Reactions of Sulphones

Reactions of Sulphones.—The first report of pyrolytic elimination of aryl-sulphinic acid from an aryl alkyl sulphone has appeared, for 2-pentyl compounds these give pent-l-ene in constant proportion with cis- and t/ /i5-pent-2-ene, with exceptions for mesityl and p-nitrophenyl 2-pentyl sulphones. Base-catalysed elimination reactions leading to vinyl sulphones are well known, amine-promoted elimination from PhSOzCHa CHF-SPh following a jy/i-stereospecific course through an Elcb mechanism involving ion-pairs. A mild decarbomethoxylative elimination is the last step in a synthesis of ( )-versimide (131).  

Organic Compounds of Sulphur, Selenium, and Tellurium COaMe Me, 

Continuation of studies aimed at preparing sulphenes by pyrolysis of sulphonyl derivatives has involved the allyl vinyl sulphone (134), which on heating at 170 °C in the liquid phase, or at 800 °C in the gas phase, gives products derived from the sulphene, itself arising through a sulpho-Cope [3,3]sigmatropic rearrangement.  

Sulphone cleavage is involved in a number of otherwise unrelated observations 2-(hydroxyamino)aryl phenyl sulphones or bis-(2-hydroxy-amino)aryl sulphones disproportionate into arylsulphinate and 2-hydroxy-2 -(arylsulphonyl)azoxybenzene (135) in aq. NaOH at 20 while 

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TABLE 2. Reductive cleavage reactions of sulphones induced by lithium in methylamine or ethylamine... 

Since sulphones 204 are easily available compounds one would expect that they could be used as starting materials for the preparation of sulphoxides via the selective removal of one oxygen atom from the sulphonyl group (equation 112). Up to now, there is only one example reported of a direct reduction of a sulphone to a sulphoxide. The bicyclic dideuterio sulphone 205 after 24 h treatment with three-fold excess of diisobutyl aluminium hydride in boiling dichloromethane gave the corresponding sulphoxide 206 in 36% yield (equation 113). A two-step procedure for the selective reduction of sulphones to sulphoxides, which involves an initial reaction of sulphone 204 with aryldiazonium tetrafluoroborate 207 to form aryloxysulphoxonium salt 208 and its subsequent reduction (equation 114), was alluded to by Shimagaki and coworkers and... 

The reactions that have been described above have indicated that sulphones interact poorly with electrophiles. However, in 1970, Whiting and coworkers announced the synthesis of aryloxysulphoxonium salts , by the reaction of sulphones with the potent electrophile produced in the thermolysis of aryldiazonium tetrafluoroborates or hexaflu-orophosphates. Fluorobenzenes are by-products of the reaction. In a subsequent paper , Whiting described the reactions of the aryloxysulphoxonium salts, 5, with oxygen and nitrogen nucleophiles. The fundamentals of these are outlined in equations (34) (oxygen nucleophile) and (35) (nitrogen nucleophile). 

J. Hill, L. Hough, and A. C. Richardson, Nucleophilic replacement reactions of sulphonates. I. The preparation of derivatives of 4,6-diamino-4,6-dideoxy-D-glucose and -D-galactose, Carbohydr. Res., 8 (1968) 7-18. 

Y. Ali and A. C. Richardson, Nucleophilic replacement reactions of sulphonates. III. The synthesis of derivatives of2,3,4,6-tetra-acetamido-2,3,4,6-tetradeoxy-D-galactose and-D-idose,/. Chem. Soc., Sect. C (1968) 1764-1769. 

These reactions of sulphonic acids with phosphorus penta-chloride and with alcohol both prove that in sulphonic acids there is one and only onCf acid hydroxyl remaining. 

Summary.—Bringing together the reactions of sulphonic acids as we have given them we see that either directly or indirectly they are capable of transformation into the following compounds ... 

Hill, J, Hough, L, Richardson, A C, Nucleophilic replacement reactions of sulphonates Part II. The synthesis of derivatives of 4,6-dithio-D-galactose and D-glucose, and their conversion into 4,6-D-xy/o-hexose, Carbohydr. Res., 8, 19-28, 1968. 

An illustrative example of the effect of counterions on selectivity is the work by Brinchi et al, in which they demonstrated that reaction of sulphonate esters in the presence of equimolar amounts of bromide and hydroxyl ions took completely different paths depending on whether the reaction was performed in a micellar system based on cationic surfactant or in a homogeneous solution, see Fig. 5.5 [29]. When there is no surfactant present, attack by the hydroxyl ion dominates. In the micellar solutions, on the other hand,... 

Thirdly, using the new heats of formation suggested by BBGW, one may readily deduce that homolysis reaction 42 is some 115kcalmol-1 exothermic. However, given that this reaction is also favourable entropically and requires but the cleavage of a single bond, it is hard to reconcile it with any of the other reactions of sulphonic acid anhydrides known to the current author. 

Fourthly, BBGW assumed the bond to H in PhS03H was of comparable strength to that found in PhS02H, namely ca 24kcalmol-1. This seems unlikely based on our knowledge of other O—H bond strengths50 and the apparent lack of radical chemistry associated with most of the reactions of sulphonic acids. 

The normal method of choice for the preparation of sulphonamides is by reaction of sulphonic acid derivatives with ammonia and amines. These reactions are covered in this section, together with other interconversions of sulphur(VI)-containing compounds to sulphonamides. 

The reaction of sulphonates has been shown to involve the singlet excited state. The reactions for the conversion of the esters into the free sulphonic acids are reasonably efficient with quantum yields in the 0.02 to 0.07 range. The processes involve homolytic... 

Sulphenes (59), generated from the reaction of sulphonate esters or sulphonyl chlorides with triethylamine, react with triphenylphosphine to form phosphonium salts. ... 

Reactions of Sulphonic Acids.—The sulphonic acids are strong acids, and resemble sulphuric acid in many of their properties. They are considered as derived from sulphuric acid by the replacement of a hydroxyl group by radicals —... 

The reactions of sulphonic acids are in accord with this view of their structure. When subjected to the action of active reducing agents they are converted into mercaptans, in which the sulphur is joined to carbon —... 

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