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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] The idealized equation for the ...
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)
To a solution of 1,3-dihydro-1,3-bis(chloromethyl)benzo[c] thiophene 2,2-dioxide (0.584 g, 2.2 mmol) in 50 ml of dry benzene was added 0.80 mL (2.8 mmol) of a 70% benzene solution of NaAlH 2 (OCH 2 CH 2 OCH 2) 2 via syringe, and the solution was refluxed for 12 hours. The mixture was cooled to 0° and decomposed with 20% sulfuric acid.
At low temperatures (below -60°C), the solution solidifies to a glassy pulverizable substance with no sharp melting point. SMEAH is a versatile hydride reducing agent. It readily converts epoxides, aldehydes, ketones, carboxylic acids, esters, acyl halides, and anhydrides to the corresponding alcohols.
Aluminum amalgam (Al/Hg) may be used for the chemoselective reduction of α-sulfonylated carbonyl groups. Carboxylic acid derivatives, acetals, thioacetals, amines, alcohols, and isolated double bonds are all inert to Al/Hg. Selective desulfonylation may be carried out on β-hydroxy sulfones without reductive elimination.
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Water and carbon dioxide are byproducts: [1] 2 RCO 2 H → R 2 CO + CO 2 + H 2 O. Bases promote this reaction. The reaction mechanism is proposed to involve nucleophilic attack of the alpha-carbon of one acid group on the other carboxylic acid group, possibly as a concerted reaction with the decarboxylation. [1]