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Lithium borohydride (LiBH 4) is a borohydride and known in organic synthesis as a reducing agent for esters.Although less common than the related sodium borohydride, the lithium salt offers some advantages, being a stronger reducing agent and highly soluble in ethers, whilst remaining safer to handle than lithium aluminium hydride.
It has also been shown to reduce aromatic esters to the corresponding alcohols as shown in eq 6 and 7. LiBHEt 3 also reduces pyridine and isoquinolines to piperidines and tetrahydroisoquinolines respectively. [7] The reduction of β-hydroxysulfinyl imines with catecholborane and LiBHEt 3 produces anti-1,3-amino alcohols shown in (8). [8]
In organic chemistry, carbonyl reduction is the conversion of any carbonyl group, usually to an alcohol. It is a common transformation that is practiced in many ways. [1] Ketones, aldehydes, carboxylic acids, esters, amides, and acid halides - some of the most pervasive functional groups, -comprise carbonyl compounds.
For example, sodium cyanoborohydride is generally incapable of reducing amides, ethers, esters and lactones, nitriles, or epoxides. [8] Therefore, it can selectively reduce some functionalities in the presence of others. Some examples of selective reduction include: Reduction of iminium ions in the presence of carbonyls [8]
Reduction via the net transfer of hydrogen from one organic molecule to another is known as transfer hydrogenation. Transfer hydrogenation to ketones leads to alcohols (the Meerwein-Ponndorf-Verley reduction ), and in the presence of a chiral transition metal catalyst, this process may be rendered enantioselective.
The classic example of a dehydration reaction is the Fischer esterification, which involves treating a carboxylic acid with an alcohol to give an ester RCO 2 H + R′OH ⇌ RCO 2 R′ + H 2 O. Often such reactions require the presence of a dehydrating agent, i.e. a substance that reacts with water.
LiH is highly reactive towards water and other protic reagents: [3]: 7 LiH + H 2 O → Li + + H 2 + OH −. LiH is less reactive with water than Li and thus is a much less powerful reducing agent for water, alcohols, and other media containing reducible solutes. This is true for all the binary saline hydrides. [3]: 22
This compound is used as a reducing agent in organic synthesis, especially for the reduction of esters, carboxylic acids, and amides. The solid is dangerously reactive toward water, releasing gaseous hydrogen (H 2). Some related derivatives have been discussed for hydrogen storage.