Functional Sulphones

Radical intermediates are involved in reactions of a-nitro-sulphones with nucleophiles, leading to products from which the sulphone grouping has been displaced. A useful method of synthesis of 1,2-dinitroalkanes emerges from 

Trifluoromethyl sulphones, neologized as triflones , are particularly reactive compared with other sulphones towards a-alkylation, and towards elimination reactions.  

Reactions of a-sulphonyl carbanions in synthesis are reviewed in the following chapter in this volume. 

---

When either of the reactants is sensitive to mineral acids, the esterification can often be successfully accomplished with the aid of a cation exchange resin (hydrogen form) in the presence of benzene. Zeo-Karb 225/H, a uni-functional sulphonated polystyrene resin in the hydrogen form, may be used. Thus good yields of isopropyl lactate may be obtained ... 

Other a-Functional Sulphones.—Nucleophilic displacement of halogen from a-halogenosulphones has long been known to be a sluggish reaction, but... 

Materials that promote the decomposition of organic hydroperoxide to form stable products rather than chain-initiating free radicals are known as peroxide decomposers. Amongst the materials that function in this way may be included a number of mercaptans, sulphonic acids, zinc dialkylthiophosphate and zinc dimethyldithiocarbamate. There is also evidence that some of the phenol and aryl amine chain-breaking antioxidants may function in addition by this mechanism. In saturated hydrocarbon polymers diauryl thiodipropionate has achieved a preeminent position as a peroxide decomposer. 

The condensation reaction is promoted by certain polar solvents and of the many which have been tested dimethyl sulphoxide appears to be the most effective. As usual with linear condensation polymers molecular equivalence and near-absence of monofunctional material is necessary to ensure a high molecular weight. Moisture and alcohols can also have a devastating effect on the molecular weight. In the case of water it is believed that 4-chlorophenyl 4-hydroxyphenyl sulphone is formed which functions as an effective chain terminator. Gross contamination with air is also believed to reduce the maximum attainable molecular weight as well as causing intense discolouration. 

Calmagite. This indicator, l-(l-hydroxyl-4-methyl-2-phenylazo)-2-naphthol-4-sulphonic acid, has the same colour change as solochrome black, but the colour change is somewhat clearer and sharper. An important advantage is that aqueous solutions of the indicator are stable almost indefinitely. It may be substituted for solochrome black without change in the experimental procedures for the titration of calcium plus magnesium (see Sections 10.54 and 10.62). Calmagite functions as an acid-base indicator ... 

Derbyshire and Waters192 measured the rates of bromination of sodium toluene-m-sulphonate (in water) and of benzoic acid (in aqueous acetic acid) by hypobromous acid with sulphuric or perchloric acids as catalysts, all at 21.5 °C. No bromination occurred in the absence of mineral acid and the reaction was strictly first-order in aromatic and in hypobromous acid. The function of the catalyst was considered to be the formation of a positive brominating species, according to the equilibrium... 

FIGURE 20. The free surface on the sulphur atom, S, (A2), as a function of ring strain for sulphide, sulphoxide and sulphone molecules. 

Hall and Robinson162 later reported pXBH+ values of various sulphones obtained from equation 27, where H is the Hammett acidity function and Kh is calculated from (28). 

This chapter deals with the reverse of these reactions. Since this is not a simple process, a brief discussion of the nature of the S—O bonds in sulphoxides and sulphones will be of assistance in understanding the requirements for reduction of these functional groups. 

One of the more interesting reactions involving the reduction of a sulphone was recently described in a paper87 that reported on a synthetic approach to biotin. The molecule in question contains a sulphone as part of a thiolane ring that is fused to a cyclic urea. As outlined in equation (33), either functionality can be reduced depending on the selection of... 

Trost found126 that aryl sulphones containing a range of other functionalities could be successfully desulphonylated without attack at alkenes, esters or nitriles, and without any detectable degree of alkene migration. 

Carbonyl oxides (formed by the reaction of diazo compounds with singlet oxygen) may also be used to oxidize sulphoxides74. The corresponding sulphone is formed in reasonable yields and the reaction may be carried out in the presence of the sulphide functionality. The reaction proceeds as shown in equation (21) and involves initial nucleophilic attack by the carbonyl oxide on the sulphoxide sulphur atom followed by the facile departure of the carbonyl compound yielding the required sulphone. 

There are many transition metal ion oxidants used in organic chemistry for the interconversion of functional groups. Those which have been used for the preparation of sulphones from sulphoxides will be discussed below. It is very interesting to note that this type of oxidant often reacts more rapidly with sulphoxides than with sulphides and so sulphoxides may be selectively oxidized with transition metal ion oxidants in the presence of sulphides. This is in direct contrast to the oxidation of sulphides and sulphoxides with peracids and periodate, for example, where the rate of reaction of the sulphide is more than 100 times that for the corresponding sulphoxide. 

If a mixture of diphenyl sulphide and the corresponding sulphoxide are treated with osmium tetroxide in boiling ether for 48 hours the sulphide is unchanged whilst the sulphoxide is converted into the sulphone in 96% yield with concomitant production of osmium trioxide140. It thus seems that this method would be useful synthetically for the preparation of sulphones from sulphoxides containing sulphide functionalities. Ruthenium tetroxide may be used in place of osmium(VIII) oxide148. 

---