Diazonium salts, reactions with sulphur

Aromatic diazonium salts react with sulphur dioxide, either in the liquid state or mixed with an organic solvent, such as acetic acid, in the presence of copper(II) chloride to give 50-90% yields of sulphonyl halides205,527-529 (equation 138). Nitrogen is evolved during the reaction and higher yields are usually obtained in the presence of a solvent. 

The experimental conditions necessary for the preparation of a solution of a diazonium salt, diazotisation of a primary amine, are as follows. The amine is dissolved in a suitable volume of water containing 2 5-3 equivalents of hydrochloric acid (or of sulphuric acid) by the application of heat if necessary, and the solution is cooled in ice when the amine hydrochloride (or sulphate) usually crystallises. The temperature is maintained at 0-5°, an aqueous solution of sodium nitrite is added portion-wise until, after allowing 3-4 minutes for reaction, the solution gives an immediate positive test for excess of nitrous acid with an external indicator—moist potassium iodide - starch paper f ... 

The preparation of all four mononitro aromatic derivatives of 1,2-benzisothiazol-3-one S,S-dioxide was reported. As an example, the preparation of the 5-nitrosaccharin 314 Method 0) from nitro-lH-benzo[d][l,3] oxazine-2,4-dione 312 is outlined in the Scheme 76. Starting from 312, which was treated with K2CO3 in MeOH, the methyl 2-amino-5-nitrobenzoate 313 was formed. The amino group was transformed into the diazonium salt (NaN02 in AcOH/HCl). Its reaction with CuCh and sulphur dioxide afforded the corresponding sulfonyl chloride, which was added to cold concentrated ammonium hydroxide and 314 was isolated in 74% yield [lOOj. 

The preparation of phenols by hydrolysis of benzediazonium ions is well known in the literature (ref. 10). It involves the preparation of a diazonium salt, e.g. the diazonium hydrogenosulfate by treatment of the aniline hydrogen sulphate with sodium nitrite in dilute aqueous sulphuric acid, followed by hydrolysis in more concentrated aqueous sulphuric acid. The temperature of the hydrolysis is maintained at the boiling point of the aqueous acid by proper adjustment of the concentration of the sulphuric acid and the phenol formed removed from the reaction medium by means of steam distillation in order to minimise the coupling of the formed phenol with the diazonium salt introduced. 

Sulphonyl halides may be prepared by reaction of some organic compounds with sulphur dioxide in the presence of a halogen or halide ion. Compounds which undergo such reactions include aromatic diazonium salts and some aliphatic species. 

A -oxide which is easily reduced to codeine with sulphur dioxide [303]. The 0-methylation of certain Erythrina alkaloids has been carried out in a similar manner [304]. A -Oxidation has also been used to protect tertiary ring nitrogen atoms in heteroaromatic compounds. Protonation of the ring nitrogen atom in 4- (and 2-) aminopyridines renders their diazonium salts very susceptible to hydrolysis, thus they cannot be converted into cyanides by the Sandmeyer reaction. The corresponding TV-oxides may, however, be used in the normal way and the oxide function removed at a later stage, as in the sequence (63) (64) used by Berson and Cohen in studies on ipecac... 

This compound is very unstable and explosive and forms hydroxy azo compounds by coupling with hydroxy compounds. Furthermore, it gives sulphur dioxide when treated with dilute acids just as sulphite salts do. It appears, therefore, that this compound is a true diazonium compound, viz., a diazonium sulphite and the reaction should be... 

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