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Aldehydes and Ketones. II. Oxidation and Reduction; Synthesis

Aldehydes and Ketones. II. Oxidation and Reduction; Synthesis. Chapter 17. Assignment for Chapter 17. Skip the following sections: Section 17.3 Sections 17.13 through 17.15 . Problem Assignment. In-Text Problems 17-1, 2, 3, 4 5 (NH 2 -NH 2 is misssing from the problem!!)

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Aldehydes and Ketones. II. Oxidation and Reduction; Synthesis

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  1. Aldehydes and Ketones. II.Oxidation and Reduction;Synthesis Chapter 17

  2. Assignment for Chapter 17 • Skip the following sections: • Section 17.3 • Sections 17.13 through 17.15

  3. Problem Assignment • In-Text Problems • 17-1, 2, 3, 4 • 5 (NH2-NH2 is misssing from the problem!!) • 6 - 11 15, 17, 18 • End-of-Chapter Problems • 1, 2, 3

  4. Oxidation and reduction -- an overview • Oxidation: add O or remove H2 • Reduction: remove O or add H2 • Oxidation numbers are relatively useless for carbon!

  5. Sect. 17.1: Hydride as a nucleophile

  6. Reactions of sodium borohydride • Aldehydes yield primary alcohols • Ketones yield secondary alcohols • Esters give no reaction! • Amides give no reaction!

  7. Keep water away from lithium aluminum hydride! LiOH + Al(OH) + 4 H2 + 4 H O LiAlH 4 2 3

  8. Reactions of lithium aluminum hydride • Aldehydes give primary alcohols • Ketones give secondary alcohols • Esters give primary alcohols from the carboxylic acid part of the ester • Amides give primary amines!!

  9. Sect. 17.2: Reduction of carbonyl groups with hydrogen • You really have to “pound” on carbonyl compounds to reduce them by using hydrogen under high pressure! • Aldehydes give primary alcohols • Ketones give secondary alcohols • Other carbonyl compounds, such as esters are virtually unreactive.

  10. Selective reduction of C=C and C=O bonds • Hydrogen/ Pt (low pressure): reduces C=C but not the C=O group • Sodium borohydride: reduces C=O but not the C=C group

  11. Sect. 17.4: The Clemmensen Reduction

  12. Sect. 17.5: Wolff-Kishner Reduction

  13. Sect. 17.6: Raney Nickel Desulfurization

  14. Sect. 17.7: Oxidations NOTE: A dehydrogenationis also a form of oxidation!

  15. Oxidation: an overview Mild oxidizers: CrO3 in pyridine CrO3 in acetone pyridinium chlorochromate (PCC) Primary alcohols give aldehydes Secondary alcohols give ketones Strong oxidizers: K2Cr2O7 in acid CrO3 in acid KMnO4 Primary alcohols give carboxylic acids Secondary alcohols give ketones

  16. Oxidation of Primary Alcohols with KMnO4

  17. Sect. 17.8: Oxidation of Primary Alcohols with K2Cr2O7 (Jones) Jones Oxidation

  18. Oxidation of Secondary Alcohols Jones Oxidation

  19. Sect. 17.9: Oxidation with Chromic Oxide and Pyridine Sarett Oxidation

  20. Important!! • Sarrett reaction: Primary alcohols get oxidized to aldehydes • Aldehydes are not further oxidized to carboxylic acids

  21. Sect. 17.10: Oxidation with Pyridinium Chlorochromate “PCC” Oxidation

  22. Important!! • PCC reactions: Primary alcohols get oxidized to aldehydes • Aldehydes are not further oxidized to carboxylic acids

  23. Sect. 17.11: Silver and Copper oxidation of aldehydes • Tollens: oxidation with silver ion yields a carboxylic acid; Ag+ is reduced to Ago (silver mirror) • Benedict’s: oxidation with copper ion yields a carboxylic acid; Cu2+ is reduced to Cu+ (Cu2O)

  24. Sect. 17.12: Reducing and non-reducing sugars • Carbohydrates that have hemi acetal structures are in equilibrium with a “free” aldehyde ---- reducing sugars • Carbohydrates that are in the acetal form, do not have free aldehyde --- non-reducing • Reducing sugar =positive Tollens/Benedicts • Non-reducing sugar = negative tests

  25. Sect. 17.16: Biological reduction and oxidation

  26. Nicotinamide Adenine Dinucleotide (NADH)

  27. Reduction of Acetaldehyde in Fermentation

  28. Reduction of Pyruvic Acid in Muscle Tissue

  29. Sect. 17.17: Preparation of aldehydes by reduction

  30. Sect. 17.18: Ketone Synthesis using Organometallic Reagents • Acid chlorides give ketones with lithium dialkyl cuprates • Acid chlorides give ketones with Grignard reagents, but only at low temperatures

  31. Ketone Synthesis using Lithium Dialkylcuprates

  32. Sect. 17.19: Synthesis Problem

  33. Now, how do we do this?

  34. Are We Having Fun Yet?

  35. Let’s Make Some Drugs! Protecting group is required!

  36. Another Synthesis Problem

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