CS224547B1 - Method of p-nitrophenetole separation - Google Patents

Description

The invention relates to a process for the isolation of p-nitrophenetol from the reaction mixture after ethoxylation of p-nitrochlorobenzene; p-Nitrophenetol is an important intermediate for the production of p-phenetidine.

The most widespread method of preparing p-nitrophenetol is by reacting p-nitrochlorobenzene with ethanol in the presence of NaOH or KOH. Depending on the reaction conditions, side reactions take place in the reaction mixture, namely the hydrolysis of p-nitrochlorobenzene to p-nitrophenol and reduction of p-nitrochlorobenzene to 4,4-dichlorazoxybenzene and other reducing products. Many catalysts have been described in the literature to prevent a reduction reaction. Metal salts or oxides are used, namely Mn, Cu, Pb. Their use is intolerable from the current ecological point of view. Another method that prevents reduction is to use air that is purged through the reaction mixture. The literature describes a method of removing unreacted p-nitrochlorobenzene by reacting with sulfur compounds, since the removal of unreacted p-nitrochlorobenzene from p-nitrophenetol is necessary since subsequent reduction to p-phenetidine results in operational and environmental problems in the presence of p-chloroaniline.

In order to achieve 99% conversion to p-nitrochlorobenzene, reaction times of more than 50 hours are required, which is operationally unbearable and still contained in the production of the undesirable substance. It therefore appeared necessary to investigate the possibility of shortening the reaction time, albeit of course at the cost of reducing the conversion and thereby causing the need for expedient separation of the reaction mixture. The equilibrium composition of the binary mixture p-nitrochlorobenzene - p-nitrophenetol is known from the literature. The eutectic temperature of this mixture was 30 ° C with a composition of 44.0 wt. % p-nitrochlorobenzene and 56.0 wt. p-nitrophenetol. These data are unfavorable for separation. However, after measuring the solubility of the individual components (p-nitro-chlorobenzene and p-nitrophenetol and ethanol (94.6% by weight), the solubility ratio proved to be considerably more favorable, especially at lower temperatures, as shown in Table I:

Solubility ratio of p-nitrochlorobenzene and p-nitrophenetol

Table I

Temperature ° C

0 1, 586 10 1,369 20 May 1, 160 30 0,924

These values show the possibility of separating both products from the reaction mixture by crystallization from ethanol. To this end, the composition of the ternary mixture ethanol (94.6% by weight), p-nitrochlorobenzene, p-nitrophenetol at the eutonic point at a given temperature was measured. Their composition is shown in Table XI below.

Based on detailed study and knowledge of the composition of the ternary mixtures at the eutonic point at a given temperature, it has been found that the product can be isolated from a reaction mixture having a content of p-nitrochlorobenzene and p-nitrophenetol higher than that of p-nitrochlorobenzene, p- nitrophenetol and ethanol at a eutonic point at a given temperature.

Table II

Composition of ternary mixtures of p-nitrochlorobenzene, p-nitrophenetol and ethanol (94.6% w / w) at eutonic points

Temperature ° C p-nitrochlorobenzene Concentration% wt. p-nitrophenetol ethanol 0 5.2 3.4 91.4 30 44.0 56.0 0

Based on the values in Table II, the product was isolated from the reaction mixture after ethoxylation by cooling and filtration. The cake was washed with ethenol and water. The final product contained max. p-nitrochlorobenzene.

The method of isolating p-nitrophenetol from the reaction mixture after ethoxylating the p-nitrochlorobenzene with ethanol in sodium or potassium hydroxide solution, crystallizing from ethanol is according to the invention, characterized in that the crystallization is carried out by disturbing the equilibrium of the ternary mixture 30 ° C by cooling to + 20 to -20 ° C and the precipitated product is isolated, washed with ethanol and water. Optionally, inorganic substances are separated from the mixture before cooling. The advantage of this process is to reduce the reaction time and to remove the ecologically disadvantageous sulfur compounds used to refine the raw product. The examples below illustrate embodiments of the invention.

He did

141.2 g of p-nitrochlorobenzene was added to a solution of 44.5 g of NaOH in 800 ml of ethanol (95% by volume) at 50 ° C and with air purging of 8-10 l / h with stirring. The temperature was raised to 75 ° C. After 15 h, the reaction mixture was filtered from inorganic salts and the cake washed with ethanol (95% v / v). The mother and wash filtrates were cooled to about 3 ° C and the precipitate was aspirated and washed with ethanol and water. 124 g of a product with 0.4 wt. p-nitrochlorobenzene.

Example 2

In an iron boiler, 90.4 g of NaOH was dissolved in 1600 ml of ethanol (95% v / v) at 50 ° C warm and 292.4 g of p-nitrochlorobenzene were added with stirring and blowing air at 12 L / h. The temperature was raised to 75 ° C and after 15 h the reaction mixture was cooled to ca. 3 ° C, the precipitate was filtered off with suction, washed with 200 ml of ethanol (95% by volume) and 1000 ml of water. The cake was suspended in 500 mL of water, heated to 60 ° C and the lower organic layer separated. 231 R of product with 0.6 wt. p-nitrochlorobenzene.

Example 3 '4' R of p-nitrochlorobenzene was added to a solution of 44.5 g of sodium hydroxide in 800 ml of ethanol (95% v / v) at 50 ° C, with air purging of 8 to 10 l / ha while stirring. The temperature was raised to 75 ° C. After 15 h, the reaction mixture was hot filtered from inorganic salts and the cake was washed with ethanol (95% v / v). 263 g of ethanol (water content 7% by weight) were distilled off from the filtrate while blowing through the air at a rate of 8-10 l / h.

The distillation residue was undiluted with 50 ml of water and after stirring the mixture was cooled to 0 ° C. The precipitate was filtered off with suction, washed with 60% ethanol and then with water and dried. 126 g of product were obtained with a content of 0.9 wt. p-nitrochlorobenzene.

Example

Apparatus, batch, and procedure similar to Example 1. After separation of the inorganic salts, the reaction mixture was cooled to -15 ° C in a cryostat and the precipitate was filtered off with suction and washed with cooled ethanol and dried. 130 g of a product with a content of 0.4% by weight were obtained. p-nitrochlorobenzene.

Claims (2)

A process for the isolation of p-nitrophenetol from a reaction mixture after ethoxylation of p-nitrochlorobenzene with ethanol in sodium or potassium hydroxide solution by crystallization from ethanol, characterized in that the crystallization is carried out by disrupting the equilibrium of the ternary mixture p-nitro-chlorobenzene, p-nitrophenetol and ethanol at above 30 ° C by cooling, optionally after prior separation of inorganic substances, to a temperature of 20 to -20 ° C, after which time the precipitated product is isolated, washed with ethanol and water. 2. Process according to claim 1, characterized in that ethanol with a water content of up to 40% by weight is used for the isolation.