CS242141B1 - Process for preparing 4-hydroxybenzonitrile or a salt thereof - Google Patents

Abstract

A method for producing p-hydroxybenzonitrile or its salts by hydroxylation of p-chlorobenzonitrile, whereby the hydroxylation of p-chlorobenzonitrile is carried out with an alkaline alcoholate, preferably a methanolic solution of sodium methanolate, at temperatures of 180 to 220 °C, preferably at a temperature of 200. °C ± 10 °C, after the reaction is complete, the alkaline chloride is filtered off from the system and the alkaline salt of p-hydroxybenzonitrile is obtained as a raw product of the process by evaporation of the solvent, or the reaction system is directly led to evaporation of the solvent after hydroxylation in order to obtain the raw alkaline salt of p-hydroxybenzonitrile with an admixture of alkaline chloride. An economically advantageous method for producing an intermediate product for herbicide preparations.

Description

The invention relates to an improved process for the preparation of 4-hydroxybenzonitrile (4-HBN) or a salt thereof. 4-HBN is a starting component for the preparation of a number of its derivatives, which are known for their herbicidal properties, therefore there is a great interest in its preparation, especially in recent years.

Several versions of the preparation of 4-HBN are known. Of interest would be its synthesis from p-cresol by methylation followed by amoxidation of the CN group and demethylation. Its main obstacle is the experimental verification of the low yield of amoxidation, less than 40%, which makes this process path a technology with high consumption standards.

Another possible procedure suggested by the experiments is the methylation of p-chlorobenzonitrile, which at 120 ° C provides p-methoxybenzonitrile, followed by its acid hydrolysis (pyridine + HCl). However, this must be practically 100% conversion, otherwise it causes unpleasant complications in the following operations, for example. in subsequent bromination. A seemingly simple workflow offers a reaction scheme for the preparation of 4-HBN from p-aminobenzoic acid via p-hydroxybenzoic amino acid diazotization and hydrolysis followed by p-hydroxybenzoic acid nitrile, for which one of these pathways would have to be selected

- Melting of the ammonium salt of p-hydroxybenzoic acid with phosphonitrile chloride (NSR Pat. 1 230 026, Japan Chem. Ind. Co)

conversion of p - hydroxybenzoic acid without isolation of intermediates to acid chloride and amide followed by dehydration (NSC Pat.

239 799, Farbwerke Hoechst A.G.)

242 141

ammonolysis of the p-hydroxybenzoic acid ester over a dehydration catalyst e.g. SPO ₄ at 200 to 600 ° C (Fr. pat.

Shone Pouleno Ind. S.A.) and others.

Thus, other yet similar processes could be mentioned, but one thing in common is that they are both technologically and technically complex multistage processes that cannot compete with the advantages provided by our invention.

It has now been found that when the Cl group in p-chlorobenzonitrile is exchanged directly with an OH group by hydroxylation with an alkali alcoholate, preferably sodium methoxide, in an anhydrous environment at temperatures of ISO to 220 ° C, this reaction proceeds as follows:

CN + 2 CH ₃ ONa + NaCl + (CH ₃ ) ₂ O

Cl

CN φ

She

In this way, the reaction takes place only in the absolute elimination of the presence of the 0H-ion in the hydroxylating agent. In their presence, for example in the form of NaOH, in a methanolic solution of sodium methoxide, the reaction is preferably carried out in the system:

COONa + 2 NaOH + CH

, 0H

οη ₃ ονϊ

NH which is a summary expression of the probable mechanism of hydrolysis.

CH ₃ OH + NaOH

CH ₃ 0Na + H ₂ 0

+ NaOH + HgO

COONa

Cl + NH

242 141

The process for the preparation of p-hydroxybenzonitrile by hydroxylation of p-chlorobenzonitrile with an alkali alcoholate, preferably a methanolic solution of sodium methoxide, consists in carrying out the reaction at a temperature of 110 ° C to 220 ° C at a pressure of 2.8-5 ° C. 8 MPa, which corresponds to the vapor pressure of methanol at said temperature. 100% conversion of p-chlorobenzonitrile is achieved with a process selectivity greater than 90%. The reaction is carried out in a closed autoclave in a closed system for several hours.

For this purpose, after cooling to normal temperature, the contents of the autoclave are freed from the gaseous reaction products and, for example, the methanolic solution of the sodium salt of p-hydroxybenzonitrile and virtually insoluble NaCl in methanol is fed to a separator where NaCl is filtered off. The filtrate, i.e. the solution of the crude sodium salt of p-hydroxybenzonitrile, is then freed of solvent by evaporation of the methanol to dryness. However, the reaction system from the autoclave can be fed directly to the evaporator without the separation of NaCl, and evaporation of methanol yields a solid sodium salt of p-hydroxybenzonitrile with admixture of NaCl. In both these cases, after distilling off the methanol, the crude hydroxylation product is ready for further operation, for example for bromination and preparation of 3,5-dibromo-4-hydroxybenzonitrile according to art. PV .....

or after acidification, p-hydroxybenzonitrile can be obtained as the product.

The examples below illustrate embodiments of the invention. Example 1

220 g of chlorobenzonitrile containing 97.7 wt. % p-chlorobenzonitrile and 2.3 wt. of its o-derivative and 948 g of a 20% methanolic methanolate solution

242 141 sodium containing 0.13 wt. NaOH. After heating the autoclave to 200 ° C, the reaction system is maintained at this temperature for 4 hours.

After cooling at 20 ° C, 92.8 g of NaCl-formed reactions are filtered off from the reaction system and 1075.2 g of the liquid phase of the hydroxylation product are obtained. After distilling off the methanol at 40 ° C and 40 kPa pressure, 227.2 g of a solid product containing salts of the following compounds are obtained: 95.8 wt. p-CBN, 1.6 wt. o-CBN, 0.8% p-chlorobenzoic acid, 1.3% wt. % p-methoxybenzoic acid and 0.5 wt. methoxybenzonitrile. At 10% conversion, the yield was 97.4%.

Example 2

275.14 g of chlorobenzonitrile containing 97.7 wt. of the β-derivative and 2.3% of the o-derivative together with 1,194 g of a 20% methanolic sodium methoxide solution containing 0.15% w / w NaOH. After heating the autoclave, the reaction system is maintained at 200 ° C for 4 hours. NaCl is not separated from the system after completion of the hydroxylation, only methanol is distilled off and the product obtained is used as a raw material for example for the preparation of 3,5-dibromo-4-hydroxybenzonitrile according to PV ...... At 100% conversion the yield was hydroxylation 96.3% th.

Example 3

220 g of chlorobenzonitrile having a 97.7% p-isomer content and 1089 g of a 20% virtually anhydrous ethanolic sodium ethanolate solution are introduced into a 2.4 L autoclave. After heating the autoclave to 200 ° C, the reaction system is maintained at this temperature for 4 hours. After the hydroxylation is complete and the system is cooled to ambient temperature, NaCl is filtered off from the reaction mixture and the filtrate is distilled off with ether.

At 100% conversion, the yield of p-hydroxybenzonitrile sodium was 92.1% th.

Claims (1)

SUBJECT OF THE INVENTION 242 141 Process for the preparation of p-hydroxybenzonitrile or its salt by hydroxylation of p-chlorobenzonitrile, characterized in that the hydroxylation of p-chlorobenzonitrile is carried out with an alkali alcoholate, preferably a methanolic solution of sodium methoxide, at temperatures from 180 to 220 ° C, preferably at 200 ° C and 10 ° C, after completion of the reaction, the alkali chloride is filtered from the system and the solvent is evaporated to obtain the alkali salt of p-hydroxybenzonitrile as the crude product of the process, or the reaction system is directly led to evaporation of the solvent after hydroxylation to obtain the crude alkali salt of p-hydroxybenzonitrile .