CS255865B2 - Process for preparing n-isopropyl-alpha-chlor-acetanilide - Google Patents

Description

From the group of N-substituted acetanilides, propachlor (N-isopropyl-χ, -chloroacetanilide) is one of the most widely produced herbicides. Due to its suitable properties, propachlor is used to kill and control perennial grasses and certain dicotyledonous plants in maize, soy and a large number of vegetable species.

Many processes are known for the synthesis of propachlor. A common feature of these syntheses is that N-isopropylaniline and a suitable means for its chloroacetylation are used as starting materials. For example, U.S. Pat. No. 2,864,752 describes a process for the preparation of N-alkyl-halo-acylanilides.

According to this process, the haloacetic acid chloride is reacted in excess with the nitrogen-substituted aniline. The course of the reaction is affected by the use of a stoichiometric amount of an acid binding agent (e.g., sodium hydroxide and / or tertiary amine) and a suitable solvent. The product is separated from the reaction mixture by distillation or fractional crystallization.

U.S. Pat. No. 3,268,584 discloses a process for the preparation of N-substituted-oC-halo-acetanilides having a secondary alkyl group or alkoxy group on the phenyl group in the ortho position relative to the substituted amino group. A variety of solvents (e.g., benzene, diethyl ether, hexane, chlorobenzene, toluene, xylene, etc.) can be used in the preparation of these compounds. .

As acid-binding agents, alkali or alkaline-earth metal targets, amines, pyridine or hydroxides or their carbonates, etc. may be used.

The resulting product is separated from the system by fractional crystallization. The patent does not disclose the product yield nor the degree of purity achieved.

According to Hungarian Patent No. 159,044, N-isopropyl-Λ-chloroacetanilide is prepared by reacting a mixture of N-isopropylaniline, phosphorus trichloride and _; monochloroacetic acid. After completion of the reaction, excess phosphorus trichloride was distilled off from the reaction mixture. The distillation residue is poured into about 80 ° C water. The yields obtained are about 77% (based on pure N-isopropylaniline). According to Hungarian patent No. 171 931, N-isopropylaniline is acylated with chloroacetyl chloride or a mixture of monochloroacetic acid and phosphorus trichloride in the preparation of N-isopropyl-X, -chloroacetanilide. In acylation, diisopropylaniline is used as the by-product as an acid binding agent. The by-product also serves as a solvent for the reactants.

A common feature of the prior art is that either a basic substance is added to bind the hydrochloric acid formed in the reaction, or the acylated substance serves as an acid binding agent in the initial stage of the reaction. In the latter embodiment, acylation is carried out at low temperature until the degree of conversion reaches 50%, near the conversion value, the system temperature is increased and the hydrochloric acid is displaced from the system by the addition of an additional amount of acylating agent.

The processes known hitherto have the common feature that the industrial acylation must be carried out in two separate steps.

Initially, the acylation is carried out at a low temperature while the system must be cooled. In the next second step, the temperature must be raised to liberate the base from the N-alkyl-aniline hydrochloride formed in the first reaction step by heat input and convert the N-alkylaniline into the reactive form by removal of hydrochloric acid.

It will be apparent to those skilled in the art that in the continuous operation of this process in industry, these steps must be separated and this requires the construction of two separate devices.

This solution is also disadvantageous in terms of energy management. In the first stage, the heat released from the formation of aniline salts must be removed from the system, while in the second stage - the decomposition of the salts - the dissipated heat must be recycled to the system for the reaction to proceed.

In the first stage, the N-alkyl-aniline hydrochloride formed is a crystalline compound which precipitates from the system and causes difficulties in operation.

It is an object of the invention to overcome the disadvantages of the above processes and to create reaction conditions under which alkylaniline hydrochloride decomposes and the process can be industrially carried out either continuously or discontinuously.

The invention is based on the finding that, when certain parameters are observed, N-isopropyl-aniline hydrochloride is not formed in the system. Under the conditions of the invention, said aniline salt is so unstable that it releases hydrogen chloride gas. The reaction of the components used thus proceeds completely, since the N-isopropyl-aniline hydrochloride produced by the known methods and eliminated by the known methods cannot form in the process according to the invention due to the existing decomposition processes.

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The present invention provides a process for the preparation of N-isopropyl-N-chloroacetanilide by acylating N-isopropylaniline with chloroacetyl chloride or a mixture of monochloroacetic acid and phosphorus trichloride, characterized in that the acylation is carried out at a temperature higher than or equal to the decomposition temperature of isopropylaniline hydrochloride which is formed in the reaction mixture to amine and hydrochloric acid.

Further details of the process according to the invention are given in the following examples, which are not intended to limit the invention in any way. In the examples both batch / continuous process is illustrated.

Example 1

135.5 kg of N-isopropylaniline and 118 kg of monochloroacetic acid are placed in a vessel equipped with a thermometer, a stirrer, a reflux condenser and a gas outlet, and the temperature of the mixture is raised to 85-90 ° C. After reaching this temperature, 78.5 kg (98%) of phosphorus trichloride are added. Upon completion of the addition, the temperature of the mixture was raised to 115 ° C to remove dissolved gases and the hydrogen chloride leaving the reaction mixture was absorbed in water.

After separation of the hydrochloric gases, the reaction mixture was poured into 500 L of water which had been preheated to 90 ° C. To prevent the reaction products from solidifying, the temperature of the reaction mixture is maintained at about 90 ° C and the mixture is stirred at this temperature for 2 hours. After stirring, the phases can be separated at this temperature.

The lower layer of N- isopropyl- [beta] -chloroacetanilide was separated from the upper aqueous layer and washed with warm water until neutral.

The reaction conditions are selected such that the combined aqueous phases are neutralized. The N-isopropyl-aniline formed by the treatment with caustic is returned to the previous reaction step after suitable purification.

The melting point of the product is 70-80 ° C.

After purification, 170 kg of N-isopropyl-1H-chloroacetanilide are obtained and after regeneration 20 kg of N-isopropylaniline are obtained.

Example 2

In the apparatus described in Example 1, 115 kg of industrial chloroacetyl chloride are placed and heated to a temperature of at least 80 ° C. 125 kg of N-isopropylaniline are added to the warm substance while maintaining the system temperature at 90-115 ° C.

Hydrogen chloride gas leaving the reactor dissolves in water. After removal of the HCl gases, the reaction mixture was poured into 300 L of water heated to 90 ° C and stirred at this temperature for one hour. The mixture was allowed to settle as in Example 1 and separated. The N-isopropyl-chloro-acetanilide is washed until neutral and granulated in cold water. Neutralization can also optionally be carried out with sodium hydrogen carbonate solution.

After purification, 190 kg of N-isopropyl-1-chloroacetanilide are obtained. Mp 79-80 ° C.

Example 3

135 kg of N-isopropylaniline and 120 kg of chloroacetal chloride were introduced into the reactor, each equipped with a foam separator, a foam disrupter, and a high-performance stirrer. During the acylation, the temperature is maintained at 100-115 ° C in the reactor.

The N-isopropyl-N-chloroacetanilide leaving the reactor was poured into a water heated to 90 ° C with a continuous stream. If necessary, the product is washed with an aqueous solution of sodium bicarbonate until neutral and the neutral melt is processed into plates.

The active compound content of the product thus obtained is greater than 98% and the yield is 200 kg per hour. Mp 79-80 ° C.

An important advantage of the process according to the invention over the known processes is a significant energy saving. Another advantage is the easy feasibility on an industrial scale, which greatly simplifies process automation. Since the process according to the invention is operated at a substantially higher temperature than normal, the reaction rate is considerably higher than in the known processes. The increased reaction rate leads to a shortening of the residence time in the reaction space and thus significantly increases the utilization of the apparatus compared to the known methods.

SUBJECT OF THE INVENTION

Claims (3)

SUBJECT OF THE INVENTION A process for the preparation of N-isopropyl-chloroacetanilide by acylating N-isopropylaniline with chloroacetyl chloride or a mixture of monochloroacetic acid and phosphorus trichloride, characterized in that the acylation is carried out at a temperature corresponding to or higher than the decomposition temperature of isopropylaniline hydrochloride. during the reaction in the reaction mixture, to the amine and hydrochloric acid. 2. Process according to claim 1, characterized in that the acylation is carried out at a temperature of 70 to 125 ° C, preferably at a temperature of 80 to 120 ° C. 3. The process according to claim 1, wherein the hydrochloric acid formed during the decomposition of N-isopropylaniline hydrochloride is continuously distilled off from the system. Severography, n. P., MOST Price 2,40 Kčs