Sodium amide

Sodium amide

Names
IUPAC name Sodium amide, sodium azanide
Other names Sodamide
Identifiers
CAS Number	7782-92-5 Y
ChemSpider	22940 N
EC Number	231-971-0
Jmol 3D model	Interactive image
PubChem	24533
UN number	1390
InChI InChI=1S/H2N.Na/h1H2;/q-1;+1 N Key: ODZPKZBBUMBTMG-UHFFFAOYSA-N N
SMILES [NH2-].[Na+]
Properties
Chemical formula	NaNH2
Molar mass	39.01 g mol−1
Appearance	Colourless crystals
Odor	ammonia-like
Density	1.39 g cm−3
Melting point	210 °C (410 °F; 483 K)
Boiling point	400 °C (752 °F; 673 K)
Solubility in water	reacts
Solubility	0.004 g/100 mL (liquid ammonia), reacts in ethanol
Acidity (pKa)	38 (conjugate acid)
Structure
Crystal structure	orthogonal
Thermochemistry
Specific heat capacity (C)	66.15 J/mol K
Std molar entropy (So298)	76.9 J/mol K
Std enthalpy of formation (ΔfHo298)	-118.8 kJ/mol
Gibbs free energy (ΔfG˚)	-59 kJ/mol
Vapor pressure	{{{value}}}
Related compounds
Other anions	Sodium bis(trimethylsilyl)amide
Other cations	Potassium amide
Related compounds	Ammonia
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Sodium amide, commonly called sodamide, is the inorganic compound with the formula NaNH₂. 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(III) nitrate as a catalyst. The reaction is fastest at the boiling point of the ammonia, c. −33 °C. An electride, [Na(NH₃)₆]⁺e⁻, is formed as an intermediate.

2 Na + 2 NH₃ → 2 NaNH₂ + H₂

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 Na(NH₃)₆⁺ and NH₂⁻ anions.

Uses

Sodium amide is mainly used as a strong base in organic chemistry, often in liquid ammonia solution. It is the reagent of choice for the drying of ammonia (liquid or gaseous). One of the main advantages to the use of sodamide is that it is rarely 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.

Pfleger's synthesis of indigo dye.

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 desired alkyne. 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.

Deprotonation of carbon and nitrogen acids

Carbon acids which can be deprotonated by sodium amide in liquid ammonia include terminal alkynes, methyl ketones, cyclohexanone, phenylacetic acid and its derivatives and diphenylmethane. Acetylacetone loses two protons to form a dianion. Sodium amide will also deprotonate indole and piperidine.

Related nonnucleophilic bases

It is however poorly soluble in solvents other than ammonia. Its use has been superseded by the related reagents sodium hydride, sodium bis(trimethylsilyl)amide (NaHMDS), and lithium diisopropylamide (LDA).

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.

NaNH₂ + H₂O → NH₃ + NaOH

2 NaNH₂ + 4 O₂ → Na₂O + 2 NO₂ + 2 H₂O

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.

See also

• Lithium amide
• Sodium bis(trimethylsilyl)amide