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In organic chemistry, hydrocyanation is a process for conversion of to . The reaction involves the addition of hydrogen cyanide and requires a catalyst if the substrate alkene is unactivated. This conversion is conducted on an industrial scale for the production of precursors to nylon. Direct hydrocyanation is rare in the laboratory because hydrogen cyanide is extremely toxic, but transfer variants can allow other nitrilic compounds to serve as hydrogen cyanide Synthon.
Nickel-based catalysts deactivate when they formation of dicyanonickel(II) species, which are unreactive toward alkenes. The dicyanide arises via two pathways (L = phosphite):
Generally acidic conditions favor 1,2-adducts, while basic conditions favor 1,4-adducts. Additions of alkali metal , for instance, lead exclusively to 1,4-addition. In contrast to alkali metal cyanides and cyanoaluminates, Lewis acidic cyanides, such as TMSCN, favor 1,2-addition. Acetylenic substrates undergo the reaction; however the scope of this reaction is limited and yields are often low. 1,4-Addition to imines has been observed in a few cases, although imines are often base labile. Esters, nitriles, and other carbonyl derivatives also undergo conjugative hydrocyanation. When alkali metal cyanides are used, at least partial neutralization of the reaction medium is usually necessary. Neutralization can be accomplished through an acidic group on the substrate itself (internal neutralization). or through the addition of an external acid (external neutralization). Acetic acid is commonly used for this purpose, in a procedure originally described by Lapworth.
Conjugative hydrocyanation was used to prepare the steroidal D ring. Diastereoselectivity is generally high in these addition reactions, and the resulting β-cyano carbonyl compounds can be converted to a number of steroidal products.
This process consists of three steps: hydrocyanation of butadiene to a mixture of 2-methyl-butene-3-nitrile (2M3BM) and pentene-3-nitrile (3PN), an isomerization step from 2M3BM (not desired) to 3PN and a second hydrocyanation (aided by a Lewis acid cocatalyst such as aluminium trichloride or triphenylboron) to adiponitrile.
Naproxen, an anti-inflammatory drug, is prepared via an asymmetric hydrocyanation of a vinylnaphthalene utilizing a phosphinite () ligand, L . The enantioselectivity of this reaction is important because only the S enantiomer is medicinally desirable, whereas the R enantiomer produces harmful health effects. This reaction can produce the S enantiomer with >90% stereoselectivity. Upon recrystallization of the crude product, the optically pure nitrile can be obtained.
Some hydrocyanation catalysts generate a reversible equilibrium, and can transfer HCN units between two different alkenes.
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