DE2606855A1 - Process for the preparation of propionic acid 3,4-dichloroanilide - Google Patents

Description

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Process for the preparation of propionic acid-3,4-dichloroanilide

The present invention relates to a new process for the preparation of the known propionic acid-3,4-dichloroanilide. This substance has been used as a herbicidal active ingredient for a long time, especially for control of weeds in rice crops.

It has already become known that propionic acid-3,4-dichloroanilide is obtained when reacting 3,4-dichloroaniline with propionic acid, propionic anhydride or propionic acid chloride in the presence of an inert organic solvent (cf. British patent specification 903 766). The course of these reactions can be illustrated by the following equations (a) - (c) :

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+ C ₂ H ₅ -COOH

NH-CC ₂ H ₅ +

b)

C ₂ H ₅ -CO

C ₂ H ₅ -CO

C ₂ H ₅ -COOH

c)

C, H, -CO-C1

base

HCl

However, these known methods have a number of disadvantages. For example, for the implementation of 3,4-dichloroaniline with propionic acid requires a fairly long reaction time. In addition, the propionic acid S ^ dichloroanilide obtained only in a relatively low yield which is due, among other things, to the fact that part of the thermally unstable and autoxidizable 3,4-dichloroaniline decomposed under the required relatively drastic reaction conditions. Further you have to isolate the propionic acid-3,4-dichloroanilide first the inert organic solvent and excess Remove propionic acid and water and then remove the crude product by recrystallization from a suitable one Remove any remaining impurities from the solvent.

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In the reaction of 3,4-dichloroaniline with propionic anhydride, the propionic acid-3 is indeed obtained _r 4-dichloroanilide in good yield, but is a disadvantage / in that also in this case, the addition of an inert organic solvent is necessary to ensure that the exotherm be controlled can. The work-up is therefore similarly laborious as in the process described above, because it is necessary to remove the inert organic solvent together with the propionic acid formed during the reaction from the reaction mixture and then to separate the propionic acid from the solvent. Such a separation can be carried out, for example, by fractional distillation, but it is technically complex and associated with losses of material.

A disadvantage in the production of propionic acid-3,4-dichloroanilide, starting from 3,4-dichloroaniline and propionic acid chloride, there is that in addition In addition to the solvent, an acid binder is required as a further auxiliary. In addition, requires Here, too, the isolation of the reaction product requires some effort, since both solvents and excess Base and salts produced in the course of the reaction have to be removed.

It has also become known that propionic acid-3,4-dichloroanilide can be synthesized by converting 3,4-dichloroaniline with phosgene into 3,4-dichloro-phenylcarbamoyl chloride and then using this in a second step

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Propionic acid converts (see. British Patent 1,063,528). d)

-HDOCl,

NH-C-Cl

Although the propionic acid-3,4-dichloroanilide after this Method is accessible in good yields, the process is nevertheless fraught with several disadvantages. For example In contrast to the other synthetic methods discussed, it is a two-step process, which entails a relatively high technical effort. As is further emphasized, must in the representation of the substituted phenylcarbamoyl chloride in the first reaction step, optionally by introducing it hydrogen chloride ensures that the formation of isocyanates is prevented. Otherwise is the addition of an inert organic solvent is required when carrying out the process. the Working up is therefore just as tedious as with the other methods described above for representing Propionic acid 3,4-dichloroanilide.

In addition, it is already known that aryl isocyanates can be reacted with carboxylic acids to form anilides (see Chem. Rev. 4_3, 209-210 (1948)). The principle of synthesis is all not generally applicable.

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When aryl isocyanates are reacted with weak aromatic or aliphatic carboxylic acids, as a rule, a mixture of different substances is not obtained (see Chem. Rev. 57, 52 (1957); HeIv. Chim. Acta V7, 931 -957 (1934) and J. Amer. Chem. Soc. T5_, 2686-2688 (1953)).

The course of such reactions can be illustrated by the following equation:

e) Ar-NCO + R-COOH

Ar-NH-CO-O-CO-R

Ar-NH-CO-R + CO,

(Ar-NH-CO-O-CO-NH-Ar) + R-CO-O-CO-R

Ar-NH-CO-NH-Ar + CO ₀

Ar = aryl

The preparation of certain substituted anilides by reaction of the corresponding aniline derivatives is also known with carboxylic acids (cf. German Offenlegungsschriften 921 841 and 1 543 612).

f)

NCO + RCOOH

NH-CO-R + CO,

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+ R ² COOH

R ¹ S-ZIVnH-CO-R +

The disadvantage is that an inert solvent must be present in each of these reactions. This requires as already mentioned several times, an increased effort in the isolation of the reaction products. Furthermore the conversions according to equations (f) and (g) require relatively long reaction times. They won't adhered to, the yields are relatively low.

It has now been found that one can use the known propionic acid 3,4-dichloroanilide the formula

0 NH-CC ₀ H,

(I)

obtained when 3,4-dichlorophenyl isocyanate of the formula

\\ _ NC0

Cl
in the absence of inert organic solvents

at temperatures between 130 ⁰ C and i60 ° C with propionic acid.

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The uniform, smooth course of the process according to the invention can be described as extremely surprising, because in view of the known prior art it was to be expected that the reaction of propionic acid with an aryl isocyanate would not result in a uniform product, but a mixture of several substances ( see Chem. Rev. j> 7, 52 (1957)). The almost exclusive formation of propionic acid-3,4-dichloroanilide is also surprising mainly because the highly exothermic reaction according to the invention, in contrast to analogous reactions described above, is carried out in the absence of inert organic solvents (cf. German Offenlegungsschriften 1 921 841 and 1 543 612). Moreover, the feasibility of the method according to the invention was by no means obvious on the basis of the technical teaching disclosed in British patent specification 1,063,528. In the patent in question it is pointed out that the formation of isocyanates must be avoided in the preparation of substituted anilides from substituted phenylcarbamoyl chlorides and carboxylic acids. It was therefore to be assumed that such a reaction would succeed with phenylcarbamoyl chlorides, but not with the corresponding isocyanates. As has been shown by the process according to the invention, however, the 3,4-dichlorophenyl isocyanate is very suitable for such a reaction. An existing technical prejudice could thus be overcome by the method according to the invention.

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The inventive method has a number of Benefits. This is how propionic acid-3,4-dichloroanilide becomes obtained in extremely high yield and excellent purity as a readily grindable product. Further requires only a small amount of equipment to carry out the process and because of its exothermic character the reaction requires only a small amount of energy. Furthermore, no inert organic Solvent / catalysts or other additives required. It is also of particular advantage that in the train Apart from gaseous carbon dioxide, no other unavoidable products are created during the conversion. This is particularly important for carrying out the process on an industrial scale, because one There is no need to fear environmental pollution from pollutants. In addition, there is also the work-up of the reaction mixture completely problem-free. The inventive method is thus a valuable asset to the Technology.

As already mentioned several times, the reaction according to the invention is carried out in the absence of inert organic solution agents, catalysts or other auxiliaries made.

The reaction temperatures can only be varied within a relatively narrow range. In general , one works at temperatures between 13O C and 16O C,

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preferably at temperatures between 135 C and 16O C. Maintaining these reaction temperatures exactly is of great importance for the success of the implementation. If you work at temperatures that are too low at the beginning of the implementation, undesired products are created - under other urea derivatives (see reaction scheme (e)) -, and the reaction mixture solidifies. One works on the other hand, if the temperatures are too high, there is a risk that the strongly exothermic reaction will be too stormy and runs uncontrollably.

The process according to the invention is in general carried out under normal pressure.

When carrying out the process according to the invention, 1 mol of 3,4-dichlorophenyl isocyanate is used to 1.1 moles of propionic acid.

The procedures according to the invention are carried out in detail Implementation in the following way:

In a reaction vessel equipped with a stirrer and condenser, propionic acid is heated to a temperature with stirring Temperature between 130 C and 15 0 C, preferably between 135 C and 145 C, and then adds without any additional Heat an equimolar amount or an up to 10% deficit of molten material with continued stirring 3,4-dichlorophenyl isocyanate is added at such a rate that the temperature of the reaction mixture,

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- due to the heat released during the implementation - remains constant or increases slightly. After the addition of the 3,4-dichlorophenyl isocyanate is complete, the reaction mixture is kept at a temperature between 145 ^° C. and 160 ^° C. for 1 to 2 hours to complete the reaction up to 10 mm Hg, preferably up to 10 mm Hg, out of the reaction mixture. The recovered propionic acid can be used again without further purification. The remaining, practically pure propionic acid-3,4-dichloroanilide can be used directly as a herbicidal active ingredient without additional purification.

The procedure described can also be carried out under otherwise identical reaction conditions in that the 3,4-dichlorophenyl isocyanate is initially introduced and the propionic acid is added.

It has long been known that propionic acid-3,4-dichloroanilide has valuable herbicidal properties and in particular for controlling weeds in rice crops can be used.

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260R855

example 1

In a 250 l kettle equipped with a stirrer and condenser, 59.45 kg (0.803 K-mol) of propionic acid are heated to 136 ° C. with stirring and then 150.4 kg (0.8 K-mol ) run in molten 3,4-dichlorophenyl isocyanate within 1.5 hours. A vigorous evolution of gas and an increase in the temperature of the reaction mixture are observed. After the addition of the 3,4-dichlorophenyl isocyanate is complete, the temperature is about 150 ^° C. The reaction mixture is kept at a temperature between 145 ^° C. and 150 ^° C. for one hour to complete the reaction. Then allowed to cool to 100 ⁰ C and then distilling the remaining excess propionic acid, at a pressure of 16 mm Hg from the reaction mixture out, the distillation residue, the 3,4-propionic dichloroanilide consists of virtually pure, is still in the liquid state from drained from the reaction vessel and cooled. In this way, 168 kg (96.6% of theory) of 3,4-dichloroanilide propionic acid with a melting point of 89 ° -91 ° C. are obtained.

The product can be used directly as a herbicidal active ingredient without further purification or other after-treatment will.

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Example 2

- 43.

In a 1 ltr. -Four neck flask equipped with stirrer, thermometer, Dropping funnel and reflux condenser, 376 g (2.0 mol) of 3,4-dichlorophenyl isocyanate submitted and heated to 140.degree.

Without additional heating, 155.4 g (2.1 mol) of propionic acid are added further stirring was added dropwise over the course of 45 minutes. A strong evolution of gas and an increase in temperature are observed of the reaction mixture to 150 C.

When the addition of the 3,4-dichlorophenyl isocyanate is complete, the reaction mixture becomes held at approx. 145-150 ° C. for a further two hours to complete the reaction.

The excess propionic acid still present is then distilled out of the reaction mixture at a pressure of 16 mm Hg. The distillation residue, which consists of practically pure propionic acid-3,4-dichloroanilide, is poured out of the reaction flask in the liquid state and cooled. Obtained in this way 435 g of pure propionic acid-3,4-dichloroanilide of melting point 88 to 89 ⁰ C.

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Example 5

"1-

Preparation of propionic acid-S ^ -dichloranilide from 3,4-dichlorophenyl isocyanate and propionic acid in the presence of a solvent:

56.4 g (0.3 mol) of molten 3,4-dichlorophenyl isocyanate are added dropwise to a solution of 22.2 g (0.3 mol) of propionic acid in 300 ml of pyridine at 100 ^{° C. with stirring over the course of 90 minutes.} A gas evolution is observed. When the addition is complete, the mixture is refluxed for a further 17.5 hours and then evaporated to dryness under reduced pressure (15 mm Hg). The distillation residue is drained from the reaction vessel while still in the liquid state and cooled. In this way 64 g of brownish-white propionic acid 3/4-dichloroanilide with a melting point of 76 ° -78 ° C. (cloudy), which are still contaminated according to thin-layer chromatogram (silica gel / chloroform), are obtained. The melted sample is still cloudy even at 300 ⁰ C.

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Claims (3)

Claims 1) Process for the preparation of propionic acid-3,4-dichloroanilide, characterized in that there is 3,4-dichlorophenyl isocyanate the formula in the absence of inert organic solvents at temperatures between 130 ° C and 160 ° C with propionic acid implements. 2) Process according to claim 1, characterized in that the reaction is carried out at temperatures between 135 C and i6o ° C. 3) Method according to claim 1, characterized in that one to 1 mole of 3,4-dichlorophenyl isocyanate 1 to 1.1 moles Propionic acid is used. Le A 16 815 - 14 - 709834/0995 ORIGINAL INSPECTED