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Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula Li[Al H 4] or LiAlH 4. It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. [4] This compound is used as a reducing agent in organic synthesis, especially for the reduction of esters, carboxylic acids, and amides.
The first step involves deprotonation of the carboxylic acid. The final step in the reduction of carboxylic acids and esters is hydrolysis of the aluminium alcoxide. [8] Esters (and amides) are more easily reduced than the parent carboxylic acids. Their reduction affords alcohols and amines, respectively. [9]
Reductions of α,β-unsaturated carbonyl compounds may occur in a 1,2 sense (direct addition) or a 1,4 sense (conjugate addition). The tendency to add in a 1,4 sense is correlated with the softness of the hydride reagent according to Pearson's hard-soft acid-base theory. [7]
As a reagent, SMEAH is comparable with lithium aluminium hydride (LAH, LiAlH 4). It is a safer alternative to LAH and related hydrides. SMEAH exhibits similar reducing effects, but does not have the inconvenient pyrophoric nature, short shelf-life, or limited solubility of LAH. Upon contact with air and moisture, SMEAH reacts exothermically but ...
Lithium aluminium hydride (LAH) modified with chiral alkoxide ligands has been shown to proceed in good yield and high enantioselectivity. Chelating ligands such as BINOL [6] are used to avoid disproportionation and background reduction by LAH. Chiral diamines and amino alcohols have also been used to modify LAH for enantioselective reductions. (4)
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In solution—typically in ethereal solvents such tetrahydrofuran or diethyl ether—aluminium hydride forms complexes with Lewis bases, and reacts selectively with particular organic functional groups (e.g., with carboxylic acids and esters over organic halides and nitro groups), and although it is not a reagent of choice, it can react with ...