DD230527A3 - METHOD FOR PRODUCING PURE FORMANILIDE - Google Patents

Abstract

The invention relates to a process for the preparation of pure formanilide, which is a valuable intermediate for the synthesis of crop protection agents, optical brighteners, dyes and anti-aging agents. Formanilide is prepared from aniline and formamide with a single addition of formic acid and / or their salts at a conversion of more than 70%, based on aniline, and in amounts of 1 to 8 mol%, based on aniline.

Description

Field of application of the invention

The invention relates to a process for the preparation of formanilide, which is versatile as an intermediate for crop protection agents, dyes, optical brighteners and anti-aging agents.

Characteristic of the known technical solutions

Formanilide is known by reacting aniline with formamide (J. Pharm. Soc., Japan 62 (1942), 531) or in the presence of aqueous sulfuric acid (Ind. Eng. Chem. 36 (1944), 192), water ( DD-PS 16573) or alkoxide (DRP 449112).

In addition, it is known that formanilide can be prepared by reacting aniline with formates (DE-PS 462303, DD-PS 113895) or formic acid (DE-OS 2850680) or formic acid methyl ester (Soc., 1948 1457).

All of these processes have the disadvantage that the reaction is incomplete even with long reaction times which lead to thermal decomposition and side reactions such as diphenylformamidine formation (J. Org. Chem. 2410 (1977),

All this reduces the quality of formanilide and influences the quality of the subsequent products, especially the production of sulfanilamide.

Thus, attempts were made early on to simplify the reaction with additives.

By addition of aqueous sulfuric acid (Ind. Eng. Chem. 36 (1944) 192), alcoholate (DRP 449112), acetic anhydrite (DD-PS 113895) or water (DD-PS 16573) was able to improve the yield achieved by lowering the reaction temperature become. However, these additives had to be added in amounts of from 10 to 100% by mass, based on the aniline used, and resulted in a hydrous formanilide, from which the water could not be completely removed despite complicated purification operations. This led to a considerable yield loss, especially in subsequent Chlorsulfonierungsreaktionen. Furthermore, the continuous addition of small amounts of formic acid (DRP 449112), as reworked, proved to be less effective, since in this case no significant reaction time reduction is achieved in comparison to a procedure without additives.

Object of the invention

The aim of the invention is to develop a process for the preparation of pure formanilide, which is characterized by short reaction times, low safety risk and high yields.

Explanation of the essence of the invention

The object of the invention was to develop a process for the preparation of pure formanilide, which, starting from the preparation of aniline and formamide, by addition of suitable additives, a product is formed, which is excellent for further processing especially to sulfanilamide. Surprisingly, it has now been found that the reaction of aniline and formamide then gives a pure formanilide, if at a conversion of more than 70%, based on the aniline used, once formic acid and / or salts thereof are added individually or in mixtures. An advantage of this addition is that the reaction is completed so quickly that no undesirable tarry by-products occurred.

Furthermore, one obtains by this one-time addition of an almost anhydrous formanilide, which can be further processed without expensive further purification operations to dyes, pesticides, optical brighteners and anti-aging agents.

The solution according to the invention was surprising and unforeseeable insofar as according to the prior art both

the continuous addition of small amounts of formic acid as well as the use of stoichiometric amounts of formic acid or acid salts leads to the desired conversion only in the case of long reactions. The formanilide prepared by known processes therefore contains an amount of impurities, in particular water and tarry reaction products, which is troublesome for further processing without additional purification operations. It could not be foreseen that the one-time addition of formic acid, its salts in mixtures or individually with a conversion of more than 70%, based on aniline used, gave the desired results.

Particularly advantageous is the use of 1 to 8mol%, based on aniline used, preferably 4 to 6.5 mol% gesjtzt.

The advantages of the method according to the invention lie in the increase in the space-time yield and the associated high efficiency and the special purity of the product, which is particularly favorable in further processing

effect. , ^

Thus, by the process according to the invention, a formanilide which can be used to prepare pure sulfanilamide, which is then free of resinous constituents, is obtained. The resulting sulfanilamide yields by known standard method an extinction of 0.024 (D = 94.6%). Sulfanilamide, which is prepared from formanilide prepared by conventional methods (Sugasawa in J. Pharm. Japan 62 (1942), 531; CA 45 (1951) 2861), is dark in color and has an absorbance of 0.3 (D = 50 %).

The following embodiments are intended to explain the invention in more detail, without, however, limiting it thereto.

Exemplary embodiments Example 1

A mixture of 190g aniline (2.04mol) and 92g formamide (2.04mol) is heated to 145 ° C for 3 hours with stirring and introduction of nitrogen. After reaching aniline conversion rate of 85%, 6 g of formic acid _t ($ = 1.193 gcm ^-3 ) (0.11 mol) are added to the reaction mixture and the nitrogen introduction is continued for a further hour. If then the aniline content detectable by gas chromatography is <1%, the reaction is stopped. The residue remains pure formanilide in a yield of 98% of theory. The formanilide thus obtained is then added dropwise with stirring to 1 022g chlorosulfonic acid (S = 1.74 gcm ~ ³ ) (8.77 mol), wherein a reaction temperature of 60 ⁰ C is not exceeded.

After completion of Formanilidzugabe the reaction mixture is stirred for a further 3 hours at 60 ⁰ C and then cooled to room temperature.

The Chlorsulfonierungsschmelze is then added dropwise with stirring and cooling in 6086 g of ice water, that the Eisungstemperatur does not exceed 5 ° C. The precipitated Formylprontylchlorid is filtered off and then 11.6 mol) was added with stirring and cooling in 870 ml of ammonia solution (0.91 liked ^"3 ^ =). The Amidierungsgemisch is stirred in an autoclave for 1 hour at 100 ⁰ C. After completion of the reaction is. After cooling the concentrated amidation mixture to room temperature, the precipitated sulfanilamide is filtered off with suction to give 264 g of crude product (86.0% strength of sulfanilamide) Aniline A dried sample of the sulfanilamide obtained in this way has an extinction of 0.024 as a 1.7% hydrochloric acid solution, which corresponds to a light transmittance of 94.6%.

Example 2

A mixture of 190 g of aniline (2.04 mol) and 101 g of formamide (2.24 mol) is heated to 145 ° C for 3 hours with stirring and introducing nitrogen. At an aniline content of 6% in the reaction mixture determined by gas chromatography, 6.4 g of ammonium formate (0.10 mol) are added and the reaction is continued for a further 3 hours while stirring and blowing in nitrogen. When the gas chromatographic aniline conversion is 99.5%, the reaction is stopped. It remains in 97% yield pure formaniline, which is further processed as in Example 1.

Example 3

By a mixture of 190g aniline (2.04 mol) and 92g formamide (2.04 mol) is passed under stirring at a temperature of 145 ⁰ C for 3 hours a glejchmäßiger nitrogen flow.

At an aniline conversion rate of 90%, 3.3 g of formic acid { .mu. = 1.199 gcm.sup.- ³ ) (0.06 mol) and 3.8 g of ammonium formate (0.06 mol) are added to the reaction mixture and the reaction is continued until no aniline is obtained by gas chromatography is more detectable. This gives a formanilide which is free of unwanted, resinous by-products.

The yield is 98% of theory.

Example 4

In a large-scale experiment, 1390 kg (14.95 KMoI) of aniline during a reaction time of 12 hours * a) with the continuous addition of 1.5 KMoI formic acid during the entire reaction (analog DRP 449112)

b) with a single addition of 0.76 KMoI formic acid after 6 hours

converted to formanilide, which is then further processed to sulfanilamide. The results are summarized in the table below.

Table: Large-scale experimental procedure

attempt Implementation degree (%) Composition of the reaction mixture Yield of form (Ma .-%) anilide (% of theory) formamide formanilide 85.4 Sulfaniiamid extinction aniline 9.2 82.0 98.5 Salary (%) 0.418 a 92.0 6.8 6.7 91.5 95.0 0.024 b 99.7 0.2 98.0

Claims (2)

Invention claim: 1. A process for the preparation of pure formanilide by reacting aniline with formamide with the addition of formic acid and / or salts of formic acid, characterized in that the addition of formic acid and / or salts thereof eimalig in an amount of 1 to 8mol%, based on Aniline used, and at a conversion of more than 70%, based on aniline, takes place. 2. The method according to item 1, characterized in that the amount of additives is 4.0 to 6.5 mol%.