Replacement of the amino group by sulfur groups

Removal of an amino group with formation of a C-S bond cannot be achieved directly it is effected by way of the diazonium salts that are readily obtained from aromatic amines. Nevertheless, to overcome the always present, great or slight, tendency for formation of organic sulfides — as in analogous alkylations — it is customary here, too, to use as aryl acceptors only those 

To avoid explosions450 it is recommended to carry out the diazonium salt reaction very cautiously with stirring — best by adding the cold diazonium salt solution to the xanthate solution pre-warmed to 60-70°. For each mole of diazonium compound it is advisable to use 1.4 moles of xanthate in the tenfold amount of water.451 

The reaction of diazonium salts with sodium disulfide proceeds in the same way, nitrogen being split off and organic disulfides formed  

For example, Chmelewsky and Friedlander453 obtained 2,2/-dithiodi(tinnamic add) by pouring odiazocinnamic acid into an excess of warm, concentrated, aqueous sodium disulfide and acidifying the mixture. For purification, a solution of the crude product in cold sodium carbonate solution is filtered and acidified the precipitate melts at 221° after recrystallization from ethanol. 

The preparation of 2,2 -dithiodi(benzoic acid) (dithiosalicylic acid)454 may be cited as a further example. 

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