DK153137B - METHOD OF PREPARING MONOHALOGENACYL HALOGENIDES - Google Patents

Description

DK 153137 B

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The present invention relates to a particular process for the preparation of monohaloacyl halides by reacting a ketene with a halogen in the presence of an ester as a solvent.

Liquid phase halogenation of ketene is well known, but prior art methods for carrying out this reaction have resulted in the formation of monohaloacyl halides contaminated with a considerable amount of dihaloacyl halides and polyhalogenated by-products. These prior methods used such solvents as chlorinated benzenes, nitrobenzene, carbon tetrachloride, chloroacetyl chloride, acetyl chloride, 1,2-dichloroethane, acetonitrile benzonitrile and nitromethane. Each of these solvents has the common disadvantage that they will all result in the formation of a considerable amount of dihaloacyl halide together with the desired product, monohaloacyl halide. In some of these solvents, undesirable trihaloacyl halides are also formed. Dihalogen derivatives have no commercial utility and their preparation from monohalogen derivatives is expensive and time consuming. For example, dichloroacetyl chloride has a boiling point of approx. 107 ° C, whereas monochloroacetyl chloride has a boiling point of approx. 105 ° C.

This close location of the boiling points of the two compounds makes their separation particularly troublesome and adds an expensive and uneconomical step to the halogenation process when using the known solvents;

The monohaloacyl halides produced by the process of the invention are valuable intermediates for the preparation of herbicidal α-haloacetanilides and other products. In contrast, the corresponding di- and trihaloacyl halides have no commercial significance. In other words, they are present only as diluents which decrease the effectiveness of the commercially valuable monohaloacyl halides. The seriousness of the problem is evident-

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2 is made by the fact that all commercially available chloroacetyl chlorides are contaminated with a considerable amount of dichloroacetyl chloride, and in some cases the content of dichloroacetyl chloride is as large as 6%.

By using the process of the invention, the disadvantages of using the known solvents in halogenating a ketene are overcome. The process according to the invention is characterized by the method of claim 1. The process of the invention comprises halogenating the chain, i.e. or substituted ketene, such as methyl chain, dimethyl chain, ethyl chain, diethyl chain, phenyl chain and diphenyl chain.

Ethylene carbonate and other 1,2- and 1,3-alicyclic carbonates may be used alone or in admixture with the present invention. Suitable carbonates include, for example: 1,2-propylene carbonate, 1,2-butylene carbonate, 1,3-propylene carbonate, 1,3-butylene carbonate, 2,2-dimethyl-1,3-propylene carbonate, 1,2-diethyl-1,3- propylene carbonate, 1,2-dimethylethylene carbonate, 1-chloromethylethylene carbonate and 1,2-diethylethylene carbonate. Alicyclic carbonates having 7 or more ring atoms, such as 1,4-butylene carbonate and the like, which are outside the invention, could be good solvents in the process, but are of little practical value in comparison with 5- and 6-membered carbonates.

In carrying out the process of the invention, a ketene and a halogen are introduced into a solvent medium where they are reacted to form monohaloacyl halides which are known in the known manner from the reaction medium, such as by distillation, preferably at reduced pressure. The process can be performed either continuously or discontinuously. The operating conditions under which the reaction 3

DK 153137 B

performed are not critical, but it is preferred to keep them within the specified limits to maximize the yield of monohaloacyl halide. It is only essential that the solvent be liquid under the reaction conditions. However, for practical reasons, the reaction is usually carried out at a temperature of 50 to 150 ° C at a pressure of 50 mm Hg to approx. 2 atmospheres. In most cases, it is preferred to operate at a temperature of 0 - 110 ° C and at a pressure of 100 - 760 mm Hg. The reaction between halogen and the ketene will proceed to form substantially pure monohaloacyl halide regardless of the mole ratio of the reactants. However, the advantage of the process of the present invention is more fully utilized when the halogen-chain molar ratio is maintained between 0.8: 1 and 2.0: 1, and optimum results are obtained when the halogen: chain molar ratio is between 1: 1 and 1. 3: 1. The presence of a solvent of the invention in the reaction medium minimizes the formation of acyl halides and essentially eliminates the formation of dihaloacyl halides and other polyhalogenated by-products.

According to the present invention, the solvent may comprise substantially all or only part of the reaction medium. The advantages of the present invention are most pronounced when the weight ratio of solvent is high, but significant benefits are also obtained even when the solvent is present only in small amounts even when the reaction medium contains a small amount of solvent and they are completely eliminated at higher ratios. . The weight ratio of solvent to the sum of solvent and product, ie. solvent to weight ratio can range from 0.05: 1 to 0.99: 1. Of course, during the normal course of a discontinuous reaction, the solvent weight ratio decreases with the formation of the product which is mixed with the solvent.

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4, which forms the reaction medium. When continuous processes are used, the solvent ratio can be kept constant or varied as desired. The process of the invention is further illustrated by the following examples. In the examples, all particulars are expressed in parts by weight unless otherwise indicated.

EXAMPLE 1

Ca. 200 parts of ethylene carbonate was poured into a suitable reaction vessel, kept at an absolute pressure of about 100 mm Hg and provided with a gas exhaust pipe, temperature sensing means and two gas syringes below the carbonate level. The reaction medium was maintained at a temperature of ca. 40-50 ° C and the ketene and chlorine were added through separate syringes in a constant and substantially equimolar amount. After approx. For 2 1/2 hours, the addition of reactants was complete.

There. 188 parts of chlorine and 85 parts of the chain were added. At the end of the reaction, the ratio of solvent to the sum of solvent to product was 0.44. The reaction mixture was essentially ethylene carbonate, chloroacetyl chloride with smaller amounts of dichloroacetyl chloride and acetyl chloride. When distilled to separate pure chloroacetyl chloride, the mole percent yield of chloroacetyl chloride was determined to be 96% together with 1.9% acetyl chloride and ca. 2% dichloroacetyl chloride. Although the reaction medium in this example was stirred, stirring is not necessary in the halogenation process of the invention. However, when halogen is bromine, it is preferred to stir the reaction medium, but good results are obtained without stirring. Following the general procedure of Example 1, but using the conditions and materials listed in Table I, the products listed in Table I were obtained.

In Examples 2, 3, 5 and 6, the yield of haloacetyl halide is high, i.e. greater than 95% and the amount of dihalogen-

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5 acetyl halide is minimized giving a halogen acetyl purity of more than 98%. In Example 4, the yield of bromoacetyl bromide is over 85% with a purity greater than 99%.

DK 153137 B

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EXAMPLE 6

To a reactor equipped with spray gun and temperature measuring means, 235 parts of 1,2-propylene carbonate were added. The chlorine chain was injected into the reactor at a pressure of 100 mm Hg at a temperature of 20-25 ° C for approx. 182 minutes. A small excess of chlorine was maintained relative to the ketene in the propylene carbonate solution during the course of the reaction. Fractionation and analysis of the products showed a chloroacetyl chloride yield of 94.6¾ and a dichloroacetyl chloride yield of 0.6¾. The acetyl chloride yield was 4.8¾. The chloracetyl chloride purity was 99.2¾. Purification of the solvent was essentially quantitative.

To further illustrate the advantages of the solvents of the invention, the procedure of Example 1 was used with various solvents. The percent yields thus obtained, together with the results of Examples 1 and 6, are given in Table II.

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8

TABLE II

Chloroacetyl Chloride Dichloro-

Acetyl Acetyl Extracted Chloride Chloride Solution

Solution Yield Yield Yield Yield Average Medium _% _% _% _% _% _

Example 1 96 98 1.9 2 95

Example 7 94.6 99.2 4.8 0.6> 95

Ethyl acetate 92 96 5 3 78

Carbon tetra-42 69 "15 75 ethylene hydroxide"

Methyl acetate 91 94 4 4 88

Acetonitrile 46 83 47 7 66

Nitromethane 48 74 39 13 75 n-butyl acetate 82 95 15 3 84 n-hexyl acetate 81 95 15 4 83

Benzonitrile 87 94 9 4 92

By comparing the same process using other solvents, it is clear that the solvents used in the process of the invention substantially suppress formation of polychloroacetyl chlorides and minimize formation of acetyl chloride. Separation of pure chloroacetyl chloride from acetyl chloride and solvent by fractionation presents no problem as there is a large difference between the boiling points of these compounds.

The favorable results of the invention are similarly obtained with other solvents of this invention together with other of the aforementioned halogenating agents.

Bromine can be introduced into the system as a liquid, combined with solvent in the solution, or in gaseous form beneath the surface of the reaction medium. In most cases,

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9, it is known to perform bromine none according to the present invention by using a solution of bromine in a solvent.

Claims (4)

A process for the preparation of monohaloacyl halides by reacting a ketene with a halogen in the presence of an ester as solvent, characterized in that an alicyclic carbonate of the formula CRR1- (CR2R3) -cr4r1 is used. wherein R, R, R, R, R and R can each independently represent hydrogen, halogen, methyl, chloromethyl or ethyl, and wherein n is 0 or 1, or a mixture of such carboxylic acids. carbonates. Process according to claim 1, characterized in that R, R, R, R, R, R and R are hydrogen. Process according to claim 1, characterized in that n is 0 or 1. Process according to claim 1, characterized in that the carbonate is ethylene carbonate. Process according to claim 1, characterized in that the ketene is unsubstituted ketene and the halogen is chlorine.