Chemical Properties
Lithium Acetylide Ethylenediamine Complex is a slightly yellow to light brown crystals, Lithium acetylide is an unstable solid which disproportionates to form lithium carbide (dilithium acetylide) and acetylene. It is soluble in liquid ammonia at its boiling point to the extent of just over one mole per liter. It is not sensitive to shock and presents a hazard due only to possible caustic burns and the hazards presented by ammonia and acetylene, which form when the material contacts the air.
Uses
- Lithium acetylide, ethylenediamine complex is a general reagent to synthesize ethynylated ketones.
- It is used as a ligand in the coordination chemistry to synthesize transition metal complexes such as 1-alkynyl-dimethyl(triorganophosphine)gold(III) complex.
- It is employed in the ring opening reaction of epoxides, as in the total synthesis of (?)-goniotrionin and englerin A.
- It can also be used in the ethynylation of alkyl halides to prepare terminal alkynes.
Uses
The largest industrial use of lithium acetylide is in the production of vitamin A. It is used to ethynylate methyl vinyl ketone to produce a tertiary carbinol, an intermediate in the multistep synthesis.
A second industrial use is in the production of Placidyl®, a tranquilizer . In this case it is used to ethynylate methyl beta-chloro vinyl ketone. Lithium acetylide is used extensively in the laboratory, mostly for the ethynylation of ketones.
Lithium acetylide is not an article of commerce since it is unstable and cannot be shipped.
Uses
Lithium acetylide ethylenediamine complex is used in the synthesis of a chiral cyclopropanol. It is also used as an alkynylating reagent for the enantioselective alkynylation of ketones catalyzed by lithium binaphtholate without using other metal sources.
Production Methods
Lithium acetylide is produced both in the laboratory and industrially by dissolving lithium metal in refluxing liquid ammonia and then bubbling acetylene into the solution. The solution of monolithium acetylide thus formed is stabilized by the complexing of the lithium ion with ammonia forming a polar acetylenic anion which does not react further with lithium metal. However, if the reaction is carried out in tetrahydrofuran, for example, the lithium acetylide reacts further with lithium to form dilithium acetylide (lithium carbide). In fact, if the ammonia is removed from a solution of lithium acetylide, it disproportionates to dilithium acetylide and acetylene.
Preparation
The ethylenediamine complex of lithium acetylide is produced by allowing lithium metal to react with ethylenediamine in benzene at reflux to form AMithioethylenediamine: H2NCH2CH2NH2+Li -> L1HNCH2CH2NH2+05H2.
