Reduction of nitrocompounds

Both aliphatic and aromatic nitro compounds can be reduced all the way to the corresponding primary amine, and this reduction can be carried out by any of three broad reagent choices. The first choice is a metal-acid combination, most commonly tin with hydrochloric acid (Sn/HCl), though iron with hydrochloric acid (Fe/HCl) or zinc with hydrochloric acid (Zn/HCl) work equally well -- the metal here is oxidised while acting as the actual reducing agent, generating the hydrogen atoms (written as [H]) that add across the nitro group. The second choice is catalytic hydrogenation, passing hydrogen gas over the nitro compound in the presence of a metal catalyst such as nickel, platinum or palladium (H2/Ni, H2/Pt or H2/Pd). The third choice is lithium aluminium hydride (LiAlH4) dissolved in dry ether, a powerful hydride-transfer reducing agent. Written as one representative equation using the metal-acid route: R-NO2 + 6 [H], with Sn/HCl, gives R-NH2 + 2 H2O -- …