Ortho-to-sulfone position

One approach is to increase the acidity and the stability of acidic function by moving the acid function from the ortho-to-ether position to the ortho-position of a strongly electron-withdrawing units i.e. ortho-to-sulfone position connecting the phenyl rings in the case of poly ether sulfone (UDEL). 

The ionic function can be added by (i) electrophilic substitution in ortho-to-ether position on arylene ether segment due to its electron-donating nature or by (ii) aromatic nucleophilic substitution in ortho-to-sulfone position. Due to the electron withdrawing nature of sulfonyl link present in arylene sulfone segment, the acidic character of hydrogen atom present ortho-to-sulfone link is quite high and hence, activated for nucleophilic substitution using lithiation chemistry. 

Ionic Function Attached Directly to Ortho-to-Sulfone Position of the Polymer... 

Kerres et al. [38] reported that the sulfonation close to electron-donating substituents (i.e. ortho-to-ether position) of the main aromatic polymer chain is normally more easily activated for hydrolytic desulfonation in acidic media compared to sulfonation close to electron-withdrawing substituents (i.e. ortho-to-sulfone position). An electrophilic route does not allow acidic ionic groups to be located on the ortho-to-sulfone position in the arylene sulfone segment where it should be, at least slightly, more dissociated than an acidic ionic function located at the ortho-to-ether position in the arylene ether segment. 

The sulfonation at ortho-to-sulfone position involves three successive steps, metalation-sulfination-oxidation as rej>orted by Kerres et al. [38] (Scheme 4.4). 

Scheme 4.4 Sulfonation and phosphonation of polysulfone in ortho-to-sulfone position.

Lafitte et al. [45] reported polysulfone ionomers functionalized with benzoyl(difluoromethylenephosphonic acid) side chain (bfp-PSU) as an alternative to sulfonic acid based PSU ionomers shown in Scheme 4.8(a) and Table 4.2. The degree of phosphonation (DP) was achieved up to 53% and this membrane took higher amount of water (6%) tmder immersed state at room temperature compared to membrane with phosphonic acid directly attached to main-chain at ortho-to-sulfone position taking 2% water as discussed before. The probable reason is the increased acidity of the phosphonic acid unit. The thermal stability was found to be inferior to sulfonated derivatives due to the presence of aryl -CF2-P linkage [45]. 

Bake sulfonation is an important variant of the normal sulfonation procedure. The reaction is restricted to aromatic amines, the sulfate salts of which ate prepared and heated (dry) at a temperature of approximately 200°C in vacuo. The sulfonic acid group migrates to the ortho or para positions of the amine to give a mixture of orthanilic acid [88-21-1] and sulfanilic acid [121 -57-3] respectively. This tendency is also apparent in polynuclear systems so that 1-naphthylamine gives 1-naphthy1amine-4-su1fonic acid. 

The steric requirements of the enhanced interaction between arylsulfinyl or arylsulfonyl groups and the benzene ring in bis(4-hydroxyphenyl)sulfoxides or sulfones were examined by Oae and colleagues through the introduction of methyl groups in two or four of the positions ortho to SO or S02. As in the work described earlier for S02Me, effective values for the combined influence of the substituents o (obs.) were determined and compared with o (calc.) computed on the basis of strict additivity of substituent effects on the dissociation... 

Oae and Khim measured the rates of hydrolysis of chlorophenyl phenyl sulfoxides and sulfones with hydroxide ion in aqueous DMSO at 158 °C. Both SOPh and S02Ph were found to activate the nucleophilic substitution from ortho- and para-positions, but the effect of SOjPh was considerably larger than that of SOPh. The results were interpreted in terms of 7t(pd) conjugation in the intermediate complexes. In a later paper it was shown that the introduction of a methyl group ortho to SOPh or S02Ph slightly retards the above and related reactions but this was attributed to the inductive effect of Me rather than steric inhibition of 7t(pd) conjugation (Section III.A.l). 

Aromatic aminosulfonic acids, which play a major role in connection with pigment lakes, are produced by sulfonating the corresponding nitro compound and then reducing it to an aminosulfonic acid. An alternative technique, known as baking process, involves exposing an amine/dihydrosulfate to a temperature of 200 to 300°C in order to effect rearrangement to p-aminosulfonic acid. Ortho-sulfonation prevails if the para position is occupied. In contrast to sulfonation techniques with sulfuric acid, this method avoids wastewater contamination with sulfuric acid. 

These ideas will be discussed in the following subsections, where most of the attention will be devoted to the mechanistic smdies with aromatic esters, which have been the subject of an overwhelming majority of the research efforts. Nevertheless, the same reaction mechanism has been shown to be valid for the PFR of anilides, thioesters, sulfonates, and so forth. Furthermore, it is also applicable to the photo-Claisen rearrangement [i.e. the migration of alkyl (or allyl, benzyl, aryl,)] groups of aromatic ethers to the ortho and para positions of the aromatic ring [21,22]. 

Nitration of coumarin gives the 6-nitro derivative and a small amount of 8-nitrocoumarin. Similarly, Friedel-Crafts acylation and sulfonation give 6-substitution but in the presence of a hydroxyl group in the benzene ring, the incoming group usually enters a position ortho to it. 

This nucleophilic replacement of halogen atoms proceeds under mild conditions due to the neighboring azo group and the presence of copper ions. The o-sulfonic acid group is also susceptible to the copper-mediated nucleophilic substitution, and other nucleophiles, such as alkoxy, alkylamino, cyano, and sulfinic acid can also replace the halogen atom in the position ortho to the azo group in the presence of copper ions. 

Molten 2-ethoxybenzoic acid (7) was added to a mixture of chlorosulfonic acid and thionyl chloride while keeping the reaction temperature below 25 °C. In this straightforward electrophilic aromatic substitution the ethoxy group directs the electrophile towards the ortho and para position whereas the carboxylic acid directs meta giving an overall selectivity for the attack at C-5. It was necessary to add thionyl chloride to transform the intermediate sulfonic acid into... 

Benzidine can be diazotized at each amino group. It can then couple with two equivalents of the aminosulfonic acid. Coupling occurs ortho to the amino group since the para position is blocked by the sulfonic acid group. 

Oxathiolane 2,2-dioxide undergoes metallation with n-butyllithium as expected at the 3-position (81JOC101). The anion may be alkylated with alkyl halides or carbonyl compounds. The isomeric 1,3-oxathiolane 3,3-dioxides also undergo metallation ortho to the sulfone and, when the 4-position is blocked, metallation at the 2-position may be used as an efficient conversion of alkyl halides into aldehydes as shown in Scheme 22 (79TL3375). 

Acyl selenophenes are chloromethylated at the free a. position (as in sulfonation and halogenation). A second chloromethyl group can be introduced ortho to the first and meta to the acyl group.61 5-Methyl-2-acetylselenophene is chloromethylated in the 4-position.61 When reduced by stannous chloride in hydrochloric acid, 5-chloro-methyl-2-acetylselenophene simply undergoes reduction of the chloromethyl group, and 2-methyl-5-acetylselenophene is formed61 (Scheme 2). 

The first step involves hydrolysis, with concentrated sulfuric acid, of p-toluene-sulfonyl chloride, which is quite cheap. The resulting sulfonic acid is chlorinated smoothly in the position ortho to the —CHs group, the reaction being carried out in sulfuric acid solution using iron as a catalyst. Finally, the sulfo group is split out with steam, yielding the desired o-chlorotoluene in excellent yield. This process is less satisfactory for use in the laboratory, but gives the best results in industrial operations. 

Xylene blue belongs to the group of so-called patent blues which are sulfonated triphenylmethane dyes that are stable to alkali. The dyes are all characterized by having a sulfo group in the position ortho to the central carbon atom as in the following general formula ... 

The driving force presumably lies in the stability of the halide leaving group. Formal replacement of hydride is possible with an appropriate nucleophile. Reaction of nitrobenzene with the anion from chloro-methylphenyl sulfone gives the substitution product in 72% yield as a 1 1 ortho to para mixture. Use of bulkier anions gives exclusively para product. When the para position is substituted, the nucleophile enters ortho. 

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