DD290189A5 - IMPROVED METHOD FOR THE PREPARATION OF 2-BENZIMIDAZOLE CARBAMINE ACID METHYL ETERS - Google Patents

Abstract

The title compound 2-benzimidazole carbamic acid methyl ester (carbendazim) is a biocidal active substance of high practical importance for crop protection, in particular against phytopathogenic fungi and bacteria. The aim and object of the invention is an improved, technologically and economically advantageous process for the preparation of this compound. The object is achieved according to the invention by reacting the dispersion of the educt o-phenylenediamine in a suitably strong acid at elevated temperatures with the solution of the cyancarbamic acid methyl ester or one of its salts, largely suppressing unwanted side reactions {chemical process; carbendazim; biocidal active substance; Plant protection; Quality improvement; Ausbeuteerhoehung}

Description

Field of application of the invention

The invention relates to an improved process for the industrial preparation of 2-Benzimidäzol-carb8minsäuremethylesters, which is used under the name carbendazim as an active ingredient in biocidal, especially fungicidal crop protection agents.

Characteristic of known technical solutions

The fungicidal active ingredient carbendazim is generally produced on an industrial scale and preferably by the known process, which starts from cyanamide. This is reacted in the presence of acid-binding agents, for example sodium hydroxide, in aqueous solution with methyl chloroformate and the resulting Cyancarbamatsalz reacted with o-phenylenediamine, with the addition of mineral acid, an acidic environment is produced (see, DE-PS 1668557 and 1795849). ,

However, the advantages of this one-pot process are offset by some serious disadvantages. During the addition of the o-phenylenediamine to the reaction mixture at elevated temperature and its residence therein prior to the adjustment of the optimum proton concentration by the subsequent addition of acid to set unavoidable side reactions, in particular oxidation and self-condensation of o-phenylenediamine.

This leads ·! The formation of coloring and toxicologically harmful impurities of the final product and thereby reduce its quality and use value for practical application.

It has therefore been proposed to add to the reaction mixture of cyano carbamate and o-pheny! Endiamine a reducing agent which is inert towards the reactants and to operate under an inert gas atmosphere (cf DE-OS 3323024). However, the achievable by this modification of the reaction control reduction in the proportion of by-products is unsatisfactory.

The subsequent separation of undesired impurities, for example by washing, extraction or recrystallization, is difficult and economically complicated because of the similar poor solubility of the main product as the by-products.

Object of the invention

It is therefore the object of the present invention to find an improved process for the preparation of 2-Benzimidazolcarbamineäuremethylesters (Carbendazlm), which shuts off the technological shortcomings of the previously customary procedure.

Essence of the invention The He Indung is based on the task, the professed and commonly used manufacturing process for the fungicidal active ingredient Carbendazim in the reaction so change and rearrange that the adhering technical and

economic disadvantages are largely avoided.

According to the invention the object is achieved in that the oxidation-sensitive and very toxic o-phenylenediamine

dispersed in an excess of a strong acid at room temperature and the dispersion heated by the exothermic neutralization reaction to a minimum temperature before being brought to the same with an optimum temperature

Solution of the Cyancarbaminsäuremethyleoters or seinor salts is reacted so that after the union of both Reactive components immediately carbendazimbildung uses. The preferred mode of this improved process is to use the o-phenylenediamine in the reaction vessel

to submit a suitable reducing agent for the suppression of oxidative side reactions and the reaction medium sufficient for the setting reaction medium sufficient amount of a strong acid and add the resulting temperature, the likewise heated reaction solution of the reaction of the Cyanamide with methyl chloroformate to Cyancarbamat salt at a rapid pace. Even after a short reaction time, the insoluble end product separates in the form of finer brighter

Crystals from which can be separated by hot filtration and washing with water in high yield and purity. Suitable reducing agents are the chemical compounds already described for this purpose (see DE-OS 3323024). The effectiveness of this antioxidant measure can be achieved by creating and maintaining an inert gas atmosphere

in the reaction vessel, for example by rinsing with noble gases or nitrogen, from its charge to the implementation of

Reaction components are reinforced to the final product. Suitable acids are all industrially available strong acids, mineral acids are preferred, for example

technical concentrated hydrochloric acid, used.

The production of the cyanocarbamate-methyl ester solution takes place in a known manner (cf., DE-PS 1668557 and 1795849),

the admixture of a suitable surfactant (see DD-WP 269697) appears to be advantageous.

The temperature of the Cyancarbamat solution is before the reaction in the range of 30-8O ⁰ C, the reaction temperature after the Combination with the heated to 50-65X o-phenylenediamine dispersion between 50 ° C and the boiling point of Reaction medium, preferably between 65-95 ⁰ C. The inventively modified Roaktionsführung has over the conventional method a number of advantages

on. Thus, the oxidation-sensitive and very toxic o-phenylenediamine is introduced at normal temperature into the reaction vessel. By immediately adding it to the reducing agent and dispersing it in the excess acid, passing it into the corresponding diamine salt, the undesirable oxidation and self-condensation-based

Side reactions to deep-colored and toxic accompanying substances largely suppressed or avoided. The at the Salification reaction between o-phenylenediamine and the acid liberated considerable heat of neutralization is added

exploited to bring the dispersion to the desired temperature for the subsequent reaction.

The optionally fresh at the same time to this process and in parallel in another reaction vessel prepared solution of Cyancarbaminsäuremethylesters can directly with the reaction temperature reached there, optionally via a Intermediate filtration to remove mechanical impurities, added to the hot diamine salt dispersion in one go

become. In this way, the reaction to the final product starts immediately, and there are longer residence times of

Prevented starting components in the reaction mixture. After completion of the reaction, the crystalline deposited end product can be separated and purified in the usual manner

become.

The inventive improved process for the preparation of 2-Benzimidazolcarbaminsäuremethylesters is by

the embodiment explained.

Aulführungsbeispiel

In a standard stirring apparatus, 30 g of o-phenyldiamine are dispersed under nitrogen purge with the addition of a few milliliters of phosphoric acid in 80 ml of semi-concentrated technical hydrochloric acid. After subsidence of the neutralization reaction is heated to 80 ° C and then rapidly with a 65 ⁰ C warm Cyanccbaminsäuremethylester sodium salt solution prepared by the reaction of 13.5 g of cyanamide with 37.5 g of 80% methyl chloroformate and 52 g of sodium hydroxide in 190ml water, was added. By heating to 95 ⁰ C and stirring for one hour, the reaction is completed. After cooling to 65 ⁰ C, the crystalline precipitate is filtered off with suction and washed with water.

This gives 51 g of 2-benzimidazole-carbamic acid methyl ester as an almost colorless crystal powder, which shows a decomposition point at 35O ⁰ C and the content of phenazine by-products is in-line chromatography below 1000 ppm.

Claims (8)

1. An improved process for the preparation of 2-Benzimidazolcarbaminsäuremethylester, characterized in that the educt) -Ph9nylendiamin first dispersed in a sufficient to adjust an acidic reaction medium excess of a strong acid and then at a higher temperature with a solution of the Cyancarbaminsäuremethylesters or one of its salts Reaction is brought. 2. The method according to claim 1, characterized in that air, acid is a mineral acid, preferably technical concentrated hydrochloric acid, is used. 3. The method according to claim 1 and 2, characterized in that prior to or during the dispersing of the reactant in the acid, a suitable inert to the reaction components reducing agent for suppressing oxidative side reactions, preferably phosphorous acid or derivatives thereof is added. 4. The method according to claim 1 to 3, characterized in that the dispersion of o-phenylenediamine presented in the reaction vessel and after setting the optimum starting temperature quickly mixed with the prepared cyancarbamate solution and reacted. 5. The method according to claim 1 to 4, characterized in that all process steps from the dispersion of the starting material to the separation of the product under an inert gas atmosphere, preferably under nitrogen purge, are performed. 6. The method according to claim 1 to 5, characterized in that the Cyancarbamat solution before the reaction to a temperature in the range of J0-80 ° C, preferably 50-65 ⁰ C, is brought. 7. The method according to claim 1 to 6, characterized in that the reaction of the dispersion of o-phenylenediamine salt with the cyanocarbamate solution in the temperature range between 5O ⁰ C and the boiling point of the reaction medium, preferably hvororzugt between 65-95 ° C, takes place. 8. The method according to claim 1 to f, characterized in that deposited during the reaction as insoluble crystalline precipitate 2-Benzimidazol-carbaminsäuremethylester from the 65-75 ⁰ C hot reaction mixture is separated by filtration.