in a relatively short reaction time when using a chloropyridine or a chlorofluoropyridine reacts with potassium fluoride in a polar aprotic solvent and the water content carefully controlled the reaction mixture.

Thus, according to the invention, a method is proposed by which chlorine is substituted by fluorine in a pyridine ring can be carried out, which process is carried out that a chloropyridine or a Chlorofluorcpjridin with potassium fluoride in a polar aprotic solvent in the presence of 0.2-2.0 parts by volume of water per 100 parts by volume of aprotic substances Reacted solvent

The process is particularly suitable for replacing chlorine substituents in the 2-, 4- or 6-position of the pyridine nucleus with fluorine , for example for the preparation of

009817/1902

3,5-dichloro-2,4,6-trifluoropyridine from pentachloropyridine _o

The proportion of water in the reaction mixture is preferably 0.2-1.0 parts by volume, for example 0.5-1.0 parts by volume, of water per 100 parts by volume of polar aprotic solvent. If larger amounts of water are used, for example, more channels 2 VoIο parts water per 100 parts by volume of solvent, there is a growing tendency that the Kaliumfluorld on the walls of the reaction vessel applies _f whereby it is inactive, and the yield is reduced.

Suitable polar aprotic solvents are, for example, "H-methyl-2-pyrrolidone, dimethyl sulfone, ethylene carbonate, -S & mmmM, «■ Mi> Uj ^> iitiBii) -, methyl formamide and tetraethylene sulfone. The use of tetramethylene sulfone is made particularly preferred.

It is preferred to use an excess of potassium fluoride, for example 1.5-2.5 mol of iftlium fluoride, for each chlorine atom to be replaced use su.

The reaction can be a big Teaperaturbereich ausgeführt- over, but ea brroreugt, use a temperature ranging from 160 to 225 ⁰ C au. In this case, one works under dump flow.

It is known that certain chlorofluoropyridines can be used as chemical intermediates in the manufacture of herbicidal compositions (see, for example, British Patent 1,161,491). In particular, it is known to use JjS-Dlobloro- ^ ß-trifluoropyridine as a chemical intermediate in the manufacture of 3,5-dichloro-2 _f 6-dlfluoro-4-hydroiypyridine * u «

009817/1902

The invention is explained in more detail by the following example « example

Potassium fluoride for 24 hours at 300 ⁰ C was dried, tetramethylene sulfone was purified by distillation over Ätznatronpellets getrocknetο 1.2 ml of water were added to 200 ml of the dried tetramethylene sulphone (d "h ₀ 0.6 vol Jt water, based on the solvent) was added, which was located in a stirred reaction vessel which was equipped with a reflux condenser, and 136 g of dry potassium fluoride was added at 100 ⁰ C ,, the mixture was heated to 150 ⁰ C and 100 g Fentachloropyridin were added "the reaction mixture was heated to 215 ⁰ C. heated at which temperature reflux began. Reflux was maintained 4K2 hours, during which the temperature of the reaction mixture to 192 ⁰ C fell. The reaction products were obtained from the reaction mixture by distillation, which was first carried out at atmospheric pressure and later at 50 mm Hg. The combined product was washed twice with equal volumes of water and then dried with magnesium sulfate.

The yield of the raw products was 95-80 (based on the Weight of Pentaohloropyridins used), and gas / liquid e-chromatography showed that the product contained the following:

3,5-dichloro-2,4,6-trifluoropyTidin (bp 156 ⁰ C) 91 * 3-Chlorotetrafluoropyridin (bp 120 ⁰ C) 6jC

2-pluorotetrachloropyridine (bp 234 ° C) 3%

009817/1902

Claims (1)

Patent claims 1 · Process for the replacement of chlorine by fluorine in a pyridine ring, characterized in that a chloropyridine or a chlorofluoropyridine with Kaliuiafluorid in a polar aprotic solvent in the presence of 0.2-2.0 vol. Share Waeser per 100 VolI ₃ -TeUe polar aprotic solvent converts o 2. The method according to claim 1, characterized in »that the chloropyridine or chloroflnoropyridine Chlorine atom in the 2-, 4- and / or 6-position of the pyridic ring contains. 3. The method according to claim 2, characterized in that the chloropyridine used is pentachloropyridine will. 4. The method according to any one of the preceding claims, characterized in that the proportion of water 0.2-1.0 parts by volume per 100 parts by volume of polar aprotic solvent. 5. The method according to claim 4 _f, characterized in that the proportion of water Q, 5-1 _f 0 parts by volume each 100 parts by volume of polar aprotic solvent is » 6ο Method according to one of the preceding claims, characterized characterized in that tetramethylene sulfonone is used as the polar aprotic solvent «. 009817/1902 7. The method according to any one of the preceding claims, characterized gekennzeichne t _r that the proportion of potassium fluoride depending is 1.5-2.5 Hole to ersetzendea chlorine atom, 8 · Method according to one of the preceding insprüche, characterized gekennze ichne t, that a temperature is used in the range of 160-225 ⁰ C. H.iOHi 009817/1902