Preparation of hydrazines from diazonium salts

Failure has repeatedly attended attempts to repeat the older procedures, and improvements have recently been proposed which may be useful also in analogous cases. It has been recommended11 that the diazonium salt solution should be heated for several hours after treatment with sodium sulfite solution and acidification. 

Tin(n) chloride has often been used for reduction of arenediazonium salts in acid solution, a procedure that usually gives the tin double salt of the arylhydrazine hydrochloride, these salts being readily decomposed by alkali. This process is simpler than the sulfite method and is very suitable for laboratory purposes the reduction occurs at a low temperature (about 0°), but it fails with diazonium salts of the anthraquinone series, with / -nitrobenzene-diazonium chloride, and with o-benzenetetrazonium dichloride. Victor Meyer exemplifies the use of tin(n) chloride by the reduction of benzenediazonium chloride to phenylhydrazine.12 

1-Naphthylhydrazine 13 1-Naphthylamine (50 g) is finely ground under concentrated hydrochloric acid (50 g), then the mixture is treated with hydrochloric acid of d 1.1 (400 g) and, with good cooling, with the calculated amount of sodium nitrite. The resulting solution is 

The following methods of reduction have also been recommended for conversion of arenediazonium salts into arylhydrazines Electrolytic reduction of benzenediazonium chloride has been carried out,15 giving a 100% yield of phenylhydrazinium chloride. Reduction with triphenylphosphine has been recommended16 as a general method of preparing arylhydrazines from arenediazonium salts. Good results were also obtained by using sulfur dioxide as reductant,17 and sodium dithionite in hydrochloric acid solution has also proved useful.18 

Phenylhydrazine and its homologs are potent blood poisons that can lead to chronic poisoning. In many people phenylhydrazine causes skin excema. 

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