Diazonium salts, reactions with sulphur dioxide

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. 

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... 

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. 

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See also in sourсe #XX -- [ , ]

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