DE539462T1 - A METHOD FOR THE PRODUCTION OF 4-CHLORO-2-METHYLPHENOXY ALKANIC ACIDS. - Google Patents

Claims (20)

Application No. 91 913 384.3 GF Patent claims 1. A process for preparing a 4-chloro-2-methylphenoxyalkanoic acid, comprising the reaction of the corresponding 2-methylphenoxyalkanoic acid with a water-compatible chlorinating agent in an aqueous medium in the presence of a catalyst which is a chemical compound comprising two carbon atoms linked together by a single bond or a methylene or methine group, one of the carbon atoms of which is substituted by an electropositive group which is a dialkyl-substituted amino, and the other carbon atom is the carbon atom in an electronegative group selected from carbonyl, thiocarbonyl and selenocarbonyl, or
in the presence of a catalyst of the general formula R' ₅ R' ₆ N - CR'^^ — (CHR _x ) _n — CR ₃ R ₄ — Z in the R' , R ¹ _, R and R each independently hydrogen or C. _.-alkyl,
η is an integer 0 or 1; and
R is hydrogen or, when η is 1, R and R. together form a carbon-carbon bond can describe;
R' and R' are each C. ,-alkyl and Z 7Q ' R_ and R are each independently C-alkyl , wherein the catalyst is capable of ensuring a ratio of the 4-chlorinated reaction product to the 6-chlorinated reaction product of at least 15, preferably of at least 25, or wherein the catalyst is capable of ensuring a ratio of 4-chloro-2-methyl-phenoxyacetic acid to 6-chloro-2-methyl-phenoxyacetic acid of at least 15, preferably of at least 25, when used as a catalyst at. the preparation of 4-chloro-2-methylphenoxyacetic acid by chlorination of 2-methylphenoxyacetic acid under conditions in which 0.15 mol of 2-methylphenoxyacetic acid (128.4 g of a mixture containing 19.4% 2-methylphenoxyacetic acid) is diluted to 175 ml, the catalyst is added (1.5 mol/mol% relative to the 2-methylphenoxyacetic acid or 13 mmol/l), the pH is maintained at 8.5 by adding HCl and the temperature is maintained at 20 'C using a water bath, 0.16 mol of active chlorine (a solution of 98 g NaOCl containing 11.7 w/w% active chlorine) is added over 1 h and then stirred for 15 min and excess NaOCl is removed with Na_S_O_ is removed. 2. Process according to claim 1, wherein the electronegatively acting group is carbonyl or thiocarbonyl and the carbon atom of the carbonyl or thiocarbonyl group additionally carries hydrogen or a group bonded via a nitrogen, carbon, oxygen or sulfur atom. 3. Process according to claim 2, wherein the electronegatively acting group is carbonyl and the carbon atom of the carbonyl group additionally carries a group R-O-, in which R is an aliphatic group, or an optionally dialiphatically substituted amido group. O559 4. A process according to claim 1, wherein the catalyst is a compound of the general formula I X— CR ₁ R ₂ — (CHR _x ) _n — CR ₃ R ₄ — Z (I) is, in the R-, R_, R- and R are each independently hydrogen or C -alkyl or R and R
together are oxo and R_ and R are each independently hydrogen or C,-alkyl, η is an integer 0 or 1; and R is hydrogen or, when η is 1, R and R together may denote a carbon-carbon bond; X, when R. and R_ together are oxo, C. ,,-alkoxy, X /. &KHgr;—&ogr; hydrogen, C, ..-alkyl or NR ₁ -R, where R _c &KHgr;—&ogr; 5 6 i> and R,. each independently hydrogen or C- -- D X —O alkyl, or
X, if R and R are not together oxo, NR ¹ R' is where R' and R' are each C-alkyl, and Z is NR R where R_ and R- are each independently C-alkyl. 5. The process of claim 4, wherein η is O. 6. A process according to claim 4 or 5, wherein R_ and R ₀ are each C 1-4 alkyl. 7. A process according to any one of claims 4 to 6, wherein R' ₅ and R' ₆ are each C^^alkyl. 8. A process according to any one of claims 4 to 7, wherein R ₅ and R ₆ are each independently C 1-6 alkyl. O559 9. A process according to claim 4, wherein the catalyst
N,N-Dimethyl-2-aminopropionic acid-N',N'dimethylamide,
N,N-Dimethyl-3-aminopropionic acid-N',N'dimethylamide,
N, N-dimethyl-2-aminobutyric acid-N · , N' -dimethylamide,
Methyl1-N,N-dimethylaminoacetate,
N,N-Dimethylaminoacetic acid-N',N'-dimethylamide,
N,N-diethylaminoacetic acid-N',N'-dimethylamide,
N,N,N',N'-Tetramethyl1-1,2-diaminoethane,
Ethyl-N,N-dimethylaminoacetate or
N,N-Dimethylaminoacetic acid amide
is. 10. A process according to any one of the preceding claims, wherein the 4-chloro-2-methylphenoxyalkanoic acid is 4-chloro-2-methylphenoxyacetic acid (MCPA), 2-(4-chloro-2-methylphenoxy)propionic acid (MCPP) or 4-(4-chloro-2-methylphenoxy)butyric acid (MCPB). 11. The process according to claim 10, wherein the 2-(4-chloro-2-methylphenoxy)alkanoic acid is the optically active R-(+)-2-(4-chloro-2-methylphenoxy)propionic acid (MCPP). 12. A process according to any one of the preceding claims, wherein the aqueous reaction medium is water. 13. A process according to any one of the preceding claims, wherein the water-compatible chlorinating agent is selected from elemental chlorine and HClO. 14. A process according to claim 13, wherein the chlorinating agent is HClO formed in situ in the reaction mixture from a salt thereof and a mineral acid. 15. A process according to any one of the preceding claims, wherein the reaction is carried out at a pH below 10, preferably a pH in the range of 5 to 9, in particular in the range of 7 to 9. 16. A process according to any one of the preceding claims, wherein the reaction is carried out at an average temperature between 0 ⁰ C and 50 ⁰ C, preferably between 10 "C and 30 "C. 17. A process according to claim 16, wherein the reaction is started at a temperature of 0 ⁰ C or below and the reaction temperature is then allowed to rise, the average temperature during the course of the reaction being in the range between 10 "C and 30 "C. 18. A process according to any one of the preceding claims, wherein the chlorinating agent is HClO (optionally formed in situ from a salt thereof) which is added continuously or intermittently during the course of the reaction, the redox potential of the reaction mixture being monitored and the addition of the chlorinating agent being stopped when the redox potential of the mixture has reached a stable value numerically higher than the initial value. 19. A process according to any one of the preceding claims, wherein the chlorination is carried out by means of HClO formed in situ from an alkali metal salt thereof and hydrochloric acid, and the reaction waste water containing alkali metal chloride formed in the chlorination is subjected to electrolysis to form alkali metal hydroxide and chlorine, a portion of the chlorine being reacted with the alkali metal hydroxide and recycled as hypochlorite and the remainder being combusted with hydrogen to form hydrochloric acid which is then recycled for use in the chlorination. 20. The process of claim 19, wherein the alkali metal salt of HClO is the potassium salt.