Chapter 18 Ketones and Aldehydes. Carbonyl Compounds. Chapter 18: Aldehydes and Ketones Slide 18-2

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1 hapter 18 Ketones and Aldehydes arbonyl ompounds hapter 18: Aldehydes and Ketones Slide

2 arbonyl Structure arbon is sp 2 hybridized. = bond is shorter, stronger, and more polar than = bond in alkenes. hapter 18: Aldehydes and Ketones Slide 18-3 IUPA Names for Ketones Replace -e with -one. Indicate the position of the carbonyl with a number. Number the chain so that carbonyl carbon has the lowest number. For cyclic ketones the carbonyl carbon is assigned the number 1. hapter 18: Aldehydes and Ketones Slide

3 Examples methyl-2-butanone 3-methylbutan-2-one Br 3-bromocyclohexanone hydroxy-3-methyl-2-butanone 4-hydroxy-3-methylbutan-2-one hapter 18: Aldehydes and Ketones Slide 18-5 Naming Aldehydes IUPA: Replace -e with -al. The aldehyde carbon is number 1. If - is attached to a ring, use the suffix -carbaldehyde. hapter 18: Aldehydes and Ketones Slide

4 Examples methylpentanal 2-cyclopentenecarbaldehyde cyclopent-2-en-1-carbaldehyde hapter 18: Aldehydes and Ketones Slide 18-7 Name as Substituent n a molecule with a higher priority functional group, = is oxo- and - is formyl. Aldehyde priority is higher than ketone methyl-4-oxopentanal 3-formylbenzoic acid hapter 18: Aldehydes and Ketones Slide

5 ommon Names for Ketones Named as alkyl attachments to -=. Use Greek letters instead of numbers Br 3 3 methyl isopropyl ketone α bromoethyl isopropyl ketone hapter 18: Aldehydes and Ketones Slide 18-9 istorical ommon Names acetone acetophenone benzophenone hapter 18: Aldehydes and Ketones Slide

6 Aldehyde ommon Names Use the common name of the acid. Drop -ic acid and add -aldehyde. 1 : formic acid, formaldehyde 2 s: acetic acid, acetaldehyde 3 s: propionic acid, propionaldehyde 4 s: butyric acid, butyraldehyde. 3 Br 2 β-bromobutyraldehyde 3-bromobutanal hapter 18: Aldehydes and Ketones Slide Boiling Points More polar, so higher boiling point than comparable alkane or ether. annot -bond to each other, so lower boiling point than comparable alcohol. hapter 18: Aldehydes and Ketones Slide

7 Solubility Good solvent for alcohols. Lone pair of electrons on oxygen of carbonyl can accept a hydrogen bond from - or N-. Acetone and acetaldehyde are miscible in water. hapter 18: Aldehydes and Ketones Slide IR Spectroscopy Very strong = stretch around 1710 cm -1. onjugation lowers frequency. Ring strain raises frequency. Additional - stretch for aldehyde: two absorptions at 2710 cm -1 and 2810 cm -1. hapter 18: Aldehydes and Ketones Slide

8 1 NMR Spectroscopy hapter 18: Aldehydes and Ketones Slide NMR Spectroscopy hapter 18: Aldehydes and Ketones Slide

9 MS for 2-Butanone hapter 18: Aldehydes and Ketones Slide MS for Butyraldehyde hapter 18: Aldehydes and Ketones Slide

10 McLafferty Rearrangement Loss of alkene (even mass number) Must have γ-hydrogen hapter 18: Aldehydes and Ketones Slide UV Spectra, π π* = conjugated with another double bond. Large molar absorptivities (> 5000) hapter 18: Aldehydes and Ketones Slide

11 UV Spectra, n π* Small molar absorptivity. Forbidden transition occurs less frequently. hapter 18: Aldehydes and Ketones Slide Synthesis Review xidation 2 alcohol Na 2 r 2 7 ketone 1 alcohol P aldehyde zonolysis of alkenes. hapter 18: Aldehydes and Ketones Slide

12 Synthesis Review (2) Friedel-rafts acylation Acid chloride/all 3 benzene ketone l All 3 /ul benzene benzaldehyde (Gatterman-Koch) ydration of terminal alkyne Use gs 4, 2 S 4, 2 for methyl ketone Use Sia 2 B followed by 2 2 in Na for aldehyde. hapter 18: Aldehydes and Ketones Slide Synthesis Using 1,3-Dithiane Remove with n-butyllithium. Alkylate with primary alkyl halide, then hydrolyze. hapter 18: Aldehydes and Ketones Slide

13 Ketones from 1,3-Dithiane After the first alkylation, remove the second, react with another primary alkyl halide, then hydrolyze. BuLi S S 2 3 S 3 Br S _ 2 3 S S 3 2 3, gl hapter 18: Aldehydes and Ketones Slide Ketones from arboxylates rganolithium compounds attack the carbonyl and form a dianion. Neutralization with aqueous acid produces an unstable hydrate that loses water to form a ketone. hapter 18: Aldehydes and Ketones Slide

14 Ketones from Nitriles A Grignard or organolithium reagent attacks the nitrile carbon. The imine salt is then hydrolyzed to form a ketone. 3 2 MgBr N ether N MgBr hapter 18: Aldehydes and Ketones Slide Aldehydes from Acid hlorides Use a mild reducing agent to prevent reduction to primary alcohol. Bulk of reagent helps also l LiAl(-t-Bu) hapter 18: Aldehydes and Ketones Slide

15 Ketones from Acid hlorides Use lithium dialkylcuprate (R 2 uli), formed by the reaction of 2 moles of R-Li with cuprous iodide Li ui ( ) 2 uli ( ) 2 uli 3 2 l hapter 18: Aldehydes and Ketones Slide 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. hapter 18: Aldehydes and Ketones Slide

16 Wittig Reaction Nucleophilic addition of phosphorus ylides. Product is alkene. = becomes =. hapter 18: Aldehydes and Ketones Slide Phosphorus Ylides Prepared from triphenylphosphine and an unhindered alkyl halide. Butyllithium then abstracts a hydrogen from the carbon attached to phosphorus. _ Ph 3 P 3 2 Br Ph 3 P 2 3 Br Ph 3 P 2 3 BuLi _ Ph 3 P 3 ylide hapter 18: Aldehydes and Ketones Slide

17 Mechanism for Wittig The negative on ylide attacks the positive of carbonyl to form a betaine. xygen combines with phosphine to form the phosphine oxide. _ Ph 3 3 P Ph 3 P 3 3 Ph 3 Ph Ph 3 P _ 3 3 Ph Ph 3 P 3 3 Ph Ph 3 P 3 3 Ph hapter 18: Aldehydes and Ketones Slide Phosphonate Modification hapter 18: Aldehydes and Ketones Slide

18 Addition of Water In acid, water is the nucleophile. In base, hydroxide is the nucleophile. Aldehydes are more electrophilic since they have fewer e - - donating alkyl groups. 2 K = K = hapter 18: Aldehydes and Ketones Slide Addition of N (yanohydrins) N is highly toxic. Use NaN or KN in base to add cyanide, then protonate to add. Reactivity formaldehyde > aldehydes > ketones >> bulky ketones. 3 2 N 3 N hapter 18: Aldehydes and Ketones Slide

19 Formation of Imines Nucleophilic addition of ammonia or primary amine, followed by elimination of water molecule. = becomes =N-R RN 2 3 Ph R 2 N 3 _ Ph R N 3 Ph 3 R 3 R N N Ph Ph hapter 18: Aldehydes and Ketones Slide p Dependence Loss of water is acid catalyzed, but acid destroys nucleophiles. N 3 N 4 (not nucleophilic). ptimum p is around 4.5. hapter 18: Aldehydes and Ketones Slide

20 ther ondensations hapter 18: Aldehydes and Ketones Slide Addition of Alcohol hapter 18: Aldehydes and Ketones Slide

21 Mechanism Must be acid-catalyzed. Adding to carbonyl makes it more reactive with weak nucleophile, R. emiacetal forms first, then acid-catalyzed loss of water, then addition of second molecule of R forms acetal. All steps are reversible. hapter 18: Aldehydes and Ketones Slide Mechanism for emiacetal xygen is protonated. Alcohol is the nucleophile. is removed. hapter 18: Aldehydes and Ketones Slide

22 emiacetal to Acetal hapter 18: Aldehydes and Ketones Slide yclic Acetals Addition of a diol produces a cyclic acetal. Sugars commonly exist as acetals or hemiacetals hapter 18: Aldehydes and Ketones Slide

23 Acetals as Protecting Groups ydrolyze easily in acid, stable in base. Aldehydes more reactive than ketones. 2 2 hapter 18: Aldehydes and Ketones Slide Selective Reaction of Ketone React with strong nucleophile (base). Remove protective group. _ MgBr 3 3 MgBr 3 3 hapter 18: Aldehydes and Ketones Slide

24 xidation of Aldehydes Easily oxidized to carboxylic acids. hapter 18: Aldehydes and Ketones Slide Tollens Test Add ammonia solution to AgN 3 solution until precipitate dissolves. Aldehyde reaction forms a silver mirror. Mild, basic way to make carboxylic acids. R 2 Ag(N 3 ) 2 3 _ 2 2 Ag R _ 4 N hapter 18: Aldehydes and Ketones Slide

25 Reduction Reagents Sodium borohydride, NaB 4, reduces =, but not =. Lithium aluminum hydride, LiAl 4, much stronger, difficult to handle. ydrogen gas with catalyst also reduces the = bond. hapter 18: Aldehydes and Ketones Slide atalytic ydrogenation Widely used in industry. Raney nickel, finely divided Ni powder saturated with hydrogen gas. Pt and Rh also used as catalysts. Raney Ni hapter 18: Aldehydes and Ketones Slide

26 Deoxygenation Reduction of = to 2 Two methods: lemmensen reduction if molecule is stable in hot acid. Wolff-Kishner reduction if molecule is stable in very strong base. hapter 18: Aldehydes and Ketones Slide lemmensen Reduction 2 3 Zn(g) l, 2 2 Zn(g) l, hapter 18: Aldehydes and Ketones Slide

27 Wolff-Kisher Reduction Form hydrazone, then heat with strong base like K or potassium t-butoxide. Use a high-boiling solvent: ethylene glycol, diethylene glycol, or DMS. 2 2 N N 2 2 NN 2 K heat 2 3 hapter 18: Aldehydes and Ketones Slide End of hapter 18 omework: 40, 46, 47, 49, 51, 52, 56, 61, 62, 66, 68, 70, 74, 75 hapter 18: Aldehydes and Ketones Slide