RU2847826C1 - Method for obtaining n,n'-diphenylurea - Google Patents

Abstract

FIELD: chemical industry.

SUBSTANCE: invention relates to an improved method for producing N,N-diphenylurea (DPU), widely used as a starting compound for the synthesis of various chemical products. The method is characterised in that urea and aniline are reacted in a molar ratio of 1:2 to 1:3 at a temperature of 110-180°C in an aromatic hydrocarbon medium with continuous distillation of the ammonia released, the reaction is carried out continuously for 10-72 hours, then the reaction mass is cooled, the precipitate is filtered off and washed with an aromatic hydrocarbon, the resulting filtrate is distilled and the aromatic hydrocarbon and aniline are returned to the process, the precipitate is dried and DFM is isolated.

EFFECT: provision of an improved method for obtaining the target product, suitable for industrial-scale implementation using simple technological techniques.

4 cl, 1 tbl, 5 ex

Description

The invention relates to an improved method for producing diphenylurea (hereinafter DU), which is widely used as a starting compound for the synthesis of various chemical products.

A known method for producing diphenylurea involves the reaction of aniline with phosgene in the presence of soda (US Patent 2,806,062, IPC C07C 273/18; C07C 275/58, published September 10, 1957). The reaction is carried out in water in the presence of an agent for effectively neutralizing hydrochloric acid. The diphenylurea thus obtained does not require purification. The neutralizing agent for hydrochloric acid can be sodium acetate, soda ash (sodium carbonate), or any substance capable of reacting with the resulting hydrochloric acid or neutralizing it. A neutralizing agent, such as soda ash, is dissolved in water, then aniline is added, and phosgene is passed into the mixture, which is thoroughly stirred. The reaction is exothermic, and moderate cooling is required to avoid the tendency of phosgene to hydrolysis. The temperature should preferably be kept below 60°C, but a range of 35 to 40°C has been found suitable and can be easily maintained with a tap water jacket at ordinary temperatures.

The disadvantage of this method is the need to use highly toxic phosgene and hydrogen chloride acceptors.

Methods for producing diphenylurea from aniline and urea in an inert gas atmosphere are known (patents CN 115724771, IPC C07C 273/18; C07C 275/28, published 03.03.2023; CN 106748891, IPC C07C 273/18; C07C 275/28, published 31.05.2017; CN 103739522, IPC C07C 273/18; C07C 275/28, published 23.04.2014; CN 101440049, IPC C07C 273/18; C07C 275/28, published 05/27/2009, CN 102001969, IPC C07C 273/18; C07C 275/28, published 04/06/2011), at elevated pressure and high reaction temperature of 160-240°C, which complicates the equipment design of the process.

A known method for producing N,N'-diphenylurea (patent CN 115724771, IPC C07C 273/18; C07C 275/28, published 03.03.2023) is carried out in the presence of a catalyst - aluminum oxide, the molar ratio of aniline to urea is 4.0, the mass ratio of aluminum oxide to urea is 0.01, the temperature is raised to 220 °C and nitrogen is supplied. The product is obtained using a spray dryer.

The production method is also complex due to the use of a catalyst and the process is carried out in an inert gas environment, which complicates the process itself and its equipment design; a nitrogen line is required for gas purging.

The closest technical solution to the claimed one is a method for producing diphenylurea from aniline and urea (patent CN 106748891, IPC C07C 273/18; C07C 275/28, published on 31.05.2017) in which ammonia is removed from the reactor only at an elevated pressure above the specified one, it is assumed that excess ammonia suppresses the decomposition of diphenylurea into isocyanic acid and ammonia, that is, it reduces the formation of by-products, and the process is carried out in an inert gas, at a pressure of 0.01-3.0 MPa, a temperature of 160-240 ° C, preferably urea and aniline are mixed with an organic solvent, the molar ratio of urea to aniline is from 1: 3 to 1: 7, the solvent is added in an amount of 1-10 to the mass of the reagents (aniline and urea).

The disadvantage of this method is the complexity of the process; high temperatures are used in the process - 160-240°C with a large excess of aniline, the supply of nitrogen complicates the equipment design of the process, and the process is carried out under excess pressure.

The objective of the invention is to develop an improved method for producing N,N'-diphenylurea, suitable for implementation on an industrial scale using simple technological methods.

The problem is solved using a method for obtaining N,N'-diphenylurea of the formula , which involves the interaction of urea and aniline in a solvent environment, which consists of the interaction of urea and aniline in a molar ratio of 1:2 to 1:3 at a temperature of 110-180°C in an aromatic hydrocarbon environment with the constant distillation of the released ammonia.

Preferably, toluene, xylene, chlorobenzene, and o-dichlorobenzene are used as aromatic hydrocarbons.

Preferably, the reaction of the mixture of urea, aniline and solvent is carried out continuously for 10-72 hours.

Preferably, the mixture of reagents is boiled for the required time, then the reaction mass is cooled, the precipitate is filtered and washed with an aromatic hydrocarbon, the resulting filtrate is distilled and the aromatic hydrocarbon and aniline are returned back to the process, the precipitate is dried and N,N'-diphenylurea is isolated.

Preferably, N,N'-diphenylurea has a purity greater than 99.0%. The main advantage of the proposed method is that there is no need for nitrogen supply at the stage of interaction of urea with aniline, which significantly simplifies the process and its equipment design.

The technical result of the proposed invention is the development of an improved method for producing N,N'-diphenylurea, suitable for implementation on an industrial scale using simple technological methods.

The proposed invention is implemented as follows.

N,N-diphenylurea (hereinafter DFM) is obtained from urea and aniline:

The structure of the compounds was confirmed by ¹ H NMR spectroscopy.

The process is carried out at a urea to aniline molar ratio of 1:(2-3) by heating in aromatic hydrocarbons (toluene, xylene, chlorobenzene, o-dichlorobenzene) at temperatures of 110-180°C for 10-72 hours with distillation of the released ammonia, which is then used in the synthesis of urea from ammonia and carbon dioxide. Upon completion of the process, the diphenylurea is filtered and dried. For improved purity, it is recrystallized from ethanol. The yield of diphenylurea is 89-96%. The reaction filtrate, which contains excess aniline in an inert solvent, can be reused. Thus, excess aniline and solvent are continuously recycled.

Table 1 presents data on the process of obtaining DFM.

The invention is illustrated by the following examples.

Example 1

A flask equipped with a reflux condenser is charged with 15.0 g (0.25 mol) of urea, 46.5 g (0.5 mol) of aniline, and 200 ml of toluene. The mixture is boiled for 72 hours. After this time, the reaction mixture is cooled, the precipitate is filtered and washed twice with 30 ml of toluene. The filtrate is distilled, returning 250 ml of toluene and 20.2 g of aniline to the process. The precipitate is air-dried and recrystallized from ethanol. The yield is 27.5 g (yield based on reacted aniline - 91.7%).

Example 2

A flask equipped with a reflux condenser is charged with 15.0 g (0.25 mol) of urea, 59.8 g (0.75 mol) of aniline, and 300 ml of chlorobenzene. The mixture is boiled for 15 hours. After this time, the reaction mixture is cooled, and the precipitate is filtered off. The filtrate is rectified, returning 290 ml of chlorobenzene and 37.9 g of aniline back to the process. The precipitate is air-dried and recrystallized from ethanol. 22.2 g are obtained (yield based on reacted aniline - 89.0%).

Example 3

A flask equipped with a reflux condenser is charged with 15.0 g (0.25 mol) of urea, 60.5 g (0.65 mol) of aniline, and 300 ml of xylene. The mixture is boiled for 20 hours. After this time, the reaction mixture is cooled, and the precipitate is filtered off. The filtrate is rectified, returning 280 ml of xylene and 15.7 g of aniline back to the process. The precipitate is air-dried and recrystallized from ethanol. 48.1 g is obtained (yield based on reacted aniline - 94.2%).

Example 4

A flask equipped with a reflux condenser is charged with 15.0 g (0.25 mol) of urea, 46.5 g (0.5 mol) of aniline, and 200 ml of o-dichlorobenzene. The mixture is boiled for 10 hours. After this time, the reaction mixture is cooled, and the precipitate is filtered off. The filtrate is reused, adding a fresh portion of urea and aniline. The precipitate is washed twice with 30 ml of toluene, air-dried, and recrystallized from ethanol. 50.9 g (yield - 96.0%) are obtained.

Example 5. According to the prototype

The process of obtaining diphenylurea from aniline and urea (carbamide) includes:

1) Urea and aniline are mixed in a molar ratio of 1:7 and added to the autoclave. The solvent is weighed with the reagent (urea and aniline) in a mass ratio of 1:3 and then added to the autoclave;

2) The reactor is purged with argon to replace the air three times and a pressure of 2.5 MPa (gauge pressure) is created, heated to 220°C, reaction for 30 min;

3) The suspension obtained in step 2 is cooled to 120°C, crystallized, filtered and washed with ethanol to obtain diphenylurea with a yield of 99.2.

Example 5* according to patent No. CN 106748891.

The examples provided demonstrate that the proposed method for producing DMF operates without catalysts, at temperatures of 120-180°C in an inert solvent environment, and without the use of an inert gas, significantly simplifying the process. Example 5 (based on the prototype) produces DMF with high yield and purity. The process is carried out at a high temperature of 220°C in an inert gas environment at a pressure of 2.5 MPa. Therefore, the known method is more complex than the proposed method.

The proposed method involves distilling off the released ammonia, making the production method cost-effective on an industrial scale. The isolated DFM is recrystallized from ethanol, yielding DFM with a yield of 89-96% and a purity of over 99%.

Thus, the proposed method for producing DFM is economical on an industrial scale.

Claims (5)

1. Method for obtaining N,N'-diphenylurea of the formula , including the interaction of urea and aniline in a solvent medium, characterized in that the interaction of urea and aniline is carried out in a molar ratio of 1:2 to 1:3 at a temperature of 110-180°C in an aromatic hydrocarbon medium with constant distillation of the released ammonia, the interaction of the mixture of urea, aniline and solvent is carried out continuously for 10-72 hours, then the reaction mass is cooled, the precipitate is filtered and washed with an aromatic hydrocarbon, the resulting filtrate is distilled by rectification and the aromatic hydrocarbon and aniline are returned back to the process, the precipitate is dried and N,N'-diphenylurea is isolated. 2. The method according to paragraph 1, characterized in that toluene and xylene are used as aromatic hydrocarbons. 3. The method according to paragraph 1, characterized in that the aromatic hydrocarbons additionally include chlorine, which is chlorobenzene, o-dichlorobenzene. 4. The method according to any one of paragraphs 1-4, characterized in that N,N'-diphenylurea has a purity greater than 99.0%.