Structure-selectivity relationship in the chemoselective hydrogenation of unsaturated nitriles

Comparison of C═C Bond Hydrogenation in C-4 Unsaturated Nitriles over Pt/Alumina

“…This is in contrast to that found when cis-2-pentenenitrile and trans-3-pentenenitrile were hydrogenated over Raney Nickel, [2] where the conjugated cis-2-pentenenitrile reacted faster than the non-conjugated trans-3-pentenenitrile to give the saturated nitrile. It is also in contrast with a study of conjugated and nonconjugated alkenyl benzenes [10] where the conjugated cis-isomer was the most reactive.…”

“…This would give an order of AC > MN, which is similar to that found experimentally except there is also the effect of conjugation; it would be expected that the conjugated C=C bond would be more reactive [2,7] but it would appear that steric effects are the dominant factor rather than any effect of conjugation. This is in contrast to that found when cis-2-pentenenitrile and trans-3-pentenenitrile were hydrogenated over Raney Nickel, [2] where the conjugated cis-2-pentenenitrile reacted faster than the non-conjugated trans-3-pentenenitrile to give the saturated nitrile.…”

“…With a short chain unsaturated nitrile or conjugated system the C=C double bond should be hydrogenated preferably over the C≡N group from a thermodynamic point of view [1,2]. In contrast when hydrogenating long chain nitriles or when the double bond is sterically hindered the hydrogenation of the double bond is slower than the CN triple bond [2]. Changing the surface character of the catalyst in bimetallic systems can also affect activity and selectivity in unsaturated nitrile hydrogenation [3].…”

The application of a supported palladium catalyst for the hydrogenation of aromatic nitriles

“…As previous reports have noted, conjugation of the nitrile group can assist reduction of that unit [36], so it was deemed useful to consider the case of cinnamonitrile within this systematic investigation. Could the presence of the double bond and conjugation between the nitrile group and the aromatic ring be used to induce hydrogenation of the nitrile group and lead to detectable products in the liquid phase?…”

Chemoselective hydrogenation of unsaturated nitriles to unsaturated primary amines: Conversion of cinnamonitrile on metal-supported catalysts

“…Besides, in order to obtain selectively primary amines the coupling reactions leading to secondary and tertiary amines have to be avoided. Previous works have reported that C C bonds are more reactive to hydrogenation than the nitrile groups [4,5] and therefore selective C≡N hydrogenation in presence of double bonds is difficult to achieve, in particular when both unsaturated groups are conjugated or in close proximity [6]. Most of the few papers dealing with the hydrogenation of unsaturated nitriles on solid catalysts have been carried out on Ni and Co-based catalysts [4,5,7,8], probably because both metals are highly active and selective to obtain saturated primary amines from the corresponding saturated nitrile [9][10][11].…”