GB2083019A - Process for the preparation of chlororocarboxylic acid chloride - Google Patents

Abstract

A process for the preparation of a chlorocarboxylic acid chloride in which, in a first stage, a chlorocarboxylic acid is reacted with acetic anhydride and the acetic acid produced by the reaction is removed, and then the product obtained in the first stage is reacted with hydrogen chloride, in the absence of water, in a second reaction stage.

Description

SPECIFICATION Process for the preparation of chlorocarboxylic acid chloride This invention relates to a process for the preparation of a chlorocarboxylic acid chloride which comprises the synthesis of a chlorocarboxylic acid chloride from a chlorocarboxylic acid starting compound, via the preparation of its acid anhydride.

Members of a group of the chlorocarboxylic acid chlorides, such as monochloroacetyl chloride, are of value as starting materials for the syntheses of agricultural chemicals and pharmaceuticals.

There have heretofore been disclosed a variety of processes for the preparation of monochloroacetyl chloride, in a large number of patent and scientific publications. These processes are generally classified into three categories, as follows: (1) the monochloroacetic acid process; (2) the acetyl chloride process; and (3) other processes.

In the monochloroacetic acid process (1), monochloroacetic acid is treated with one of a variety of different chlorine donating agents, for example, phosgene and thionyl chloride, optionally in the presence of a catalyst, to produce monochloroacetyl chloride. This process, however, has the drawback that a chlorine donating agent, which is not readily available for industrial uses, is necessarily employed in a stoichiometric amount. The process further involves a reduction of the product quality if the chlorine donating agent and the catalyst remain in the product.

In the acetyl chloride process (2), acetyl chloride is directly chlorinated with chlorine or the like to produce the monochloroacetyl chloride. This process, however, has the drawback that an additional contrivance is required to recover the acetyl chloride, the starting compound, that escapes from the reaction system together with the by-product gaseous hydrogen chloride. This process also inevitably forms a dichlorinated by-product, as is produced unavoidably in general chlorination procedures, and it is difficult to separate this by-product from the desired product.

Examples of other processes in the above category (3) include a process comprising the reaction of a gaseous ketene with gaseous chlorine in an organic solvent to produce monochlbroacetyl chloride.

These processes are not considered to be appropriate for industrial purposes.

As a result of studies for the purpose of providing a process for the preparation of a chlorocarboxylic acid chloride, particularly, monochloroacetyl chloride, the present inventors have found that a chlorocarboxylic acid chloride is easily obtained, with high purity, by employing a process which is entirely different from the conventional processes. The present invention is based on this finding.

The present inventors firstly studied the possibility of providing a process for the preparation of a chlorocarboxylic acid chloride which comprises employing, as an intermediate compound, the reaction product obtained from the reaction of a chlorocarboxylic acid and acetic anhydride. The study was carried out from a viewpoint that is unobviously different from the previous studies. As a result, the present invention was discovered. Accordingly, the present invention is based on the combination of two reaction stages which have been found in the course of the study and which provide an excellent process for the preparation of a chlorocarboxylic acid chloride.The invention is based on the findings that a reaction product consisting mainly of a chlorocarboxylic acid anhydride can be easily produced by reacting a chlorocarboxylic acid with acetic anhydride while removing, by distillation, the acetic acid produced by the reaction (this stage is referred to as the first stage), and a chlorocarboxylic chloride can then be produced by reacting the reaction product obtained in the first stage with hydrogen chloride in the absence of water.

It has been previously known that the reaction between a carboxylic acid and acetic anhydride yields an anhydride of acetic acid -- carboxylic acid, and that a disproportionation reaction takes place concurrently with that reaction to yield a carboxylic acid anhydride. Nevertheless, there has been no previous disclosure relating to the reaction of acetic anhydride with a chlorocarboxylic acid, the starting compound employed in this invention. There also has been no previous disclosure relating to the properties, such as the thermostability, of an anhydride of acetic acid - chlorocarboxylic acid, an assumed first reaction product, and of a chlorocarboxylic acid an hydride, an assumed second reaction product, of the first stage of the process according to the invention.Moreover, it has not been known that the acid anhydride containing a chlorocarboxylic acid group in the molecular structure practically reacts with hydrogen chloride to yield a chlorocarboxylic acid chloride, this reaction being involved in the second stage of the present invention. Accordingly, such a two-stage reaction scheme has not been proposed for the preparation of a chlorocarboxylic acid chloride.

According to the process of the invention, a chlorocarboxylic acid chloride can be obtained with a high purity (e.g. not less than 99 ,6) and in a high yield (e.g. 93-96%). Since any by-product chlorocarboxylic acid can be recycled for use again in the first stage of the invention process and there is no need to add other substances that do not participate in the reaction, the amount of waste from the process is greatly reduced. Particularly, polychlorinated products that are difficult to separate from the desired chlorocarboxylic acid chloride are not produced by the invention process, provided that the starting compound, the chlorocarboxylic acid, does not contain any poly-chlorinated compounds.

Moreover, although the reasons are not clear, the results obtained in the experiments carried out by the present inventors show that even if the starting material contains poly-chlorinated compounds as impurities, the reaction product of the invention process contains a lesser amount of poly-chlorinated compounds, as compared with the amount of poly-chlorinated compounds that were contained in the starting material of the invention process. These advantageous features are of great value in applying the process of the invention to industrial-scale manufacture of chlorocarboxylic acid chlorides.

The chlorocarboxylic acid chloride obtained by the process of the invention may be, for example, a chloride of a chlorinated, saturated, aliphatic carboxylic acid containing from 2 to 4 carbon atoms in the molecule, in which the saturated aliphatic carboxylic acid is exemplified by acetic acid, propionic acid and butyric acid. There is no specific limitation on the number and locations of the chlorine atoms included in the molecule of the starting chlorocarboxylic acid. However, a monochloro-substituted compound containing a chlorine atom attached to the cr-carbon-position is preferred. Examples of chlorocarboxylic chlorides which are of great value for industrial uses include monochloroacetyl chloride and e-monochloropropionyl chloride.

The reaction conditions employed in the process of the invention are generally selected from those set out in Table 1.

TABLE 1

First Stage Second Stage Reaction scheme Ch lorocarboxy I i c acid Ch lorocarboxy I ic acid + Acetic anhydride -, anhydride + Hydrogen Chlorocarboxylic acid chloride -, Ohlorocarb- anhydride + Acetic oxylic acid chloride + acid Ohlorocarboxylic acid Molar Ratio of Acetic anhydride Hydrogen chloride Charged Starting Chiorocarboxylic acid .Chlorocarboxylic acid Compounds = about 0.4 - 0.7/1.0 anhydride = about 1.0 - 2.0/1.0 Pressure Reduced pressure or Reduced pressure or Atmospheric pressure Atmospheric pressure Temperature About 100 - 15000 About 100 - 150 'C Reaction Type Liquid - liquid Gas - liquid chemical and Apparatus chemical reaction reaction Tank Bubble Tower The reaction conditions set forth in Table 1 are provided to show the preferred conditions only.

The pressure is set according to the vapor pressure at the reaction temperature employed. The apparatus can be, in principle, selected from ali types of apparatus that are able to be employed for the reaction type set forth in Table 1.

Each of the acetic anhydride and the hydrogen chloride is preferably employed in an amount more than the stoichiometric amount. The employment of the excess amounts bring about improvements in the completion of the reaction and the yield. The reaction temperature should preferably be maintained not higher than 1 500C. The chlorocarboxylic acid anhydride relatively lacks thermostability at an elevated temperature and is apt to change, in part. into a nonvolatile tar. The reason for maintaining the reaction temperature as set forth above is to suppress the production of the tar.

Although the amount of any poly-chlorinated compounds initially contained in the chlorocarboxylic acid, the starting compound, is reduced by the process of the invention approximately one-half of the initial amount thereof remains in the produced chlorocarboxylic acid chloride in the polychlorinated form. Therefore, a high quality starting material is employed depending on the quality requirement of the final product, particularly as to the amount of poly-chlorinated compounds permitted in the final product.

The crude chlorocarboxylic acid anhydride produced in the first stage can be subjected to the second stage with no intermediate treatment. According to the experiments carried out by the inventors, the crude chlorocarboxylic acid an hydride is, in part, changed into a tar due to the lack of thermostability when it is subjected to distillation, and the distillation therefore reduces the yield (generally, by approximately 5%), contrary to the general expectation. Thus, the crude chlorocarboxylic acid anhydride obtained in the first stage is not distilled, but rather, it is directly used in the second stage.

Preferred embodiments of the invention are, for example, as follows.

In the first stage, a chlorocarboxylic acid and the acetic an hydride are supplied and heated under the aforementioned reaction conditions. The by-product acetic acid and excess acetic anhydride are distilled off under rectification (number of plates: 10 N, reflux ratio = 3-5 approx.) to advance the reaction. Completion of the reaction is confirmed by checking elevation of the temperature at the top of the distilling column. The crude chlorocarboxylic acid anhydride obtained as an intermediate remains in the reaction vessel as the residue therein and is then subjected to the second state without further treatment.

In the second stage, the crude liquid comprising the chlorocarboxylic acid anhydride obtained in the first stage is heated under the aforementioned reaction conditions. Into the reaction liquid is continuously introduced gaseous hydrogen chloride (bubbles). The unreacted hydrogen chloride and the produced chlorocarboxylic acid chloride are distilled off to advance the reaction. Completion of the reaction is confirmed by checking the elevation of the temperature at the top of the bubble tower. The by-product chlorocarboxylic acid remains in the bubble tower, and can be sent back to the first stage for reuse without purification by distillation.

The thus-obtained distillate comprises the unreacted hydrogen chloride, the chlorocarboxylic acid and the desired chlorocarboxylic acid chloride in the ratio corresponding to the partial vapor pressures of the constituents. The distillate is then distilled under rectification (number of plates: 1 0-20 N, reflux ratio = 2 approx.) to give a substantially pure chlorocarboxylic acid chloride (e.g. purity: not less than 99%). In the above-mentioned stage, the reverse reaction consisting of the reaction of the chlorocarboxylic acid and chlorocarboxylic acid chloride also takes place, at a low level, to give some chlorocarboxylic acid an hydride and hydrogen chloride.However, the by-product chlorocarboxylic acid anhydride is sent back to the second stage for reuse, and, therefore, the reverse reaction does not bring about substantial loss in the reaction. Nevertheless, a rapid reaction procedure is preferred and a high reaction temperature is still necessarily avoided in order to suppress the reverse reaction and the production of the tar due to the aforementioned low thermostability of the chloro-substituted compound.

The reverse reaction can be preferably suppressed by carrying out the reaction of the second stage simultaneously with the distillation of the product. More in detail, a reaction-distillation procedure which comprises supplying continuously the chlorocarboxylic acid an hydride and hydrogen chloride to react with each other and removing continuously the produced chlorocarboxylic acid chloride by rectifying distillation is preferably employed.

The reactions of the first and second stages in the process of the invention can be carried out in a continuous process, as well as in a (semi)batch process. The continuous process involving a shorter residence time is preferably employed so as to suppress the thermo-decomposition that is caused by the low thermostability of the chloro-substituted compound.

The present invention is illustrated more in detail by the following Examples, in which the constituents and results are calculated on the basis of gas chromatographic analysis.

EXAMPLE 1 Synthesis of monochloroacetic anhydride (first stage) Into a 2 1., four-necked flask equipped with a distillation column having a diameter of 4 cm and with the number of plates being 10, were charged 2.167 g. (22.9 mol.) of monochloroacetic acid (purity 99%, with 1% of dichloroacetic acid) and 1,404 g. (13.9 mol.) of acetic anhydride.The reaction mixture was refluxed for one hour under the conditions of a pressure of 300--1 50 mm Hg and a reaction temperature of 1 00--1 500 C. The by-produced acetic acid and the excess acetic anhydride were removed by distillation in the reflux ratio of 3-5. As the reaction proceeded, 1,369 g. of acetic acid (the amount corresponding approximately to the theoretical yield) was initially removed and then 200 g. of acetic an hydride was removed. There was obtained 2,000 g. of crude monochloroacetic anhydride (purity 96%) as a residue remaining in the vessel. The yield based on the charged monochloroacetic acid was 98.

Synthesis of monochloroacetyl chloride (second stage) Into a bubble tower of a diameter of 8 cm and a length of 20 cm, equipped with a condenser and piping for distillation on the upper part, was charged 1,660 9. (9.32 mol.) of the crude monochloroacetic anhydride (purity 96%) obtained in the first stage. The reaction temperature was kept at 120-1 250C.

Upon blowing gaseous hydrogen chloride into the tower through the lower part of the tower for 6.5 hours at a rate of 64 Nl./Hr. 1 8.6 mol.), monochloroacetyl chloride was removed from the reaction system through the abovementioned piping, as well as the unreacted hydrogen chloride and the byproduced monochloroacetic acid. The distillation took place at a temperature of 1 15--1200C. There was obtained 1,111 g. of crude monochloroacetyl chloride (purity 90%, with 7% of monochloroacetic acid) as a distillate. The yield based on the charged monochloroacetic anhydride was 95%. In the bubble tower, 889 g. of crude monochloroacetic acid (purity 88%, with 5% of nonvolatile tar) was left.

The thus-obtained crude monochloroacetyl chloride was rectified under the conditions of a pressure of 200 mm Hg and reflux ratio = 1-2, to give 907 g. of pure monochloroacetyl chloride (purity 99%, with 0.5% of dichloroacetyl chloride). There was obtained 143 g. of monochloroacetic anhydride (purity 98%) as a residue, and the monochloroacetic anhydride was sent back for subjecting it to the reaction with hydrogen chloride.

EXAMPLE 2 Synthesis of ct-monochloropropionic anhydride (first stage) The procedure of Example 1 was repeated using 985 g. (9.08 mol.) of ar-monochloropropionic acid (purity 98%, with 2% of ar,ar-dichlornprnpionic acid) and 612 g. (5.99 mol.) of acetic anhydride in place of the combination of monochloroacetic acid and acetic anhydride used in Example 1. The total amount of acetic acid and acetic anhydride that were distilled off was 700 g. There was left 885 g. of crude cz-monochloropropiOnic acid anhydride (purity 97%), and the yield based on the charged (1- monochloropropionic acid was 98%.

Synthesis of cz-monochloropropionyl chloride (second stage) The procedure of Example 1 was repeated using 885 g. (4.37 mol.) of the crude (E- monochloropropionic acid anhydride (purity 97%) obtained in the second stage and 43 Nl./Hr. x 4.5 Hr.

(8.64 mol.) of gaseous hydrogen chloride in place of the combination of crude cl-monochloroacetic anhydride and hydrogen chloride used in the second stage of Example 1. The distillation temperature was in the range of 1 100--105"C. The distilled crude cz-monochloropropionyl chloride (purity 91%, with 6% of a-monochloropropionic acid) amounted to 580 g., and the yield based on the charged c > - monochloropropionic acid anhydride was 95%. There was left 440 g. of crude a-monochloropropionic acid (purity 90%) in the bubble tower.

The rectification was subsequently carried out in the same manner as in Example 1 to give 436 g.

of pure cz-monochloropropionyl chloride (purity 98.5%, with 1.0% of cz,cz-dichloropropionyi chloride).

There was left 11 5 g. of cr-monochloropropionic acid anhydride (purity 96%) in the distillation still.

There were also obtained dichloroacetyl chloride from dichloroacetic acid; ar,ar-dichlornprnpionyl chloride from cz,cz-dichloropropionic acid; and cz,/3-dichloropropionyl chloride from !r.B-dichloropropionic acid in the same manner as described in the above Examples.

Claims (13)

1. A process for preparing a chlorocarboxylic acid chloride, which comprises, in a first reaction stage, reacting a chlorocarboxylic acid with acetic anhydride to form a reaction product containing the corresponding chlorocarboxylic acid anhydride and removing the by-product acetic acid from the reaction product; and then, in a second reaction stage, reacting the reaction product from the first stage with hydrogen chloride, in the absence of water, to produce a second reaction product containing the corresponding chlorocarboxylic acid chloride.

2. A process according to claim 1, in which the chlorocarboxylic acid chloride is recovered.

3. A process according to claim 1 or 2 in which the reaction or the first stage is carried out simultaneously with removal of the acetic acid.

4. A process according to claim 1,2, or 3, in which the chlorocarboxylic acid has the formula RCOOH wherein R is chloro-substituted alkyl having 1 to 3 carbon atoms.

5. A process according to claim 4, in which the chlorocarboxylic acid is a monochloro-substituted acid with a chlorine atom attached to the ar-carbon atom.

6. A process according to claim 5, in which the chlorocarboxylic acid is monochloroacetic acid or cu-monochloropropionic acid.

7. A process according to any of claims 1 to 6, in which the acetic anhydride and the hydrogen chloride are each used in an amount greater than the stoichiometric amount.

8. A process according to any of claims 1 to 7, in which the chlorocarboxylic acid an hydride obtained in the first stage is used directly in the second stage.

9. A process according to any of claims 1 to 8, in which the reactions in the first and second stages are carried out in a continuous process.

1 0. A process according to any of claims 1 to 9, in which the reaction temperature in the first stage and in the second stage is from 1000 to 1 500 C.

11. A process according to any of claims 1 to 10, in which the reaction in the second stage is carried out simultaneously with distillation of the chlorocarboxylic acid chloride produced.

12. A process for preparing a chlorocarboxylic acid chloride, which consists essentially of, in a first stage reaction vessel, reacting liquid chlorocarboxylic acid having the formula RCOOH, wherein R is chlorosubstituted alkyl having 1 to 3 carbon atoms, with liquid acetic anhydride. wherein the molar ratio of acetic anhydride/chlorocarboxylic acid is from about 0.4/1.0 to about 0.7/1.0, at a temperature of 100' to 1 500C. while distilling off by-product acetic acid and excess acetic anhydride, to obtain a first stage liquid reaction product consisting essentially of crude chlorocarboxylic an hydride; ; and then in a second stage reaction vessel bubbling water-free hydrogen chloride gas through said first stage liquid reaction product, at a temperature of 100 to 1 500 C, wherein the molar ratio of hydrogen chloride/chlorocarboxylic acid anhydride is from about 1.0/1.0 to 2.0/1.0 and distilling off a distillate containing crude chlorocarboxylic acid chloride; and then effecting rectifying distillation of said distillate to recover substantially pure chlorocarboxylic acid chloride.

13. A process for preparing a chlorocarboxylic acid chloride substantially as herein described with reference to and as illustrated in either of the Examples.