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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.
The Guerbet reaction, reported in 1899, [5] is an early example of a hydrogen auto-transfer process. The Guerbet reaction converts primary alcohols to β-alkylated dimers via alcohol dehydrogenation followed by aldol condensation and reduction of the resulting enones.
Reductions with hydrosilanes are methods used for hydrogenation and hydrogenolysis of organic compounds.The approach is a subset of ionic hydrogenation.In this particular method, the substrate is treated with a hydrosilane and auxiliary reagent, often a strong acid, resulting in formal transfer of hydride from silicon to carbon. [1]
Instead, as the reaction proceeds, the imine becomes favoured for reduction over the carbonyl starting material. [2] The two most common methods for direct reductive amination are hydrogenation with catalytic platinum, palladium, or nickel catalysts and the use of hydride reducing agents like cyanoborohydride (NaBH 3 CN).
Carbonyl reduction, the net addition of H 2 across a carbon-oxygen double bond, is an important way to prepare alcohols. Stoichiometric reducing agents to accomplish this task include lithium aluminium hydride , sodium borohydride , alkoxy borohydrides, alkoxy aluminium hydrides, and boranes.
α-Functionalized carbonyl compounds are reduced to afford the corresponding carbonyl compounds. A number of functional groups can be replaced with hydrogen using this method; one transformation that is relatively unique to samarium(II) iodide is the reduction of α-hydroxy ketones and α-hydroxy lactones.
For carbonyl and imine substrates, end-on, η 1 coordination can compete with η 2 mode. For η 1-bound substrates, the hydrogen-accepting carbon is removed from the catalyst and resists hydrogenation. [51] Iridium/P,N ligand-based systems have been effective for some ketones and imines.
This terminology is always centered on the organic compound. For example, it is usual to refer to the reduction of a ketone by lithium aluminium hydride, but not to the oxidation of lithium aluminium hydride by a ketone. Many oxidations involve removal of hydrogen atoms from the organic molecule, and reduction adds hydrogens to an organic molecule.