Sulphinic acids oxidative amidation

Oxidative amidation of sulphinic acids occurs under rather forcing conditions (18% oleum) to give a sulphonamide as product (equation 109)446. The severity of the reaction conditions means that this approach is not one that is generally applicable for the conversion. A far preferable method involves the rather mild oxidation of the ammonium salts of arenesulphinic acids with either hypochlorite ions or chlorine, in aqueous solution (equation 110)447. 

A possible route to 2- and 3-t-aminophenothiazines is afforded by the reaction of chloro-lO-alkylphenothiazines with sodium or lithium derivatives of secondary amines. Thus, treatment of 1-chloro- or 2-chloro-lO-methylphenothiazine with sodium amide-morpholine leads to the same product, i.e. 2-morpholino-lO-methylphenothiazine, presumably by way of the same phenothiazyne intermediate (121). 3-Chloro- and 4-chloro-lO-methylphenothiazine react similarly giving, as expected, the same 3-mor-pholino-derivative via an analogous phenothiazyne intermediate. The phenazathionium cation (122), generated oxidatively in situ with ferric chloride, reacts readily with toluene-p-sulphinic acid, nitrite, or thiourea to... 

Sulphonamides.— Oxidative amidation of sulphinic acids gives primary sulphon-amides, though the severe reaction conditions (18% oleum with NaNj) restrict the potential of this route. Selective amino sulphonation of anilines, using CISOjNCO and AlClj, depends on the formation of cyclic A-carbamoyl-sulphonamides. More conventional preparative methods are covered in the conversion of naphthalene-1-thiol into 4-(2-hydroxyethylsulphonyl)naphthalene-1-sulphonamide (an assessment of standard routes has been made), and in the preparation of alkanesulphonyl- and trifluoromethanesulphonyl-hydroxyl-amines from hydroxylamines and the sulphonyl chlorides. In the latter study,conditions favouring N- rather than 0-sulphonylation were established. 

The participation of sulphine intermediates has been reported in the periodate-promoted oxidative rearrangement of C-sulphonylthioform-amides to S-sulphonylthiourethanes, and in the formation of a-toluenesul-phinic acid or benzhydryl benzyl sulphone by the reaction of benzhydryl benzyl sulphoxides with sulphuryl chloride. ... 

The hydrogen peroxide oxidation of N-(ethoxycarbonyl)pyrrole-2-thio-carboxamide (225) has been the subject of a recent study by Papadopoulos, who found that in basic media (225) is converted into the corresponding amide, whereas in acidic solution the sulphine (271) is formed. The thiocarbonyl group in (272) [the cyclization product obtained by heating (225) in quinoline] behaved similarly. Several examples of the formation of heterocyclic compounds, especially isothiazole derivatives, by oxidative treatment of appropriate thioamides have appeared. The... 

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