Benzenesulphinic acid

Sulphinic acids. Aromatic sulphinic acids are found in Solubility Group II. They may be detected by dissolving in cold concentrated sulphuric acid and adding one drop of phenetole or anisole when a blue colour is produced (Smiles s test), due to the formation of a para-substituted aromatic sulphoxide. Thus the reaction with benzenesulphinic acid is ... 

XI XI, 1st 1928 1505-1591 Other Acids. Sulphinic acids Benzenesulphinic acid. 

Phenazine reacts with benzenesulphinic acid in alcoholic hydrogen chloride to give 2-phenazinyl phenyl sulfone (26 Scheme 4), presumably by an intermediate 5,10-dihy-drophenazine this reaction is evidently a useful method of preparing 2-substituted phenazines, since the sulfone is readily displaced in substitution reactions. 

The most important reaction of benzenesulphohydroxamic acid is its decomposition by alkalis. This decomposition does not consist in a reversal of the process of formation (i.e. conversion into benzenesul-phonic acid and hydroxylamine). An exchange of the state of oxidation takes place benzenesulphinic acid and nitroxyl are produced ... 

The kinetics of the nitrosation of benzenesulphinic acid have been determined79. The reaction is very rapid and requires stopped-flow techniques. This makes benzenesulphinic acid an excellent trap for free nitrous acid, on par with the more well-known hydrazoic acid and hydrazinium ion80. In mildly acid solution reaction occurs via the sulphinic acid molecule and also the sulphinate ion. As expected, the latter is the more reactive and reaction takes place at the diffusion limit. All evidence points to the fact that the first nitrosation by NO+ is the rate-limiting step. 

An alternative synthesis of benzenesulphinic acid by way of the diazonium salt is given in Expt 6.75. 

In a beautifully straightforward synthesis5 of D-norgestrel (16) (Scheme 3) the key reaction is the transformation of dextrorotatory (13b) into (14) (85%) with paraformaldehyde and benzenesulphinic acid in triethanolamine-acetic acid. To avoid dialkylation at least a 3 1 volume ratio of triethanolamine to acetic acid is needed. Catalytic reduction to (15) followed by reaction with the anion of (5) yielded (6b X = O). Further elaboration produced dextrorotatory norgestrel (16). Monoalkylation of the diones (13) with l,3-dichlorobut-2-ene yields6 the compounds (17) and then, after steps, the laevorotatory ketones (18). 

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