4,4â²-Bipyridine (abbreviated to 4,4â²-bipy or 4,4â²-bpy) is an organic compound with the formula . It is one of several isomers of bipyridine. It is a colorless solid that is soluble in organic solvents. is mainly used as a precursor to N,Nâ²-dimethyl-4,4â²-bipyridinium [(C<sub>5</sub>H<sub>4</sub>NCH<sub>3</sub>)<sub>2</sub>]<sup>2+</sup>, known as paraquat.
4,4â²-Bipyridine was first obtained in 1868 by the Scottish chemist Thomas Anderson via heating pyridine with sodium metal. However, Anderson's empirical formula for 4,4â²-bipyridine was incorrect. The correct empirical formula, and the correct molecular structure, for 4,4â²-bipyridine was provided in 1882 by the Austrian chemist Hugo Weidel and his student M. Russo.
4,4'-Bipyridine is an intermediate in the production of paraquat, a widely used herbicide. In this process, pyridine is oxidized to 4,4'-bipyridine in a coupling reaction, followed by dimethylation to form paraquat.
The reducing agent N,N'-bis(trimethylsilyl)-4,4'-bipyridinylidene is produced by reduction of 4,4'-bipyridine in the presence of trimethylsilyl chloride (Me = CH<sub>3</sub>):
The silylated derivative, which is red, is used in salt-free reductions.
4,4â²-bipyridine forms a variety of coordination polymers.