Where did all the bpy go? - Synthesis, crystal and molecular structure of 4-nitropicolinic acid monohydrate

The conversion of 2,2-bipyridine (bpy) to 4,4'-disubstituted derivatives is commonly achieved by a route involving preparation of the NAP-dioxide and subsequent nitration with HNO3/H2SO4. The yields in the latter reaction are of the order of 50% and we now show that a competing ring oxidation process leads to the formation of 4-nitropicolinic acid. The solid state structure of the monohydrate of 4-nitropicolinic acid is reported, which exhibits a series of interesting packing motifs arising from hydrogen bonding networks.