Organic Chemistry Aldehydes and Ketones

1. Organic ChemistryAldehydes and Ketones Chapter 17

2. Aldehydes and Ketones • Carbonyl Group C=O • Present in aldehydes and ketones Aldehydes Ketones

3. Aldehydes • Aldehydes • Sometimes abbreviated RCHO • Contain at least one H connected to the C Aldehydes

4. Ketones • Ketones • Carbonyl C is connected to two alkyl groups • RCOR’ Ketones

5. Nomenclature • IUPAC • Suffix is “-al” for the aldehydes • Suffix is “-one” for the ketones • # indicates position of ketone

6. Nomenclature NOTE: Ketone, Not keytone From Yahoo Images

7. Nomenclature • An Aldehyde or Ketone takes precedence over any previously considered group

8. Nomenclature • Common names - aldehydes

9. Nomenclature • Common names - ketones • Some are always used - Others name each R group and end with “ketone”

10. Physical Properties Carbonyls: • Cannot form H bonding with each other: • There is NOT an H connected to a F, N, O • Aldehydes and Ketones are POLAR molecules and form dipole interactions • Gives higher boiling and melting points

11. Physical Properties • Aldehydes and Ketones • can form H bonds with water! • solubility in water is about the same as alcohols yes!

12. Physical Properties • Strong odors • Ketones generally have pleasant odors • perfumes, flavoring agents • Aldehydes odors vary • some pleasant • cinnaminaldehyde, vanillin • some not pleasant • formaldehyde Many are found in natural products http://www.youtube.com/watch?v=KDohVakqkic

13. How do you make Aldehydes? • Aldehydes from Oxidation of 1o alcohols • Problem is over oxidation to ACID! Practice a couple …………..

14. How do you make Ketones? • Ketones from Oxidation of 2o alcohols Practice a couple …………..

15. Oxidation of Aldehydes • Aldehydes are easily oxidized • KMnO4 • K2Cr2O7 • even air oxidation carboxylic acid!

16. [O] Oxidation of Ketones • Ketones resist oxidation: • under mild or normal conditions, no reaction • more severe conditions yield mixtures • CO2 and H2O under extreme conditions This difference in reactivity can be used to Tell the difference between an aldehyde and ketone

18. Reaction 1. Oxidation – Tollens Test - Benedicts Test 2. Reduction – Hydrogen addition – NaBH4 reagent 3. Addition of Alcohols – hemiacetal/acetal and tautomerism

19. Tollen’s Test • The Silver Mirror Test • Oxidation of Aldehydes • Ag+ ion in aq. ammonia • NO reaction with KETONES Ag(NH3)2+ + aldehyde Silver Mirror Ag+ + 2 NH3 Ag(NH3)2+ Ag(NH3)2+ + RCHO Ago + RCOO- + 4NH3

20. Cu+ Cu2+ Benedict’s Test • Oxidation of Aldehydes • Cu++ ion, aqueous • Orange to red ppt. • NO reaction with KETONES Cu+++ aldehyde Cu+(oxide)+ acid

21. Cu2O Benedict’s Test • Oxidation of Aldehydes • overall reaction

22. Chemical Properties • Addition to C=O • Other reactions are ADDITION Reactions • Bond is polar + and - • Negatives are attracted to C • Positives are attracted to O - + B

23. Addition of H2 • Reduction to Alcohols • Hydrogen gas and a catalyst (Ni, Pd, Pt) • Similar to alkene to alkane reduction B

24. Addition of H2 • Reduction to Alcohols • Will reduce ketones to 2o alcohols • Slower reaction than reduction of C=C • C=C is reduced faster (first) if both C=O and C=C B

25. Addition of H2 using NaBH4 • Reduction to Alcohols • NaBH4 does not allow the reaction of the carbon carbon double bond B

26. Addition of Alcohol • In the addition of R-OH to form an “acetal” the First step is the formation of a “hemiacetal” • This is when an -OH and -OR are both on same C B

27. Formation of Acetals IF strong acid (HCl) is present, a second alcohol reacts to form the acetal (two -OR groups on C) + H2O B

28. Addition of Alcohol - Acetals Step 1 Step 2 + H2O B

29. Formation of Acetals • Addition of R-OH • acid catalyzed, 2 moles of alcohol react ? B

30. Formation of Acetals • Addition of R-OH • acid catalyzed, 2 moles of alcohol react Draw the Hemi B

31. Formation of Acetals • Acetal reaction in equilibrium B

32. Formation of Acetals • Acetal reactions ? B

33. Formation of Acetals • Acetal reactions ? 1o alcohol B

34. H O O OH 5 4 3 2 1 O 5 1 CH CH CH CH CH or 2 2 2 2 2 4 OH O 3 a cyclic hemiacetal Formation of Acetals • Hemiacetal reactions (formation of hemiacetals) • likely when within the same molecule 1o alcohol B

35. Formation of Acetals • Cyclic hemiacetals • Reacts with a 2nd. molecule of alcohol • Results in a cyclic acetal 1o alcohol B

36. Formation of Acetals • Which are hemiacetals / acetals? 1 2 3 4 5 6 7 8 9 10 B

37. Keto-Enol Tautomerism • Equilibrium that exists • Keto (carbonyl) to Enol (alkene/alcohol) B

38. Keto form (more stable) (less stable) Keto-Enol Tautomerism • Equilibrium called Tautomerism 1o alcohol B

39. Keto-Enol Tautomerism • Equilibrium called Tautomerism Most enols are less stable 1o alcohol B

40. Important Compounds • Formaldehyde • Gas at RT • Soluble in H2O • Formalin • 37% formaldehyde • found in labs • preserves by denaturing proteins • Used to produce polymers B

41. Important Compounds • Acetaldehyde • bp 21o C • Converted to trimer • 3 units of acetaldehyde • called paraldehyde • once used as a hypnotic/sleep-producer B

42. Important Compounds • Acetone • bp 56o C • Infinitely soluble in H2O • Excellent industrial solvent: • paints, varnishes, resins • coatings, nail polish • Produced in the body • diabetic ketoacidosis • “acetone breath” B

43. Important Compounds • -chloroacetophenone • lachrymators • tearing of eyes, etc. • Used as a tear gas • Active ingredient in “Mace” B