CHAPTER 23 ALDEHYDES AND KETONES SOLUTIONS TO REVIEW QUESTIONS. aldehyde ketone a dialdehyde H O. a hemiacetal a hemiketal an acetal

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1 APTER 23 ALDEYDES AND KETNES SLUTINS T REVIEW QUESTINS 1. ( 2 ) n aldehyde ketone a dialdehyde R (d) (e) (f) R R R a hemiacetal a hemiketal an acetal R (g) (h) and R N R R a ketal a cyanohydrin 2. Propanal propanone 2 3 Each has the molecular formula of so aldehydes and ketones appear to be isomeric with each other. Butanal butanone Each has the molecular formula so the generalization seems to check out. The general formula for aldehydes and ketones is n 2n. 3. The strength of collagen depends on aldol condensations. After collagen is formed, aldehydes add along its length. ollagen fibers adjacent to each other undergo an aldol condensation. The cross linking bonds between collagen strands form a strong network, giving collagen its strength

2 4. 1-Butanol has a boiling point of 118 while the boiling point for butanal is 76 and for butanone, 80. f these three compounds, only 1-butanol can hydrogen bond to itself. This additional bonding holds the molecules together more tightly and accounts for the much higher boiling point. 5. The versatile aldol condensation reaction allows Streptomyces to synthesize a wide variety of different antibiotics. 6. Acetaldehyde carries a reactive aldehyde functional group that can bond to many different biochemicals: by reacting with amino acids, acetaldehyde slows protein synthesis; by reacting with antioxidants, acetaldehyde increases oxidative damage to the liver; by reacting with specific proteins, acetaldehyde hampers the liver s ability to export needed chemicals to the blood stream. Acetaldehyde can cause liver cirrhosis. 7. A ketone is a carbonyl functional group that is bonded to two alkyl or aryl groups. ortisone is a ketone-containing hormone. The sugar, fructose, contains a ketone. Ketones are also found in Vitamin K When an aldehyde reacts with Benedict solution, the blue color of copper ion disappears and a red-brown precipitate forms. When an aldehyde reacts with Tollens solution, the silver ion in solution forms a thin silver metal mirror on the inside of the glass container used in the test. 9. The phenol-formaldehyde polymer is rigid because covalent bonds not only form the polymers but also cross-link the polymers to each other. 10. MEK is an abbreviation for methyl ethyl ketone. Its main use is as a solvent, especially for lacquers and paints. 11. A ketone group,, cannot be located at the end of a carbon-carbon chain. onsequently its only possible location in both propanone and butanone is on -2 of these ketones. Therefore its location need not be numbered

3 SLUTINS T EXERISES 1. Names of aldehydes. (d) 2 2 methanal, formaldehyde 3-methylbutanal butanedial 3-phenylpropenal (e) cis-2-butenal 2. Names of aldehydes ethanal, acetaldehyde butanal, butyraldehyde benzaldehyde (d) l 2-chloro-5-isopropylbenzaldehyde

4 (e) 3-hydroxybutanal 3. Names of ketones propanone, acetone, dimethyl ketone 1-phenyl-l-propanone, ethyl phenyl ketone cyclopentanone (d) 4-hydroxy-4-methyl-2-pentanone 4. Names of ketones butanone, methyl ethyl ketone (MEK) 3,3-dimethylbutanone, t-butyl methyl ketone 2,5-hexanedione (d) 1-phenyl-2-propanone, benzyl methyl ketone 5. Structural formulas 1,3-dichloropropanone butenal 4-phenyl-3-hexanone (d) (e) hexanal 3-ethyl-2-pentanone

5 6. Structural formulas 3-hydroxypropanal 4-methyl-3-hexanone cyclohexanone (d) l l l 2,4,6-trichloroheptanal (e) 3-pentenal 7. Acetaldehyde is a common name. The IUPA name is ethanal. 2-Methyl-3-butanone is numbered incorrectly. The correct IUPA name is 3-methyl-2-butanone. 1-exanal is incorrect because the aldehyde needs no number. The correct IUPA name is hexanal Methyl-3-propanal is numbered incorrectly and the aldehyde needs no number. The correct IUPA name is 2-methylpropanal. Formaldehyde is a common name. The IUPA name is methanal. 4-exanone is numbered incorrectly. The correct IUPA name is 3-hexanone. 9. Boiling points depend on molecular size (larger molecules have higher boiling points) and intermolecular bonding (molecules that hydrogen bond have higher boiling points than molecules that don t hydrogen bond; polar molecules have higher boiling points than non-polar molecules). Although 3-pentanone and 2-pentanol are about the same size, 2-pentanol can hydrogen bond to itself. 2-Pentanol has the higher boiling point. Ethanal is both larger and more polar than ethane. Ethanal has the higher boiling point. 1,3-Propanediol is larger and hydrogen bonds to itself while propanone is smaller and can t hydrogen bond to itself. 1,3-Propanediol has the higher boiling point

6 (d) Pentanal is both larger and more polar than propane. Pentanal has the higher boiling point. 10. Boiling points depend on molecular size (larger molecules have a higher boiling points) and intermolecular bonding (molecules that hydrogen bond have higher boiling points than molecules that don t hydrogen bond; polar molecules have higher boiling points than non-polar molecules). Butanone is both larger and more polar than butane. Butanone has the higher boiling point. Although 2-butanol and butanone are about the same size, 2-butanol can hydrogen bond to itself while butanone can t. 2-Butanol has the higher boiling point. 2-Pentanone is both larger and more polar than propane. 2-Pentanone has the higher boiling point. (d) 1,2-Propanediol is larger and can hydrogen bond to itself while propanal is smaller and can t hydrogen bond to itself. 1,2-Propanediol has the higher boiling point. 11. Aqueous solubility depends on the size of the alkyl chain (the smaller alkyl chain has more aqueous solubility) and bonding between the solute and water (hydrogen bonding solutes have higher aqueous solubilities; more polar solutes have higher aqueous solubilities). Both 2-heptanone and propanone are ketones but propanone has a much smaller alkyl chain. Propanone has a higher aqueous solubility. Pentane and pentanal have the same sized alkyl chains but pentanal can hydrogen bond to water. Pentanal has the higher water solubility. 3-Pentanone and 2,4-pentanedione have the same sized alkyl chains but 2,4-pentanedione has two ketone functional groups while 3-pentanone has only one. 2,4-Pentanedione can hydrogen bond more strongly to water and has the higher aqueous solubility. 12. Aqueous solubility depends on the size of the alkyl chain (the smaller alkyl chain has more aqueous solubility) and bonding between the solute and water (hydrogen bonding solutes have higher aqueous solubilities; more polar solutes have higher aqueous solubilities). 3-ydroxypentanal has a smaller alkyl chain and two functional groups that can hydrogen bond to water while 3-hexanone has a larger alkyl chain and only one functional group that can hydrogen bond to water. 3-ydroxypentanal has the higher aqueous solubility. yclohexanone and cyclohexane have the same sized alkyl chains but cyclohexanone can hydrogen bond to water. yclohexanone has the higher aqueous solubility

7 Propanone and 2-pentanone are both ketones but propanone has the smaller alkyl chain. Propanone has the higher aqueous solubility. 13. Equations for the oxidation of: 3-pentanol same product for air 3-methyl-l-hexanol 14. Equations for the oxidation of: 1-propanol K 2 r : 2 S oxidation K 2 r : 2 S 4 u Ag 2 2 u K 2 r : 2 S 4 K 2 r : 2 S " 2 2 " or No reaction (3 alcohol) with either oxidizing agent

8 propanal, 2 butanone, 2 butanal,

9 18. formaldehyde (methanal) propanal, 2 2 propanal, An aldehyde group,, must be present to give a positive Tollens test. The visible evidence for a positive Tollens test is the formation of a silver mirror on the inner walls of a test tube. (silver mirror) 20. An aldehyde group,, must be present to give a positive Fehling test. The visible evidence for a positive Fehling test is the formation of brick red u 2, which precipitates during the reaction. N Ag + 99: The aldehyde is oxidized in the Tollens test: 2 N Na N Ag(s) 3 2 (brick-red) The ketone is reduced: The aldehyde is oxidized in the Benedict test: Na

10 (d) The aldehyde is reduced: The aldehyde is reduced: 2 2 The aldehyde is oxidized in the Benedict test: Na The ketone is reduced: (d) The aldehyde is oxidized in the Tollens test: 2 N N adds to a carbonyl functional group to form a cyanohydrin. In turn, the cyanohydrin can be reacted with water to make an α-hydroxy acid

11 24. N adds to a carbonyl functional group to form a cyanohydrin. In turn, the cyanohydrin can be reacted with water to make an α-hydroxy acid Aldol condensation butanal phenylethanal dilute Na dilute Na " Aldol condensation pentanone dilute Na " dilute " Na 3 2 propanal

12 27. The completed equations are: dryly ERF ERF ( ) : The completed equations are: dryly ERF ± + Δ 2 2 ( ) Sequence of reactions: 2 999: N N 3 N

13 2 + dryl " 30. Sequence of reactions: ± N N N ± 2 ± K 2 r S : 32. ethanal

14 33. Four aldol condensation products from a mixture of ethanal (E) and propanal (P) are possible. EE PP EP PE 3 EE is 3 2 PP is 2 EP is 3 PE is A hemiacetal forms when an alcohol adds to a carbonyl group. 2 five-membered cyclic hemiacetal 2 six-membered cyclic hemiacetal and 3 3. The Tollens test (silver mirror) or Fehling test (red with propanal but not with acetone. ) will give positive results 3 2 and 2 Bromine will decolorize immediately with the second compound (propenal) but not with propanal

15 2 2 and xidize both compounds: 2-phenylethanol will give 2-phenylethanal and 1-phenylethanol will give methyl phenyl ketone. 1-phenylethanal will give a positive Tollens or Benedict test and methyl phenyl ketone will not give a positive test N N 2 999: + lactic acid 37. N + ± N benzaldehyde 38. Pyruvic acid is changed to lactic acid by a reduction reaction. 39. The alcohols which should be oxidized to give these ketones. 3-pentanone: 3-pentanol 2 2 methyl ethyl ketone: 2-butanol 2 4-phenyl-2-butanone: 4-phenyl-2-butanol

16 Ketones will not react in the Fehling test. The following are all the ketones with the formula, 6 12 : This step is an aldol condensation that occurs in dilute Na. 2. This step oxidizes the aldehyde to a carboxylic acid. ommon oxidizing conditions are set by the Tollens test (Ag +,N 3, 2 ) or the Fehling/Benedict test (u 2+, Na, 2 ). 1. This step forms a cyanohydrin and the conditions require hydroxide ( ). 2. This step reacts the cyanohydrin with water to form an α-hydroxy acid. onditions require acid ( + ) as well as water. 1. This step is an aldol condensation that occurs in dilute Na. 2. This step reduces the aldehyde to form a primary alcohol. ommon reducing conditions involve heat (Δ), hydrogen gas, and a nickel catalyst

17 43. a a b b 44. In phenol,three positions, ortho, ortho, and para to the group are used in the reaction to form a thermosetting polymer. owever, in p-cresol the para position is occupied by a methyl group and cannot react with formaldehyde. This leaves the p-cresol molecule as a bifunctional monomer, resulting in a linear, thermoplastic polymer. n 45. 2,3-dihydroxypropanal 2 2 1,3-dihydroxypropanone 2 2 and