Reduction of nitrosamines to asymmetrically disubstituted hydrazines

Asymmetrically disubstituted hydrazines can be obtained by reduction of nitrosamines. Singly substituted hydrazines can be prepared, in principle, analogously through the intermediacy of alkylnitrosoureas. These reductions are usually carried out by zinc in acetic acid if mineral acid is used the nitroso group is split off. The method goes back to work by Emil Fischer.124 

2- Dimethylhydrazine125 and l-methyl-2-phenylhydrazine126 are obtained similarly. A preparation of ethylhydrazine by way of 1,3-diethyl-l-nitrourea is due to Fischer.127 Ethyl 3-(ethylnitrosoamino)propionates can also be reduced 

Alteration of nitrogen groups in carbon-nitrogen compounds 

Reducing nitrosamines by one mole of lithium tetrahydridoaluminate per mole of nitrosamine in ether or tetrahydrofuran271 129 130 has led to, e.g., 1 -methyl-1 -phenylhydrazine (77%), 1,1 -dicyclohexylhydrazine (48%), and 1-aminopiperidine (75%), but if too great an excess of the aluminate is used the N-N bond may be cleaved and to avoid this it is recommended that the aluminate be added gradually to the nitrosamine.129 

Nitrosamines can also be reduced electrolytically. l-Deoxy-l-(methyl-nitrosoamino) sugar alcohols in hydrochloric acid solution are reduced to 1-methyl-l-(pentahydroxyhexyl)hydrazines in very good yield at a stirred mercury cathode of large surface area.131 Reduction by this method does not require addition of substances that are later hard to separate about 8 hours are required for reduction of 50 mmoles at constant potential. 

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