Reaction Type: Addition
Alkynes can be reduced to trans-alkenes using Na in NH3 (l)
This reaction is stereospecific giving only the trans-alkene via an anti addition.
The stereochemistry of this reaction complements that of catalytic hydrogenation (syn)
The reaction proceeds via single electron transfer from the Na with H coming from the NH3
These reaction conditions do not reduce alkenes, hence the product is the alkene.
MECHANISM FOR THE REDUCTION OF ALKYNES WITH Na / NH3
Sodium transfers an electron to the alkyne giving a radical anion.
The radical anion removes a proton from the ammonia in an acid / base reaction.
A second atom of sodium transfers another electron to the alkyne giving an anion.
The anion removes a proton from the ammonia in an acid / base reaction.