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Reduction reactions

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Organic chemistry

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Reduction reactions

  1. 1. Reduction Reactions
  2. 2. Classification of reductionreactions Catalytic hyrdogenation (H2 with metals) Hydride transfer reactions, using hydride sources such as LiAlH4, NaBH4,.. Dissolving metal reductions (Na, Li in ammonia solution) (Birch reduction)
  3. 3. Classification of reductionreactions Replacement of oxygen by hydrogen Removing oxygen from the substrate Reduction with cleavage Reductive coupling
  4. 4. Catalytic Hydrogenation Addition of H2 to unsat. bond (double , triple bonds, NO2 , CN,.. Without catalysts ,it needs 480 co Pt group metals (Pd, Ni ,Ru and Rh) used as catalysts Can be selective reduction, depends on conditions
  5. 5. Catalytic Hydrogenation
  6. 6. Catalytic Hydrogenation
  7. 7. Pd/C reduction Pd powder spread on charcoal after reduction of PdCl2 with H2 Homogenous catalyst, can be recovered by filtration
  8. 8. Raney Nickel Treatment of Al-Ni alloy with NaOH To reduce alkenes, alkynes, nitriles aromatics and carbonyl compounds Syn addition product
  9. 9. Raney Nickel Hydrogenolysis: removal of sulphur (C-S to C-H) in desulphurization reaction Use after open immediately????
  10. 10. PtO2( Adams catalyst) PtO2 reduced to Pt with H2
  11. 11. Lindlar`s catalyst Pd supported with CaCO3 instead of charcoal,then treated with Pb to deactivate. Selective reduction of alkynes to Z-alkenes only via syn addition
  12. 12. NaBH4 Selective (chemoselectivity) reagent White crystals, safe and easy to handle Reduces aldehydes, ketones. Can`t reduce esters ,acids, amides
  13. 13. NaBH4Generally Still reducing agent
  14. 14. NaBH4Luche reduction
  15. 15. LiAlH4 Powerful reducing agent compared to NaBH4 due to weaker Al-H bond. Pure sample is white but commercially is grey???? Dangerous, reacts violently with water Reduce aldehyde, ketones, esters, amides and nitro compounds.
  16. 16. LiAlH4
  17. 17. DIBAL Selective reagent (alkyne to alkene, ester or ketone to aldehyde). Specialist reductant of nitrile to aldehyde
  18. 18. Borane BH3 gas dissolved in THF or Et2O or DMS Selective reducing agent Hydroboration is syn addition, highly regioselective
  19. 19. Borane Regioselectivity
  20. 20. Borane chemoselectivity
  21. 21. Borane Amide to amineDialkyl borane
  22. 22. CBS ??? Borane complexed with oxazoborolidine Enantioselective reduction of ketones So, CBS is a catalyst, not reagent
  23. 23. CBS ??? R,R` difference is very important High ee, high yield Easy recovered
  24. 24. Wolff-Kishner reduction Reduction of aldehydes, ketones to alkane Using hydrazine in basic media
  25. 25. Metal dissolving reduction Dissolving Li or Na in NH3 solution Birch reduction in case of aromatics Good access to cyclohexadienes
  26. 26. Metal dissolving reduction+I, -I effect
  27. 27. Metal dissolving reductionWhy 1,4 not 1,3 ???
  28. 28. Clemmensen reduction  Kind of electron reduction reactions  Zinc metal in Conc. HCl  Carbonyl to alkane (CH ) 2Carbenoid mechanism
  29. 29. Asymmetric hydrogenation Using catalytic amounts of chiral ligands with H2.
  30. 30. Asymmetric hydrogenation
  31. 31. Staudinger reduction Azide to amide (possible via hydrogenation) Mild conditions