FIELD OF INVENTION

The invention is generally related to a method of making a sulfonic group-containing aromatic compound.

BACKGROUND OF THE INVENTION

Proton exchange membrane full cell (PEMFC) is a highly efficiency and low-pollution generating set using hydrogen as fuel and oxygen as oxidant. The main components of a PEMFC include a proton exchange membrane, a Pt catalyst, a fluid flow plate and a cooling plate. The examples of the commercially available proton exchange membranes are perfluorosulfonic acid membranes, such as Nafion membrane from DuPont company, Dow membrane from Dow company, Aciplex membrane from Asahi Kasei company and Flemion membrane from Asahi Glass company. The Perfluorosulfonic acid membranes have good comprehensive properties, such as chemical stability, remarkable mechanical strength, high proton conductivity at a high humidity, large current density at a low temperature, and higher oxygen reduction rate than other acidic electrolytes. However, the development and application of PEMFC is greatly limited by the high price of perfluorosulfonic acid membranes caused by its complex preparation process and technological monopoly. The proton conductivity of a perfluorosulfonic acid membrane heavily depends on the water content of the membrane, so the proton conductivity decreases at a low humidity, and at elevated temperatures over than 100°C because of dehydration. In addition to the above, other drawbacks, such as potential environmental damages of fluorine element in the case of the membrane decomposing, and of leaking of methanol used as fuel, also limit the application fields of the perfluorosulfonic acid membranes. For effective and extensive applications, the development of a highly efficient, low cost and environmentally friendly polymer useful as a proton exchange membrane without the above problems is highly desired.

All the aromatic polymers are believed to be ones of the most promising compounds useful for high performance proton exchange membranes because of their availability, processability, wide variety in chemical composition, and expectable stability in a fuel cell environment. Especially, poly(arylene ether) materials such as poly(ether ether ketone) (PEEK), poly(ether ether sulfone) (PEES) and their derivatives are the focus of many investigations, and the synthesis of these materials has been widely reported. There are two ways to introduce an active proton exchange site to PEEK, i.e., post-sulfonation approach and direct copolymerization of sulfonated monomers. Sulfonated poly (ether ether ketone) (SPEEK) can be easily prepared by post-sulfonation using a sulfonating agent, such as fuming sulfuric acid, sulfur trioxide-phosphoric ether, chlorosulfonic acid (see Journal of Membrane Science, 372 (2011), p40-48 ; Journal of Membrane Science, 350 (2010), pl48-153 ; Polymer, 50 (2009), p2664-2673). SPEEK can also be obtained via nucleophilic aromatic substitution condensation polymerization of sulfonated dihalide ketone monomer, dihalide ketone monomer and bisphenol monomer (see Journal of Membrane Science, 234 (2004), p75-81 ; CN1680457A; CN101463129A).

Although the post-sulfonation process is simple, easy to perform and low cost, and polymers prepared thereby generally have high molecular weights and are easy to prepare a membrane, a sulfonic acid group is usually introduced into the position of ortho to the activated aromatic ether linkage of the polymer, and the sulfonic acid group is thus relatively easy to be hydrolyzed. As a result, introduction of only one sulfonic acid per repeat unit can be achieved. On the other hand, in a direct copolymerization process, SPEEK with a higher sulfonation degree and better stability can be obtained and the sulfonation degree can be controlled by adjusting the molar ratio of the monomers for the SPEEK. For the above advantages, there is an increasing tendency to use a direct copolymerization process to synthesize SPEEK.

The sulfonation degree of SPEEK obtained through direct copolymerization is greatly affected by sulfonation degree of the monomer as used, that is, a polymer with a higher sulfonation degree can be obtained if the monomer as used has more sulfonic groups. At present, disodium 5,5'-carbonylbis(2-fluorobenzenesulfonate) and disodium 3,3'-disulfonated-4,4'- dichlorodiphenyl sulfone having the following formulas are most used as a functional monomer for synthesis of SPEEK and sulfonated PEES (SPEES).

Disodium 3,3-Disulfonated-4,4-dichlorodiphenyl sulfone

Due to the limitation of sulfonic group content of a monomer for SPEEK, it has been very difficult to produce SPEEK with a higher sulfonation degree from the monomer. Summary of the Invention

The invention provides a method of making a sulfonic group-containing aromatic compound. By using the method, multi-substituted sulfonated aromatic compounds can be obtained, which are very important monomers necessary for preparing sulfonated poly(ether ether ketone)s (SPEEKs) with higher sulfonation degrees.

The purpose of the invention can be achieved through the following measures: A method of making a sulfonic group-containing aromatic compound comprising reacting an aromatic compound having the following formula (Ml) with fuming sulfuric acid, wherein the reaction is carried out at 120°C to 250°C in a closed system under an elevated pressure; and wherein the grou -containing aromatic compound have the following formula (M2):

In the formulas (Ml) and (M2), X is one of a ketone group, a sulfone group, a direct linkage, -POCR ¹ )- (where R ¹ is any organic group), -(CF ₂ ) _f - (where f is an integer from 1 to 5) or -C(CF ₃ ) ₂ -; Y is at least one kind of F, CI, Br or I; m is 0 or 1 ; n is 0 or 1 ; M is a metal cation or an ammonium cation.

From the view of chemical point, R ¹ is preferably at least one kind of hydroxyl, carboxyl, amino, halogen, alkyl, cycloalkyl, alkenyl, cycloalkene, aryl, silyl, ester group, oxyalkyl, oxyaryl or their derivatives. From the view of structure stability, R ¹ is more preferably at least one kind of alkyl with C1-C10, cycloalkyl with C3-C10, aryl, sulfonic group-containing aryl, oxyalkyl with C1-C10, oxyaryl, sulfonic group-containing oxyaryl or their derivatives. From the view of difficulty to obtain the compounds, R ¹ is particularly preferable at least one kind of aryl, sulfonic group-containing aryl or their derivatives. Sulfonic group-containing phenyl is most preferred.

M is a metal cation or an ammonium cation, wherein the metal cation is preferably at least one ion of sodium, potassium, aluminum, magnesium, calcium, copper, nickel, cobalt, lead, zinc, tin, antimony, bismuth, silver, platinum, ruthenium, rhodium, palladium, osmium, tungsten, molybdenum, tantalum, niobium, zirconium, hafnium, vanadium, titanium, indium, thallium, germanium, selenium or tellurium. From the view of the cost and availability of the starting compound, sodium, potassium, aluminum, magnesium, calcium, copper, zinc or silver are more preferred. In the method of making a sulfonic group-containing aromatic compound according to the present invention, the reaction is carried out at 120°C to 250°C in a closed system and under an elevated pressure. In the closed system with pressure, vaporization of sulfuric trioxide in fuming sulfuric acid can be prevented; on the other hand, the collision between reaction molecules can be increased and the reaction efficiency can thus be improved.

If the reaction temperature is lower than 120°C, the desired reaction scarcely proceeds, and if the temperature is higher than 250°C, thermal decomposition of the raw material and the reaction product may occur. In the method according to the present invention, the reaction time is directly correlated with the reaction temperature, and is therefore not particularly limited. Less reaction time is needed at a higher temperature, and much reaction time is required at a lower temperature. The reaction time should be controlled such that the sulfonic group-containing aromatic compound having the formula (M2) can be obtained. The reaction time is preferably in the range of 1 to 48 hrs. If the time is shorter than 1 hr, it may be difficult to obtain the desired compound; on the other hand, if the reaction time is more than 48 hrs, the side reactions such as decomposition reaction of the reaction product may occur.

In the method according to the present invention, the closed system is a pressure-resistant, heat-resistant and corrosion-resistant sealed container, and is preferably an autoclave lined with polytetrafluoroethene (PTFE).

In the method according to the present invention, the reaction pressure should be higher than a normal atmosphere. It will be hard to obtain the sulfonic group-containing aromatic compound having the formula (M2) under a normal atmosphere. In the method according to the present invention, there are no limitations on the upper limit of the reaction pressure. However, from the viewpoint of reaction safety, the higher the reaction pressure, the more dangerous the reaction is. In view of that the sulfur trioxide used in the method has high causticity, and considering the cost of equipment, the reaction pressure is preferably in a range of 0.12 MPa to 5.0 MPa, and more preferably 0.15 MPa to 3.0 MPa, and particularly preferably 0.4 MPa to 2.9 MPa, and most preferably 2.4 MPa to 2.9 Mpa.

In the method according to the present invention, the concentration of sulfur trioxide in fuming sulfuric acid is 20% to 65% by weight. A fuming sulfuric acid having a concentration of sulfur trioxide in the range of 20% to 65% by weight is commercially available.

In the method according to the present invention, from the view of the difficulty of occurrence of substitution reaction, the sulfonic group-containing aromatic compound of formula (Ml) preferably has the formula (M3) as shown below:

In the formula (M3), X is one of a ketone group, a sulfone group, a direct linkage, -POCR ¹ )- (where R ¹ is any organic group), -(CF ₂ ) _f - (where f is an integer from 1 to 5) or -C(CF ₃ ) ₂ -; Y is at least one kind of F, CI, Br or I; m is 0 or 1 ; n is 0 or 1 ; M is a metal cation or an ammonium cation.

From the view of availability of the starting compound, X is preferably one kind of a ketone group, or a sulfone group. From the view of the reactivity, Y is preferably at least one kind of F, or CI.

From the view of structure stability, R ¹ is further preferably at least one kind of alkyl with C1-C10, cycloalkyl with C3-C10, aryl, sulfonic group-containing aryl, oxyalkyl with C1-C10, oxyaryl, sulfonic group-containing oxyaryl or their derivatives. Further, taking the availability of the starting compound into consideration, at least one kind of aryl, sulfonic group-containing aryl or their derivatives is preferred.

M is a metal cation or an ammonium cation. In view of the cost and availability of the starting compound, sodium, potassium, aluminum, magnesium, calcium, copper, zinc or silver are preferred.

From the view of the cost and reactivity, the resulting sulfonic group-containing aromatic compound particularly preferably has the formula (M4) as shown below:

In the formula (M4), M is a metal cation or an ammonium cation.

M is preferable as described above.

In the present invention, in addition to the step of reacting an aromatic compound having the formula (Ml) with fuming sulfuric acid, the method of making a sulfonic group-containing aromatic compound having the formula (M2) further comprises the steps (1) to (3):

( 1 ) reacting an aromatic compound having the formula (Ml) with fuming sulfuric acid, and then neutralizing the reaction mixture, and removing the solvent therein;

( 2 ) redissolving the reaction mixture obtained from the step (1) with a solvent, removing the undissolved matter in the reaction mixture, and then removing the solvent;

( 3 ) recrystallizing the reaction mixture obtained from the step (2) in a solvent.

During the method of reacting an aromatic compound having the formula (Ml) with fuming sulfuric acid to form a sulfonic group-containing aromatic compound having the formula (M2), sulfuric trioxide in the fuming sulfuric acid plays a major role, so the structure of the final product is greatly affected by the equivalent ratio of sulfur trioxide in the fuming sulfuric acid to the aromatic compound having the formula (Ml). The equivalent ratio of sulfur trioxide in the fuming sulfuric acid to the aromatic compound having the formula (Ml) is 2-30: 1. If the equivalent ratio is lower than 2: 1, a sulfonic group-containing aromatic compound having the formula (M2) may not be obtained. On the other hand, if the equivalent ratio is higher than 30: 1, the concentration of sulfur trioxide is too high, and may not be favorable for the post treatment of the reaction product.

During the synthesis method of a sulfonic group-containing aromatic compound having the formula (M2), fuming sulfuric acid is used as the raw materials, and therefore, when the reaction is completed, the reaction system is acidic. Thus, the system is firstly neutralized with a base until the pH value thereof reaches to 7.0-7.5. In the method according to the present invention, the base used for neutralizing is at least one kind of alkali metal hydroxide, alkali metal carbonate, alkali metal bicarbonate or ammonia. In view of the cost and availability thereof, the base is preferably at least one kind of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate or ammonia water.

In the method of making a sulfonic group-containing aromatic compound according to the present invention, the solvent used for redissolving in the step (2) is at least one kind of dimethyl sulfoxide, thionyl chloride, 4,4'-diaminodiphenyl sulfone, 4,4'-sulfonyl diphenol, 4,4'-dimethyl diphenyl sulfoxide, sulfolane, diphenyl sulfone or phenyl sulfoxide. From the view of the properties, cost and toxicity of the solvent, dimethyl sulfoxide is most preferred.

In the method of making a sulfonic group-containing aromatic compound according to the present invention, removal of the dissolved matter in the step (2) is achieved through precipitation and separation processes of the sulfone solution of the reaction product. In the precipitation process, the sulfone solution of the reaction product is precipitated in an alcohol or ketone solvent. The alcohol solvent is at least one kind of methanol, ethanol, isopropanol, n-propanol, n-butanol, tertiary butyl alcohol, isopropyl alcohol, n-butyl alcohol, isoamyl alcohol, amyl alcohol, tertiary amyl alcohol, cyclopentanol, hexanol, octanol, cyclohexanol, octanol, decanol, or benzyl alcohol; the ketone solvent is at least one kind of acetone, methyl ethyl ketone, methyl amyl ketone, methyl isopropyl ketone, methyl isobutyl ketone or cyclohexanone. Considering the properties, cost and toxicity of the solvent, the alcohol solvent is preferably at least one kind of methanol or ethanol, and the ketone solvent is preferably acetone. The separation process is usually a filtration or centrifugation process.

In the method of making a sulfonic group-containing aromatic compound according to the present invention, removal of the solvent in the step (2) is a drying process, which is carried out at 100 to 150°C for 6 to 72 hrs. To completely remove the residual solvent and water in the reaction product, the drying process is preferably carried out in vacuum condition.

In the method of making a sulfonic group-containing aromatic compound according to the present invention, recrystallizing in the step (3) is carried out at 4 to 25 °C in deionized water or a mixture of deionized water and an alcohol or ketone solvent, the volume ratio of alcohol or ketone and deionized water in the mixture is 0 to 4:1

According to the present invention, it is provided a method of making a sulfonic group-containing aromatic compound. By using the method, a tetra-substituted sulfonated aromatic compound can be obtained, which is an important monomer necessary for preparing sulfonated poly(ether ether ketone)s (SPEEKs) with higher sulfonation degree, which can be widely used in the fields of fuel cell or water treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the ^-NMR spectrum of the reaction product of Example 1.

Figure 2 shows the ^-NMR spectrum of the reaction product of Example 6. Figure 3 shows the ^-NMR spectrum of the reaction product of Example 9. Figure 4 shows the ^-NMR spectrum of the reaction product of Comparative Example 1.

Figure 5 shows the ^-NMR spectrum of the reaction product of Comparative

Example 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is further described in details by reference to the examples set forth below. The following examples are provided to illustrate the present invention, and are not intended to limit the scope of the invention described in this application.

Raw materials used in the Examples:

(a) 4,4' -Difluorobenzophene purchased from Aladdin-reagent Co. :

(b) 4,4'-Dichlorobenzophene purchased from Aladdin-reagent Co.:

(c) 4,4'-Dibromobenzophene purchased from Aladdin-reagent Co.:

(d) Sodium 5,5'-carbonylbis(2-fluorobenzenesulfonate) synthesized according to the m 54A:

(e) Fuming sulfuric acid (H ₂ S0 ₄ /S0 ₃ ): a fuming sulfuric acid solution with a sulfur trioxide concentration of 20% by weight was purchased from Sinopharm Chemical Reagent Co; a fuming sulfuric acid solution with a sulfur trioxide concentration of 50% by weight from Sinopharm Chemical Reagent Co; a fuming sulfuric acid solution with a sulfur trioxide concentration of 65% by weight from Aladdin-reagent Co.

(f) Organic solvents: dimethyl sulfoxide (DMSO), methanol, ethanol and acetone were purchased from Sinopharm Chemical Reagent Co.

(g) Base: sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate and ammonia water were purchased from Sinopharm Chemical Reagent Co.

The structures of sulfonated products obtained in the Examples and the Comparative Examples were analyzed and characterized by H-Nuclear magnetic resonance (NMR): ECX-400p JEOL, 400MHZ, DMSO-^ as solvent.

Example 1

(1) 4,4'-Difluorobenzophenone (22.9 mmol) and fuming sulfuric acid with a sulfur trioxide concentration of 50% by weight containing 126.1 mmol S0 ₃ were placed in an autoclave, and reacted at 175°C and under a pressure of 0.15 MPa for 16 hrs. After the reaction finished, the reaction mixture was poured into deionized water, and then neutralized with sodium hydroxide until the pH value thereof reached to 7.0, and then a crude product was obtained by vaporizing the mixture solution.

(2) The crude product obtained from the step (1) was entirely dissolved in DMSO and the undissolved matter was separated by centrifugation. The DMSO solution of reaction product was precipitated in ethanol, and filtered and dried at 120°C in vacuum for 24 hrs, the resulting product was obtained.

(3) The product obtained in the step (2) was recrystallized in a mixture of ethanol and deionized water (volume ratio of 2: 1) and purified 4,4'-difluoro-3,3',5,5'- tetrasulfonate benzophenone-tetrasodium was obtained and its structure was determined by NMR (as shown in Figure 1)

Example 2

(1) 4,4'-Dichlorobenzophene (25 mmol) and fuming sulfuric acid with a sulfur trioxide concentration of 65% by weight containing 150 mmol S0 ₃ were placed in an autoclave, and reacted at 200°C and under a pressure of 0.9 MPa for 6 hrs. After the reaction finished, the reaction mixture was poured into deionized water, and then neutralized with sodium carbonate until the pH value thereof reached to 7.1, and then a crude product was obtained by vaporizing the mixture solution.

(2) The crude product obtained from the step (1) was entirely dissolved in DMSO and the undissolved matter was separated by centrifugation. The DMSO solution of the reaction product was precipitated in methanol, and filtered and dried at 100°C in vacuum for 72 hrs, the resulting product was obtained.

(3) The product obtained in the step (2) was recrystallized in a mixture of ethanol and deionized water (volume ratio of 3: 1) and purified 4,4'-dichloro-3,3',5,5'- tetrasulfonate benzophenone-tetrasodium was obtained and its structure was determined by NMR.

Example 3

(1) 4,4'-4,4'-Dibromobenzophene (26.7 mmol) and fuming sulfuric acid with a sulfur trioxide concentration of 50% by weight containing 260 mmol S0 ₃ were placed in an autoclave, and reacted at 165°C and under a pressure of 0.7 MPa for 22 hrs. After the reaction finished, the reaction mixture was poured into deionized water, and then neutralized with sodium bicarbonate, until the pH value thereof reached to 7.0, and then a crude product was obtained by vaporizing the mixture solution.

(2) The crude product obtained from the step (1) was entirely dissolved in DMSO and the dissolved matter was separated by centrifugation. The DMSO solution of the reaction product was precipitated in methanol, and filtered and dried at 110°C in vacuum for 48 hrs, the resulting product was obtained.

(3) The product obtained in the step (2) was recrystallized in a mixture of ethanol and deionized water (volume ratio of 1 : 1) and purified 4,4'-dibromo-3,3',5,5'- tetrasulfonate benzophenone-tetrasodium was obtained and its structure was determined by NMR. Example 4

(1) 4,4'-Difluorobenzophenone (22.9 mmol) and fuming sulfuric acid with a sulfur trioxide concentration of 50% by weight containing 190 mmol S0 ₃ were placed in an autoclave, and reacted at 200°C and under a pressure of 1.6 MPa for 6 hrs. After the reaction finished, the reaction mixture was poured into deionized water, and then neutralized with potassium hydroxide until the pH value threof reached to 7.4, and then a crude product was obtained by vaporizing the mixture solution.

(2) The crude product obtained from the step (1) was entirely dissolved in DMSO and the undissolved matter was separated by centrifugation. The DMSO solution of the reaction product was precipitated in acetone, and filtered and dried at 150°C in vacuum for 6 hrs, the resulting product was obtained.

(3) The product obtained in the step (2) was recrystallized in a mixture of ethanol and deionized water (volume ratio of 2.7:1) and purified 4,4'-difluoro-3,3',5,5'- tetrasulfonate benzophenone-tetrapotassium was obtained and its structure was determined by NMR.

Example 5

(1) 4,4'-Difluorobenzophenone (45 mmol) and fuming sulfuric acid with a sulfur trioxide concentration of 50% by weight containing 495 mmol S0 ₃ were placed in an autoclave, and reacted at 200°C and under a pressure of 2.4 MPa for 6 hrs. After the reaction finished, the reaction mixture was poured into deionized water, and then neutralized with potassium carbonate until the pH value thereof reached to 7.1, and then a crude product was obtained by vaporizing the mixture solution.

(2) The crude product obtained from the step (1) was entirely dissolved in DMSO and the undissolved matter was separated by centrifugation. The DMSO solution of the reaction product was precipitated in methanol, and filtered and dried at 120°C in vacuum for 36 hrs, the resulting product was obtained.

(3) The product obtained in the step (2) was recrystallized in a mixture of methanol and deionized water (volume ratio of 1 :1) and purified 4,4'-difluoro- 3,3',5,5'-tetrasulfonate benzophenone-tetrapotassium was obtained and its structure was determined by NMR.

Example 6

(1) 4,4'-Difluorobenzophenone (50 mmol) and fuming sulfuric acid with a sulfur trioxide concentration of 20% by weight containing 1500 mmol S0 ₃ were placed in an autoclave, and reacted at 150°C and under a pressure of 2.9 MPa for 24 hrs. After the reaction finished, the reaction mixture was poured into deionized water, and then neutralized with potassium bicarbonate until the pH value thereof reached to 7.0, and then a crude product was obtained by vaporizing the mixture solution.

(2) The crude product obtained from the step (1) was entirely dissolved in DMSO and the undissolved matter was separated by centrifugation. The DMSO solution of the reaction product was precipitated in methanol, and filtered and dried at 120°C in vacuum for 20 hrs, the resulting product was obtained.

(3) The product obtained in the step (2) was recrystallized in a mixture of ethanoland deionized water (volume ratio of 3.2: 1) and purified 4,4'-difluoro- 3,3',5,5'-tetrasulfonate benzophenone-tetrapotassium was obtained and its structure was determined by NMR (as shown in Figure 2).

Example 7

(1) 4,4'-Difluorobenzophenone (25 mmol) and fuming sulfuric acid with a sulfur trioxide concentration of 50% by weight containing 140 mmol S0 ₃ were placed in an autoclave, and reacted at 250°C under a pressure of 0.5 MPa for 1 hr. After the reaction finished, the reaction mixture was poured into deionized water, and then neutralized with sodium hydroxide until the pH value thereof reached to 7.0, and then a crude product was obtained by vaporizing the mixture solution.

(2) The crude product obtained from the step (1) was entirely dissolved in DMSO and the undissolved matter was separated by centrifugation. The DMSO solution of the reaction product was precipitated in methanol, and filtered and dried at 120°C in vacuum for 16 hrs, the resulting product was obtained.

(3) The product obtained in the step (2) was recrystallized in a mixture of ethanol and deionized water (volume ratio of 2.1 :1) and purified 4,4'-difluoro-3,3',5,5'- tetrasulfonate benzophenone-tetrasodium was obtained and its structure was determined by NMR.

Example 8

(1) 4,4'-Difluorobenzophenone (25 mmol) and fuming sulfuric acid with sulfur trioxide concentration of 50% by weight containing 275 mmol S0 ₃ were placed in an autoclave, and reacted at 175°C for 16 hrs and under a pressure of 0.4 MPa. After the reaction finished, the reaction mixture was poured into deionized water, and then neutralized with ammonia water until the pH value thereof reached to 7.3, and then a crude product was obtained by vaporizing the mixture solution.

(2) The crude product obtained from the step (1) was entirely dissolved in DMSO and the dissolved matters was separated by centrifugation. The DMSO solution of the reaction product was precipitated in acetone, and filtered and dried at 120°C in vacuum for 24 hrs, the resulting product was obtained.

(3) The product obtained in the step (2) was recrystallized in a mixture of ethanol and deionized water (volume ratio of 2: 1) and purified 4,4'-difluoro-3,3',5,5'- tetrasulfonate benzophenone-tetraammonium was obtained and its structure was determined by NMR. Example 9

(1) Sodium 5,5'-carbonylbis(2-fluorobenzenesulfonate) (25 mmol) and fuming sulfuric acid with a sulfur trioxide concentration of 50% by weight containing 50mmol S0 ₃ were placed in an autoclave, and reacted at 200°C and under a pressure of 0.4 MPa for 12 hrs. After the reaction finished, the reaction mixture was poured into deionized water, and then neutralized with sodium hydroxide until the pH value thereof reached to 7.1, and then a crude product was obtained by vaporizing the mixture solution.

(2) The crude product obtained from the step (1) was entirely dissolved in DMSO and the undissolved matter was separated by centrifugation. The DMSO solution of the reaction product was precipitated in acetone, and filtered and dried at 120°C in vacuum for 24 hrs, the resulting product was obtained.

(3) The product obtained in the step (2) was recrystallized in deionized water, and purified 4,4'-difluoro-3,3',5,5'- tetrasulfonate benzophenone- tetrasodium was obtained and its structure was determined by NMR (as shown in Figure 3). Example 10

(1) 4,4'-Difluorobenzophenone (25 mmol) and fuming sulfuric acid with a sulfur trioxide concentration of 65% by weight containing 200 mmol S0 ₃ were placed in an autoclave, and reacted at 120°C and under a pressure of 3.0 MPa for 48 hrs. After the reaction finished, the reaction mixture was poured into deionized water, and then neutralized with sodium hydroxide until the pH value thereof reached to 7.1, and then a crude product was obtained by vaporizing the mixture solution.

(2) The crude product obtained from the step (1) was entirely dissolved in DMSO and the undissolved matter was separated by centrifugation. The DMSO solution of the reaction product was precipitated in acetone, and filtered and dried at 110°C in vacuum for 20 hrs, the resulting product was obtained.

(3) The product obtained in the step (2) was recrystallized in deionized water and purified 4,4'-difluoro-3,3',5,5'-tetrasulfonate benzophenone- tetrasodium was obtained and its structure was determined by NMR.

Comparative Example 1

(1) 4,4'-Difluorobenzophenone (25 mmol) and fuming sulfuric acid with a sulfur trioxide concentration of 50% by weight containing 800 mmol S0 ₃ were placed in a 3-neck flask, and reacted at 200°C under a normal atmosphere for 6 hrs. After the reaction finished, the reaction mixture was poured into deionized water, and then neutralized with sodium hydroxide until the pH value thereof reached to 7.1, and then a crude product was obtained by vaporizing the mixture solution.

(2) The crude product obtained from the step (1) was entirely dissolved in DMSO and the undissolved matter was separated by centrifugation. The DMSO solution of the reaction product was precipitated in ethanol, and filtered and dried at 120°C in vacuum for 12 hrs, the resulting product was obtained.

(3) The product obtained in the step (2) was recrystallized in a mixture of ethanol and deionized water (volume ratio of 2: 1) and purified disodium 5,5'-carbonyl bis(2-fluorobenzenesulfonate) was obtained and its structure was determined by NMR (as shown in Figure 4). Comparative Example 2

(1) 4,4'-Difluorobenzophenone (25 mmol) and fuming sulfuric acid with a sulfur trioxide concentration of 50% by weight containing 200 mmol S0 ₃ were placed in an autoclave, and reacted at 260°C and under a pressure of 0.5 MPa for 50 hrs. After the reaction finished, the reaction mixture was poured into deionized water, and then neutralized with sodium hydroxide until the pH value thereof reached to 7.4, and then a crude product was obtained by vaporizing the mixture solution.

(2) The crude product obtained from the step (1) was entirely dissolved in DMSO and the undissolved matter was separated by centrifugation. The DMSO solution of the reaction product was precipitated in ethanol, and filtered and dried at 120°C in vacuum for 12 hrs, the resulting product was obtained.

(3) The product obtained in the step (2) was recrystallized in a mixture of ethanol and deionized water (volume ratio of 2: 1). No crystallization occurred, and the structure of the product obtained in the step (2) was characterized by NMR (as shown in Figure 5). The result reveals that the product is not 4,4'-difluoro- 3,3',5,5'-tetrasulfonate benzophenone-tetrasodium, and may be a decomposition product of an unknown structure. Comparing the products obtained in the Examples and the Comparative

Examples, it can be seen that according to the invention, multi-substituted sulfonated aromatic compounds can be obtained by reacting an aromatic compound with fuming sulfuric acid having a sulfur trioxide concentration of 20% to 65% by weight at 120°C to 250°C in a closed system under an elevated pressure. Multi-substituted sulfonated aromatic compounds are important monomers necessary for preparing sulfonated poly(ether ether ketone)s (SPEEKs) with higher sulfonation degrees.