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Hydrogenation is a chemical reaction between molecular hydrogen (H 2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic compounds .
The hydrogenation of alkynes is troublesome to control since alkynes tend to be reduced to alkanes, via intermediacy of the cis-alkene. [14] Ethylene reacts with Wilkinson's catalyst to give RhCl(C 2 H 4 )(PPh 3 ) 2 , but it is not a substrate for hydrogenation.
The hydrogenation of alkenes to alkanes is exothermic. The amount of energy released during a hydrogenation reaction, known as the heat of hydrogenation, is inversely related to the stability of the starting alkene: the more stable the alkene, the lower its heat of hydrogenation.
Crabtree's catalyst is an organoiridium compound with the formula [C 8 H 12 IrP(C 6 H 11) 3 C 5 H 5 N]PF 6.It is a homogeneous catalyst for hydrogenation and hydrogen-transfer reactions, developed by Robert H. Crabtree.
Alkenes that are particularly amenable to asymmetric hydrogenation often feature a polar functional group adjacent to the site to be hydrogenated. In the absence of this functional group, catalysis often results in low ee's. For some unfunctionalized olefins, iridium with P,N-based ligands) have proven effective, however. Alkene substrates are ...
Alkyne hydrogenation is stereospecific, occurring via syn addition to give the cis-alkene. [4] For example the hydrogenation of acetylenedicarboxylic acid using Lindlar catalyst gives maleic acid rather than fumaric acid. An example of commercial use is the organic synthesis of vitamin A which involves an alkyne reduction with the Lindlar catalyst.
Side reactions of the alkenes are the isomerization and hydrogenation of the double bond. While the alkanes resulting from hydrogenation of the double bond do not participate further in the reaction, the isomerization of the double bond with subsequent formation of the n-alkyl complexes is a desired reaction.
The barrier for the rotation of the alkene about the M-centroid vector is a measure of the strength of the M-alkene pi-bond. Low symmetry complexes are suitable for analysis of these rotational barriers associated with the metal-ethene bond.In Cp Rh(C 2 H 4 )(C 2 F 4 ), the ethene ligand is observed to rotate with a barrier near 12 kcal/mol but ...