EP2560950A1

EP2560950A1 - Method for the production of 4,4'-dichlorodiphenyl sulfone

Info

Publication number: EP2560950A1
Application number: EP11714787A
Authority: EP
Inventors: Patrick Deck; Heiner Schelling; Florian Garlichs
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2010-04-22
Filing date: 2011-04-19
Publication date: 2013-02-27
Also published as: EP2383256A1; CN102858737A; KR20130091657A; BR112012026760A2; JP2013525328A; WO2011131665A1

Abstract

The invention relates to a method for producing 4,4'-dichlorodiphenyl sulfone from monochlorobenzene in which the maximum concentration of hydrocarbons containing 5 to 8 carbon atoms is 100 ppm relative to the total weight of the monochlorobenzene including the secondary components used. The invention further relates to the use of monochlorobenzene having said properties for the production of 4,4'-dichlorodiphenyl sulfone.

Description

The invention relates to a process for the preparation of 4,4'-dichlorodiphenylsulfone starting from monochlorobenzene, wherein the content of monochlorobenzene used in hydrocarbons having from 5 to 8 carbon atoms at most 100 ppm, based on the Total weight of the monochlorobenzene used, including the minor components, is.

Moreover, the present invention relates to the use of monochlorobenzene having the stated properties for the preparation of 4,4'-dichlorodiphenylsulfone.

4,4'-dichlorodiphenyl sulfone is used in particular as a monomer in the synthesis of polyarylene ether sulfones. Commercially significant examples are polyether sulphone (polymerization of 4,4'-dihydroxydiphenysulfone with 4,4'-dichlorodiphenyl sulfone), polysulfone (polymerization of bisphenol A with 4,4'-dichlorodiphenyl sulfone) and polyphenylene sulfone (polymerization of 4,4 '). Dihydroxybiphenyl with 4,4'-dichlorodiphenyl sulfone). 4,4'-dichlorodiphenyl sulfone is thus a central building block for the production of these engineering plastics.

Highly pure 4,4'-dichlorodiphenyl sulfone is preferred as the starting material for the preparation of polyarylene ether sulfones, on the one hand because exclusively from the 4,4'-isomer arise linear, non-angled polymers which have the desired product properties, such as, for example, Chemical and temperature resistance, high dimensional stability and flame retardancy on the other hand, since impurities often lead to undesirable discoloration and deterioration of the properties of the polymers. Methods of preparing 4,4'-dichlorodiphenyl sulfone from monochlorobenzene are known in the art. The known processes comprise, in particular, the preparation starting from monochlorobenzene and a sulfonating agent via 4-chlorobenzenesulfonic acid as intermediate, which is generally not isolated.

No. 2,593,001 describes a continuous process for the preparation of diaryl sulfones by reaction of aromatic sulfonic acids with aromatics, wherein the water of reaction is continuously removed from the reaction zone by the countercurrently added gaseous aromatic compound.

US 2,971,985 discloses the synthesis of dichlorodiphenyl sulfone using SO3, dimethyl sulfate and monochlorobenzene. EP 0 381 049 A1 also describes a process for the preparation of 4,4'-dichlorodiphenylsulfone. In this case, sulfur trioxide, dimethyl sulfate and chlorobenzene at 50 to 100 ° C is reacted.

Reaction discharges from the synthesis of 4,4'-dichlorodiphenyl sulfone according to US

2,593,001, US 2,971,985 or EP 0 381 049 A1 are usually colored. This coloration by strongly coloring by-products in very low concentrations can be prevented by working up by crystallization only incomplete or only in a very complex manner. In order to obtain 4,4'-dichlorodiphenyl sulfone in a quality necessary for use as a polymer unit, a work-up of the initially obtained crude product, d. H. a mixture containing 4,4'-dichlorodiphenylsulfone required. For this purpose, different methods are known from the prior art. US Pat. No. 4,937,387 describes, based on the synthesis according to US Pat. No. 2,593,001, the separation of the reaction mixture by addition of water, separation of the two resulting liquid phases and subsequent isolation of dichlorodiphenyl sulfone. Mixtures of the dichlorodiphenylsulfone isomers may e.g. be worked up by crystallization with or from alcohols, so as to obtain increased purities of the desired 4,4'-dichlorodiphenylsulfone. In EP-A 279387 this type of purification by recrystallization is described. US Pat. No. 4,016,210 describes the crystallization of 4,4'-dichlorodiphenyl sulfone from a reaction mixture resulting from the reaction of chlorobenzenesulfonic acid and chlorobenzene.

A disadvantage of the known processes for the preparation of 4,4'-dichlorodiphenyl sulfone is thus the complexity of the workup, which is followed by the recovery of the crude product initially obtained. The degree of complexity is largely determined by the nature and amount of minor components. Secondary components of 4,4'-dichlorodiphenylsulfone are usually difficult to separate by crystallization. To make matters worse, that coloring minor components already discolored in very small amounts, the 4,4'-dichlorodiphenyl sulfone and optionally produced therefrom polymers in an undesirable manner. It would thus be desirable to provide a process for the preparation of 4,4'-dichlorodiphenyl sulfone which reduces or eliminates the formation of minor coloring components of 4,4'-dichlorodiphenyl sulfone.

It was therefore the object of the present invention to provide a process for the preparation of 4,4'-dichlorodiphenyl sulfone, which does not have the aforementioned disadvantages or to a lesser extent. In particular, the process should provide 4,4'-dichlorodiphenyl sulfone in a high purity in a technically simple manner. The proportion of secondary components of 4,4'-dichlorodiphenyl sulfone formed in the preparation, in particular coloring secondary components, should be reduced or even avoided compared to the prior art.

The abovementioned objects are achieved by the process according to the invention for preparing 4,4'-dichlorodiphenyl sulfone. Preferred embodiments are given in the claims and the following description. Combinations of preferred embodiments do not depart from the scope of the present invention.

The process according to the invention for the preparation of 4,4'-dichlorodiphenyl sulfone is carried out starting from monochlorobenzene, the content of the monochlorobenzene used in hydrocarbons having from 5 to 8 carbon atoms being at most 100 ppm, based in each case on the total weight of the monochlorobenzene used, including the secondary components ,

The content of monochlorobenzene used in hydrocarbons having from 5 to 8 carbon atoms in the context of the present invention is calculated in principle as the amount by weight of the hydrocarbons (in the unit ppm, which denotes parts by weight in the context of the present invention) and on the total weight of the monochlorobenzene used, including all secondary components based. The content of monochlorobenzene used in hydrocarbons is determined in the context of the present invention by means of gas chromatographic separation and subsequent detection by means of flame ionization. The quantitative determination of the secondary components takes place via the addition of a standard. Corresponding quantitative methods are known to the person skilled in the art. The usually achievable detection limit of this method is 0.1 ppm.

In principle, all known processes for the preparation of 4,4'-dichlorodiphenylsulfone which originate from monochlorobenzene, in particular processes which comprise the reaction of monochlorobenzene with a sulfonating agent, in particular those which react via 4-chlorobenzenesulfonic acid, are suitable for the purposes of the process according to the invention as an intermediate. Corresponding methods are known to the person skilled in the art. Preferred methods for the preparation of 4,4'-dichlorodiphenylsulfone are described below in the context of step (b) of a preferred embodiment.

The monochlorobenzene used preferably has a purity of at least 99.8% by weight at the same time. A purity of at least 99.8 wt .-% means in Within the scope of the present invention, the monochlorobenzene used consists of at least 99.8% by weight of the chemical compound monochlorobenzene. The indication of the wt .-% refers to the total weight of the monochlorobenzene used. It is known to the person skilled in the art that the monochlorobenzene used contains, in addition to the chemical compound monochlorobenzene, what are known as impurities, referred to below as secondary components. The indication of the purity thus relates in principle to the total weight of the monochlorobenzene used and includes all secondary components including the hydrocarbons mentioned.

According to the present invention, the proportion of minor components in the monochlorobenzene used in the preparation of 4,4'-dichlorodiphenyl sulfone is preferably at most 0.2 wt .-%, based on the total weight of the monochlorobenzene used, including all secondary components. The proportion of hydrocarbons, which by definition consist exclusively of carbon and hydrogen, with 5 to 8 carbon atoms in the total weight of monochlorobenzene used according to the invention is at most 100 ppm.

The proportion of hydrocarbons having 5 to 8 carbon atoms in the total weight of the monochlorobenzene used is preferably not more than 80 ppm, more preferably not more than 50 ppm, in particular not more than 20 ppm, very particularly preferably not more than 10 ppm, in particular not more than 5 ppm Total weight of the monochlorobenzene used, including the minor components.

In the context of the present invention, the lower limit for the hydrocarbons according to the invention having 5 to 8 carbon atoms per se is zero. However, it is not possible, or only with great effort, to reach the lower limit of zero. In this respect, a common, procedural conditional lower limit for the proportion of hydrocarbons having 5 to 8 carbon atoms in the total weight of monochlorobenzene used, for example, 0.1 ppm and 0.01 ppm, based on the total weight of the monochlorobenzene used, including the minor components. For the determination of contents of minor components which are contained with less than 0.1 ppm, the expert uses known trace analytical methods.

For the purposes of the present invention, hydrocarbons are understood as meaning compounds which are composed exclusively of carbon and hydrogen. If other types of atoms than carbon and hydrogen are present, the corresponding compounds are referred to differently, for. As halogenated hydrocarbons. Hydrocarbons having 5 to 8 carbon atoms include, in particular, saturated linear aliphatic hydrocarbons (n-pentane, n-hexane, n-heptane, n-octane), saturated branched aliphatic hydrocarbons, saturated cycloaliphatic hydrocarbons, unsaturated hydrocarbons other than those mentioned above derived by computational elimination of hydrogen, and aromatic hydrocarbons.

The group of hydrocarbons having 5 to 8 carbon atoms includes in particular saturated or unsaturated cycloaliphatic hydrocarbons and saturated or unsaturated linear or branched aliphatic hydrocarbons, hereinafter collectively referred to as (cyclo) aliphatic hydrocarbons, wherein the (cyclo) aliphatic hydrocarbons having 5 to 8 carbon atoms in total preferably not more than 80 ppm, more preferably not more than 50 ppm, in particular not more than 20 ppm, very particularly preferably not more than 10 ppm, in each case based on the total weight of the monochlorobenzene used, including the secondary components.

It is furthermore preferred to limit the proportion of hydrocarbons having 6 or 7 carbon atoms in the monochlorobenzene used to a total of at most 80 ppm, preferably at most 50 ppm, in particular at most 20 ppm, very particularly preferably at most 10 ppm, in particular at most 5 ppm.

The monochlorobenzene used preferably has a purity of at least 99.9% by weight, in particular 99.95% by weight, based on the total weight of the monochlorobenzene used, including the secondary components. The monochlorobenzene used particularly preferably has a purity of at least 99.99% by weight, in particular at least 99.995% by weight, very particularly preferably at least 99.999% by weight, based on the total weight of the monochlorobenzene used, including the secondary components. The determination of the proportion of secondary components in the monochlorobenzene used is carried out in the context of the present invention basically by means of gas chromatographic separation and subsequent detection by means of flame ionization. The quantitative determination of the secondary components takes place via the addition of a standard. Hydrocarbons having 5 to 8 carbon atoms have a particularly unfavorable influence on the color number of the 4,4'-dichlorodiphenyl sulfone formed in the process according to the invention.

Particularly relevant with regard to the influence on the color number are saturated cycloaliphatic hydrocarbons of the empirical formula C6H12 and C7H14, unsaturated hydrocarbons of the empirical formula C7H12 and saturated aliphatic, linear or branched hydrocarbons of the empirical formulas C5H12 and Ce +. sen. The content of the monochlorobenzene used in the (cyclo) aliphatic compounds having 6 or 7 carbon atoms mentioned in the preceding sentence is preferably not more than 80 ppm, more preferably not more than 50 ppm, in particular not more than 20 ppm, very particularly preferably not more than 10 ppm, in particular at most 5 ppm, in each case based on the total weight of the monochlorobenzene used, including the secondary components.

The (cyclo) aliphatic compounds having 6 carbon atoms, in particular cyclohexane, methylcyclopentane, methylcyclopentene, linear or branched hexane and the (cyclo) aliphatic compounds having 7 carbon atoms, in particular methylcyclohexane, methylcyclohexene and linear or branched heptane have a particularly unfavorable Influence on the color number of the resulting 4,4'-dichlorodiphenylsulfone. In addition, the proportion of halogenated hydrocarbons having 5 to 8 carbon atoms except monochlorobenzene monochlorobenzene used in the present invention is preferably at most 100 ppm, more preferably at most 50 ppm, especially at most 20 ppm, most preferably at most 10 ppm, especially at most 5 ppm , in each case based on the total weight of the monochlorobenzene used, including the secondary components. At the same time, the monochlorobenzene used has a proportion of hydrocarbons having 5 to 8 carbon atoms in the preferred range explained above. Halogenated hydrocarbons having 5 to 8 carbon atoms except monochlorobenzene are compounds containing carbon, hydrogen and at least one halogen atom, in particular chlorine and / or bromine, in particular chlorine. This class of compounds includes in particular monobromobenzene and dichlorobenzene. The present invention furthermore relates to a process for the preparation of 4,4'-dichlorodiphenyl sulfone comprising at least the following steps:

(a) Purification of monochlorobenzene to give monochlorobenzene having the properties according to the invention in respect of the minor components, and subsequently

(b) reacting the monochlorobenzene obtained in step (a) to obtain a mixture comprising 4,4'-dichlorobenzenesulfone, and then

(c) preferably separating 4,4'-dichlorobenzenesulfone from the mixture obtained according to step (b). The individual steps are explained below.

Step (a) Methods for purifying the monochlorobenzene are known per se to the person skilled in the art. It is essential to the invention that the monochlorobenzene used in step (b) has the abovementioned inventive or preferred properties in terms of purity and secondary components.

Preferably, the purification of the monochlorobenzene according to step (a) is carried out by distillation. Corresponding distillative processes are likewise known to the person skilled in the art. In particular, a batch distillation or the distillative purification by means of dividing wall column into consideration. The distillative purification by means of a dividing wall column is particularly preferred since it is possible with this technique to separate off both the high-boiling and the low-boiling part in just one step.

Step (b)

Processes for the preparation of 4,4'-dichlorodiphenylsulfone starting from monochlorobenzene are known per se and can be implemented as process steps (b) of the present process. Said step (b) relates to the reaction of the monochlorobenzene obtained in step (a) to give a mixture containing 4,4'-dichlorodiphenyl sulfone (crude product). As by-products of the reaction starting from monochlorobenzene, in particular 2,4'-dichlorodiphenyl sulfone and / or 3,4'-dichlorodiphenyl sulfone are formed (incorrect isomers of 4,4'-dichlorodiphenyl sulfone). In addition, 2-chlorobenzenesulfonic acid, 3-chlorobenzenesulfonic acid and / or 4-chlorobenzenesulfonic acid are generally formed. The abovementioned hydrocarbons having 5 to 8 carbon atoms as secondary components of monochlorobenzene additionally lead to a complex spectrum of colorant compounds in said crude product. Usually, the reaction of monochlorobenzene with a sulfonating agent to form 4-chlorobenzenesulfonic acid. However, this inevitably gives rise to misisomers of 4-monochlorobenzenesulfonic acid as undesirable by-products. Subsequently, the 4-chlorobenzenesulfonic acid and its isomers of 2-chlorobenzenesulfonic acid and / or 3-chlorobenzenesulfonic acid are reacted with monochlorobenzene to 4,4'-dichlorodiphenylsulfone, wherein the above-mentioned false isomers of 4,4'-dichlorodiphenylsulfone are formed. The formation of monochlorobenzenesulfonic acid can also be carried out as an intermediate which is not isolated.

In a preferred first embodiment, the preparation of 4,4'-dichloro-diphenylsulfone by reaction of 4-chlorobenzenesulfonic acid with monochlorobenzene. The reaction is preferably carried out in a countercurrent column, wherein the water of reaction by the aromatics added in gaseous form in the bottom of the column is continuously stripped overhead. For the synthesis of 4,4'-dichlorodiphenyl sulfone, 4-chlorobenzenesulfonic acid or even sulfuric acid can be added at the top of the column. The latter first reacts with monochlorobenzene in the column to form monochlorobenzenesulfonic acid, which subsequently likewise reacts with monochlorobenzene to give dichlorodiphenylsulfone. The corresponding method is described, for example, in US Pat. No. 2,593,001, the content of which is hereby fully incorporated.

In a second preferred embodiment, the preparation of dichlorodiphenylsulfone using SO3, dimethyl sulfate and monochlorobenzene. Preferably, at moderate conditions, SO3 and dimethyl sulfate are first allowed to react in the molar ratio of 2 to 1. Part of the SO3 reacts with dimethyl sulfate to the corresponding pyrosulfate. The remaining SO3 remains dissolved in the resulting liquid. This mixture is then added at temperatures below 100 ° C to 2 mol monochlorobenzene per 2 mol SO3 and 1 mol of dimethyl sulfate. The dissolved SO3, dimethylpyrosulfate and monochlorobenzene give 1 mol of dichlorodiphenyl sulfone and 2 mol of monomethylsulfate. The reaction mixture is then passed into water. It precipitates dichlorodiphenyl sulfone. This is filtered off and dried. The corresponding process is described, for example, in US Pat. No. 2,971,985, the contents of which are hereby fully incorporated by reference.

The person skilled in the art is aware that he can combine the above-described reactions with other work-up methods than those listed above. Step (c)

In the context of step (c) is preferably carried out the separation of 4,4'-dichloro-diphenylsulfone from the mixture obtained in step (b), d. H. the workup of the crude product containing the desired reaction product and by-products.

Suitable processes for working up the crude product are known per se to the person skilled in the art. In one embodiment, the separation of the reaction mixture by addition of water and the separation of the two resulting liquid phases. The aqueous phase contains unreacted monochlorobenzenesulfonic acid. The water is evaporated off and the monochlorobenzenesulphonic acid recovered as starting material. From the organic phase, which consists predominantly of monochlorobenzene and dichlorodiphenyl sulfone, dichlorodiphenyl sulfone can be isolated. A corresponding method is described, for example, in US Pat. No. 4,937,387, the content of which is hereby fully incorporated by reference. The separation of 4,4'-dichlorodiphenyl sulfone from the crude product can be carried out, for example, by chromatography. The separation preferably takes place by recrystallization, as described, for example, in EP 279 387, the contents of which are hereby fully incorporated by reference.

Examples

example 1

According to gas chromatographic separation and subsequent detection by means of flame ionization, the monochlorobenzene used in Example 1 contained the following secondary components: 30 ppm of methylcyclohexane and 10 ppm of methylcyclohexene. 126.1 g (1 mol) of dimethyl sulfate were heated to 70-75 ° C under exclusion of atmospheric moisture and 80.1 g (1 mol) of liquid sulfur trioxide were added at this temperature. The mixture was stirred for 30 minutes at this temperature and then cooled to 20 ° C from. Another 80.1 g (1 mol) of liquid sulfur trioxide was added so that the temperature does not exceed 30 ° C. The reaction mixture was added over 20 minutes to 225.1 g (2 mol) of monochlorobenzene preheated to 50 ° C. The mixture was then stirred at 50 ° C for a further 1 h. After cooling, a yellowish orange solution was obtained.

Example 2

According to gas chromatographic separation and subsequent detection by means of flame ionization, the monochlorobenzene used in Example 2 contained the following secondary components: hydrocarbons having from 5 to 8 carbon atoms in total <1 ppm.

126.1 g (1 mol) of dimethyl sulfate were heated to 70-75 ° C under exclusion of atmospheric moisture and 80.1 g (1 mol) of liquid sulfur trioxide were added at this temperature. The mixture was stirred for 30 minutes at this temperature and then cooled to 20 ° C from. Another 80.1 g (1 mol) of liquid sulfur trioxide was added so that the temperature does not exceed 30 ° C. The reaction mixture was added over 20 minutes to 225.1 g (2 mol) of monochlorobenzene preheated to 50 ° C. The mixture was then stirred at 50 ° C for a further 1 h. After cooling, a pale yellow solution was obtained.

Example 3 (comparative example) 126.1 g (1 mol) of dimethyl sulfate were heated to 70-75 ° C under exclusion of atmospheric moisture and 80.1 g (1 mol) of liquid sulfur trioxide were added at this temperature. The mixture was stirred for 30 minutes at this temperature and then cooled to 20 ° C from. Another 80.1 g (1 mol) of liquid sulfur trioxide was added so that the temperature does not exceed 30 ° C. The reaction mixture was added over 20 minutes to a mixture of 1.68 g (0.02 mol) of cyclohexane and 225.1 g (2 mol) of monochlorobenzene preheated to 50 ° C. (identical to Example 1) C. After cooling, a dark orange solution was obtained.

By the method according to the invention, a crude product of 4,4'-dichlorodiphenyl sulfone is obtained, which has a significantly lower color number and thus a significantly higher purity. The crude product of 4,4'-dichlorodiphenyl sulfone obtained in accordance with the invention can be subjected to known processes for working up and recovering pure 4,4'-dichlorodiphenyl sulfone. The workup can be carried out with less complexity, in particular in which the known methods are carried out faster and / or in a lower repetition number.

Example 4

According to gas chromatographic separation and subsequent detection by flame ionization, the monochlorobenzene used in Example 4 contained the following secondary components: 20 ppm hexane, 20 ppm cyclohexane, 10 ppm methylcyclohexane, 10 ppm bromobenzene and 10 ppm dichlorobenzene.

680 g (8.5 mol) of freshly distilled sulfur trioxide were added to 1914 g (17 mol) monochlorobenzene with the exclusion of atmospheric moisture at a maximum of 45 ° C. The resulting dark gray-brown solution (chlorobenzenesulfonic acid in monochlorobenzene) can be used for the synthesis of dichlorodiphenyl sulfone, for example according to US Pat. No. 2,593,001.

Example 5

The monochlorobenzene used in Example 5 was obtained by additionally adding the monochlorobenzene used in Example 1 subsequently in a batch process.

Distillation column was distilled over P2O5 and thus purified. According to gas chromatographic separation and subsequent detection by means of flame ionization, the monochlorobenzene used in Example 5 contained the following secondary components: hydrocarbons having from 5 to 8 carbon atoms <1 ppm.

680 g (8.5 mol) of freshly distilled sulfur trioxide were added to 1914 g (17 mol) monochlorobenzene with the exclusion of atmospheric moisture at a maximum of 45 ° C. The weakly brown solution (chlorobenzenesulfonic acid in monochlorobenzene) can be used for the synthesis of dichlorodiphenyl sulfone, for example according to US Pat. No. 2,593,001.

Example 6 (comparative example)

To a mixture of 1914 g (17 mol) of monochlorobenzene (identical to Example 5) and 8.4 g (0.1 mol) of cyclohexane 680 g (8.5 mol) of freshly distilled sulfur trioxide were at a maximum of 45 ° C under exclusion of atmospheric moisture added. The resulting solution (chlorobenzenesulfonic acid in monochlorobenzene) was black-brown.

Claims

claims

A process for the preparation of 4,4'-dichlorodiphenylsulfone starting from monochlorobenzene, wherein the content of the monochlorobenzene used in hydrocarbons having from 5 to 8 carbon atoms is at most 100 ppm, based on the total weight of the monochlorobenzene used, including the secondary components.

A process according to claim 1, wherein the content of the monochlorobenzene used in halogenated hydrocarbons having 5 to 8 carbon atoms except monochlorobenzene is at most 50 ppm and the content of the monochlorobenzene used in hydrocarbons having from 5 to 8 carbon atoms is not more than 50 ppm, based on the total weight of monochlorobenzene used the minor components.

A process as claimed in claim 1 or 2, wherein the content of the monochlorobenzene used in hydrocarbons having from 5 to 8 carbon atoms is at most 20 ppm, based on the total weight of the monochlorobenzene used, including the secondary components.

Process according to one or more of claims 1 to 3, wherein the content of the monochlorobenzene used in hydrocarbons having from 5 to 8 carbon atoms is at most 10 ppm, based on the total weight of the monochlorobenzene used, including the secondary components.

Method according to one or more of claims 1 to 4, wherein the monochlorobenzene used has a purity of at least 99.9 wt .-%, based on the total weight of the monochlorobenzene used including the minor components having.

Method according to one or more of claims 1 to 5, wherein the monochlorobenzene used has a purity of at least 99.99 wt .-%.

Method according to one or more of claims 1 to 6, wherein the content of monochlorobenzene used in (cyclo) aliphatic hydrocarbons having 6 or 7 carbon atoms in total not more than 50 ppm, based on the total weight of the monochlorobenzene used, including the secondary components.

Method according to one or more of claims 1 to 7, wherein the content of monochlorobenzene used in (cyclo) aliphatic hydrocarbons having 6 or 7 carbon atoms in total not more than 10 ppm, based on the total weight of the monochlorobenzene used, including the minor components, is.

9. A process for the preparation of 4,4'-dichlorodiphenyl sulfone comprising

(a) Purification of monochlorobenzene to give monochlorobenzene as defined in one or more of claims 1 to 8, and then (b) reacting the monochlorobenzene obtained in step (a) to a mixture containing 4,4'-dichlorodiphenyl sulfone.

10. The method of claim 9, wherein subsequent to step (b) according to step (c), the separation of 4,4'-dichlorodiphenyl sulfone from the mixture obtained according to step (b).

1 1. Process according to claim 9 or 10, wherein the purification of the monochlorobenzene according to step (a) is carried out by distillation.

12. The method according to one or more of claims 9 to 1 1, wherein the purification of the monochlorobenzene according to step (a) is carried out by distillation in a dividing wall column.

13. The use of monochlorobenzene for the preparation of 4,4'-dichlorophenylsulfone, wherein the content of monochlorobenzene of hydrocarbons having 5 to 8 carbon atoms is at most 100 ppm, each based on the total weight of the monochlorobenzene used including the Nebenkom- components.