Preparation
Lithium amide is obtained by dissolution of lithium metal in liquid ammonia. The reaction is slow, but may be catalyzed by cobalt nitrate:
2Li + 2NH
3 → 2LiNH
2 + H
2
It also is obtained by passing gaseous ammonia over lithium hydride:
LiH + NH
3 → LiNH
2 + H
2
Reactions
Lithium amide decomposes to imide when heated above 400°C: 2LiNH2 → Li2NH + NH3
It is used in several organic syntheses. Some of these synthetic reactions are based on the mechanism that the terminal alkynes react with the stronger base, the anion, forming the weaker conjugate base:
It converts vic dibromide to bromoalkene and then alkyne:
Ketones can be converted into alkynes:
Chemical Properties
white to grey fine powder
Physical properties
Colorless needles; tetragonal structure; density 1.178 g/cm
3 at 17.5°C; melts around 375°C; starts to decompose at 320°C; decomposes at 400°C; soluble in cold water; decomposes in hot water; slightly soluble in ethanol and liquid ammonia; insoluble in benzene and ether.
Uses
Reagent for synthesis of: Antiinflamatory and preoresolving protectin D11 Chemotype dipeptidyl peptidase IV inhibitors2 Sterically congested triarylamines3 Dyes displaying large Stokes shifts4 GM1 ganglioside derivatives5Reagent for cross-coupling of aryl chlorides and amines6
Uses
Lithium amide is used in the preparation of active pharmaceutical ingredients and antioxidants. It acts as a catalyst for polymers, as nucleophiles and as strong bases. It serves as a reagent in the synthesis of antiinflamatory and preoresolving protectin D1, chemotype dipeptidyl peptidase IV inhibitors and sterically congested triarylamines. It finds application in dyes displaying large stokes shifts. In addition to this, it is used as a reagent for cross-coupling of aryl chlorides and amine.
Uses
In Claisen condensations, alkylation of nitriles and ketones, synthesis of ethynyl Compounds, acetylenic carbinols.
Preparation
Lithium amide, LiNH2 , may be considered the ammonia analogue of lithium hydroxide
in the water system. Lithium amide may be prepared from lithium hydride or lithium
metal and ammonia. Industrial preparations use lithium hydride as a starting material.
The reaction of lithium metal in a stream of ammonia gas at about 400°C may be used
successfully as a preparative method. Lithium may also be reacted with liquid ammonia
in the presence of an iron compound as a catalyst.
Since amide ion is the strongest base which can exist in ammonia, lithium amide is a
very strong base. The compound has a low solubility in liquid ammonia. Lithium amide is
hydrolyzed by water to yield lithium hydroxide and ammonia. It is readily oxidized. For
example, the substance may be oxidized with dinitrogen oxide to yield lithium azide.
Amides of the alkali metals in general must be guarded against air oxidation to prevent the
formation of potentially explosive substances.
General Description
White crystalline powder with an odor of ammonia. Denser than water.
Reactivity Profile
Powdered Lithium amide is highly reactive. A strong base. Reacts to release toxic ammonia gas with water. Forms explosive peroxide on storage.
Health Hazard
Highly toxic: contact with water produces toxic gas, may be fatal if inhaled. Inhalation or contact with vapors, substance or decomposition products may cause severe injury or death. May produce corrosive solutions on contact with water. Fire will produce irritating, corrosive and/or toxic gases. Runoff from fire control may cause pollution.
Fire Hazard
Produce flammable and toxic gases on contact with water. May ignite on contact with water or moist air. Some react vigorously or explosively on contact with water. May be ignited by heat, sparks or flames. May re-ignite after fire is extinguished. Some are transported in highly flammable liquids. Containers may explode when heated. Runoff may create fire or explosion hazard.
Flammability and Explosibility
Substances and mixtures which in contact with water emit flammable gases
Safety Profile
A powerful irritant to
skin, eyes, and mucous membranes.
Flammable when exposed to heat or flame.
Ammonia is liberated and lithmm hydroxide
is formed when this compound is exposed
to moisture. Reacts violently with water or
steam to produce toxic and flammable
vapors. Vigorous reaction with oxilzing
materials. Exothermic reaction with acid or
acid fumes. When heated to decomposition
it emits very toxic fumes of LiO, NH3, and
NO,. Used in synthesis of drugs, vitamins,
steroids, and other organics. See also
LITHIUM COMPOUNDS, AMIDES,
AMMONIA, and LITHIUM
HYDROXIDE.
Purification Methods
Purify it by heating at 400o while NH3 is passed over it in the upper of two crucibles (the upper crucible is perforated). The LiNH2 will drip into the lower crucible through the holes in the upper crucible. The product is cooled in a stream of NH3. Protect it from air and moisture, store it under N2 in a clear glass bottle sealed with paraffin. Store it in small quantities so that all the material is used once the bottle is opened. If the colour of the amide is yellow, it should be destroyed as it is likely to have oxidised and to EXPLODE. On heating above 450o it is decomposed to Li2NH, which is stable up to 750-800o. [Schenk in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I p 463 1963, Greenlee & Henne Inorg Synth II 135 1953.]
