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CHE 242 Unit VII The Physical and Chemical Properties, and Reactions of Ketones, Aldehydes, and Amines CHAPTER EIGHTEEN

CHE 242 Unit VII The Physical and Chemical Properties, and Reactions of Ketones, Aldehydes, and Amines CHAPTER EIGHTEEN. Terrence P. Sherlock Burlington County College 2004. Carbonyl Compounds. =>. Examples. 3-methyl-2-butanone. 3-bromocyclohexanone. 4-hydroxy-3-methyl-2-butanone

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CHE 242 Unit VII The Physical and Chemical Properties, and Reactions of Ketones, Aldehydes, and Amines CHAPTER EIGHTEEN

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  1. CHE 242Unit VIIThe Physical and Chemical Properties, and Reactions of Ketones, Aldehydes, and AminesCHAPTER EIGHTEEN Terrence P. Sherlock Burlington County College 2004

  2. Carbonyl Compounds => Chapter 18

  3. Examples 3-methyl-2-butanone 3-bromocyclohexanone 4-hydroxy-3-methyl-2-butanone => Chapter 18

  4. Name as Substituent • On a molecule with a higher priority functional group, C=O is oxo- and -CHO is formyl. • Aldehyde priority is higher than ketone. 3-methyl-4-oxopentanal 3-formylbenzoic acid => Chapter 18

  5. Historical Common Names acetophenone acetone benzophenone => Chapter 18

  6. Aldehyde Common Names • Use the common name of the acid. • Drop -ic acid and add -aldehyde. • 1 C: formic acid, formaldehyde • 2 C’s: acetic acid, acetaldehyde • 3 C’s: propionic acid, propionaldehyde • 4 C’s: butyric acid, butyraldehyde. => Chapter 18

  7. => Boiling Points • More polar, so higher boiling point than comparable alkane or ether. • Cannot H-bond to each other, so lower boiling point than comparable alcohol. Chapter 18

  8. Solubility • Good solvent for alcohols. • Lone pair of electrons on oxygen of carbonyl can accept a hydrogen bond from O-H or N-H. • Acetone and acetaldehyde are miscible in water. => Chapter 18

  9. formaldehyde, b.p. -21C formalin trioxane, m.p. 62C => Formaldehyde • Gas at room temperature. • Formalin is a 40% aqueous solution. Chapter 18

  10. IR Spectroscopy • Very strong C=O stretch around 1710 cm-1. • Conjugation lowers frequency. • Ring strain raises frequency. • Additional C-H stretch for aldehyde: two absorptions at 2710 cm-1 and 2810 cm-1.=> Chapter 18

  11. 1H NMR Spectroscopy => Chapter 18

  12. => McLafferty Rearrangement • Loss of alkene (even mass number) • Must have -hydrogen Chapter 18

  13. => UV Spectra,   * • C=O conjugated with another double bond. • Large molar absorptivities (> 5000) Chapter 18

  14. => UV Spectra, n * • Small molar absorptivity. • “Forbidden” transition occurs less frequently. Chapter 18

  15. => Synthesis Review • Oxidation • 2 alcohol + Na2Cr2O7  ketone • 1 alcohol + PCC  aldehyde • Ozonolysis of alkenes. Chapter 18

  16. Synthesis Review (2) • Friedel-Crafts acylation • Acid chloride/AlCl3 + benzene  ketone • CO + HCl + AlCl3/CuCl + benzene  benzaldehyde (Gatterman-Koch) • Hydration of terminal alkyne • Use HgSO4, H2SO4, H2O for methyl ketone • Use Sia2BH followed by H2O2 in NaOH for aldehyde. => Chapter 18

  17. => Ketones from Nitriles • A Grignard or organolithium reagent attacks the nitrile carbon. • The imine salt is then hydrolyzed to form a ketone. Chapter 18

  18. Aldehydes from Acid Chlorides Use a mild reducing agent to prevent reduction to primary alcohol. => Chapter 18

  19. Ketones from Acid Chlorides Use lithium dialkylcuprate (R2CuLi), formed by the reaction of 2 moles of R-Li with cuprous iodide. => Chapter 18

  20. => Nucleophilic Addition • A strong nucleophile attacks the carbonyl carbon, forming an alkoxide ion that is then protonated. • A weak nucleophile will attack a carbonyl if it has been protonated, thus increasing its reactivity. • Aldehydes are more reactive than ketones. Chapter 18

  21. => Wittig Reaction • Nucleophilic addition of phosphorus ylides. • Product is alkene. C=O becomes C=C. Chapter 18

  22. => Addition of HCN • HCN is highly toxic. • Use NaCN or KCN in base to add cyanide, then protonate to add H. • Reactivity formaldehyde > aldehydes > ketones >> bulky ketones. Chapter 18

  23. Other Condensations => Chapter 18

  24. Addition of Alcohol => Chapter 18

  25. => Acetals as Protecting Groups • Hydrolyze easily in acid, stable in base. • Aldehydes more reactive than ketones. Chapter 18

  26. => Selective Reaction of Ketone • React with strong nucleophile (base) • Remove protective group. Chapter 18

  27. Oxidation of Aldehydes Easily oxidized to carboxylic acids. => Chapter 18

  28. => Tollens Test • Add ammonia solution to AgNO3 solution until precipitate dissolves. • Aldehyde reaction forms a silver mirror. Chapter 18

  29. Reduction Reagents • Sodium borohydride, NaBH4, reduces C=O, but not C=C. • Lithium aluminum hydride, LiAlH4, much stronger, difficult to handle. • Hydrogen gas with catalyst also reduces the C=C bond. => Chapter 18

  30. => Catalytic Hydrogenation • Widely used in industry. • Raney nickel, finely divided Ni powder saturated with hydrogen gas. • Pt and Rh also used as catalysts. Chapter 18

  31. Deoxygenation • Reduction of C=O to CH2 • Two methods: • Clemmensen reduction if molecule is stable in hot acid. • Wolff-Kishner reduction if molecule is stable in very strong base. => Chapter 18

  32. => Clemmensen Reduction Chapter 18

  33. => Wolff-Kisher Reduction • Form hydrazone, then heat with strong base like KOH or potassium t-butoxide. • Use a high-boiling solvent: ethylene glycol, diethylene glycol, or DMSO. Chapter 18

  34. POWER POINT IMAGES FROM “ORGANIC CHEMISTRY, 5TH EDITION”L.G. WADEALL MATERIALS USED WITH PERMISSION OF AUTHORPRESENTATION ADAPTED FOR BURLINGTON COUNTY COLLEGEORGANIC CHEMISTRY COURSEBY:ANNALICIA POEHLER STEFANIE LAYMAN CALY MARTIN Chapter 18

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