Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Hydrogenation

4,468 views

Published on

  • Dating direct: ❶❶❶ http://bit.ly/39mQKz3 ❶❶❶
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
  • Dating for everyone is here: ❤❤❤ http://bit.ly/39mQKz3 ❤❤❤
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here

Hydrogenation

  1. 1. HHydrogenationydrogenation Sumeet chavanSumeet chavan Msc-II, Sem-IVMsc-II, Sem-IV Paper- IIPaper- II
  2. 2. ContentContent - Introduction.- Introduction. - Wilkinson catalyst .- Wilkinson catalyst . -Mechanism of hydrogenation.-Mechanism of hydrogenation.
  3. 3. IntroductionIntroduction ▪ The addition of hydrogen to an alkeneThe addition of hydrogen to an alkene to form an alkane is favouredto form an alkane is favoured thermodynamically. however thethermodynamically. however the reaction rates is negligible at ordinaryreaction rates is negligible at ordinary conditions in the absence of theconditions in the absence of the catalyst.catalyst. ▪ Efficient homogenous andEfficient homogenous and heterogenous catalyst are known for theheterogenous catalyst are known for the hydrogenation of alkenes.hydrogenation of alkenes.
  4. 4. Wilkinson catalystWilkinson catalyst Chlorotris (triphenylphosphine) rhodium(I)Chlorotris (triphenylphosphine) rhodium(I) Rh Ph3P PPh3 PPh3Cl
  5. 5. Basic properties and SynthesisBasic properties and Synthesis ▪ The compound is a square planar, 16-electronThe compound is a square planar, 16-electron complex. It is usually obtained in the form of acomplex. It is usually obtained in the form of a red-violet crystalline solid from the reaction ofred-violet crystalline solid from the reaction of rhodium(III) chloride with excessrhodium(III) chloride with excess triphenylphosphine.triphenylphosphine. Rh Ph3P PPh3 PPh3Cl + EtOH 78 o C + Ph3PORhCl3 3 H2O + >4 PPh3
  6. 6. Step-1 Oxidative addition.Step-1 Oxidative addition. The given reaction involves the oxidativeThe given reaction involves the oxidative addition of H2 to the 16e- complexaddition of H2 to the 16e- complex RhCl(PPh3)3 to form a 18e- dihydro complex. Rh Ph3P Cl Ph3P PPh3 + H2 Rh Ph3P Cl Ph3P PPh3 H H RhRh3+3+ RhRh+1+1
  7. 7. Step-2 Ligand dissociation. The dissociation of a phosphine ligand from dihydro complex results in the formation of the co-ordinatively unsaturated complex. Rh Ph3P Cl Ph3P PPh3 H H Rh Ph3P Cl Ph3P H H + PPh3
  8. 8. Step- 3 Alkene coordination. The co-ordinatively unsaturated complex forms the alkene complex. Rh Ph3P Cl Ph3P H H CH2 CH2 Rh Ph3P Cl Ph3P H H CH2 CH2+
  9. 9. Step-4 migratory insertion.Step-4 migratory insertion. Hydrogen atom transfers from the Rh atomHydrogen atom transfers from the Rh atom in alkene complex to the co-ordinated alkenein alkene complex to the co-ordinated alkene yield a transient 16e- alkyl complex.yield a transient 16e- alkyl complex. Rh Ph3P Cl Ph3P H H CH2 CH2 Rh Ph3P Cl Ph3P CH2 H CH2H
  10. 10. Step-5 Ligand association.Step-5 Ligand association. The phosphine ligand is then added to theThe phosphine ligand is then added to the 16e- complex.16e- complex. + PPh3Rh Ph3P Cl Ph3P CH2 H CH2H Rh Ph3P Cl Ph3P CH2 H CH2H PPh3
  11. 11. Step-6 Reductive elimination.Step-6 Reductive elimination. Hydrogen get migrated to carbon which resultsHydrogen get migrated to carbon which results in reductive elimination of the alkane andin reductive elimination of the alkane and regeneration of the catalyst takes place.regeneration of the catalyst takes place. Rh Ph3P Cl Ph3P PPh3Rh Ph3P Cl Ph3P CH2 H CH2H PPh3 + CH3 CH3 (note: regeneration of the catalyst)
  12. 12. - The rates of hydrogenations decrease with- The rates of hydrogenations decrease with increase in the alkyl group substitution on doubleincrease in the alkyl group substitution on double bond mirroring their relative binding affinities tobond mirroring their relative binding affinities to the metal center. It is also partly due to stericthe metal center. It is also partly due to steric factors. Therefore, for a successfulfactors. Therefore, for a successful hydrogenation, oxidative addition of dihydrogenhydrogenation, oxidative addition of dihydrogen prior to the binding of olefin is crucial.prior to the binding of olefin is crucial.
  13. 13. SELECTIVE HYDROGENATIONSELECTIVE HYDROGENATION BY WILKINSON'S CATALYSTBY WILKINSON'S CATALYST ▪ Less substituted and sterically lessLess substituted and sterically less hindered double bonds are selectivelyhindered double bonds are selectively hydrogenated.hydrogenated.
  14. 14. - Exocyclic double bonds are- Exocyclic double bonds are selectively hydrogenated overselectively hydrogenated over endocyclic double bonds.endocyclic double bonds.
  15. 15. - Cis alkenes are reduced rapidly than- Cis alkenes are reduced rapidly than trans alkenes.trans alkenes. - Isolated double bonds are rapidly hydrogenated over conjugated dienes.
  16. 16. References -References - ▪ R.C.Mehrotra and A.Singh,R.C.Mehrotra and A.Singh, Organometallic Chemistry-A UnifiedOrganometallic Chemistry-A Unified Approach.Approach. ▪ D.F.Shriver, P.W.Atkins and C.H.D.F.Shriver, P.W.Atkins and C.H. Langford, Inorganic Chemistry.Langford, Inorganic Chemistry.

×