Sodium amide, commonly called sodamide, is the inorganic compound with the formula NaNH2. It is a saltcomposed of the sodium cation and the azanide anion. This solid, which is dangerously reactive toward water, is white, but commercial samples are typically gray due to the presence of small quantities of metallic iron from the manufacturing process. Such impurities do not usually affect the utility of the reagent. NaNH2 conducts electricity in the fused state, its conductance being similar to that of NaOH in a similar state. NaNH2 has been widely employed as a strong base in organic synthesis.
Preparation and structure
Sodium amide can be prepared by the reaction of sodium with ammonia gas, but it is usually prepared by the reaction in liquid ammonia using iron nitrate as a catalyst. The reaction is fastest at the boiling point of the ammonia, c. −33 °C. An electride, +e−, is formed as a reaction intermediate. NaNH2 is a salt-like material and as such, crystallizes as an infinite polymer. The geometry about sodium is tetrahedral. In ammonia, NaNH2 forms conductive solutions, consistent with the presence of Na6+ and NH2− ions.
Uses
Sodium amide is mainly used as a strongbase in organic chemistry, often in liquid ammonia solution. It is the reagent of choice for the drying of ammonia. One of the main advantages to the use of sodium amide is that it mainly functions as a nucleophile. In the industrial production of indigo, sodium amide is a component of the highly basic mixture that induces cyclisation of N-phenylglycine. The reaction produces ammonia, which is recycled typically. .
Dehydrohalogenation
Sodium amide induces the loss of two equivalents of hydrogen bromide from a vicinal dibromoalkane to give a carbon-carbon triple bond, as in a preparation of phenylacetylene. Usually two equivalents of sodium amide yields the desiredalkyne. Three equivalents are necessary in the preparation of a terminal alkynes because the terminal CH of the resulting alkyne protonates an equivalent amount of base. Hydrogen chloride and ethanol can also be eliminated in this way, as in the preparation of 1-ethoxy-1-butyne.
Cyclization reactions
Where there is no β-hydrogen to be eliminated, cyclic compounds may be formed, as in the preparation of methylenecyclopropane below. Cyclopropenes, aziridines and cyclobutanes may be formed in a similar manner.
It is however poorly soluble in solvents other than ammonia. Its use has been superseded by the related reagents sodium hydride, sodium bisamide, and lithium diisopropylamide.
Other reactions
Rearrangement with orthodeprotonation
Oxirane synthesis
Indole synthesis
Chichibabin reaction
Safety
Sodium amide reacts violently with water to produce ammonia and sodium hydroxide and will burn in air to give oxides of sodium and nitrogen dioxide. In the presence of limited quantities of air and moisture, such as in a poorly closed container, explosive mixtures of peroxides may form. This is accompanied by a yellowing or browning of the solid. As such, sodium amide is to be stored in a tightly closed container, under an atmosphere of an inert gas. Sodium amide samples which are yellow or brown in color represent explosion risks.
