Sodium Aluminum Hydride

NaAlH4

[13770-96-2]  · AlH4Na  · Sodium Aluminum Hydride  · (MW 54.01)

(reducing agent similar in activity to LiAlH4;1 deoxygenative dimerization of carbonyls and alcohols;11a hydroalumination of alkenes and alkynes11b)

Physical Data: mp 180-183 °C (dec with evolution of H2); d 1.28 g cm-3.

Solubility: sol THF, DME, diglyme; insol ether, hydrocarbons.

Form Supplied in: white crystalline solid.

Analysis of Reagent Purity: iodometric titration;10b H content determined by gas evolution analysis; Al content determined by EDTA-Zn(OAc)2 back titration at pH 4 using dithizone as an indicator.9a

Purification: recrystallization from a THF-benzene solvent mixture by addition of benzene, followed by partial removal of the solvent under vacuum. The white solid is collected and dried under vacuum before dissolving in freshly distilled THF.

Handling, Storage, and Precautions: severe fire and explosion hazard in contact with oxidizing agents and water, forms caustic and irritant compounds; stable in dry air at room temperature. Solutions in THF or diglyme appear to be stable for at least several months if not exposed to air. To preserve reactivity it is best to store wet with toluene than to store dry. Use in a fume hood.

Functional Group Reductions.

This reagent reduces aldehydes, ketones, carboxylic acids, esters, and acid chlorides to give alcohols. Amides, nitriles, and aliphatic nitro compounds give amines. Aromatic nitro compounds yield azo compounds. Yields are usually within 10% of those reported for Lithium Aluminum Hydride.1 NaAlH4 is about 10-11 times less reactive than LiAlH4 in the reduction of ketones.2 Heterogenous reductions of esters in diethyl ether, benzene, toluene, or heptane give good yields of the alcohols.1a,3 Hydrogenolysis of alkyl halides occurs at a rate considerably slower than with LiAlH4.1,4a,b Aromatic iodides and bromides are readily reduced in THF but diglyme is a better solvent for chlorides.4c Ethers and double and triple bonds are normally stable to this reagent. Under controlled conditions, the reaction with esters, dialkylamides, and aromatic nitriles can provide aldehydes in good yields.5 Aliphatic nitriles proceed mainly to the amines with only 15-25% yield of the aldehydes. Best yields are obtained by inverse addition of the hydride at low temperatures. Certain lactones can be partially reduced.6a Phthalic anhydrides are sluggishly converted to the lactones and substituent effects on regioselectivity have been studied.6b Quaternary pyridinium iodides are reduced to piperidines.7 Reduction of N-cyclopropylimines gives the cyclopropylamines as well as the n-propylamines resulting from ring cleavage.8

Stereoselective Reductions.

NaAlH4 gives a slightly smaller extent of axial addition to 4-t-butylcyclohexanone than is observed for LiAlH4 (88% and 92%, respectively).9 The stereochemical features of a number of ketone reductions by this reagent have been examined.9,10 Greater degrees of stereoselectivity are generally found with LiAlH4. In the case of cyclic a-amino ketones, larger amounts of trans-isomers are produced compared to LiAlH4 (eq 1).10d-f

Deoxygenative Dimerization Reactions.

In the presence of NaAlH4/NbCl5, aromatic carbonyl compounds undergo deoxygenative dimerization to yield alkenes (56-99%).11a Purely aliphatic carbonyls give trace to low yields of alkenes. Allylic and benzylic alcohols form symmetrical coupling products (eq 2). Allylic rearrangements occur in some cases. Under these conditions, epoxides can be deoxygenated to give the corresponding alkenes.

Hydrometalation.

Internal alkynes are converted to (Z)-alkenes with high stereoselectivities (>20:1) using the NaAlH4/NbCl5 system.11a Terminal alkenes and internal alkynes are reduced rapidly and in high yield by NaAlH4 in the presence of a catalytic amount of Dichlorobis(cyclopentadienyl)titanium.11b The reduction of 2-alkyn-1-ols by NaAlH4 via a cyclic alanate provides b- or g-substituted allyl alcohols, depending on the solvent and the electronic character of the substituent.12


1. (a) Finholt, A. E.; Jacobson, E. C.; Ogard, A. E.; Thompson, P. JACS 1955, 77, 4163. (b) Clasen, H. AG 1961, 73, 322.
2. (a) Ashby, E. C.; Boone, J. R. JACS 1976, 98, 5524. (b) Wiegers, K. E.; Smith, S. G. JOC 1978, 43, 1126.
3. Prokhorenko, O. A.; Polovtsev, S. V.; Dmitrieva, Z. T.; Soldatov, S. N.; Katsnel'son, E. Z. Zh. Prikl. Khim. (S.-Petersburg) 1991, 64, 941 (CA 1992, 117, 153 148p).
4. (a) Krishnamurthy, S.; Brown, H. C. JOC 1980, 45, 849. (b) Mirsaidov, U.; Palatov, M. S.; Gatina, R. F.; Dymova, T. N. Izv. Akad. Nauk Tadzh SSR, Otd. Fiz.-Mat. Geol.-Khim. Nauk 1981, 27 (CA 1982, 97, 109 508a). (c) Zakharkin, L. I.; Gavrilenko, V. V.; Rukasov, A. F. DOK 1972, 205, 93.
5. (a) Zakharkin, L. I.; Gavrilenko, V. V.; Maslin, D. N.; Khorlina, I. M. TL 1963, 2087. (b) Zakharkin, L. I.; Maslin, D. N.; Gavrilenko, V. V. T 1969, 25, 5555. (c) Zakharkin, L. I.; Maslin, D. N.; Gavrilenko, V. V. BAU 1964, 1415.
6. (a) Nemec, J.; Jary, J. CCC 1969, 34, 843. (b) Soucy, C.; Favreau, D.; Kayser, M. M. JOC 1987, 52, 129.
7. Ferles, M.; Attia, A.; Silhankova, A. CCC 1973, 38, 615.
8. Bumgardner, C. L.; Lawton, E. L.; Carver, J. G. JOC 1972, 37, 407.
9. (a) Ashby, E. C.; Boone, J. R. JOC 1976, 41, 2890. (b) Handel, H.; Pierre, J.-L. TL 1976, 2029.
10. (a) Biesemans, M.; Van de Woude, G.; Van Hove, L. BSB 1990, 99, 29. (b) Ibarra, C. A.; Perez-Ossorio, R.; Quiroga, M. L.; Perez, M. S. A.; Dominguez, M. J. F. JCS(P2) 1988, 101. (c) Handel, H.; Pierre, J.-L. TL 1976, 741. (d) Benard, C.; Maurette, M. T.; Lattes, A. BSF(2) 1976, 145. (e) Benard, C.; Maurette, M. T.; Lattes, A. TL, 1973, 2763. (f) Benard, C.; Maurette, M. T.; Lattes, A. TL 1973, 2305.
11. (a) Sato, M.; Oshima, K. CL 1982, 157. (b) Ashby, E. C.; Noding, S. A. JOC 1980, 45, 1035.
12. Zakharkin, L. I.; Vinnikova, M. I.; Gavrilenko, V. V. IZV 1987, 641.

Melinda Gugelchuk

University of Waterloo, Ontario, Canada



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