IL34800A - Process for the preparation of phosphonyl halides - Google Patents

Description

PROCESS FOR THE PREPARATION OF PHOSPHONYL HAUDES This invention relates to a process for the preparation of 2-haloethylphosphonyl dihalides from ethylene, phosphorus trihalides and an oxygen-containing gas . 2-Haloetthiylphosphonyl dihalides, and specifically 2-chloroethylphosphonyl dichloride, are known in the art as useful in various fields, particularly as intermediate products useful for various chemical synthesis such as for example the preparation of esters, amides and the like. Due to their phosphorus content, compounds of this kind are important in various applications in that they have a fungicidal effect and can be used as pesticides for plants. In addition, 2-chloroethylphosphonyl dichloride is an important additive in the preparation of difficultly inflammable polyesters. Also, by splitting off hydrogen chloride, it may be converted into vinyl phosphonic acid dichloride which, because of its double bond, can be polymerized and copolymerized to prepare important polymeric products. In addition this material can be easily hydrolyzed to 2-chloroethyl phosphonic acid which has recently been found to be useful as a plant growth stimulant for increasing crop yields.

Various procedures are known in the art for the preparation of these compounds. Thus, it has been suggested in U.S. Patent 3,206,508 that ethylene, phosphorus trichloride and oxygen will react in the liquid phase to provide 2-chloroethylphosphonyl dichloride and phosphorus oxychloride. This reaction is conducted at atmospheric pressure or in an autoclave at ambient temperature and high pressure. However, this procedure is not commercially satisfactory as both of the reaction conditions are potentially hazardous since they require the contact of large volumes of pure oxygen with highly flammable ethylene.

In addition, an article by Soborovskii et al. Chemical Abstracts, Volume 44, page 1401, (1950), states that below 400eC, olefins and .phosphorous will i not react in the absence of oxygen. Therefore, it is to be expected from this prior art that if ethylene and phosphorus trichloride are mixed in an inert atmosphere and the ethylene then replaced by oxygen, there would be not net reaction. The process of this invention however provides a procedure by which a reaction of this type can be carried out.

A clear need therefore remains in the art for a process for preparing 2-haloethylphosphony1 dihalides which will obviate the necessity of contacting large volumes of oxygen with highly flammable ethylene.

This invention satisfies these requirements.

The present invention provides a process for the preparation of 2-haloethylphosphony1 dihalides, which comprises contacting a phosphorus trihalide and a free-radical catalyst with ethylene at a temperature of about 20-200°C. in a closed system under a pressure of about 1 to 100 atmospheres, and contacting the inert resulting mixture with an oxygen-containing/ gas. This reaction may be illustrated by the following equations: H2C ■ CH2 + P 3 ^ XCH2CH2-P-X X o '· XCH2CH2-P-X + [0] XCH2C¾-P-X X X wherein X is a halogen atom, preferably chlorine or bromine, and the oxygen is utilized preferably in admixture with an inert gas, with air being a most preferred reactant.

According to the process of the invention, this reaction is conducted via a two ste rocedure.

Initially, the phosphorus trihalide, preferably phosphorus trichloride, is admixed with a catalytic amount of a free-radical catalyst. Free-radical catalysts which may be used include, for example, azo bis-isobutlyroni rile or any of the other well-known free-radical catalysts, such as the peroxides, hydroperoxides and the like, for example benzoyl peroxide, dialkyl peroxides, diacyl peroxides, or the azonitrile catalysts mentioned in U.S. Patent Number 2,471,959.

In this reaction the phosphorus trihalide and free-radical catalyst are initially charged to a closed system preferably an autoclave, at a temperature of about 20-200eC, preferably 50-100eC, and pressurized with an excess of ethylene gas. Thereafter the reaction mixture is heated under a pressure of about 1-100 atmospheres at the desired temperature and held under those conditions until the reaction is completed. Completion of the reaction will be indicated by failure of the mixture to consume further ethylene. Thereafter the reaction mixture is preferably allowed to cool to about room temperature and any excess ethylene present in the system is vented off. The product resulting from this step comprises 2-haloethyl phosphorus dihalide and it may then be utilized directly in the second step without isolation or purification.

Thereafter, the resulting reaction mixture is then preferably stirred while passing an oxygen-containing gas such as air through the mixture at X about ambient temperature. In a batch process, passage of the gas through the solution for about 2 hours has been found to be satisfactory. During this procedure, any ethylene remaining in the system is removed and replaced by oxygen in the oxygen-containing gas. Thus at no time in the reaction is there contact of large amounts of oxygen with the highly flammable ethylene, which is a significant safety feature of the invention.

During the passage of the oxygen-containing gas through the mixture, oxidation of the intermediate product occurs to form the desired 2-haloethylphosphonyl dihalide product. After completion of the oxidation reaction, the excess phosphorus trihalide remaining in the mixture is distilled off to result in the desired 2-haloethylphosphonyl dihalide product which may be recovered and purified by known means.

In conducting the reaction the amount of free-radical catalyst which should be employed may range from about 0.1% to 5% by weight based on the amount of phosphorus trihalide initially employed.

In addition, the amount of ethylene to be reacted with the phosphorus trihalide will be dependent on the amount of phosphorus trihalide present and is easily determined by completion of the takeup period for the ethylene. The oxygen-containing gas is preferably air but any other combination of oxygen and inert gas may be employed. In fact, pure oxygen may be employed if desired.

The reaction may be conducted as a batch system such as described herein or may be conducted as a continuous flow operation with modification of the invention to achieve the continuous flow procedure being well-known to those skilled in the art.

It is theorized that the initial reaction between the ethylene and the phosphorous trihalide in the presence of the free-radical catalyst gives rise to the preparation of a phosphine derivative specifically, 2-haloethyl phosphorus dihalide, which material, after removal of the ethylene is then oxidized with the oxygen-containing gas to form the resulting desired product. However, in practicing the process it is preferred not to isolate this intermediate product, and therefore applicants do not intend to be bound by this theoretical explanation for the process.

The most preferred phosphorus trihalide reactant is phosphorus trichloride. The preferred product resulting from the process of this invention is 2-chloroethylphosphonyl dichloride.

The following examples are given for the purpose of illustrating the process of the invention.

EXAMPLE I Into a one liter glass-lined autoclave was char ed 200 ml. (2.3 moles) of hos horus trichloride and 1.0 grams of azo bis-isobutyronitrile . Then the autoclave was pressurized to 200 psig with ethylene and heated to 75°C. for 8 hours. During this period 60 psig of ethylene was taken up. The system was then allowed to cool to room temperature and the excess ethylene vented from the- system. The resulting reaction mixture was then stirred while air was passed through the system for 2 hours at ambient temperature. After completion of this aspect, the excess phosphorus trichloride was distilled off to provide 28 grams of a brown liquid residue. This was shown by vapor phase chromatography to contain 10% of 2-chloroethylphosphonyl dichloride .

EXAMPLE II The reaction of Example I was repeated except that the catalyst employed was 1.0 gram of benzoyl peroxide The reaction was again,pressurized with 200 psig. with ethylene but was heated at 100°C. for 6 hours under which conditions 65 psig. ethylene was consumed. From this reaction, there was obtained 26.5 grams of a brown liquid residue which was shown to contain 12% of 2-chloroethylphosphonyl dichloride .

It is an advantage of the process of the present invention that it proceeds under moderate reaction conditions and that it avoids the use of large volume of oxygen and of highly flammable ethylene in direct contact with each other.

Claims (8)

WHAT WE CLAIM IS

1. A process for the preparation of 2-haloethyl-phosphonyl dihalides, which comprises reacting phosphorus trihalide with ethylene in the presence of a free-radical catalyst at a temperature of 20° to 200eC. and a pressure of 1 to 100 atmospheres, removing the excess ethylene from the mixture and contacting the resulting mixture inert with an oxygen-containing /gas .

2. The process according to Claim 1, wherein the phosphorus trihalide is phosphorus trichloride.

3. The process according to Claim 2, wherein first stage of the the/ reaction is conducted in a closed system under ethylene pressure.

4. The process according to Claim 3, wherein the oxygen-containing gas is added after ethylene ceases to be taken up by the reaction.

5. The process according to Claim 4, wherein the catalyst is selected from the group consisting of the azo nitriles, the organic peroxides and mixtures thereof.

6. The process according to Claim 5, wherein the oxygen-containirig gas is contacted with the reaction mixture at about room temperature.

7. The process according to Claim 6, wherein the product is recovered by distilling off the excess phosphorus trichloride.

8. The process according to Claim 7, wherein the oxygen-containing gas is air.