Reactions and characterisation of aromatic sulphonamides

Sulphonamides are most readily identified by hydrolysis with concentrated hydrochloric acid or with 80 per cent, sulphuric acid (for experimental details, see Section X.,7,12)  

The amine is removed by the addition of alkali and characterised by a suitable derivative the sulphonic acid may then be recovered as the sodium salt and converted into a crystalline derivative, e.g., the S-benzyl-iso-thiuronium salt. 

Primary sulphonamides RSOjNHj may be most simply characterised by condensation with xanthhydrol to yield the corresponding IV-xanthyl-sulphonamides  

The best results are obtained with freshly prepared xanthhydrol (reduction of xanthone with sodium amalgam. Section VII,16). Dissolve 0-25 g. of xanthhydrol and 0 -25g. of the primary sulphonamide in 10 ml. of glacial acetic acid. Shake for 2-3 minutes at the laboratory temperature and allow to stand for 60-90 minutes. Filter ofiF the derivative, recrystallise it from dioxan-water (3 1), and dry at room temperature under water pump suction for 30 minutes. 

The melting points of a number of iV-xanthylsulphonamides are collected in Table IV,33A. 

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