2. WWU -- Chemistry Aldehydes and Ketones II. Oxidation and Reduction: Synthesis Chapter 17

3. WWU -- Chemistry Assignment for Chapter 17 Sections 17.0 through 17.2 Section 17.3 -- SKIP Sections 17.4 through 17.12 Section 17.13 through 17.15 -- SKIP Sections 17.16 through 17.20 Problems

4. WWU -- Chemistry Problem Assignment In-Text Problems –17-1 through 17-11 –17-15 through 17-18 End-of-Chapter Problems –1 through 4 (all parts)

5. WWU -- Chemistry Reduction of a Carbonyl Group to an Alcohol

6. WWU -- Chemistry What If We Had the World’s Simplest Nucleophile?

7. WWU -- Chemistry If we could make this work, we would have means of reducing the carbonyl group. Go back and re-read the Special Topics box at the beginning of Chapter 14.

8. WWU -- Chemistry Lithium Aluminum Hydride Lithium aluminum hydride, LiAlH 4, is a very powerful hydride donor, and thus it is an excellent reducing agent.

9. WWU -- Chemistry Outline

10. Lithium Aluminum Hydride Reduction of Aldehydes and Ketones These reactions typically go in very high yield.

11. WWU -- Chemistry Learn it this way:

12. WWU -- Chemistry Aluminum is required to coordinate with the oxygen of the carbonyl group. For example, in the absence of aluminum (using sodium hydride, NaH as the reducing agent), there is no reduction.

13. WWU -- Chemistry You Must Be Careful! You Must Be Careful! LiAlH 4 + 4 H 2 O LiOH + Al(OH) 3 + 4 H 2

14. WWU -- Chemistry A similar, but less reactive, reducing agent is sodium borohydride, NaBH 4.

15. WWU -- Chemistry Sodium Borohydride Reduction of Aldehydes and Ketones

16. WWU -- Chemistry Example In general, the reduction should proceed equally easily from either side, yielding two mirror-image products.

17. WWU -- Chemistry Sodium Borohydride Reduction of Camphor (endo) (exo) In this case, approach by borohydride from the upper side is sterically hindered by the bridge methyl group. The result is a predominance of exo alcohol.

18. WWU -- Chemistry Sodium Borohydride Reduction of Norcamphor Here, it is the underside of the molecule that is more sterically hindered, so the favored alcohol is the endo alcohol. Similar results are obtained with lithium aluminum hydride.

19. WWU -- Chemistry Another example:

20. WWU -- Chemistry Contrast these two reactions Note that sodium borohydride is more selective.

21. WWU -- Chemistry Catalytic Hydrogenation of Aldehydes and Ketones

22. WWU -- Chemistry Reduction of a Carbonyl Group to a Methylene Group

23. WWU -- Chemistry We are trying to accomplish...

24. WWU -- Chemistry Clemmensen Reduction Zn(Hg) is a zinc amalgam

25. WWU -- Chemistry The mechanism of the Clemmensen reduction involves the formation of some sort of zinc- ketone complex. This reaction is a good method for the reduction of acid-stable carbonyl compounds (Note that the reaction takes place in the presence of concentrated HCl).

26. WWU -- Chemistry Example of a Clemmensen Reduction Notice that the reduction does not affect the carboxyl group

27. WWU -- Chemistry Wolff-Kishner Reduction

28. WWU -- Chemistry The mechanism involves the formation of a hydrazine adduct, which loses water to form a hydrazone. The hydrazone then rearranges to lose a molecule of nitrogen gas, leaving behind a carbanion. The carbanion picks up a proton from the solvent to form the product.

29. WWU -- Chemistry This will never show up on any of my exams!

30. WWU -- Chemistry The Wolff-Kishner reduction is useful for the reduction of carbonyl compounds that are stable in strong base. (Note that the reaction takes place in the presence of concentrated KOH or other base)

31. WWU -- Chemistry Example

32. Desulfurization

33. Advantages: High yields Mild and nearly neutral reaction conditions Disadvantages: Stinky! Raney Nickel is tricky to prepare

34. WWU -- Chemistry Example of a Raney Nickel Desulfurization

35. WWU -- Chemistry