Pyridine-4-carboxamide, reduction

Carboxamides can be cathodically reduced to amines or alcohols, depending on the reaction conditions the reaction is carried out industrially. One example is the reduction of pyridine carboxamides at Reilly 543) ... 

The reduction of acyl hydrazines has been investigated very little. Polarography of 4-pyridine carboxylic acid hydrazide in acid and neutral solution shows that it is reduced in two, two-electrons steps [141]. The result of controlled potential electrolysis is cleavage of the N-N bond to form 4-pyridine-carboxamide, which then undergoes reduction to the aldehyde in the second step. Other hydrazides of heterocyclic carboxylic acids behave analogously. 

The side chain at C-3 undergoes profound redox-dependent alterations in its chemical properties. The electron orbitals of the carboxamide in NAD are not delocalized into the pyridine ring. On reduction, however, the side chain becomes effectively a vinylogous urea. It shows strong resonance delocalization into the double bonds, with the carbonyl coplanar [although skewed conformations at 150° also represent local minima in the torsional conformation space... 

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