DE1795849C3 - Process for the preparation of 2-benzimidazole-carbamic acid methyl ester - Google Patents

Description

by reacting methyl cyanocarbamate of the formula

Il

CH ₁ OC-NH-CN
with o-phenylenediamine of the formula

NH ₂

characterized in that the reaction in the presence of water at a pH of the reaction medium of 2.5 to 4.5 and a temperature of 40 to 130 ° C undertakes.

The 2-benzimidazole-carbamic acid methyl ester is a good fungicide.

In US Pat. No. 3,010,968 there is a process for the preparation of 2-benzimidazole-carbamic acid alkyl esters described, whereby thiourea reacted with dimethyl sulfate to form 2-methyl-thiopseudourea sulfate will. This reaction product then becomes one with an alkyl chloroformate and a base acylated 2-methyl-thiopseudourea reacted, which then further with an o-phenylenediamine in The presence of a protonic acid is converted to the desired product. This procedure has the Disadvantage that a relatively expensive material, namely thiourea, must be used and that methyl mercaptan is formed.

It is also known from the published documents of the Belgian patent 6 66 795, 2-benzimidazole-carbamic acid alkyl ester to produce by alkyl chloroformates with cyanamide to form an alkyl cyanocarbamate and this product with a converts o-phenylenediamine compound. These reactions are expedient in organic solvents Pyridine. The yields of 2-benzimidazole-carbamic acid alkyl ester obtained are very low.

The method according to the invention is defined in the claim

In order to carry out the ring closure, the pH value must be between 2.5 and 4.5 can be echoed. Any acid can be used for this, for example formic acid, acetic acid, Hydrochloric acid, sulfuric acid, phosphoric acid, hydroxyacetic acid or sulfamic acid. That o-Phenylenediamine can optionally be added in the form of a mineral acid salt or as an aqueous solution will. If o-phenylenediamine salts are used, the amount of acid required to achieve the desired pH value is correspondingly smaller.

The reaction occurs at temperatures above 40 ^° C .; heating is preferably carried out during the reaction in order to accelerate the reaction to completion. The supply of heat is important because the reaction would be too slow at low temperatures. The reaction mixture should preferably be kept in the temperature range from 60 to 105 ° C. If desired, the reaction can also be carried out under pressure. When this happens, the temperature can rise to 130 "C.

During the heating, the desired product precipitates. The completion of the precipitation is thus an indication that the reaction mixture has been heated long enough to complete the reaction. The length of time is not critical and depends on the temperature and the pH. For example, the reaction time at a temperature between 70 and 105 ^° C. can be from 5 to 30 minutes. If lower temperatures are used, the reaction time will be longer.

The desired product can then be obtained by any of the conventional methods, for example by Spray drying, filtration or centrifugation, or it can be obtained by distillation of the Water can be transferred to any other liquid medium.

In the reaction, the reactants can be used in the molar equivalent ratios shown in the table below be used:

Reactants

Molar Equivalents Preferred

Mola equivalent c

Methyl cyan carbamate 1 to 3

o-phenylenediamine 1
"jo or derivatives thereof

1 to 1.8

It goes without saying that the molar concentrations at the upper limit are not critical; however that is Procedure in the higher concentralizations inexpedient or uneconomical.

Serving as the starting substance Methylcyancar-; bamat can be according to the following equations getting produced:

O CN

Il pH 6-13

mM ^ NCN + mCI — C —OCH, > MCl _n , + M (N —CO ₂ CH,) ,,,

NH (CN) -CO ₂ CH,

CN

Il pH 6-13 I.

)? iH ₂ NCN + / π Cl- C-OCH ₃ + 2M (OH) _n , - M (N- CO ₂ CH ₃ J _n , + MCl _1n + 2, "H, O

H ₂ O

H ⁺

¹ here mean

M is an alkali metal or an alkaline earth metal and

m is the valence of M,

H + can come from any acid.

example

49.5 parts of o-phenylenediamine, 140 parts of water and 54 parts of methyl cyanocarbamate are added to a round-bottom flask equipped with charging openings, stirrer, reflux condenser and measuring head for the pH. The reaction mixture is heated to 95.degree. C. and kept at 95 to 97.degree. C. for 1 hour and 15 minutes. During this time, the pH of the reaction mixture is kept at 3.8 to 4.2 by adding concentrated hydrochloric acid. The reaction mixture is cooled to 20 ^° C., the solid product is filtered off, washed with water and acetone and dried in the air. 80.3 parts of methyl 2-benzimidazole carbamate are obtained in this way; F. ⁰ 310 -320 C (decomposition); Yield: 93% based on o-phenylenediamine.

NH (CN) -CO ₂ CH ₃

The methyl cyanocarbamate used is obtained as follows:

In a 1-1 flask equipped with a stirrer and a thermometer, 90.4 parts of a 47% strength cyanamide solution are placed together with 122 parts of water. This solution is stirred and 97.5 parts of methyl chloroformate and 169 parts of a 50% strength sodium hydroxide solution are gradually and simultaneously added. The temperature is maintained at 45 to 50 ° C. and the pH of the mixture at 6.8 to 7.2 during the addition. The resulting solution is acidified with concentrated hydrochloric acid to 83 parts of a pH value of 1 and cooled to 20 ⁰ C. Then extracted 6 times with the solution 125 parts of methylene chloride. The combined methylene chloride solutions are dried over 35 parts of anhydrous sodium sulfate and the solution is concentrated. The pale yellow oil obtained consists of 84.59 parts of methyl cyanocarbamate. 0.5913 parts of this compound are titrated with 55.2 parts of 0.1 N sodium hydroxide solution against phenolphthalein. This gives a purity of 93.3% and a yield of 79% based on cyanamide. The index of refraction of this compound is 1.439834.

Claims (1)

Claim: Process for the preparation of 2-benzimidazole carbamic acid methyl ester the formula .A / N ^. j Il CN-COOCH ₃ \ An ⁷ η