DE3229589A1 - METHOD FOR PRODUCING PHENMEDIPHAM - Google Patents

Description

Process for the production of phenmedipham

The present invention relates to a process for the preparation of a herbicidal compound which known under the name "Phenmedipham".

Phenmedipham is the compound of the formula

(D

From FR-PS 1 475 241 it is known that this compound is produced by reacting N- (hydroxyphenyl) urethane to react with an isocyanate or with a carbamic acid chloride. In this case, find thus the following reactions take place;

CH ^ -0-CO-NH

or

OH + O = C = N-

(D

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1A-56 134 - J? -

(D

These processes are associated with difficulties because the reactants are each separate need to be made; above all, the methyl chloroformate, which is used to produce the Methyl m-hydroxyphenyl carbamate is used, an economically expensive connection.

An improved process for the production of phenmedipham was therefore developed (Chem.

Paragraph 78 147614 χ = HU registration SO-1018 = HU-PS 164323) which consists in the fact that one m-aminophenol with a methanolic phosgene solution reacts in the presence of an acid acceptor such as MgO and in a second stage the obtained Hydroxycarbanilate (or hydroxyphenyl carbamate) with phosgene in the presence of dimethylaniline and causes sodium carbonate to react; in a third stage the resulting Carbomethoxyaminophenyl chloroformate reacted with m-toluidine. This method but also offers various disadvantages insofar as a considerable one in the first stage Amount of base (MgO) is consumed, which serves to convert the HCl formed during the reaction to neutralize and prevent the formation of aminophenol chlorohydrate. Farther In the further course of the process, the HCl formed must be neutralized with the aid of a base and, in addition, is through the joint presence of HCl and

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1Α-56 134 "'ä * ''

"Water corrosive the medium, which in industrial Scale is very cumbersome.

One might think of solving these first stage problems with the help of working methods such as they are described in US Pat. No. 3,933 W and French Pat. No. 1,554. Thereafter, m-hydroxyphenoxycarbamate by heating aminophenol with phosgene and then with methanol. But it is difficult the reaction of the isocyanate formed either with the aminophenol or with itself to prevent, so that oligomers are formed which lead to an insufficiently pure phenmedipham to lead.

There is therefore a need for a simple and economical process for the production of Phenmedipham; In spite of numerous possibilities and attempts, such a method has been used so far not found. In addition, such a process is said to have improved purity for phenmedipham deliver.

The aim of the invention is to provide such a method.

The process according to the invention is characterized in that m-aminophenol is mixed with phosgene reacted at low temperature in a solvent of the alkyl alkanoate type, then Lets methanol react with the resulting reaction solution, then, in the same solution, brings m-toluyl isocyanate in the presence of an organic base to the reaction.

1A-56 134

The compound of the formula is formed in the course of the first reaction stage

NH-CO-Cl

which is also called m-hydroxyphenylcarbamic acid chloride referred to as.

After the reaction with the methanol, this acid chloride is converted into methyl m-hydroxyphenyl carbamate emerged, the phenmedipham with m-toluyl isocyanate results.

The preferred alkyl alkanoate (alkyl esters of aliphatic carboxylic acids) are methyl alkanoates and in particular methyl acetate or methyl propionate are used. In practice it will be in the implementation of phosgene with m-aminophenol preferably (with stirring) the m-aminophenol to a solution of the phosgene given in the alkanoate provided as the solvent.

The reaction temperature is generally in the range of -20 to +40 ⁰ C, preferably in the range 10-30 ⁰ C.

The m-aminophenol is added in the form of its solution in the alkanoate solvent. To over If you have concentrated solutions, you can use hot solutions.

The concentration of phosgene changes in the course of the reaction; but the initial concentration is generally 10 to 60 wt .- ^. At the end of the reaction, this concentration can be very high become low and even be zero *

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The reactants are used in such amounts that the phosgene / m-aminophenol molar ratio 1 to 2, preferably 1.05 to 1.4.

In the course of the realüon arises at least partially insoluble m-aminophenol chlorohydrate. at further course of the reaction with stirring in the temperature range given above this chlorohydrate and the reaction usually leads to a solution of the m-hydroxyphenylcarbamic acid chloride in the alkanoate.

If the reaction medium still contains phosgene after the reaction has ended, this is preferably removed by evaporation or distillation or entrainment (with the aid of an entrainer); this generally takes place at a temperature of 10 to 40 ^° C.
20th

The following reaction with methanol can be conveniently carried out by adding methanol to the previous one run the solution obtained. There is generally so much methanol used that the molar ratio of methanol used to originally abandoned m-aminophenol 1 to 10 and is preferably 3 to 8.

The reaction is generally carried out at a temperature of from 20 to 100 ^° C. and under pressure if the mixture is operated above the boiling point. In this way, a solution of methyl m-hydroxyphenyl carbamate is obtained, from which certain volatile substances, for example by distillation,

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removed). Materials that can be removed include hydrogen chloride and Excess methanol and, if appropriate, part of the solvent used Alkanoic acid ester.

In the third and last stage of the process according to the invention, m-toluyl isocyanate and an organic base to the solution of methyl mhydroxyphenyl carbamate obtained as described above given in the alkanoate. Other substances may be present, as explained in more detail below.

Preferably enough m-toluyl isocyanate is added that the molar ratio of m-toluyl isocyanate to m-aminophenol used in the first stage is 1 to 1.5 and preferably 1.02 to 1.2.

The reaction usually takes place in a temperature range from 20 to 120 ⁰ C, if necessary under pressure, and preferably between 40 and

80 - ⁰ C.

Tertiary amines, such as the trialkylamines, and in particular, are preferred as the organic base Triethylamine. 0.1 to 10 mol- 6 base are used, based on the m-toluyl isocyanate used.

After the reaction has ended, the resulting phenmedipham can be conveniently cooled by cooling separating the reaction mixture; here Phenmedipham crystallizes with excellent Purity.

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The mother liquor obtained during crystallization, which, in addition to the alkanoate solvent Phenmedipham, Excess m-toluyl isocyanate and the organic base can be used in a further operation be used again in the third stage of the process according to the invention.

In this case, three solutions are mixed: The recycled mother liquor, which in the course of the second stage obtained solution of methyl mhydroxyphenylcarbamate and a solution of m-toluyl isocyanate. Separate addition of organic base is then not advisable. the The third stage of the process according to the invention is then carried out as already indicated. It may be necessary to distill off some of the solvent so that the Phenmedipham crystallized out.

The yields in the various reaction stages of the process according to the invention are practically quantitative.

An advantage of the process according to the invention is that phenmedipham is higher Maintains purity thanks to the high purity of the methyl m-hydroxyphenyl carbamate produced as an intermediate.

The following example serves to explain the invention in more detail.

example

In a 0.5 liter flask with a stirrer and

/8th

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An inert gas atmosphere was initially charged with 13.95 g of methyl acetate.

The contents were cooled to -20 ⁰ C; then phosgene was passed in, which liquefied at this temperature; the addition of phosgene was continued until 14.04 g had been added.

Then heated to 50 ⁰ C solution of 11.9 g of m-aminophenol in 120 ml of methyl acetate was added gradually in the course of 7 minutes, while the temperature of the reaction mixture maintained by a cooling bath at 6 to 8 ⁰ C w as.

The temperature was allowed to rise to 26 ^° C. and the mixture was then stirred at this temperature for 45 minutes. The reaction mixture was then clear and colorless.

The excess phosgene was then distilled off ^{at 30 ° C. in vacuo.}

To the obtained solution of the carbamoyl chloride in methyl acetate were added 22 ml of methanol and the whole is about 1.5 hours at reflux, heated at the boil (temperature about 50 ⁰ C).

Various volatile components (ternary mixture HCl, CH ₃ OH, CH ₃ COOCH ₃ ⁴ , azeotrope CH ₃ OH ^ h ₃ COOCH ₃ ; CH ₃ COOCH ₃ ) were then distilled off; the distillation was interrupted as soon as the temperature of the reaction mixture had reached 80.degree.

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To the reaction mixture obtained in this way, 0.1117 g of triethylamine and 16.8 g of m-toluyl isocyanate were added; copious amounts of precipitate formed. Then 100 ml of methyl acetate were added and the whole thing was ^{boiled for 1 hour (temperature close to 60 °} C.). The reaction mixture was then homogeneous. It was then allowed to cool to room temperature. Phenmedipham precipitated out and was filtered off. The filtrate was concentrated and filtered again; the total yield of phenmedipham was 29 »3 g, corresponding to 89.6 %.

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Claims (1)

Claims Process for the preparation of Phenmedipham, 'a characterized in that one m-aminophenol with phosgene at low temperature in an alkyl alkanoate as a solvent for converts m-hydroxyphenylcarbamic acid chloride, then methanol with that obtained in the first stage Brings reaction solution to the reaction and on this solution m-toluyl isocyanate in the presence an organic base can act. 2 · The method according to claim 1, characterized in that the alkanoate is an acetate or a propionate. 3. Process according to claim 1 or 2, characterized in that the temperature of the reaction between phosgene and m-aminophenol is -20 to +40 ⁰ C and / or the temperature of the reaction between methanol and the reaction medium is 20 to 100 ⁰ C and / or the temperature of the reaction between m-toluyl isocyanate and methyl-m-hydroxyphenylcarbamate 20 to 120 ⁰ C. / 2 1A-56 134 - 2 - 4. The method according to claim 3, characterized in that the temperature of the reaction between phosgene and m-aminophenol is 10 to 30 ⁰ C and / or the temperature of the reaction between m-toluene isocyanate and methyl m-hydroxyphenyl carbamate 40 to 80 ⁰ C. 5. The method according to any one of claims 1 to 4, characterized in that the Molar ratio to m-aminophenol used for phosgene 1 to 2 and / or for methanol 1 to 10 and / or for m-toluyl isocyanate is 1 to 1.5. 6. The method according to claim 5 »characterized in that the molar ratio to m-aminophenol for phosgene 1.05 to 1.4 and / each for methanol 3 to 8 and / or for m-toluyl isocyanate is 1.02 to 1.2. 7. The method according to any one of claims 1 to 6, characterized in that the organic base is a trialkylamine, preferably triethylamine. 8. The method according to any one of claims 1 to 7, characterized in that the Phenmedipham separated by cooling and the remaining solution in the stage of the reaction between m-toluyl isocyanate and methyl m-hydroxyphenyl carbamate is recycled. 7249