Reaction of Sodium Aluminum Hydride with Selected Organic Compounds Containing Representative Functional Groups. Comparison of the Reducing Characteristics of Lithium and Sodium Aluminum Hydrides

Article abstract of DOI:10.1021/jo00069a042

The approximate rate and stoichiometry of the reaction of excess sodium aluminum hydride (SAH) with organic compounds containing representative functional groups under standarized conditions (tetrahydrofuran, 0 deg C) were examined in order to define the reducing characteristics of the reagent and compare the reducing power with lithium aluminum hydride (LAH).In general, the reducing action and power of the reagent are similar to those of LAH.All of the active hydrogen compounds including alcohols, amines, and thiols evolve hydrogen instantly.Aldehydes and ketones are reduced very rapidly and quantitatively to give the corresponding alcohols.Unlike LAH, SAH reduces carboxylic acids and their salts only slowly to the corresponding alcohols.Similarly, anhydrides are reduced slowly to the diols.Acid chlorides, esters, and lactones consume 2 equiv of hydride in less than 15 min at 0 deg C to give the corresponding alcohols.However, the reaction of epoxides with this reagent proceeds at a much slower rate than LAH, requiring 6-24 h at 0 deg C and 1-6 h at room temperature.Both primary aliphatic and aromatic amides examined evolve 2 equiv of hydrogen rapidly and are reduced slowly to the alcohols.Tertiary amides rapidly utilize 2 equiv of hydride for reduction.The reaction of tertiary amides with a limiting amount of the reagent provides the aldehydes in yields of around 80percent.Benzonitrile also readily reacts to give the amine, while the reaction of capronitrile liberates ca. 0.4 equiv of hydrogen and consumes less than 2 equiv of hydride for reduction both at 0 deg C and room temperature.Aromatic nitro compounds examined also undergo the reaction readily to give the hydrazobenzene derivatives similar to the case with LAH.Oximes, phenyl isocyanate, disulfides, and sulfoxides are also readily reduced, while sulfides, sulfones, and tosylates are inert to this reagent.Finally, the similarities and differences in the reaction of organic compounds with LAH and SAH are established in this study.