Lithium naphthalene is an organic salt with the chemical formula . In the research laboratory, it is used as a reductant in the synthesis of organic, organometallic, and inorganic chemistry. It is usually generated in situ. Lithium naphthalene crystallizes with ligands bound to . The anion is a well-known example of an organic radical.
The compound is prepared by stirring the metallic lithium with naphthalene in an ethereal solvent, usually as tetrahydrofuran or dimethoxyethane. The resulting salt is dark green. The reaction of naphthalene with lithium can be accelerated by sonication. Methods for assaying lithium naphthalene have been developed as well. As a radical, its solutions show a strong EPR signal near g = 2.0. Its deep green color arises from absorptions at 463, 735 nm.
Several solvates of lithium naphthalene have been characterized by X-ray crystallography. The effects are subtle, the outer pair of HCâÂÂCH bonds contract by 3 pm and the other nine CâÂÂC bonds elongate by 2âÂÂ3 pm. Net: reduction weakens the bonding.
With a reduction potential near âÂÂ2.5 V versus the normal hydrogen electrode, the naphthalene radical anion is a strong reducing agent. Lithium naphthalene has often been used to cleave carbon-heteroatom bonds.
The anion is strongly basic, and a typical degradation pathway involves reaction with water and related protic sources such as alcohols. These reactions give dihydronaphthalene:
Alkali metal salts of the naphthalene radical anion are used to prepare complexes of naphthalene.
Many related radical anions are known such as those derived from anthracene, with other alkali metals (especially sodium), and with diverse ligands attached to the alkali metal cations. Dilithium naphthalene is also known in the form .