Sodium amide

Sodium amide, commonly called sodamide, is the chemical compound with the formula NaNH₂. This solid, which is dangerously reactive toward water, is white when pure, 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 has been widely employed as a strong base in organic synthesis.

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Preparation and structure

Sodium amide can be prepared by the reaction of sodium with ammonia gas,^[1] 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, ca. -33 °C.^[2]

2 Na + 2 NH₃ → 2 NaNH₂ + H₂

NaNH₂ is a salt-like material and as such, crystallizes as an infinite polymer.^[3] The geometry about sodium is tetrahedral.^[4] In ammonia, NaNH₂ forms conductive solutions, consistent with the presence of Na(NH₃)₆⁺ and NH₂^- anions.

Uses

Sodium amide is used in the industrial production of indigo, hydrazine, and sodium cyanide.^[5] It is the reagent of choice for the drying of ammonia (liquid or gaseous) and is also widely used as a strong base in organic chemistry, often in liquid ammonia solution. One of the main advantages to the use of sodamide is that it is an excellent base and rarely serves as a nucleophile. It is however poorly soluble and its use has been superseded by the related reagents such as sodium hydride, sodium bis(trimethylsilyl)amide (NaHMDS), and lithium diisopropylamide (LDA).

Preparation of alkynes

Sodium amide induces the loss of two molecules of hydrogen bromide from a vicinal dibromoalkane to give a carbon-carbon triple bond, as in the preparation of phenylacetylene below.^[6]

Hydrogen chloride and/or ethanol can also be eliminated in this way,^[7] as in the preparation of 1-ethoxy-1-butyne.^[8]

Cyclization reactions

Where there is no β-hydrogen to be eliminated, cyclic compounds may be formed, as in the preparation of methylenecyclopropane below.^[9]

Cyclopropenes,^[10] aziridines^[11] and cyclobutanes^[12] 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,^[13] methyl ketones,^[14] cyclohexanone,^[15] phenylacetic acid and its derivatives^[16] and diphenylmethane.^[17] Acetylacetone loses two protons to form a dianion.^[18]

Sodium amide will also deprotonate indole^[19] and piperidine.^[20]

Other reactions

• Rearrangement with orthodeprotonation^[21]
• Oxirane synthesis (by carbene reaction?)^[22]
• Indole synthesis^[23]

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

2NaNH₂ + 4O₂ → Na₂O₂ + 2NO₂ + 2H₂O

In the presence of limited quantities of air and moisture, such as in a poorly closed container, explosive mixtures of oxidation products can form. This is accompanied by a yellowing or browning of the solid. As such, sodium amide should always be stored in a tightly closed container, if possible under an atmosphere of nitrogen gas. Sodium amide samples which are yellow or brown in color should be destroyed immediately: one method for destruction is the careful addition of ethanol to a suspension of sodium amide in a hydrocarbon solvent.

Sodium amide may be expected to be corrosive to the skin, eyes and mucous membranes. Care should be taken to avoid dispersal of the dust.

See also

• Lithium amide
• Sodium bis(trimethylsilyl)amide

References

1. ^ Bergstrom, F. W. (1955). "Sodium amide". Org. Synth. Coll. Vol. 3:778.
2. ^ Greenlee, K. W.; Henne, A. L. (1946). "Sodium Amide". Inorganic Syntheses 2:128–35.
3. ^ Zalkin, A.; Templeton, D. H. "The Crystal Structure Of Sodium Amide" Journal of Physical Chemistry 1956, Volume 60, pp 821 - 823. DOI: 10.1021/j150540a042
4. ^ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
5. ^ Merck Index (12th Edn.)
6. ^ Campbell, Kenneth N.; Campbell, Barbara K. (1950). "Phenylacetylene". Org. Synth. 30:72; Coll. Vol. 4:763.
7. ^ Jones, E. R. H.; Eglinton, Geoffrey; Whiting, M. C.; Shaw, B. L. (1954). "Ethoxyacetylene". Org. Synth. 34:46; Coll. Vol. 4:404.
   Bou, Anna; Pericàs, Miquel A.; Riera, Antoni; Serratosa, Fèlix (1987). "Dialkoxyacetylenes: di-tert-butoxyethyne, a valuable synthetic intermediate". Org. Synth. 65:68; Coll. Vol. 8:161.
   Magriotis, Plato A.; Brown, John T. (1995). "Phenylthioacetylene". Org. Synth. 72:252; Coll. Vol. 9:656.
   Ashworth, P. J.; Mansfield, G. H.; Whiting, M. C. (1955). "2-Butyn-1-ol". Org. Synth. 35:20; Coll. Vol. 4:128.
8. ^ Newman, Melvin S.; Stalick, W. M. (1977). "1-Ethoxy-1-butyne". Org. Synth. 57:65; 6:564.
9. ^ Salaun, J. R.; Champion, J.; Conia, J. M. (1977). "Cyclobutanone from methylenecyclopropane via oxaspiropentane". Org. Synth. 57:36; Coll. Vol. 6:320.
10. ^ Nakamura, Masuharu; Wang, Xio Qun; Isaka, Masahiko; Yamago, Shigeru; Nakamura, Eiichi (2003). "Synthesis and (3+2)-cycloaddition of a 2,2-dialkoxy-1-methylenecyclopropane: 6,6-dimethyl-1-methylene-4,8-dioxaspiro(2.5)octane and cis-5-(5,5-dimethyl-1,3-dioxan-2-ylidene)hexahydro-1(2H)-pentalen-2-one". Org. Synth. 80:144.
11. ^ Bottini, Albert T.; Olsen, Robert E. (1964). "N-Ethylallenimine". Org. Synth. 44:53; Coll. Vol. 5:541.
12. ^ Skorcz, J. A.; Kaminski, F. E. (1968). "1-Cyanobenzocyclobutene". Org. Synth. 48:55; Coll. Vol. 5:263.
13. ^ Saunders, J. H. (1949). "1-Ethynylcyclohexanol". Org. Synth. 29:47; Coll. Vol. 3:416.
    Peterson, P. E.; Dunham, M. (1977). "(Z)-4-Chloro-4-hexenyl trifluoroacetate". Org. Synth. 57:26; Coll. Vol. 6:273.
    Kauer, J. C.; Brown, M. (1962). "Tetrolic acid". Org. Synth. 42:97; Coll. Vol. 5:1043.
14. ^ Coffman, Donald D. (1940). "Dimethylethynylcarbinol". Org. Synth. 20:40; Coll. Vol. 3:320.
    Hauser, C. R.; Adams, J. T.; Levine, R. (1948). "Diisovalerylmethane". Org. Synth. 28:44; Coll. Vol. 3:291.
15. ^ Vanderwerf, Calvin A.; Lemmerman, Leo V. (1948). "2-Allylcyclohexanone". Org. Synth. 28:8; Coll. Vol. 3:44.
16. ^ Hauser, Charles R.; Dunnavant, W. R. (1960). "α,β-Diphenylpropionic acid". Org. Synth. 40:38; Coll. Vol. 5:526.
    Kaiser, Edwin M.; Kenyon, William G.; Hauser, Charles R. (1967). "Ethyl 2,4-diphenylbutanoate". Org. Synth. 47:72; Coll. Vol. 5:559.
    Wawzonek, Stanley; Smolin, Edwin M. (1951). "α,β-Diphenylcinnamonitrile". Org. Synth. 31:52; Coll. Vol. 4:387.
17. ^ Murphy, William S.; Hamrick, Phillip J.; Hauser, Charles R. (1968). "1,1-Diphenylpentane". Org. Synth. 48:80; Coll. Vol. 5:523.
18. ^ Hampton, K. Gerald; Harris, Thomas M.; Hauser, Charles R. (1971). "Phenylation of diphenyliodonium chloride: 1-phenyl-2,4-pentanedione". Org. Synth. 51:128; Coll. Vol. 6:928.
    Hampton, K. Gerald; Harris, Thomas M.; Hauser, Charles R. (1967).
19. ^ Potts, K. T.; Saxton, J. E. (1960). "1-Methylindole". Org. Synth. 40:68; Coll. Vol. 5:769.
20. ^ Bunnett, J. F.; Brotherton, T. K.; Williamson, S. M. (1960). "N-β-Naphthylpiperidine". Org. Synth. 40:74; Coll. Vol. 5:816.
21. ^ Brazen, W. R.; Hauser, C. R. (1954). "2-Methylbenzyldimethylamine". Org. Synth. 34:61; Coll. Vol. 4:585.
22. ^ Allen, C. F. H.; VanAllen, J. (1944). "Phenylmethylglycidic ester". Org. Synth. 24:82; Coll. Vol. 3:727.
23. ^ Allen, C. F. H.; VanAllen, James (1942). "2-Methylindole". Org. Synth. 22:94; Coll. Vol. 3:597.