Background of the Invention

1. Field of the invention

The present invention refers to a new and useful proc¬ ess for the preparation of para sulfonated calixarenes. In particular, the invention relates to a process for the preparation of calixarene p-sulfonic acids starting from calixarenes which are para substituted by a blocking group, e.g. p-alkyl calixarenes.

Calixarenes are macrocyclic phenolic compounds that are generally prepared from phenolic compounds by condensa¬ tion in an acid or basic environment with an aldehyde such as formaldehyde, an alkylaldehyde, an arylaldehyde, or a heteroarylaldehyde, preferably formaldehyde. These macro- cycles which are shortly named "calixarenes" are of the type of tetra-p-tert-butyl-calix[4] arenes or pentacyclo- [19.3.l. ¹³ < ⁷ .l ⁹ _' ¹³ .l ¹⁵ < ¹⁹ ]octacosa-l (25) ,3,5,7(28) ,9,11,13- (27) , 15, 17, 19 (26) , 21, 23-dodecaene and their analogous com- pounds, namely the [5] , [6] , [7] , [8] , [9] and [10] arene analogues .

The utility of the calixarenes is based on their capa¬ bility of forming complexes, adducts and/or inclusion com¬ pounds with neutral or ionic organic and inorganic com- pounds; furthermore, calixarenes are outstandingly stable

and resistant to high temperatures and chemical attacks in aggressive environments .

A serious problem which is encountered in the indus¬ trial application of these macrocycles stems from their in- solubility in protic solvents such as water and the alco¬ hols . One possibility of overcoming this problem and to make them soluble is to introduce solubilizing groups, preferably sulfonic acid groups, in the para position to the hydroxy groups in the phenolic nuclei, giving sul- fonated calixarenes. Such water soluble calixarene deriva¬ tives have proven to be useful in a great number of fields, especially in pharmacology, and still more application fields are currently opened, such as catalysts or catalyst intermediates .

2 . Description of the Prior Art

Sulfonation of calixarenes that are unsubstituted in the para position of the phenolic OH group has already be¬ come known, see, e.g., Japanese patent No. 61-083156 to Sugai Chemical Industry Co. Ltd. However, calixarenes must be prepared from para substituted phenols where this para substituent is a blocking group to render the para position inaccessible; otherwise, a free para position of the phenol does not yield appreciable amounts of calixarenes during reaction with aldehydes but rather the well known phenolic resins. Therefore, it is necessary in the synthesis of calixarenes to start from para substituted phenols. Of course, such starting phenols are preferred where the para blocking substituent is rather easily removable; such sub- stituents are, e.g., alkyl groups such as the tert-butyl group.

Until now, sulfonation of para alkyl substituted calixarenes has been effected by a multistep process. First, the para alkylated calixarene is prepared which is then dealkylated by an reversed Friedel-Crafts reaction to yield the para unsubstituted calixarenes. In a further step, the calixarene is reacted with hot concentrated sul- furic acid.

Summary of the Invention

A first and major objective of the present invention is to develop and to provide an improved process for the preparation of p-sulfonated calixarenes starting from p- alkylated calixarenes which avoids the drawbacks of the known multistage method; these drawbacks are mainly: low yield of the final product, necessity of using special rea- gents for dealkylation, of working in an anhydrous medium, of conducting an intermediate isolation and sometimes puri¬ fication step, and waste of time.

Another object of the invention is to provide such a preparation process which gives high yields and which does not normally require a special purification of the sul¬ fonated calixarenes to be obtained.

These objects are now met by the new process which comprises a one-step reaction of para substituted calixare¬ nes with a sulfonating agent and the recovering of the calixarene sulfonic acids directly from the reaction mix¬ ture.

It has been highly surprising that the simultaneous dealkylation and sulfonation could be obtained, according to the invention, in one step and with a sulfonating agent

O 97/49677 PC17IB97/00769

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only; the one skilled in the art would have expected an electrophilic substitution reaction of one or more of the free hydrogen atoms of the p-substituted calixarenes and never an ipso-electrophilic substitution on the para carbon atoms which carry the blocking substituent.

A preferred sulfonating agent is concentrated sulfuric acid. However, other known sulfonating agents may also be used.

The reaction is preferably carried out at a tempera- ture that should not substantially exceed 80 °C in order to avoid secondary reactions. The time period of the reaction is about 2 to 4 hours. After this time, the reaction mix¬ ture is cooled down and filtered, in a manner which will be described below, in order to eliminate the excess of sui¬ fonating agent and unreacted starting calixarene.

Preferably, the process is conducted in such a manner that, at the beginning of the reaction, the molar ratio of sulfuric acid to p-substituted calixarenes is essentially selected to the stcechiometric one in order to avoid losses of the valuable sulfonated product during processing after the sulfonation. It should however be noted that the sul¬ fonating agent, i.e. concentrated sulfuric acid, does addi¬ tionally act as a solvent for the rection products. Thus, an excess is to be added over the stoechiometric amount, and the minimum volume of sulfuric acid to be used will be different for each calixarene species. However, if the re¬ action time is increased, a substantially complete trans¬ formation into calixarene sulfonic acids can be achieved.

The process of the invention can thus be summarized by the following reaction scheme:

n = 1,2, 3, 4, 5, 6, etc. n= 1.2, 3, 4, 5,6, etc...

These and other objects and features of the invention will be better understood by reference to the detailed de¬ scription which follows.

Detailed Description of the Invention

As to the recovery of the sulfonated products already summarily described above, the reaction mixture, comprising sulfonating agent (typically sulfuric acid) , sulfonated calixarene and unsulfonated, residual calixarene, is cooled down or allowed to cool to room temperature. The heteroge¬ neous reaction mixture is then filtered and smoothly com¬ pressed on the filter in order to eliminate most of the ex¬ cess sulfonating agent, i.e. sulfuric acid; the acidic fil¬ trate is put aside. The solid residue, comprising sul- fonated calixarene, unreacted, residual starting calix¬ arene, and traces of sulfonating agent, is very rapid washed with a very small volume of cold ethanol in order to remove said traces of sulfonating agent. The corresponding filtrate is put aside. The washed filter residue is sus- pended at room temperature in methanol and filtered to ob¬ tain a second, purified residue that is constituted by un¬ reacted calixarene.

The methanolic filtrate is concentrated, discolored by means of active charcoal and then poured into excess ethyl

acetate under stirring. The cream white precipitate is filtered, the residue is dried during several hours in vacuo at 30 to 40 °C. The analyses of the sulfonated ca¬ lixarenes thus obtained are in conformity with literature values with the exception that they contain less water. The absence of free sulfuric acid is made by barium sulfate precipitation in a test solution of the sulfonated calix¬ arenes to which a barium chloride solution is added.

The unreacted calixarene derivative may be recycled to another, new reaction batch.

The following Examples further illustrate the inven¬ tion. These Examples are thus given for illustration pur¬ poses only and are not construed to limit the invention in any way.

Example 1

Preparation of calix [4] arene-5, 11, 17 , 23-tetrasulfonic acid

In a flask equipped with a reflux condenser and a mag¬ netic stirrer, 5 grams (7.7 mmoles) of tetra-p-tert-butyl- calix [4] arene are carefully added, portionwise and under stirring, to 20 ml of concentrated sulfuric acid (95 to 97 %, Merck) . The suspension which is formed is heated during 4 hours to about 80 °C. The real duration of the reaction depends upon the result of a final water solubility test of a sample taken from the mixture from time to time.

When there is no precipitate detectable with the naked eye any more, the mixture is allowed to cool, and the pre¬ cipitate is carefully filtered off on a fritted glass fil-

ter having the porosity of 3 or 4. The porosity of 3 is preferred since it requires a low suction force and a bet¬ ter flow of the viscous filtrate. The brown solid recov¬ ered on the filter is washed twice with 2.5 ml of ice cold ethanol, the washings being collected in another vessel. The residue which is now freed from excess sulfuric acid is treated until total solution with several fractions of methanol, and the final volume of this solution is about 100 ml.

The solution is now treated with 1 gram of decoloring charcoal, filtered on celite, and added to 500 ml of ethyl acetate under stirring. The precipitate which forms gradu¬ ally acquires a structural form and is then filtered, and the residue is dried under high vacuum at 30 to 40 °C, yielding 5 grams (6.7 mrnoles, 87 %) of calix [4] arene-5, 11, - 17, 23-tetrasulfonic acid as a clear brown powder.

Analysis: ⁱ H-NMR: 5.08 (s, 4 Ar-CH ₂ -Ar) ; 5.97 (s, 14H, (8 acidic H exchanged + 3 H ₂ 0) ) ; 8.66 (s, 8H of Ar) . ¹³ C- NMR: 35.02 (Ar-CH ₂ -Ar) ; 131.02 (C(H) of Ar) ; 132.53 (Ar- CH ₂ -Ar) ;140.29 and 155.95 (C-OH and C-S0 ₃ H) . ES-MS, nega¬ tive mode: 743 (M-H) ^" ; 371 (M-2H) ^2" /2; 247 (M-3H) ^3~ /3; 185 (M-4H) ⁴ - I A ; 393(M-2H-2H + 2Na) ^2' /2 ; 382 (M-2H-H + Na) ^2~ /2; 254 (M-3H-H + Na) ^3~ /3.

Example 2

Preparation of calix [8] arene-5, 11, 17, 23 , 29, 35, 41, 47- octasulfonic acid

Example 1 was repeated with the exception that 5 grams (3.85 mrnoles) of octa-p-tert-butylcalix [8] arene were used instead of the corresponding calix[4] arene derivative.

2.75 grams of calix[8] arene-5, 11, 17, 23, 29, 35, 41, 47-octasul- fonic acid were finally obtained in a 48 % yield.

Analysis: 1H-NMR: 4.40 (s, 8 Ar-CH ₂ -Ar); 5.26(s, 28 H,

16 exchanged acid H + 6H ₂ 0) ; 7.87 (s, 8 H of Ar) . 13C-NMR: 33.91 (Ar-CH ₂ -Ar) ,- 129.50 C(H) of Ar) ; 131.36 (Ar-CH ₂ -Ar) ;

138.49 and 156.63 (C-OH and C-S0 ₃ H) . ES-MS, negative mode:

743 (M-2H) ^2" /2; 495 (M-3H) ^3" /3 ; 371 (M-4H) ^4" /4.

The following compounds have been synthesized by the process of the present invention:

l) Calix[4] arene-5, 11, 17, 23-tetrasulfonic acid,

2) calix [5] arene-5, 11, 17, 23, 29-pentasulfonic acid,

3) calix[6] arene-5, 11, 17, 23 , 29, 35-hexasulfonic acid,

4) calix [7] arene-5, 11, 17, 23, 29, 35, 41-heptasulfonic acid, 5) calix[8] arene-5, 11, 17, 23, 29, 35, 41, 47-octasulfonic acid,

6) calix[9]arene-5, 11,17,23,29,35,41,47,53- nonasulfonic acid,

7) calix [10] arene-5, 11,17,23,29,35,41,47,53,59- decasulfonic acid.

The invention is not limited to the disclosure in the detailed description above. For example, reaction and post-treatment conditions may be changed and optimized without departing from the scope of the invention as de- fined in the appended claims.