PROCESS FOR PRODUCING 4,4'-DICHLORODIPHENYL SULFOXIDE

Abstract

The invention relates to a process for producing 4,4′-dichlorodiphenyl sulfoxide comprising: (a) reacting thionyl chloride, chlorobenzene and aluminum chloride in a molar ratio of thionyl chloride:chlorobenzene:aluminum chloride of 1:(6 to 9):(1 to 1.5) at a temperature in the range from 0 to below 20° C., forming an intermediate reaction product and hydrogen chloride, (b) mixing aqueous hydrochloric acid and the intermediate reaction product at a temperature in the range from 70 to 110° C. to obtain a crude reaction product comprising 4,4′-dichlorodiphenyl sulfoxide, (c) separating the crude reaction product into an organic phase comprising the 4,4′-dichlorodiphenyl sulfoxide and an aqueous phase, (d) washing the organic phase with an extraction liquid.

Claims

1.-10. (canceled)

11. A process for producing 4,4′-dichlorodiphenyl sulfoxide comprising: (a) reacting thionyl chloride, chlorobenzene and aluminum chloride in a molar ratio of thionyl chloride:chlorobenzene:aluminum chloride of 1:(6 to 9):(1 to 1.5) at a temperature in the range from 0 to below 20° C., forming an intermediate reaction product and hydrogen chloride, (b) mixing aqueous hydrochloric acid and the intermediate reaction product at a temperature in the range from 70 to 110° C. to obtain a crude reaction product comprising 4,4′-dichlorodiphenyl sulfoxide, wherein the aqueous hydrochloric acid has a concentration above 3 wt. % based on the total amount of hydrogen chloride and water in the aqueous hydrochloric acid, (c) separating the crude reaction product into an organic phase comprising the 4,4′-dichlorodiphenyl sulfoxide and an aqueous phase, (d) washing the organic phase with an extraction liquid.

12. The process according to claim 11, wherein the hydrogen chloride obtained in (a) is mixed with water to obtain the aqueous hydrochloric acid which is added in (b).

13. The process according to claim 11, wherein the extraction liquid is water.

14. The process according to claim 13, wherein the water which is used for the washing the organic phase is separated off and mixed with the hydrogen chloride obtained in (a) to obtain the aqueous hydrochloric acid.

15. The process according to claim 11, wherein the washing is carried out at a temperature in the range from 70 to 110° C.

16. The process according to claim 11, wherein the aqueous hydrochloric acid has a concentration in the range from 3 to 12 wt. %.

17. The process according to claim 11, wherein aluminum chloride and chlorobenzene are first fed into a reactor and the thionyl chloride is added to the aluminum chloride and chlorobenzene.

18. The process according to claim 11, wherein the amount of aqueous hydrochloric acid is such that the weight ratio of aqueous phase to organic phase of the crude reaction product is in the range from 0.6 to 1.5 kg/kg.

19. The process according to claim 11, wherein the amount of water used for washing in (d) is such that a weight ratio of aqueous phase to organic phase in the range from 0.3 to 1.2 kg/kg is obtained.

20. The process according to claim 11, wherein the reaction is carried out in a first reactor and the mixing of aqueous hydrochloric acid and the intermediate reaction product is carried out in a second reactor.

Description

[0049] In the drawing:

[0050] FIG. 1 shows a schematic flow diagram of the process for producing DCDPSO.

[0051] An embodiment of the inventive process for producing DCDPSO is shown in the only FIGURE.

[0052] The process for producing DCDPSO according to the embodiment as shown in FIG. 1 is carried out in a first reactor 1 and a second reactor 3. Chlorobenzene 5, thionyl chloride 7 as reactants and aluminum chloride 9 as catalyst are fed into the first reactor 1. The reactants and the catalyst can be fed simultaneously into the first reactor 1. However, preferably aluminum chloride 9 and chlorobenzene 5 are firstly fed into the first reactor 1 and mixed and the thionyl chloride 7 is then added to the mixture of aluminum chloride and chlorobenzene in a controlled way. In the first reactor 1 an intermediate reaction product is produced which is solved in excess chlorobenzene. The reaction in the first reactor is carried out at a temperature in the range from 0 to 15° C. and ambient pressure. After the reaction is completed, the intermediate reaction product is withdrawn from the first reactor 1 and fed into the second reactor 3. Additionally, aqueous hydrochloric acid 11 with a concentration in the range from 3 to 12 wt % is fed into the second reactor 3. In the second reactor 3 DCDPSO is produced from the intermediate product by hydrolysis.

[0053] The hydrolysis in the second reactor is performed at a temperature in the range from 70 to 110° C. and at ambient pressure for 30 to 120 min. After finishing the hydrolysis, a phase separation into an aqueous phase and an organic phase takes place in the second reactor 3. The aqueous phase 13 containing aluminum chloride is removed from the process and the organic phase 15 comprising DCDPSO as product and chlorobenzene is fed into a washing device 17.

[0054] In the washing device 17, the organic phase 15 comprising DCDPSO as product and chlorobenzene as solvent are mixed with water 18 to remove residual catalyst. The washing is performed at a temperature from 70 to 110° C. and at ambient pressure. After the washing, the mixture separates into two phases, an aqueous phase comprising traces of chlorobenzene and aluminum chloride and an organic phase comprising DCDPSO as product and chlorobenzene as solvent. The organic phase is withdrawn from the process as product 19.

[0055] The organic phase withdrawn as product 19 then can be further treated to separate the DCDPSO from the chlorobenzene. One possibility to obtain DCDPSO is cooling the mixture whereby the DCDPSO precipitates and then can be filtered off.

[0056] Besides the intermediate reaction product hydrogen chloride accrues during the reaction in the first reactor 1. As the hydrogen chloride is gaseous, it easily can be withdrawn from the first reactor 1. The gaseous hydrogen chloride 23 preferably is fed into an absorbing device 25 as shown in the FIGURE. In the absorbing device 25 aqueous hydrochloric acid is produced by absorbing the hydrogen chloride in water. This aqueous hydrochloric acid preferably is used for the hydrolysis in the second reactor 3 as shown in the FIGURE.

[0057] The water for producing the aqueous hydrochloric acid in the absorption device 25 preferably is the aqueous phase 21 which emanates from the washing in the washing device 17. By using the aqueous phase 21 from the washing the total amount of fresh water can be reduced and thus a much smaller amount of wastewater accrues.

[0058] This wastewater is the aqueous phase from the hydrolysis in the second reactor 3. The wastewater can be disposed after cleaning.

EXAMPLES

Effect of the Temperature in the First Reaction

[0059] In all examples 5.5 mol aluminum chloride and 40 mol chlorobenzene were fed into a stirred tank reactor as first reactor. 5 mol thionyl chloride were added to the reaction mixture in 160 min. The reaction in the first reactor was carried out at different temperatures according to table 1. Hydrogen chloride produced in the reaction was withdrawn from the process. After finishing the addition of thionyl chloride, the reaction mixture was heated to 60° C.

[0060] After finishing the reaction in the first reactor, the resulting reaction mixture was fed into a second stirred tank reactor which contained 3400 g aqueous hydrochloric acid with a concentration of 11 wt %. The second stirred tank reactor was heated to a temperature of 90° C. After 30 min the reaction was finished, and the resulting reaction mixture was analyzed by GC analysis to determine the selectivity. The selectivity at the different reaction temperatures in the first reaction is also listed in table 1.

TABLE-US-00001 TABLE 1 Selectivity towards 4,4′-dichlorodiphenyl sulfoxide at different temperatures of the first reaction Example 1 2 3 4 5 6 7 Temperature [° C.] −3 0 6 10 20 30 40 Selectivity [%] 95.7 94.8 94.6 94.3 94 92.8 91.9

[0061] As can be seen from table 1, the selectivity decreases with increasing temperature, wherein there is only a small decrease in the range from 0 to 20° C. The highest selectivity can be observed at a temperature of −3° C. But since the reaction stops at temperatures below −3° C. and thus a precise temperature control is necessary to avoid the temperature to fall below −3° C. particularly in industrial scale processes the reaction is carried out at temperatures above −3° C.

Effect of the Concentration of the Aqueous Hydrochloric Acid Used in the Hydrolysis

[0062] In all examples 5.5 mol aluminum chloride and 40 mol chlorobenzene were fed into a stirred tank reactor as first reactor. 5 mol thionyl chloride were added to the reaction mixture in 160 min. The reaction in the first reactor was carried out at 40° C. Hydrogen chloride produced in the reaction was withdrawn from the process. After finishing the addition of thionyl chloride the reaction mixture was heated to 60° C.

[0063] The intermediate reaction product produced in the first reaction was subjected to a hydrolysis in a second stirred tank reactor by adding aqueous hydrochloric acid. The amount and the concentration of the aqueous hydrochloric acid and the reaction time of the hydrolysis are listed in table 2. During hydrolysis, the mixture was stirred with a three-step cross-arm stirrer at 200 rpm. After hydrolysis, the mixing was stopped, and the mixture separated into an aqueous phase and an organic phase.

[0064] The aqueous phase was withdrawn, and the organic phase was washed with water while stirring. The washing duration and the amount of water also are listed in table 2. During washing the mixture was stirred with a three-step cross-arm stirrer at 100 rpm. After washing, stirring was finished and the mixture separated into an aqueous phase and an organic phase.

[0065] After phase separation the organic phase was subjected to a crystallization process. At 30° C. the resulting suspension was filtered, and the filter cake washed with monochlorobenzene. Drying of the wet filter cake yielded the desired 4,4′-dichlorodiphenyl sulfoxide as a white crystalline solid.

TABLE-US-00002 TABLE 2 Reaction conditions Example 1 2 3 4 5 Hydro- Concen- 3 6 10.7 16 12 lysis tration HCl [wt %] Amount HCl 6990 3495 3495 2330 1747.5 [g] reaction time 60 60 60 60 60 hydrolysis [min] Phase 130 140 140 165 n.d. separation time [s] Washing Amount 4000 2000 2000 1333.3 1000 Water [g] washing time 30 30 30 30 30 [min] Phase 30 40 30 30 50 separation time [s] Yield Final 80.1 81.5 80.4 80.8 79.5 isolated yield [%]

[0066] In example 5 it was not possible to separate the phases after hydrolysis because due to solubility issues the aluminum chloride precipitated.

[0067] In example 1 the aqueous phase was the upper phase after hydrolysis and after washing, in examples 2, 3 and 4 the aqueous phase was the bottom phase after hydrolysis and the upper phase after washing. In example 4, the aqueous phase after hydrolysis was very turbid.