WO1992001663A1 - Procede de preparation d'acides 4-chloro-2-methylphenoxyalcanoiques - Google Patents

Procede de preparation d'acides 4-chloro-2-methylphenoxyalcanoiques Download PDF

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WO1992001663A1
WO1992001663A1 PCT/DK1991/000208 DK9100208W WO9201663A1 WO 1992001663 A1 WO1992001663 A1 WO 1992001663A1 DK 9100208 W DK9100208 W DK 9100208W WO 9201663 A1 WO9201663 A1 WO 9201663A1
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acid
chloro
alkyl
reaction
hydrogen
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Arne OXBØL
Bjarne Holm-Jensen
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KVK Agro AS
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KVK Agro AS
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
    • C07C51/347—Preparation of carboxylic acids or their salts, halides or anhydrides by reactions not involving formation of carboxyl groups
    • C07C51/363—Preparation of carboxylic acids or their salts, halides or anhydrides by reactions not involving formation of carboxyl groups by introduction of halogen; by substitution of halogen atoms by other halogen atoms

Definitions

  • the present invention relates to a method for preparing 4- chloro-2-methylphenoxyalkanoic acids which are widely used as hormone-type herbicides for controlling the growth of dicotyledonous weeds in cereals and grass lands.
  • Particu ⁇ larly interesting 4-chloro-2-methylphenoxyalkanoic acids used as herbicides are:
  • MCPA 4-chloro-2-methylphenoxyacetic acid
  • MCPP 2-(4-chloro-2-methylphenoxy)propionic acid
  • MCPB 4-(4-chloro-2-methylphenoxy)butyric acid
  • MCPP may exist as pure enantiomers thereof or as mixtures of these such as the racemic mixture.
  • n is an integer 1, 2 or 3, have been prepared according to the following method:
  • 2-Methylphenol (o-cresol) is chlorinated by means of sul- furylchloride (SO2CI2) at a temperature of 30-40°C to yield a mixture of chlorocresols containing approximately 93% w/w 4-chloro-o-cresol and 6% w/w 6-chloro-o-cresol.
  • SO2CI2 sul- furylchloride
  • the mixture is distilled in order to obtain a satisfactory purity of the desired product.
  • the purity of the distilled product is 97-98% w/w 4-chloro-o-cresol.
  • a by-product of the chlorina- tion step is sulfur dioxide (S0 2 ) which is recycled by reaction with chlorine (Cl 2 ) to form S0 2 C1 2 .
  • the 4-chloro-o-cresol is reacted either with a chloroalka- noic acid (for the preparation of MCPA or MCPP) or with a lactone (for the preparation of MCPB) in a strongly alka ⁇ line medium at reflux temperature.
  • This is a condensation type reaction.
  • the reaction mixture is extracted with e.g. an organic solvent at neutral pH whereby unreacted 4-chloro-o-cresol is removed from the mixture.
  • the aqueous phase containing the desired material is acidified with mineral acid (HC1 or H 2 S0 4 ) whereby the phenoxyalkanoic acid is precipitated.
  • the resulting phenoxyalkanoic acid may be formulated di ⁇ rectly into a herbicidal composition without further sepa ⁇ ration or the phenoxyalkanoic acid can be crystallized as granules or flakes.
  • the yield of 4-chloro-2-methylphen- oxyalkanoic acid based on 2-methylphenol (o-cresol) is only approximately 88%.
  • the losses are mainly due to chlorina- tion at undesired positions in the molecule, e.g. chlorina- tion at the 6-position or at both the 4- and 6-position, and also losses in the distillation step contribute con ⁇ siderably to lower the total yield.
  • the condensation of 2-methylphenol should be followed by a chlorination of the 2-methylphenoxyalkanoic acid which is the product of the condensation step. This chlorination step is termed an after-chlorination reaction.
  • US 3,920,757 discloses the chlorination of 2-methylphenoxy- acetic acid (MPA) dissolved in glacial acetic acid (i.e. an organic solvent) by using S0 2 C1 2 and a catalyst.
  • the pro ⁇ duct contained 90.8% w/w MCPA and the ratio of 4-chlorina- ted to 6-chlorinated product, i.e. MCPA to 6-chloro-2- methylphenoxyacetic acid, is 15.6.
  • PL 100642 and PL 115188 disclose the chlorination of MPA with Cl 2 in aqueous organic solvents, namely tetrachloro- ethane or chlorobenzene.
  • the reported yields are as high as 95% and the purities are as high as 93%.
  • the chlorination of MPA is carried out at high temperatures and comprises chlorination in two steps with several separa ⁇ tions of the reaction mixture and, consequently, the chlo ⁇ rination process described is not an improvement in rela ⁇ tion to the traditional method of preparing the present phenoxy acids.
  • EP 55 357 discloses the chlorination of MPA as a suspension in water with Cl 2 at 60°C. The reported yield is 92.1% and the purity is 96%.
  • the Applicant of the present application 4 has carried out experiments according to the chlorination process described in the European patent (Example 5) where ⁇ by a product was obtained with the following composition:
  • CS 226909 discloses the chlorination of 2-methylphenoxy- acetic acid with NaOCl at such pH which results in the conversion of NaOCl into HCIO in the reaction mixture; in this process, the HCIO is actually the chlorinating agent.
  • the product of the chlorination process is reported to contain:
  • the total yield of MCPA is reported to be 82.8% w/w. As above, neither the yield of MCPA nor the relative amounts of the various resulting compounds in the product mixture can be considered completely satisfactory.
  • the ratio of 4- chlorinated (MCPA) to 6-chlorinated phenoxy acid is 10.2.
  • the object of the present invention is to provide a simple and easy method for preparing 4-chloro-2-methylphenoxyalka- noic acids by chlorination of the corresponding 2-methyl- phenoxyalkanoic acid to obtain high yields of the desired product, with a high selectivity for chlorination in the 4- position, which process can be carried out in simple and cheap equipment and with improved relations to the environ ⁇ ment, using reagents and additives which are acceptable from an environmental point of view and from the point of view of labour safety and acceptability.
  • an electropositively functioning group designates a group which is capable of attracting an electronegative part of the chlorinating agent (such as the oxygen atom of hypo- chlorous acid or one of the chlorine atoms when the chlorinating agent is Cl 2 ) .
  • an electronegatively functioning group designates a group which is capable of attracting an electropositive part of the chlorinating agent (such as the chlorine atom of hypo- chlorous acid or one of the chlorine atoms when the chlorinating agent is Cl 2 ) .
  • the electropositivity of the electropositive function and the electronegativity of the electronegative function should, of course, be of a sufficient strength so that the desired catalytic effect is above a certain level with respect to selective 4-chlorination.
  • a suitable catalyst may be defined as a compound of the kind identified above which is capable of ensuring, in the chlorination in question, a ratio between 4-chlorinated and 6-chlorinated reaction product of at least 15, preferably at least 25.
  • a suitable catalyst may be defined as a compound of the kind defined above which is capable of ensuring a ratio between 4-chloro-2-methylphenoxyacetic acid and 6-chloro-2- methylphenox acetic acid of at least 15, preferably at least 25, when used as the catalyst in the production of 4- chloro-2-methylphenoxyacetic acid by chlorination of 2- methylphenoxyacetic acid under the conditions as defined in Example 8 herein.
  • catalysts corresponding to the above definition are compounds in which the electropositively functioning group is dialkylsubstituted amino, and the electronegatively functioning group is selected from carbonyl, thiocarbonyl and selenocarbonyl.
  • interesting catalysts are compounds wherein the elec ⁇ tronegatively functioning group is carbonyl or thiocar ⁇ bonyl, and the carbon atom of the carbonyl or thiocarbonyl group additionally carries hydrogen or a group attached through a nitrogen, carbon, oxygen, or sulfur atom, such as an amido, hydrazido, alkoxy, or thioether group.
  • Effective and interesting catalysts are compounds in which the electronegatively functioning group is carbonyl, and the carbon atom of the carbonyl group additionally carries a group R-O- in which R is an aliphatic group, such as an alkoxy group, or additionally carries an optionally dialiphatic-substituted amido group, such as a dialkyla ido group.
  • R-O- a group R-O- in which R is an aliphatic group, such as an alkoxy group, or additionally carries an optionally dialiphatic-substituted amido group, such as a dialkyla ido group.
  • R- , R 2 , R 3 and R4 each independently is hydrogen or C ] __ 4 alkyl; or R- j _ and R 2 together are oxo, and R 3 and R 4 each independently is hydrogen or C -_- - alkyl; n is an integer 0 or 1; and R x is hydrogen; or, when n is 1, R ⁇ and R4 may together designate a carbon- carbon bond; X, when R ⁇ and R 2 together are oxo, is
  • NR' 5 R' 6 wherein R' 5 and R' 6 each is C 1 _ 4 alkyl; and Z is NR 7 R 3 wherein R 7 and R 8 each independently is C- ] __4 alkyl.
  • FR 1,470,160 discloses a method for preparing 2-methyl-4- chlorophenoxycarboxylic acids, in which a 2-methyl- phenoxycarboxylic acid dissolved in an organic solvent or in suspension is reacted with sulfuryl chloride at 40-150°C in the presence of a catalyst.
  • the catalyst may be an a ine.
  • the amines disclosed in FR 1,470,160 do not correspond to the definition given above for the catalysts to be used according to the invention.
  • R 5 and R 6 are hydrogen.
  • each of R 5 and R 6 is C-* ⁇ alkyl.
  • each of R 7 and R 8 is C-*__ 2 alkyl.
  • each of R' 5 and R'g is C- j __ 2 alkyl.
  • Preferred compounds of formula I are compounds wherein R*-_ and R 2 together are oxo, and X is NRsRg, wherein R 6 and R 5 each preferably is C ⁇ «4 alkyl; these compounds are amides of aminosubstituted alkanoic acids.
  • N,N-diethylaminoacetic acid N' ,N'-diethylamide, N,N,N' ,N'-tetramethyl-l,2-diaminoethane, ethyl N,N-dimethylaminoacetate, and
  • N,N-dimethylaminoacetic acid amide N,N-dimethylaminoacetic acid amide.
  • the compounds to be used as catalysts in the method of the invention are either known compounds or can be prepared analogously with known compounds.
  • Compounds which are amides of aminosubstituted alkanoic acids as indicated above may be prepared by separate amida- tion and amination of the corresponding acid comprising a leaving group in the position of the amine function. How- ever, if the substituents on the a ine and amide nitrogens, respectively, are identical, the amination and amidation reactions may be conducted simultaneously by treating the leaving group-substituted acid (or an activated derivative thereof such as the acid chloride) with 2 equivalents of the appropriate amine.
  • the amount of catalyst to be used in the method according to the invention should preferably be in the range, of 0.2-5% w/w (based on the 2-(2-methylphenoxy)alkanoic acid). Usually an amount of 0.5-1% w/w catalyst will be sufficient to obtain satisfactory results in terms of yield and ratio of desired product to undesired by-product.
  • the chlorination of 2-methyl-phenoxyalkanoic acid in the presence of a catalyst as defined above ensures high conversion of the starting material and, most importantly, a very high ratio of desired product (4-chlorinated phenoxyalkanoic acids) to by-product (6-chlorinated and 4,6-dichlorinated phenoxyalkanoic acids, the amount of the dichlorinated by-product being insignificant) .
  • water-compatible chlori ⁇ nating agent denotes a chlorinating agent which in the presence of water does not hydrolyze to a compound incap- able of chlorinating 2-methyl-phenoxyalkanoic acids.
  • the water-compatible chlorinating agent as used in the method according to the invention is preferably selected from elementary chlorine and HCIO, normally formed in situ from a salt thereof, in particular an alkali metal salt, such as the sodium salt or the potassium salt, and a mineral acid.
  • HCIO is preferred, but it is contemplated that elementary chlorine will also be useful in the process of the invention.
  • aqueous medium designates water and mixtures of water and one or several organic solvents which do not to any sig ⁇ nificant extent react with the chlorinating agent, the mixtures being mixtures containing a sufficient proportion of water to secure that the 4-chloro-2-methylphenoxyalkan- oic acid salt formed does not precipitate, in other words, remains in solution in the aqueous medium.
  • the organic solvent or solvents which may be present in the mixture will normally be solvents which are miscible with water, but mixtures of water and organic solvents which are not miscible with water are within the definition herein of the aqueous medium, provided such mixtures do not give rise to precipitation of the salt of the desired acid such as explained above.
  • Examples of mixtures of water and water- miscible or water-immiscible solvents are, e.g., a mixture of 180 ml of water and 25 ml of acetone (water-miscible) and a mixture of 180 ml of water and 25 ml of xylene (wa- ter-immiscible) . Both of these examples have been found to be useful and to perform excellently in the method of the invention, such as appears from Example 12.
  • water-immiscible solvents which are contemplated to be useful as constituents of the aqueous medium are petroleum ether, cyclohexane and xylene, diethylether, methylene chloride, chloroform, carbontetrachloride and 1,1,1- trichloroethane.
  • the method according to the invention is carried out in water.
  • the method of the invention should preferably be carried out at a pH below 10, preferably at a pH in the range of 0-9, more preferably in the range of 3-9, most preferably in the range of 5-9.
  • hypochlorous acid is a preferred chlorinating reagent; an advantage of HCIO is that it results primarily in monochlorination of the starting material.
  • pH higher than 6.3, at which pH practically no Cl 2 is present.
  • not all HCIO present should be in the form of a salt thereof.
  • pH should preferably be maintained below 9.4, at and above which pH practically no HCIO is present.
  • HCIO undergoes disproportionation into oxygen and hydro ⁇ chloric acid on prolonged standing and under influence of light and heat:
  • the disproportionation reaction becomes more important as compared to the chlori ⁇ nation reaction which results in a lower yield of phenoxy ⁇ alkanoic acid based on HCIO which in turn results in the requirement for an excess of HCIO in the reaction mixture. Consequently, it is particularly preferred that the reac ⁇ tion is carried out at a pH in the range of 7-9 to ensure a satisfactory yield based on HCIO, especially in the range of 7-8.5.
  • the method according to the invention is car ⁇ ried out at a temperature between 0°C and 50°C, more preferably between 10°C and 30°C. It has been found that the temperature has a significant influence on the ratio of the 4-chlorinated to the 6-chlorinated phenoxyalkanoic acids. Experiments have shown that when chlorinating 2-(2- methylphenoxy)propionic acid to obtain MCPP, the above- mentioned ratio is approximately 180 when the method according to the invention is carried out at approximately 10°C, and that the ratio is approximately 100 when the method according to the invention is carried out at approximately 30°C (see Example 7).
  • the amount of starting material which is not converted is approximately 3-4% higher when the method according to the invention is carried out at 30°C than when carried out at 10°C. It is believed that this is due to the disproportionation of HCIO (see Example 7).
  • the reaction is started at a temperature of 0 ⁇ C or below, and the reaction temperature is allowed to increase, the average temperature being in the range between 10°C and 20°C over the course of the reaction.
  • the background for the preference of this embodiment is as follows:
  • an elegant embodiment is to use direct cooling by adding ice to the chlorination reaction mixture.
  • the ice can be added either before the start of the chlorination process, thereby lowering the starting temperature to approx. -5°C and the " end temperature to approx. 30°C, the average temperature then being approx. 12-15°C which is a very preferred average temperature.
  • the variation in temperature during the process in this embodiment will give rise to a variation in selectivity of the chlorination, the selectivity being very high at the lower temperature at the beginning and somewhat lower at the higher temperature at the end; however, the average selectivity will be very satisfactory.
  • Another embodiment of direct cooling is to continuously add ice to the chlorination reaction mixture, thereby keeping the temperature at the desired level. Besides its function as a cooling measure, the addition of ice during the reaction serves the purpose of keeping the concentration of the phenoxyacid in the final chlorination reaction mixture at a suitable level.
  • hypochlorous acid as chlorinating agent offers an excellent opportunity of controlling the process.
  • An aque ⁇ ous solution containing minor amounts of hypochlorite has a redox-potential significantly different from pure water.
  • the redox-potential can be measured by means of a mV-meter using a platinum and a calomel or mercury sulphate electro ⁇ de.
  • hypochlorite Due to the influence of the catalyst, which in addition to the selective effects raises the reaction rate, the chlori ⁇ nation is very fast and, consequently, the hypochlorite is used in the reaction as fast as it is added. When all of the 2-methylphenoxyalkanoic acid is reacted, there is no consumption of hypochlorite and, consequently, the redox- potential changes significantly. Using the principle of end-point titration, the addition of hypochlorite can be stopped automatically. The advantages of this control are obvious:
  • the method of the invention may be carried out batchwise or continuously, the continuous operation being possible because the reaction rate is so fast due to the catalyst that only a very short retention time in the reaction vessel is necessary.
  • solutions of 2-methylphenoxyalkanoic acid and hypochlorite can be added continuously to the reaction vessel in stoich- iometric amounts, the amounts being determined on the basis of analysis of the solutions, in such concentrations that the chlorination ends with a solution of product in a concentration not leading to precipitation.
  • pH is measured and regulated in the reaction vessel, and the addition of hypoclorite can be controlled by measuring the redox poten ⁇ tial.
  • the solution leaving the reaction vessel may be treated batchwise or continuously to obtain the final product. This embodiment is illustrated in Example 15.
  • the method of the invention may be used as the chlorinating step when prepar ⁇ ing 4-chloro-2-methyl-phenoxyalkanoic acids of formula II from 2-methylphenol (o-cresol) by e.g.
  • the reac ⁇ tion mixture is water vapour-distilled or extracted with e.g. an organic solvent whereby unreacted o-cresol is removed from the mixture.
  • the resulting mixture is cooled to the chlorination temperature, i.e. at least below 50°C, and if necessary diluted with water to a suitable content of 2-methyl-phenoxyalkanoic acid;
  • a suitable amount of a catalyst as defined above, such as a compound of formula I is added to the reaction mixture followed by thorough agitation of the mixture while maintaining the average temperature thereof at 0-50°C and pH below 10.
  • a chlorinating agent e.g. elementary chlorine, HCIO, normally formed in situ by adding an aqueous solution of an alkali metal salt of HCIO, is added over a period of up to several hours, monitored by measuring the redox potential.
  • the reaction mixture is allowed to stand for about 15 minutes, followed by addition of Na 2 S ⁇ 3 to remove the excess of the chlorina ⁇ ting agent.
  • the resulting mixture contains approximately 8- 20% w/w 4-chloro-2-methyl-phenoxyalkanoic acid;
  • a preferred method of separation is to heat the reaction mixture to about 60-90°C and add an equimolar amount of a mineral acid, whereby the acid prepared is liberated as a heavy oil which easily separates from the water. After decanting the water, the oil is washed once with an equal volume of water and either crystallized as flakes or formu- lated directly as a salt.
  • the corre ⁇ sponding 2-methylphenoxyalkanoic acid is subjected to chlorination in water as the reaction medium and with an alkali metal salt of HC10 added thereto to provide the chlorinating agent.
  • the pH of the reaction mixture is maintained at about 8.5 whereby the added alkali metal salt of HCIO is partly converted into HCIO which then is the chemical compound which is believed to be the actual reac- tant in the chlorination reaction process.
  • More alkali metal salt of HOC1 is converted into HCIO when HCIO is removed in the chlorination process, thus maintaining the equilibrium between HOC1 salt and HCIO.
  • the temperature is maintained at about 20°C.
  • the reaction mixture subjected to the method of the inven ⁇ tion i.e. the resulting reaction mixture from step a) in the above-mentioned process for preparing 4-chloro-2-meth- ylphenoxyalkanoic acids from 2-methylphenol (o-cresol)
  • the chlorinating agent is HCIO, optionally added as an alkali metal salt thereof, this 2-methylphenol will be oxidized to water-soluble aliphatic acids during the chlorination process step since HCIO acts as oxidizing agent.
  • the chlorination is performed by means of HCIO formed in situ from an alkali metal salt thereof and hydro- chloric acid, and the waste water from the reaction con ⁇ taining alkali metal chloride formed in the chlorination is subjected to electrolysis to form alkali metal hydroxide and chlorine, some of the chlorine being reacted with some of the alkali metal hydroxide and recycled as hypochlorite, the rest being burned with hydrogen to form hydrochloric acid, which is then recycled for use in the chlorination.
  • the alkali metal hydroxide formed in the electrolysis may be recycled for use in the preparation of the 2-(2-methyl- phenoxy)alkanoic acid.
  • the electrolysis may be performed in any suitable electro- lysis plant.
  • the concentration of chloride in the waste water should be as high as possible.
  • a high content of chloride results when the concentration of phenoxyalkanoic acid is high.
  • a particularly high concentration of phenoxyalkanoic acid is obtained when the salt of the phenoxyalkanoic acid formed is the potassium salt, which is considerably more soluble than the sodium salt.
  • the alkali metal salt of HCIO should preferably be the potassium salt.
  • the yield of MCPA > 98%.
  • the reaction mixture was slowly poured into 100 ml of HC1 37% w/w (1.22 mol) at 50°C to precipitate MCPA in the acid form.
  • the precipitated acid was removed by filtration and washed with 3 x 400 ml of water followed by melting the acid at 87°C whereby water was released.
  • the melted acid was further heated to 130°C to release and remove the remaining water and poured into a tray to obtain crystal ⁇ line material resembling industrial flakes.
  • Example 1 0.1 mol of 2MPA was chlorinated as described in Example 1 with and without the presence of a catalyst, respectively.
  • the catalyst was N,N-dimethyl-2-amino- propionic acid N' ,N'-dimethylamide which was added in an amount of 0.2 g. Analysis of the two reaction mixtures appears from Table I:
  • the yield of MCPA was 96.4%.
  • the washing water was recirculated to the next batch and used for dilution of the initial 2MPA solution. This resul ⁇ ted in an increase in the total yield to a total of 97.7% (96.4% + 1.3%) .
  • the reaction mixture was divided into two parts. The first part was subjected to treatment with 10 ml of NaOCl at pH > 9.5 whereas the second part was untreated.
  • the temperatures were maintained at 10°C, 20°C and 30°C, respectively, and the pH was maintained at 7.0, 8.0 and 9.0, respectively.
  • the various catalysts were prepared from a chloroalkanoic acid and an amine or from an amino acid and an alkanol or are commercially available, cf. Example 9 and 10 below.
  • Table 5 shows the results in terms of the calculated ratios of MCPA product to 6C2MPA, i.e. the ratio of 4- to 6-chlor- inated product as a function of the catalyst (the various catalysts are represented by their starting materials) .
  • the ratio between 4- and 6- chlorinated product is 8.0, which means that a ratio of 8.0 or very close thereto indicates no catalytic effect.
  • N,N-dimethyl-2- aminopropionic acid N' ,N'-dimethylamide
  • F N,N,N' ,N'-tetramethy1-1,2-diaminoethane
  • N,N-dimethyl-4-aminobutyric acid N' ,N'-dimethyl mide 12 N,N,N',N'-tetramethylurea
  • N,N-dimethyl-3-aminopropionic acid N' ,N'-dimethylamide, N,N-dimethylaminoacetic acid N' ,N'-dimethylamide, and N,N-diethylaminoacetic acid N' ,N'-diethylamide.
  • Start temperature -5.5°C
  • Start redox potential * 320 V pH was kept at 8.5 by addition of HCl.
  • pH was measured in the reactor and controlled by addition of HCl.

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Abstract

On prépare des acides 4-chloro-2-méthylphénoxyalcanoïques, utiles comme herbicides, tel que l'acide 4-chloro-2-méthylphénoxyacétique (MCPP), l'acide 2-(4-chloro-2-méthylphénoxy)propionique (MCPB), et l'acide 4-(4-chloro-2-méthylphénoxy)butyrique (MCPB), en faisant réagir l'acide 2-méthylphénoxyalcanoïque correspondant avec un agent chlorant compatible avec l'eau dans un milieu aqueux en présence d'un catalyseur, lequel est constitué par un composé chimique comprenant deux atomes de carbone liés ensemble par une liaison simple ou par l'intermédiaire d'un groupe méthylène ou méthine, l'un des atomes de carbone étant substitué par un groupe fonctionnant électropositivement, et l'autre atome de carbone étant l'atome de carbone d'un groupe fonctionnant électronégativement. Le catalyseur est en particulier un composé représenté par la formule générale X - CR1R2 - (CHRx)n - CR3R4 - Z où R1, R2 R3 et R4 représentent séparément l'hydrogène ou un alkyle C1-4; ou R1 et R2 forment ensemble un oxo, et R6 et R4 représentent séparément l'hydrogène ou un alkyle C1-4; n est égal à un nombre entier égal à 0 ou à 1; et Rx représente l'hydrogène; ou, lorsque n est égal à 1, Rx et R4 peuvent représenter ensemble une liaison carbone-carbone; lorsque R1 et R2 forment ensemble un oxo, X représente un alcoxy C1-6, un hydrogène, un alkyle C1-6 ou NR5R6, où R5 et R6 représentent chacun séparément l'hydrogène ou un alkyle C1-6; ou, lorsque R1 et R2 ne forment pas ensemble un oxo, X représente NR'5R'6 où R'5 et R'6 représentent chacun un alkyle C1-4; et Z représente NR7R8, ou avec R7 et R8 représentent chacun séparément un alkyle C1-4. Le catalyseur permet d'assurer un rapport élevé entre les produits de réaction 4-chloré et 6-chloré, qui est égal à au moins 15 et de préférence à au moins 25 et qui peut monter jusqu'à 50-150 voire plus haut. Un tel procédé se caractérise par un degré élevé d'acceptabilité par l'environnement.
PCT/DK1991/000208 1990-07-16 1991-07-16 Procede de preparation d'acides 4-chloro-2-methylphenoxyalcanoiques Ceased WO1992001663A1 (fr)

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DE1991913384 DE539462T1 (de) 1990-07-16 1991-07-16 Eine methode zur herstellung von 4-chloro-2-methylphenoxy-alkansaeuren.

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DK170790A DK170790D0 (da) 1990-07-16 1990-07-16 Fremgangsmaade til fremstilling af alkansyrederivater
DK1707/90 1990-07-16

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CN113861012A (zh) * 2021-10-27 2021-12-31 安徽华星化工有限公司 2-甲基-4-氯苯氧乙酸的连续化制备方法及制备系统
CN119492694A (zh) * 2024-11-12 2025-02-21 科顺防水科技股份有限公司 化学阻根剂手性分布的测量方法

Citations (5)

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GB744475A (en) * 1952-11-06 1956-02-08 Boots Pure Drug Co Ltd Process for the manufacture of 2-methyl-4-chlorophenoxyacetic acid and herbicidal compositions containing the same
DE1014092B (de) * 1954-12-30 1957-08-22 Basf Ag Verfahren zur Herstellung von ª‡-Chlorfettsaeuren
FR1470160A (fr) * 1965-03-05 1967-02-17 Chemie Linz Ag Procédé de préparation d'acides 2-méthyl-4-chlorophénoxycarboxyliques
US3751461A (en) * 1971-11-29 1973-08-07 Dow Chemical Co Alpha chlorination of acid chlorides
US3764617A (en) * 1970-06-29 1973-10-09 Procter & Gamble Process for preparing vicinal glycols from olefins

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Publication number Priority date Publication date Assignee Title
GB744475A (en) * 1952-11-06 1956-02-08 Boots Pure Drug Co Ltd Process for the manufacture of 2-methyl-4-chlorophenoxyacetic acid and herbicidal compositions containing the same
DE1014092B (de) * 1954-12-30 1957-08-22 Basf Ag Verfahren zur Herstellung von ª‡-Chlorfettsaeuren
FR1470160A (fr) * 1965-03-05 1967-02-17 Chemie Linz Ag Procédé de préparation d'acides 2-méthyl-4-chlorophénoxycarboxyliques
US3764617A (en) * 1970-06-29 1973-10-09 Procter & Gamble Process for preparing vicinal glycols from olefins
US3751461A (en) * 1971-11-29 1973-08-07 Dow Chemical Co Alpha chlorination of acid chlorides

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Publication number Priority date Publication date Assignee Title
CN113861012A (zh) * 2021-10-27 2021-12-31 安徽华星化工有限公司 2-甲基-4-氯苯氧乙酸的连续化制备方法及制备系统
CN119492694A (zh) * 2024-11-12 2025-02-21 科顺防水科技股份有限公司 化学阻根剂手性分布的测量方法

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