CS252609B1 - Process for preparing 2,5-diiodo-4-hydroxybenzonitrile - Google Patents

Abstract

The method for preparing 2,5-diiodo-4-hydroxybenzonitrile or its salts by iodination of 4-hydroxybenzonitrile is carried out by the action of an iodination system, formed by introducing gaseous chlorine into a solution of iodine in methanol or acetic acid at 15 to 30 ° C, on 4-hydroxybenzonitrile or its alkali salt. Preferably, the procedure is to add solid iodine to a solution of 4-hydroxybenzonitrile or its alkali salt in methanol or acetic acid, after which gaseous chlorine is introduced into the reaction mixture at a temperature of 15 to 30 ° C.

Description

The present invention relates to a process for the preparation of 2,5-diiodo-4-hydroxybenzonitrile or a salt thereof by iodinating 4-hydroxybenzonitrile.

2,5-diiodo-4-hydroxybenzonitrile and its salts are used as an active ingredient of herbicidal formulations. The well-known production process of May and Baker and Amchem Products Xno is a four-step process, starting from p-hydroxybenzaldehyde.

It involves the initial iodination of the starting material followed by conversion to oxime, acetylaol and hydrolysis to 2,5-diiodo-4-hydroxybenzonitrile. It is a paraphrase of the laboratory preparative procedure published by K. Auwers and J. Reis (Ber. 29, 2355, 1896).

The novel process for preparing 2,5-diiodo-4-hydroxybenzonitrile of the present invention uses 4-hydroxybenzonitrile as the starting material. Follows on MS. AO 242 141, which protects the method of its production. The process of the present invention addresses both the choice of a suitable iodinating agent and the creation of optimum process conditions.

The effective method of each iodination depends on the type of iodination agent selected and the conditions for its preparation. An aqueous solution of an alkali iodide and an iodate in an acidic medium is generally known as iodination systems, iodination can also be carried out with an alkali iodide in the presence of an oxidizing agent or iodo monochloride in a suitable solvent (Brit. Pat. 1,067,031;

However, all these iodination systems have certain disadvantages in the technical implementation. These are either high production costs, technical difficulty or a significant proportion of side reactions, e.g. during iodination with the necessary presence of an oxidizing agent and the possibility of an explosion.

However, among these agents, iodmonochloride has proven to be the most attractive for some time, especially for good reactivity in the iodination process. However, its use in operational applications still has a number of drawbacks. One essential is the strict control of the introduction of chlorine into the iodine present and the need to control the exothermic reaction (Buckles et al., Inorg. Synth., Bd 9,

130 (1967)).

Another disadvantage is the possibility of hydrolysis of the iodo monochloride and subsequent decomposition of its products, so that the final products of this undesirable iodo-monochloride lability are hydrochloric and iodic acid and a lower iodization effect is required.

An important contribution is the work of Japanese authors (German Pat. No. 1,961,289), who use systems as the iodinating agent containing: iodine and chlorine in acetic acid or methanol.

It is prepared by mixing iodine with CH 2 COOH or methanol and introducing about 1 atom-equivalent of gaseous or liquid chlorine into the system under cooling before the mixture is slightly warmed for a short period of time.

In the examples of the Japanese patent, the temperature of preparation of the iodinating agent is fixed at a temperature range of -5 to 0 ° C and a slight heating of the thus prepared iodination system to 0 to +4 ° C.

Although a relatively high yield of iodinated aroma in relatively high purity is also obtained by the iodination system thus prepared, it has been shown that the value achieved is difficult to reduce. The reasons are to be found in the fact that when preparing an iodine system containing iodine and chlorine at low temperatures of -5 to 0 ° C, ie under cooling, iodine is in many cases not dissolved even after the subsequent heating of the system to +4 Ca the equivalent of chlorine to be dissolved or dissolved in the system at low temperatures; absorb.

This factor also results in variations in the yield and purity of the product. This can be avoided by using a larger amount of methanol, respectively. CH 2 COOH in the preparation of the iodine system, which, however, has a negative effect in reducing the yield by increasing product losses and at higher costs of removing and recycling larger amounts of methanol, respectively. CH 3 COOH from the reaction system after iodination.

These drawbacks are eliminated and the process for producing 2,5-diiodo-4-hydroxybenzonitrile according to the present invention provides the prerequisites for a high yield of high-quality product at reproducible values.

2,5-diiodo-4-hydroxybenzonitrile is prepared by iodinating 4-hydroxybenzonitrile by treating the 4-hydroxybenzonitrile with an iodine system formed by bringing chlorine gas into a solution of iodine in methanol or acetic acid at 15-30 ° C.

Advantageously, the process may be carried out by adding solid iodine to a solution of 4-hydroxybenzonitrile in methanol or acetic acid, followed by the addition of chlorine gas at a temperature of 15-30 ° C. The invention solves two nodal moments of production.

The first is the preparation of the iodine reagent, which is prepared by dissolving iodine without cooling at normal temperature, ranging from +15 to +30 ° C, in a solvent (methanol or CH 2 COOH, respectively) at this temperature. the chlorine atom equivalent being introduced into the system, the rate of chlorine introduction being controlled by the system's ability to maintain its temperature within the range of +15 to +30 ° C.

An equimolar ratio of iodine and chlorine is obtained which, upon introduction of the aroma into this system, yields iodinated hydroxybenzonitrile at yields of more than 98% of theory and quality at iodination reaction temperatures below 80 ° C, expressed as 2,5-diiodo-4. -hydroxybenzonitrile in the technical product higher than 97 i.

The second nodal moment is the nature of the key process component, 4-hydroxybenzonitrile, entering the process. The aromate can be contacted with the iodination system either in a phenolic form such as 4-hydroxybenzonitrile or in the form of its alkali salt in connection with MS. A.O.

242 141 in the form of a solid respectively. evaporator.

Experimentally, however, has now been found that in connection with MS. A.O. 242 141, the preparation of the iodinating agent, i.e. the dissolution of iodine and chlorine, can be carried out not separately from the aroma, but directly in the methanolic solution of the alkali metal salt of hydroxybenzonitrile leaving the hydroxylation process of A.O. 242 141 under the same operating conditions for the preparation of the iodination system as for its separate preparation, and virtually the same aromatic yield, but also virtually the same product quality, is achieved.

The advantages of the new process consist mainly in high yields and product quality.

These two novel approaches for the preparation of 2,5-diiodo-4-hydroxybenzonitrile by iodination of 4-hydroxybenzonitrile respectively. its alkali salts are documented by the following examples.

Example 1

To 75 g of methanol (containing 0.07% by weight of water) was added 60.5 g of resublimed iodine, and dried under stirring at 15 [deg.] C. to the dried chlorine gas at a rate of 9 g / h for 2 hours. To the iodinated reagent thus prepared was added a residue of the reaction system after hydroxylation of p-chlorobenzonitrile with sodium methoxide containing 33.7 g (0.24 mol) of sodium salt of p-hydroxybenzonitrile dissolved in 500 g of distilled water.

The resulting reaction mixture was heated to 80 ° C and held at this temperature for 20 minutes.

Then the reaction system was cooled to 25 ° C, free halogens were discarded by addition of 10% solution

Na ₂ SO ₃ to the negative reaction of KJ-starch paper. The precipitated 2,5-diiodo-4-hydroxybenzonitrile was filtered off under suction and washed with 500 ml of distilled water at 20 ° C.

The paste obtained is dried in an oven at 60 ° C overnight. 85.8 g of a product containing 97.6% of 3,5-diiodo-4-hydroxybenzonitrile, i.e. 98.2% of theory, were obtained.

Example 2

To 100 g of glacial acetic acid (containing 0.05% by weight of water) was added 63.5 g of resublimed iodine and, at 17 ° C, dried chlorine gas was introduced into the system at stirring at a rate of 9 g per hour for 2 hours. To the iodinated reagent thus prepared was added a residue of the reaction system after hydroxylao of p-chlorobenzonitrile with sodium methoxide containing 0.25 moles, i.e. 35.3 g of sodium salt of 4-hydroxybenzonitrile. After 10 minutes of recovery, 500 g of distilled water and the reaction system heated to 80 ° C in a water bath were added and maintained at this temperature for 20 minutes.

Then the reaction system was cooled to 25 ° C, the free halogens were destroyed by the addition of Na ₂ SO ₃ and the reaction was completed according to the procedure of Example 1. 1. 91.6 g of a product containing 97.2% were obtained.

Of 3,5-diiodo-4-hydroxybenzonitrile.

Example 3

To 175 g of the methanolic reaction system after hydroxylation of p-chlorobenzonitrile with sodium methoxide containing 35.3 g, i.e. 0.25 mol of sodium salt of 4-hydroxybenzonitrile, was added 63.5 g of resublimed iodine. With stirring at 15 ° C, dried chlorine gas was introduced into the system at a rate of 9 g per hour for 2 hours.

Then, 500 g of distilled water was added to the system, and the reaction system was heated to 80 ° C in a water bath and maintained at this temperature for 20 minutes with stirring. After completion of the reaction, the system was cooled to 25 ° C and treated as in Example 1. 76.1 g of a product dried at 80 ° C overnight containing 96.8% of 3,5-diiodo-4-hydroxybenzonitrile were obtained.

Claims (2)

Process for the preparation of 2,5-diiodo-4-hydroxybenzonitrile or its salt by iodination of 4-hydroxy benzonitrile, characterized in that the 4-hydroxybenzonitrile or its alkali salt is treated with an iodine system formed by bringing chlorine gas into solution of iodine in methanol or acetic acid. at 15 to 30 ° C. 2. A process according to claim 1, wherein solid iodine is added to a solution of 4-hydroxybenzonitrile or its alkali salt in methanol or acetic acid, and then chlorine gas is added to the reaction mixture at a temperature of 15-30 [deg.] C.