1. 1 Jerry Poteat Science Department Georgia Perimeter College © John Wiley and Sons, Inc. Version 1.0 Chapter 23 Aldehydes and Ketones Hein * Pattison * Arena * Best *

2. Chapter Outline 23.1 Structures of Aldehydes and Ketones 23.2 Naming Aldehydes and Ketones 23.3 Bonding and Physical Properties 23.4 Chemical Properties of Aldehydes and Ketones 23.5 Common Aldehydes and Ketones 23.6 Condensation Polymers

3. 23.1 Structures of Aldehydes and Ketones

4. 4 Aldehydes (i.e. RCHO) and ketones ( i.e. R 2 CO) are compounds with a chemical structure that contain the characteristic carbonyl (C=O) functional group as shown here.

5. 5 The aldehyde group is often written as CHO. For example, The ketone group is often written as CO. For example,

6. 23.2 Naming Aldehydes and Ketones

7. 7 IUPAC Rules for Naming Aldehydes 1.Name the longest continuous carbon chain containing the CHO group. 2. The CHO carbon is numbered carbon one

8. 8 IUPAC Rules for Naming Aldehydes 3. Drop an –e from the corresponding alkane parent name and add the suffix –al. 4. Number and name groups attached to the chain as we have done before.

9. 9 Examples of Naming Aldehydes

10. 10 Some aldehydes have common names as seen this table. Benzaldehyde is a common aromatic aldehyde.

11. 11 Dialdehydes are named by adding the suffix –dial to the corresponding hydrocarbon name. For example a molecule with four carbons and two aldehyde groups would be named butanedial. Dialdehydes

12. 12 IUPAC Rules for Naming Ketones 1.Name the longest continuous carbon chain containing the C=O group. 2. Drop an –e from the corresponding alkane parent name and add the suffix –one.

13. 13 IUPAC Rules for Naming Ketones 3. Carbon chains with four or more carbon atoms are numbered so the carbonyl (C=O) carbon is given the lowest possible number and this number is given as a prefix. 4. Attached groups are named and numbered as stated previously.

14. 14 Common Names of Ketones Propanone and 2-butanone are widely available ketones and are referred to by their common names as shown here.

15. 23.3 Bonding and Physical Properties

16. 16 Bonding The carbonyl (C=O) carbon is sp 2 -hybridized with one pi (π) bond and three sigma(σ) bonds. The pi (π ) bond of the C=O group is reactive and undergoes addition reactions. The C=O group is polarized which causes aldehydes and ketones to be reactive.

17. 17 Effect of Hydrogen Bonding on Physical Properties

18. 18 Notice the alcohol in each group has the higher boiling point due to hydrogen bonding.

19. 19 Figure 23.1 Naturally occurring aldehydes and ketones

20. 20 Figure 23.1(continued)

21. 23.4 Chemical Properties of Aldehydes and Ketones

22. 22 Reactions of Aldehydes & Ketones Oxidation Reduction Addition Aldehydes Only Both Reaction Type Aldehydes or Ketones The carbonyl functional group is the reactive site for aldehydes and ketones. These compounds undergo the three broad classes of reactions shown here. However aldehydes easily undergo oxidation while ketones are much more difficult to oxidize.

23. 23 Aldehydes (RCHO) are oxidized with dichromate to carboxylic acids (RCOOH) as shown here. Oxidation with Dichromate Three well-known identification tests for RCHOs are based on the fact that RCHOs are much easier to oxidize than R 2 COs. These tests are Tollens, Fehling, and Benedict tests.

24. 24 Oxidation with Ag + (Tollens test) Aldehydes can be identified using the Tollens test ( i.e. the silver-mirror test) as seen here.

25. 25 Oxidation with Cu 2+ ( Fehling and Benedict Tests) The aldehyde group (RCHO) is oxidized to a carboxylic acid by Cu 2+ ions in both the Fehling and Benedict tests. Both tests are carried out in an alkaline solution. The tests are very similar except the Fehling test uses tartaric acid to complex Cu 2+ while the Benedict test uses citric acid. Tollens Fehling Benedict Silver mirror Blue → Brick-red Test Positive Test Result for RCHO

26. 26 Ketones and the Tollens/Fehling/ Benedict Tests All three tests are used to distinguish aldehydes from ketones. All three tests give a positive test result for aldehydes and a negative test result for ketones.

27. 27 Reduction of Aldehydes & Ketones Aldehydes and ketones are easily reduced to alcohols using LiAlH 4, NaBH 4, or H 2 /Ni. Aldehydes yield primary alcohols (1  ) while ketones yield secondary alcohols ( 2  ).

28. 28 Reduction of Aldehydes & Ketones These are specific examples of an aldehyde and a ketone being reduced to a primary and secondary alcohol respectively.

29. 29 Applications in Biochemistry Oxidation and reduction of RCHOs/R 2 COs is important in biochemistry. For example pyruvic acid is reduced to lactic acid in muscle cells and then lactic acid is oxidized back to pyruvic acid in the liver as shown below. This reaction sequence is important because the body uses this sequence as an additional pathway to regenerate glucose.

30. 30 Addition Reactions of Aldehydes & Ketones RCHO + ROH R 2 CO + ROH RCHO + 2ROH R 2 CO + 2ROH RCHO or R 2 CO + HCN 2RCHO 2R 2 CO Hemiacetal Hemiketal Acetal Ketal Cyanohydrin Aldol  - hydroxy ketone Reactants Product This table summarizes addition reactions of aldehydes (RCHO) and ketones (R 2 CO)

31. 31 Hemiacetals, Hemiketals, Acetals, and Ketals

32. 32 Addition of Alcohols Aldehydes react with alcohols and a trace of acid to yield hemiacetals as shown here.

33. 33 Addition of Alcohols In the presence of excess alcohol and a strong acid such as dry HCl, aldehydes or hemiacetals react with a second molecule of the alcohol to yield an acetal.

34. 34 Intramolecular Addition of Alcohols Cyclic hemiacetals or hemiketals can form when the alcohol and the carbonyl group exist within the same molecule.

35. 35 Addition of HCN The addition of HCN to aldehydes and ketones yields cyanohydrins. A cyanohydrin is a compound that has a cyano group(-CN) and a hydroxyl group (-OH) on the same carbon as shown below.

36. 36 Synthetic Importance of Cyanohydrins Hydrolysis of cyanohydrins yields an  -hydroxy carboxylic acid. Consequently cyanohydrins are important synthetic intermediates for  -hydroxy acids as well as amino acids.

37. 37 Aldol Condensation (Self-Addition) An Aldol condensation is an addition reaction between two molecules of the same aldehyde to yield a  -hydroxyaldehyde or a  -hydroxyketone in the case of a ketone. The notations , , etc. refer to the carbon atoms next to the carbonyl group carbon as shown here. The  -hydrogen is a hydrogen atom attached to an  -carbon atom.  -Hydrogen atoms are slightly acidic and are more easily released than , , or  H atoms during an aldol reaction.

38. 38 Mechanism of the Aldol Condensation Step I Step II Note the transfer of the  -hydrogen in step I and the addition of the anion to the cation in step II.

39. 39 Mechanism of the Aldol Condensation Ketones with  -hydrogen atoms also undergo aldol reactions. Aldol reactions occur naturally in collagen molecules that are layered together as shown here.

40. 40 23.5 Common Aldehydes and Ketones 23.6 Condensation Polymers

41. 41 Common Aldehydes & Ketones (23.5) Formaldehyde and Acetaldehyde Formaldehyde is used in manufacturing polymers, fumigation, and preserving biological specimens. It is prepared over a copper or silver catalyst. Acetaldehyde is used as an intermediate in the manufacture of other chemicals such as acetic acid.

42. 42 Acetone and Methyl Ethyl Ketone(MEK) Acetone and MEK are widely used solvents used in industry and research laboratories. For example acetone is found in fingernail polish remover while MEK is found in lacquers. Also, acetone is used as an indicator of diabetes because it a product of lipid metabolism. Acetone and MEK are prepared by oxidizing alcohols.

43. 43 Condensation polymers are substances that produce a small molecule like water during polymerization. Polyesters, polyamides, polyurethanes, and phenolics represent four important classes of condensation polymers. (23.6) Condensation Polymers

44. 44 A phenolic is a condensation polymer made from phenol as shown here. Preparation of a Condensation Polymer This is a section of a phenolic ( i.e. Bakelite) which is an example of a thermosetting polymer. These polymers are used in electrical equipment because of their insulating and fire-resistant properties.

45. 45 Chapter 23 Summary  The properties of aldehydes and ketones are largely determined by the polarized carbonyl group( ).  Both class of compounds have lower boiling points than alcohols because hydrogen bonding is not possible in pure samples of these substances.  Aldehydes undergo oxidation but ketones generally do not undergo oxidation under the same conditions as aldehydes which leads to the Tollens/Fehling/Benedict tests that are specific for differentiating RCHOs from R 2 COs.  Both class of compounds undergo reduction to alcohols with reducing agents such as LiAlH 4, NaBH 4, and H 2 /Ni.

46. 46 Chapter 23 Summary  Both class of compounds undergo addition reactions: (1)yielding hemiacetals, hemiketals, acetals, and ketals when reacted with alcohols, (2) yielding cyanohydrins when reacted with hydrogen cyanide (HCN), and …. (3)yielding aldol products when undergoing self-addition.