FR2488602A1 - PROCESS FOR PREPARING HEXACHLOROACETONE - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS A PROCESS FOR THE PREPARATION OF HEXACHLOROACETONE. THE PROCESS OF THE INVENTION FIRST CONSISTS OF PREPARING A MIXTURE OF LOW-CHLORINATED ACETONES CONTAINING ON AVERAGE 2 TO 2.5 ATOMS OF CHLORINE PER MOLECULE IN A STATE ABSORBED IN A LIQUID ORGANIC MEDIUM, THEN CHLORINATING THE SAID LOW-CHLORINE ACETONES ON THE AVERAGE. HEXACHLOROACETONE BY ADDITION OF CHLORINE GAS INTO THE LIQUID, WHICH IS HEATED TO ABOUT 150C, AND BY USE OF EITHER PHOSPHINE OR A COMBINATION OF PHOSPHINE AND AN AMINE AS A CHLORINATION CATALYST. PREFERREDLY, ACETONE IS INITIALLY CHLORINATED BY VAPOR PHASE CONTACT REACTION WITH AN EXCESS OF CHLORINE AT A TEMPERATURE OF 70-100C TO OBTAIN A CHLOROACETONE WITH AN AVERAGE OF 1.6 TO 1.8 ATOMS OF CHLORINE PER MOLECULE. THIS CHLOROACETONE IS ABSORBED IN AN ORGANIC LIQUID WITH CHLORINE HAVING NOT REACTED TO CONTINUE FURTHER CHLORINATION AT A TEMPERATURE OF 25-80C TO GIVE A CHLOROACETONE WITH AN AVERAGE OF 2 TO 2.5 ATOMS OF CHLORINE PER MOLECULE. THIS PROCESS PROVIDES A HEXACHLOROACETONE CONTAINING A VERY LOW QUANTITY OF LOW CHLORINATED ACETONES WITH A GOOD YIELD. THE PRESENT INVENTION APPLIES IN PARTICULAR TO THE CHEMICAL INDUSTRY.

Description

The present invention relates to and relates essentially to a process

  of hexachloroacetone preparation

  by gradual chlorination of acetone with chlorine gas.

  Hexachloroacetone is an important industrial chemical component. For example, hydrolysis of this compound under basic conditions produces chloroform-and trichloroacetic acid, and hexafluoroacetone is obtained

  by substituting fluorine for chlorine in hexachloroacetone.

  More generally, hexachloroacetone is useful as an intermediate of many and varied chemicals

  used in agriculture or in the medical field.

  The preparation of hexachloroacetone by chlorate

  Acetone has been known for a long time and many processes have been developed in the past since

several decades.

  In a relatively recent proposal, the method according to T. Ambrus published in Revue Chimiquevolume 14 (Ne 9), 506-508 (1963) including a first step of

  weakly chlorinated acetones which are mainly

  trichloroacetone, by parallel flow contact reaction between one mole of vaporized acetone and three moles of chlorine gas at 80-90 ° C. in a column packed with Raschig rings and a subsequent step in which the weakly chlorinated acetones react with an excess of chlorine at a temperature, raised to 150-1601C in the presence of an activated carbon catalyst. However, from an industrial point of view, this process is rather unfavorable because there is an unavoidable and considerable loss of the part of acetone which has not reacted and which has a high vapor pressure, at the beginning of the step of vapor phase chlorination, and also because of the need to have a large excess

  chlorine gas in the final stage of chlorination.

  U.S. Patent No. 3,265,740, issued in 1966, proposes to obtain hexachloroacetone by the steps of firstly preparing weakly chlorinated acetones by vapor phase reaction between one mole of acetone plus pyridine and two moles of chlorine gas, and then complete further chlorination of weakly chlorinated acetones in the liquid phase containing a catalytic amount of pyridine by the addition of chlorine gas. This process also fears the loss of the unreacted portion of the vaporized acetone. As other disadvantages, the product obtained from this process

  tends to contain a considerable amount of 1,1,1-

  trichloroacetone because this specific trichloride is less sensitive to the effect of pyridine used as a chlorination catalyst than dichloroacetones and trichloroacetones

other forms.

  The first publication of Japanese Patent Application No. 49 (1974) 24909 proposes a method of chlorination

  three-step process for the preparation of hexachloroacetone.

  The initial step and a liquid phase chlorination of acetone has a relatively low temperature. The resulting weakly chlorinated acetones are again chlorinated under heating and in the presence of an organic base such as pyridine or its salts to obtain a product containing 3 to 4.5 chlorine atoms per molecule on average. In the final step, weakly chlorinated acetones react with

  additional chlorine in the presence of an organic base

  above as catalyst under heating and irradiation with actinic rays. An advantage of this process is that the chlorination can be complete and performed in a time

  relatively short and at relatively low temperatures.

  However, there is a very strong possibility for secondary reactions to occur during the first chlorination stage caused by the contact between acetone and hydrogen chloride in the liquid phase reaction system, and furthermore, the irradiation by the actinic rays in the final stage of chlorination lead to complexity and inconvenience in the construction and maintenance of the apparatus. So, it is very doubtful that

  this process is capable of being carried out industrially.

  It is an object of the invention to provide a novel process for the efficient preparation of hexachloroacetone

  of high purity and with a good yield.

  The first characteristic of the inventin lies in the fact that it uses as catalyst a phosphine with the exception of triphenylphosphine for the chlorination in the liquid phase of weakly chlorinated acetones

in hexachloroacetone.

  By the process according to the invention, the hexagonal

  Chloroacetone is prepared following the steps of firstly preparing a mixture of weakly chlorinated acetones having 2 to 2.5 chlorine atoms per molecule on average in an absorbed state in a liquid organic medium, and then chlorinating again these weakly chlorinated acetones to hexachloroacetone by introducing gaseous chloride into said liquid medium containing the weakly chlorinated acetones in the presence of a catalyst which comprises a phosphine with the exception of triphenylphosphine, while the liquid medium is kept heated to a temperature

  between 600C and 1500C approximately.

  A phosphine alone can be used as a catalyst, but it can also be used and preferably a mixture of phosphine (with the exception of triphenylphosphine) and an organic base such as

than an amine or the like.

  It is recommended to prepare the weakly chlorinated acetones mentioned above by the steps of firstly preparing very weakly chlorinated acetones having 1.6 to 1.8 chlorine atoms per molecule on average by a vapor phase contact reaction between the acetone and an excess of chlorine gas, and allow an organic liquid medium to adsorb the product of this vapor phase reaction and residual reagents while maintaining the resulting liquid phase reaction system at a temperature of between about 25 and 801C for thus chlorinate again very weakly chlorinated acetones and to obtain a value of chlorine atoms per molecule

between 2 and 2.5 on average.

  It is also advantageous to use either hexachloroacetone or a weakly chlorinated acetone as an organic liquid medium. However, these examples of

  Organic liquid media are not limiting.

  The chlorination process according to the present invention can easily be carried out and leads to

  relatively low temperatures and gives hexachloro-

  acetone with very low concentrations of trichloroacetone and pentachloroacetone. By the preparation of low chlorinated acetones as recommended, the purity of hexachloroacetone and the yield of the reaction on the basis of acetone are remarkably increased. The process according to the invention can be carried out

  either discontinuously or continuously.

  The essential point of the present invention is the use of phosphine, either alone or in combination with an organic base, as a catalyst for the chlorination of weakly chlorinated acetones in an organic solvent

to obtain hexachloroacetone.

  A large number of phosphines can be used with the exception of triphenylphosphine. By way of example, phosphine which can be validly used as a chlorination catalyst according to the invention will be given below:

  monophenylphosphine, diphenylphosphine, dimethylphenylphosphine

  phine, triethylphosphine, tris (4-methylphenyl) -phosphine, tri-n-butylphosphine and tri-n-octylphosphine. In the case of using phosphine alone as a catalyst, the appropriate amount of phosphine is between 0.1 and mol% and preferably between 0.2 and 1 mol% of the total of weakly chlorinated acetones. The use of a quantity of phosphine greater than 5 mol% is not favorable from an economic point of view. If the amount of phosphine is less than 0.1 mole%, the product obtained will have a relatively low purity and a concentration of

  pentachloroacetone relatively high.

  It has been found and confirmed by experi-

  that the amount of phosphine used as a catalyst can be reduced by using a suitable amount

  and adequate amine or salts added to said phosphorus

  phine. However, it is not possible to replace the total amount of phosphine with an amine because it results in a significant and considerable amount of 1,1,1 trichloroacetone in the product obtained. It is preferable to use an amine having a thermal stability and a relatively high boiling point. Examples of preferred amine compounds are pyridine, quinoline,

  n-tributylamine and n-trioctylamine, or the like.

  It is also preferred that each of the additional amounts of phosphine and amine be in the range of 0.05-2 mole% and preferably 0.1-0.5 mole%

  total of weakly chlorinated acetone.

  The catalyst can be added to the liquid organic medium after the absorption of weakly chlorinated acetones, but it is also possible and this does not provide

  no problem that the addition of the catalyst precedes the absorption

  tion of weakly chlorinated acetones in said medium

  organic liquid. A liquid catalyst such as tri-n-

  butylphosphine can be poured directly into the medium

  organic liquid. A solid catalyst such as tris (4-

  methylphenyl) phosphine must be introduced into the liquid medium in a solution form, for example in a weakly chlorinated acetone. In the case of use

  of a mixture of phosphine and amine, there is no difference

  whether these two catalytic products are added together

  separately or mixed together in advance.

  As a liquid organic medium it is preferable and appropriate to use either hexachloroacetone or weakly chlorinated acetone. In the case of using a different solvent, it is important to choose a solvent that does not affect the desired chlorination reaction, and has a relatively low vapor pressure and can be easily separated from hexachloroacetone. Examples of suitable solvents are carbon tetrachloride, chlorobenzene and trichlorotrifluoroethane. In any case, the suitable amount of liquid organic media should be from about 10 to about 100 mole percent and preferably from about 20 to about 50 mole percent of the total acetone.

  poorly chlorinated which must be absorbed.

  The liquid organic medium or absorbent is used mainly because of its ability and efficiency in the absorption of weakly chlorinated acetones and also because of the possibility of a moderate thermal load on the reflux condenser to be mounted above the apparatus for phase chlorination

  liquidity, and also because of its contribution to the

  the conversion of chlorine. The final stage of chlorination

  The low chlorinated acetones in hexachloroacetone are accomplished by heating the liquid containing the weakly chlorinated acetones and the catalyst at a temperature above 60 ° C. The chlorine gas is introduced into the liquid.

  liquid at an appropriate rate and gradually increasing

  the temperature of the liquid up to about 1500C while the chlorine gas is continuously introduced. When using a relatively large amount of catalyst, it will be sufficient to heat the liquid to about 140 ° C. Substantially complete chlorination of weakly chlorinated acetones to hexachloroacetone can be achieved by the use of a theoretical amount or

  a significantly larger amount of chlorine.

  The chlorination reaction is conducted almost stoichiometrically during the initial stage of the operation, but the rate of reaction tends to decrease when the chlorination tends to be complete. Therefore, in the last stage of the operation, the rate of introduction of the chlorine gas can be reduced so as to avoid a significant loss.

chlorine.

  The presence of water in the reaction system is not desirable because the water acts as a phosphine catalyst poison and also the presence of water accelerates the corrosion of the devices used. In practice, however, there are no serious problems as long as the amount of water in the reaction system is less than about

0.25% by weight of acetone.

  The best way to prepare weakly chlorinated acetones having 2 to 2.5 chlorine atoms per molecule on average is to first chlorinate acetone to obtain an average value of chlorine atoms per molecule of 1.6 to 1.8. by a contact reaction

  in the vapor phase between acetone and chlorine in a proportion

  1: 2 to 1: 3 mol, followed by absorption of the thus chlorinated acetone and the unreacted portion of the chlorine in an organic liquid medium, and maintaining the liquid reaction system obtained under heating moderated for a certain time to allow a new reaction between the chlorine and the chloroacetones absorbed in the liquid medium. Thus, accomplishing this initial step of vapor phase chlorination avoids side reactions that would produce undesirable products such as phorone and / or mesityl oxide. The vapor phase reaction is conducted as a parallel flow contact reaction at a reaction temperature of 70 to 1000 ° C. It is

  possible to determine the contact time in a relative-

  wide range such as from 5 to 20

  seconds taking into consideration that the chlorination is-

  also conducted in the liquid organic medium. In

  the liquid phase reaction for the chlorination of chlorine

  ketones containing from 1.6 to 1.8 chlorine atoms per mole of chloroacetone containing from 2 to 2.5 chlorine atoms per mole, it is preferable and appropriate to maintain the liquid phase reaction system at a temperature of between and 800C to increase the conversion of chlorine and minimize losses in organic products. Other features, details and advantages of the invention will be more clearly

  described in the description below with reference

  to the examples given without limitation.

EXAMPLE 1

  From an evaporator, the acetone is introduced into a horizontally disposed reaction glass tube (inside diameter 21 mm and length 270 mm) at a constant flow rate of 0.36 mole per hour. Simultaneously, and in the same direction, chlorine gas is passed through the reaction tube at a constant rate of 0.9 mole per hour so that the molar ratio of acetone to chlorine is 1: 2.5. The reaction tube is maintained heated by electrical heating to a temperature within the tube of 70-800 ° C to effect a parallel flow contact reaction between the acetone vapor and the chlorine gas. The outlet of the reaction tube is connected to a 500 ml four-necked flask which contains g (0.57 moles) of hexachloroacetone and which is equipped with a reflux condenser cooled to -50c-0C for

  maintain the temperature of hexachloroacetone at 50-700C.

  The supply of acetone and chlorine in the reaction tube is conducted for 2 hours and 47 minutes, so that the total amount of acetone introduced is equal

at 1 mole.

  The degree of chlorination of the weakly chlorinated acetone mixture obtained by the vapor phase contact reaction and chlorinated again in hexachloroacetone

  heated is equal, on average to 2.5 chlorine atoms per.

  molecule. This degree is determined by a quantitative analysis of the hydrogen chloride obtained as a by-product and by a gas chromatographic analysis of the products. Added to the liquid reaction system

  containing weakly chlorinated acetones in hexachloro

  roacetone, 0.4 gram of tri-n-butylphosphine (0.2 mol% of the total amount of acetone introduced into the reaction tube) as a catalyst. After that, the temperature of the liquid reaction system is raised to 600 ° C. and chlorine gas is introduced into said liquid reaction system at a rate of 1 mole per hour. The temperature of the liquid reaction system is gradually increased to 1461C, the introduction of chlorine being continued

for 3.7 hours.

  This process produces a bright yellow hexachloroacetone. Quantitative analysis

  gas chromatography shows that hexachloro

  crude acetone has a purity of 95.4% and it contains 0.2%

  1,1,1-trichloroacetone and 4.4% pentachloroacetone.

  The total yield of hexachloroacetone based on acetone is 91.2%, excluding hexachloroacetone

used as an absorbent.

REFERENCE 1

  According to the method described in Example 1, one mole of acetone is chlorinated to obtain a product

  containing on average 2.5 chlorine atoms per molecule.

  The amount of hexachloroacetone used as absorbent

  is slightly modified and is decreased to 100 g (0.38 mol).

  In the final stage of chlorination we use

  0.3 gram of quinoline alone as a catalyst. The temperature

  of the liquid reaction system from the introductory

  chlorine gas (1 mole / hour) is 70 ° C and is gradually increased to 144 ° C.

  Chlorine gas is continued for 3.6 hours.

  The crude hexachloroacetone obtained in this experiment has a purity of 94.7% and contains 4.2% trichloroacetone and 1.1% pentachloroacetone. The yield

  in hexachloroacetone based on acetone is 91.1%.

REFERENCE 2

  The procedure of reference 1 is repeated generally but 0.3 gram of pyridine is used as a catalyst in the final chlorination step in place of the quinoline used in reference 1. Another modification is that

  the liquid reaction system is heated to 146 C.

  The crude hexachloroacetone obtained in this experiment has a purity of 94.4% and contains 5.3% trichloroacetone and 0.3% pentachloroacetone. The yield

  in hexachloroacetone is 86.1%.

EXAMPLE 2

  In a manner generally in accordance with Example 1, 1 mole of acetone is chlorinated to obtain a product.

  containing on average 2.3 chlorine atoms per mole.

  After the addition of 1.12 grams of diphenylphosphonate

  phine (0.6 mole% of the total low chlorinated acetones) to the liquid reaction system, 4.4 moles of chlorine gas are introduced into the liquid reaction system for 75 hours, while heating the reaction system gradually from its initial 700C to

a maximum temperature of 1491C.

  The hexachloroacetone obtained in this example is colorless and transparent and has a purity of 96.1%. The hexachloroacetone yield based on acetone is, 2%.

EXAMPLES 3 to 8

  In these examples, the chlorination of 1 mole of acetone to obtain a product containing on average 2.5 chlorine atoms per mole is carried out according to the method described in Example 1, except that the amount of hexachloroacetone used as absorbent is decreased

100 grams.

  The weakly chlorinated acetones in the liquid phase are chlorinated to hexachloroacetone by the method of Example 1, but in each of Examples 3 to 8 a combination of phosphine (0.1 mole) and amine (0.1 mole) is used. as a chlorination catalyst. In each example the chlorine gas is introduced into the heated liquid reaction system for a period of 3.6

  under a flow rate of 1 mole per hour, but the temperatures

  initial and maximum temperatures of the reaction system are

  significantly different from one example to another. Catalysts

  The reaction temperatures and temperatures of Examples 3 and 8 are shown in the following table with the results.

  product analyzes as well as Hexachloro-

roacétone.

EXAMPLE 3

triphenylphosphine quinoline

-142 C

EXAMPLE 4

triphenylphosphine pyridine

-142'C

EXAMPLE 5

tri-n-butylphosphine quinoline

-144 C

EXAMPLE 6

tri-n-butylphosphine pyridine

-1450C

EXAMPLE 7

  tri-n-butylphosphine tri-n-butylamine

-1460C

EXAMPLE 8

diphenylphosphine quinoline

-150 C

Analysis

trichloroethane

roacé-

tone

penta

chloro

acetone

2.1% 0.4%

  2.3% 0.9% 0.7% 0.4% 1.4% 0.4% 0.3% 0.3% 1.5% 1.8% Hexa-

chloro

  acetone 97.5% 97.3% 98.8% 99.0% 98.1% 96.8%

yield

  93.8% 91.2% 89.2% 94.5% 93.5%, 5%

Claims (11)

  1. A process for the preparation of hexachloroacetone, characterized in that it comprises the steps of: - - preparing a mixture of weakly chlorinated acetonescomprising an average of 2 to 2.5 chlorine atoms per molecule in an absorbed state in an organic medium liquid; and chlorinating said weakly chlorinated acetones to hexachloroacetone by introducing chlorine gas into said liquid medium containing said acetones weakly   chlorinated in the presence of a catalyst which comprises a phosphorus   with the exception of triphenylphosphine, while the liquid reaction system is heated and maintained at   a temperature of between 60 C and 150 C.   2. Method according to claim 1, characterized in that the aforementioned mixture of weakly chlorinated acetones is prepared by the subsidiary steps of firstly chlorinate acetone to give products containing on average 1.6 to 1.8 chlorine atom per molecule in a parallel-flow vapor phase contact reaction between acetone and chlorine at a temperature of between 100 ° C. and 100 ° C., the molar ratio of acetone to chlorine subjected   with the reaction being between 1: 2 and 1: 3, absorbing the -   products of the vapor phase contact reaction and the residual reactants in a liquid organic medium; and maintain the resulting liquid phase reaction system   at a temperature between 25 and 80 C.   3. Method according to claim 1 or 2, characterized in that the catalyst is the aforementioned phosphine alone in an amount of 0.1 to 5 mole% of the   total amount of weakly chlorinated acetones.   4. Method according to claim 3, characterized in that said phosphine is chosen from the group consisting of monophenylphosphine, diphenylphosphine,   dimethylphenylphosphine, triethylphosphine, tris (4-methyl)   phenyl) phosphine, tri-n-butylphosphine and tri-n-octylphosphine.   5. Method according to one of claims 1, 2 or   4, characterized in that the aforementioned catalyst is constituted   of a phosphine and an organic base.   6. Process according to claim 5, characterized in that the abovementioned organic base is an amine, each of the respective amounts of phosphine and amine respectively being between 0.05 and 2 mole% of the total amount.   weakly chlorinated acetones mentioned above.   7. Process according to claim 5 or 6, characterized in that the abovementioned amine is chosen from the group consisting of pyridine, quinoline and n-tributylamine. and n-trioctylamine.   8. Method according to one of claims 2 to   7, characterized in that the amount of said liquid organic medium is between 10 and 100 mol% of   the total amount of the weakly chlorinated acetones mentioned above.   9. Method according to one of the claims   preceding characterized in that the liquid organic medium   aforementioned is hexachloroacetone.   10. A method according to any of the claims   cations 1 to 8, characterized in that the organic medium   aforementioned liquid is a chlorinated acetone.   11. Method according to one of claims 1 to   8, characterized in that said liquid organic medium is selected from the group consisting of tetrachloride of   carbon, chlorobenzene and trichlorotrifluoroethane.