GB1559907A - Process for preparation aryl sulphone sulphonic acids - Google Patents

Description

(54) IMPROVEMENTS IN PROCESS FOR PREPARING ARYL SULFONE SULFONIC ACIDS (71) We, GENERAL ELECTRIC COM- PANY, a Corporation organized and existing under the laws of the State of New York, United States of America, of 1 River Road, Schnectady 12305, State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is directed to a process for preparing aryl sulfone sulfonic acids by reacting aryl sulfone in the molten state with sulfur trioxide under substantially anhydrous conditions.

Aryl sulfone sulfonic acids are useful as leveling agents for certain nylons and as starting materials for a variety of additives especially flame-retardant additives for polymer systems. The aryl sulfone sulfonic acids have been previously prepared by several different methods as, for example, by the reaction of a phenylsulfone and chlorosulfonic acid or oleum.

Both of these methods, however, have serious drawbacks. When using chlorosulfonic acid, the primary product is the sulfonyl chloride that has to be converted to the acid by an additional hydrolysis step.

This has the disadvantage, not only of requiring additional reagents and an extra reaction step, but it also requires the disposition of the co-product, hydrochloric acid.

Sulfonation by oleum has, of course, the disadvantage of employing large amounts of sulfuric acid, which not only have to be separated from the desired sulfonic acid product, but also have to be disposed of in an ecologically acceptable manner. While these drawbacks of these two sulfonating reagents points to the use of liquid S08 as the desirable reagent, the prior art of sulfonation, as exemplified by Evert Gilbert, "Sulfonation and Related Reactions", Interscience publishers, (1965), requires the use 6f compatible solvents.

The discovery has been made that under carefully controlled conditions, molten aryl sulfone, specifically diphenylsulfone, can be sulfonated directly in the absence of solvent by liquid SO, with the formation of only trace amounts of sulfonic acid, The small amounts of the latter by-product can be quantitatively separated from the arylsulfone sulfonic acids by the use of stoichiometric amounts of barium hydroxide, for example.

Furthermore, and surprisingly, carefully controlled conditions can also lead to diaryl sulfone disulfonic acids, again with minimum amounts of by-product sulfuric acid formation, The avoidance of solvents, few of which are chemically compatible with liquid SO3, not only results in the formation of better product but also leads to economical processes.

The present invention is directed to a process for preparing aryl sulfone sulfonic acids by reacting an aryl sulfone in the molten state with sulfur trioxide under substantially anhydrous conditions.

The aryl sulfone starting materials are of the following formula: R-SO2-R1 wherein R and Rl are independently selected from C1-C1 alkyl, benzyl, aryl of 6 to 14 carbon atoms, or substituted aryl wherein the substituents are Cl, Br, F, C,C. alkyl, C1-C1 alkoxy, aryloxy of 6 to 14 carbon atoms. arylthio of 6 to 14 carbon atoms, nitro, or trifluoromethyl, with the proviso that one of R or Rl is aryl or substituted aryl.

The preferred aryl sulfones include diphenyl sulfone, di(p-tolyl) sulfone; phenyl 4-chlorophenyl sulfone; 4A1- dibromodi- phenyl sulfone; 4-chloro-41-nitrodiphenyl sulfone; 4-chloro-31-(trifluoromethyl) diphenyl sulfone: 4,41-dichlorodiphenyl sulfone; 4,2',41,51-tetrachlorodiphenyl sulfone; 4,41-dichloro-1,1l-dinaphthyl sulfone; methyl phenyl sulfone; and benzyl phenyl sulfone.

The nature of sulfurtrioxide used in the process according to the invention, is not critical and it is possible to use either the liquid stabilized gamma modification of sulfurtrioxide, or even a gaseous mixture containing gaseous sulfurtrioxide, such as obtained in the conversion of SO2 into S03 by oxidation with'air.

The aryl sulfone will determine the reaction temperature since the reaction is carried at or above the melting point of the arcyl sulfone. The absence of solvents in the process allows the use of a wider tem- perature range in the process, since it is not limited by the boiling point of any solvent.

The temperature range may encompass temperature of 25"C to 200"C. Preferably, this temperature range encompasses compounds which melt between 50"C and 1500C.

Since the sulfonation reaction is exothermic, cooling may be required to maintain the reaction within the desired temperature range, Conversely, the rate of introduction of sulfur trioxide may be conducted such- that the desired reaction temperature is maintained.

Pressure is not critical, thus the reaction can be conducted at atmospheric or superatmospheric pressures.

The ratio of S03 to aryl sulfone is determined by whether mono-, di-, or polysulfonation is desired. Since the reaction of arvl sulfone is quantitative- stoichiometric or slight excess of- SO3 is used. When anhydrous conditions are maintained, no by-product sulfuric acid is formed and also, by-product sulfone formation is minimized.

Since at the reaction temperature, the reaction is almost instantaneous, very short reaction times are feasible, and reaction cycles of one or a few hours are thus obtainable.

The workup of the reaction product mixture is best carried out with the use of water, since the sulfonic acid products, but not the starting materials, are water soluble.

Simple filtration, for example, allows separation of the water soluble sulfonic acid and water ' insoluble starting materials. Subsequent workup is determined by the nature of desired product. If, for instance, the neutral- alkali or alkaline earth metal salts of the sulfonic acids are desired, the aqueous phase is simply neutralized by the appropriate base, and the water removed either by distillation or drying or, if the salt is insoluble, then by filtration. If a sulfuric acid-free product is desired, stoichiometric amounts of barium hydroxide are added, which quantitatively precipitates the sulfuric acid as barium sulfate and this is removable by filtration, leaving behind the sulfuric acid-free sulfonic acid product.

The following non-limiting examples illustrate the process of this invention.

EXAMPLE 1 In a I liter, 4-necked flask, equipped with polytetrafluoroethylene stirrer, reflux condenser, 100 ml addition funnel and thermometer dipping into the reaction mixture, is charged 218.3 g (1.0 mole) of pure diphenyl sulfone and heated to its melting point of 125--1270C with the aid of a heating mantle. When all of the fulfone is melted, 128.0 g (1.6 mole) of stabilized, liquid sulfur trioxide is added gradually, while maintaining the temperature of the reaction mixture between 125"C and 1300C by regulating the rates of addition of sulfur trioxide and external heating or cooling. The addition requires about 20-30 minutes, after which heating is continued for an additional 30minute period within the above temperature range. The resultant melt is added to 650 ml of cold water, whereby a white slurry results, which is stirred and filtered, after it is cooled to 250C, through a sintered glass funnel by suction, the filter cake is washed twice with 100 ml portions of water and dried. Its dry weight of 9.17 g. indicates that 95.8% of the sulfone was converted into sulfonic acids. The clear, aqueous filtrate, 1180 g., was analyzed for sulfuric acid content and for the ratio of mono- and disulfonic acids.

Determination of sulfuric acid in the aqueous phase by amperometric titration using lead nitrate as preciptating agent indicated its presence as 0.96% or 11.3 g. or 0.115 mole of sulfuric acid, or 7.2% based on the amount of S03 employed. The monoto disulfonic acid ratio was determined by neutralizing an aliquot of the acid solution by potassium hydroxide, evaporation of water-methanol mixture as diluent. The salt mixture and defining its composition by reverse phase liquid chromatography using water-methanol mixture as dilpent. The dry weight of the neutralized aliquot was equivalent to 381.1 g. of potassium salt of the sulfonic mixture, which was found to consist of 47.6% of potassium diphenyl sulfone-3-sulfonate and 52.4% of dipotassium diphenyl sulfone-3,31-disulfonate. These data indicate that in the sulfonation of one mole of molten diphenyl sulfone by 1.6 mole of liquid SOq, 0.53 mole of mono- and 0.43 mole of disulfonic acids were formed, giving a 96% yield based on the sulfone.

EXAMPLE 2 The. procedure of Example 1 was exactly repeated. except that gaseous instead of liquid S03 was employed. There was no significant. difference either in yield or in product composition.

EXAMPLE 3 The procedure of Example 1 was repeated except that 4-chiorodiphenyl sulfone was used instead of diphenyl sulfone. An over 90% yield of sulfonated products were obtained comprising 76% of 4-chiorodiphenyl sulfone-31-sulfonic acid and 24% of 4chlorodiphenyl sulfone-3,3 1disulfonic acid.

EXAMPLE 4 The procedure of Example 1 was repeated except that methyl phenyl sulfone was used instead of diphenyl sulfone. A 92% yield of methyl phenyl sulfone-3-sulfonic acid was obtained and identified by nmr, ir and liquid chromatorgraphy retention time. No disulfonic acid was detectable.

EXAMPLE 5 The procedure of Example 1 was repeated using 4,21,4l,5l-tetrachlorodiphenyl sulfone in place of diphenyl sulfone. An 87% yield of 4,21,4l,5l-tetrachlorodiphenyl sulfone- 3sulfonic acid was obtained.

ERAMPLE 6 The advantages of the present method over the conventional sulfonation technique using oleum is herein illustrated whereby oleum is used as the sulfonating agent.

Employing 266.8 g. of 30% oleum for one mole of diphenyl sulfone and carrying out the reaction as described in Example 1, there was recovered 31.6 g. of unreacted sulfone, including a maximum yield of only 85% of the theoretical. In addition to the diphenyl sulfonesulfonic acids produced, the reaction mixture also contained 201 g. of sulfuric acid. This required enormous amounts of barium or calcium hydroxide to yield a sulfuric acid-free product.

EXAMPLE 7 To further illustrate the advantage of the present method over a conventional method using solvents, the sulfonation of diphenyl sulfone was carried out in 1,2-dichloroethane solution at 700C. By employing even a 2:1 mole ratio of S03 to diphenyl sulfone, there was realized a maximum of only 80% conversion to sulfonic acids, consisting of 1.7 to 1.0 weight ratio of mono- to disulfonic acid or diphenyl sulfone. Emulsion formation plus the relatively large amounts of solvent required are additional disadvantages of the process.

Obviously, other modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that changes may be made in the particular embodiment described which will be within the full intended scope of the invention as defined by the

Claims (8)

appended claims. WHAT WE CLAIM IS:-

1. A process for preparing aryl sulfone sulfonic acids which comprises reacting an aryl sulfone of the following formula: R-SO2-R1 wherein R and R1 which can be the same or different, are each C1-C15 alkyl, benzyl, aryl of 6 to 14 carbon atoms, or substituted aryl, substituted by C1 Br, F, C1C15 alkyl, -C1 alkoxy, aryloxy of 6 to 14 carbon atoms, arylthio of 6 to 14 carbon atoms, nitro, or trifluoromethyl, with the proviso that at least one of R or R1 is aryl or substituted aryl, in its molten state with sulfur trioxide under substantially anhydrous conditions.

2. A process as claimed in Claim 1, wherein the aryl sulfone is diphenyl sulfone di(p-tolyl) sulfone; phenyl 4-chlorophenyl sulfone; 4,41dibromo-diphenyl sulfone; 4chloro-41-nitrodiphenyl sulfone; 4-chloro-3l- (trifluoromethyl) diphenyl sulfone; 4,41-di- chlorodiphenyl sulfone, 4,2,41,51-tetrachlorodiphenyl sulfone; 4,41-dichloro- 1,11 - dinaphthyI sulfone; methyl phenyl sulfone; or benzyl phenyl sulfone.

3. A process as claimed in Claim 1 or 2, wherein the sulfur trioxide is in liquid form.

4. A process as claimed in Claim I or 2, wherein the sulfur trioxide is in gaseous form.

5. A process as claimed in any preceding claim, wherein reaction is carried out at a temperature of from 25 to 2000 C.

6. A process as claimed in Claim 5, wherein the temperature is from 50 to 1500C.

7. A process as claimed in Claim 1, substantially as hereinbefore described with reference to any of Examples 1 to 5.

8. Aryl sulfone sulfonic acids when prepared by a process as claimed in any of the preceding claims.