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Chapter 12 Aldehydes and Ketones Nucleophilic Addition to

Chapter 12 Aldehydes and Ketones Nucleophilic Addition to Carbonyl Group. 12.1 Nomenclature 12.2 Structure of Carbonyl Group 12.3 Preparation of aldehydes and ketones 12.4 Nucleophilic addition of aldehydes and ketones

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Chapter 12 Aldehydes and Ketones Nucleophilic Addition to

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  1. Chapter 12 Aldehydes and Ketones Nucleophilic Addition to Carbonyl Group 12.1 Nomenclature 12.2 Structure of Carbonyl Group 12.3 Preparation of aldehydes and ketones 12.4 Nucleophilic addition of aldehydes and ketones 12.4.1 Hydration of aldehydes and ketones 12.4.2 The addition of hydrogen cyanide 12.4.3 The addition of alcohols 12.4.4 The addition of amines

  2. 12. 5The Addition of Ylides: the Wittig Reaction 12.5.1Ylides (叶立德)and Preparation of phosphorous ylides 12.5.2 Mechanism of the Wittig reaction 12.5.3 Synthesis of alkenes by Wittig reactions 12.6 Oxidation of Aldehydes and ketones 12.6.1 Oxidation of Aldehydes 12.6.2 Baeyer-Villiger oxidation of ketones 12.7 Spectroscopic analysis of aldehydes and ketones

  3. Aldehyde 醛 Formaldehyde 甲醛 Ketone 酮 • General role: • The longest continuous chain with • carbonyl group is as a parent, suffix: • e al or one. To ketones, numbered • the number of carbonyl group. Aldehydes and Ketones Carbonyl group 羰基 12.1 Nomenclature Formyl 醛基 Aroyl 芳酰基 Acyl 酰基 Benzoyl 芳酰基

  4. P284 9.3 3-Methylbutanal 3-甲基丁醛 4-Methyl-3-hexanone 4-甲基-3-己酮 4-Methylcyclohexanone 4-甲基环己酮 Benzophenone 二苯甲酮 Benzaldehyde 苯甲醛 2,3-Dimethyl-4-pentenal 2,3-二甲基-4-戊烯醛 • 2. When –CHOis attached to a ring, • suffix is -aldehyde or -carbaldehyde • (以甲醛为母体) • Alkyl groups are as substitutes, • “ketone” are as parent Benzyl ethyl ketone 乙基苄基甲酮

  5. 12.2 Structure of Carbonyl Group

  6. A B Nucleophilic Electrophilic - OH-,Nu: sp2-hybridized πbond Trigonal plane Acetaldehyde (乙醛) Polarized Electron delocalization Dipole moment μ = 2.3 ~ 2.9D Polar solvent Resonance structures: Acetone (丙酮) H+,E+ P283, 9.2

  7. Reaction sites and reactions of aldehydes and ketones Nucleophilic addition Oxidation And reduction Reaction of α -hydrogen

  8. : − Nu: OH−, H− , R3C − , H2O, NH3, ROH Intermediate: an alkoxide ion sp2 sp3 The trigonal planar structure of C=O is relatively open to attack from above or below by Nu−. : 12.4Nucleophilic Addition of Aldehydes and Ketones P288 9.6

  9. [RCH(OH)2] K = [RCHO] [H2O] Khydr22,000 41 1.8 × 10-2 4.1 × 10-3 2.5 × 10-5 12.4.1Hydration of Aldehydes and ketones P290 9.7 Reversible Geminal diol （同碳二醇） Hydrate(水合物) Reactivitydecreases

  10. Hybridization: sp2 sp3 The bond angle: 120° 109.5° Factors affecting the reactivity: 1. Electronic effects of alkyl groups Electron-donating effect of alkyl Substituents stabilizes the carbonyl group; Electron-withdrawing effect destabilizes the carbonyl group 2. Steric effect of alkyl groups H < CH3 < tert-Butyl The crowding in the products is increased by the larger group

  11. An aldehyde A ketone

  12. Step 1 An alkoxide ion A hydroxide ion Mechanism of Hydration The addition of water is subject to catalysis by both an acid and a base. The mechanism for the base-catalyzed reaction: A hydroxide ion attacks the carbon of the carbonyl group. Nucleophile: HO－> H2O This step is rate-determining.

  13. Step 2 Step 1 An alkoxide ion attracts a proton from water, yielding geminal diol. The mechanism for the acid-catalyzed reaction: Protonation of carbonyl group:

  14. Step 2 Step 3 Water as a nucleophile attacks the protonated carbonyl group The step is rate-determining Transformation of the proton

  15. The mechanism for the base-catalyzed reaction:

  16. Characteristics of the reaction • Base-catalyzed,reagent: KCN • Formation of C－C bond • －CN COOH, －NH2 12.4.2 The addition of hydrogen cyanide (氢氰酸) －Cyanohydrin (氰基醇)formation

  17. 12.4.3 The addition of alcohols Acid catalysis Aldehydes react with alcohols to yeld hemiacetals (半缩醛) or acetals(缩醛) Aldehyde hemiacetal acetal Benzaldehyde diethyl acetal 苯甲醛缩 二乙醇(60%) Benzaldehyde Ethanol

  18. Mechanism of the reaction:

  19. R ' H O H R ' O H R ' O H C R ' R ' O H C O R R O R ' R ' + R ' H C O O H 2 R The position of equilibrium is favorable for acetal formation from most aldehydes. For most ketones, the position of equilibrium is unfavorable. excess alcohol as solvent

  20. Diols react with aldehydes or ketones to form cyclic acetals by removing the water: Acetals are susceptible to hydrolysis in aqueous acid: Acetal hydrolysis is favored by excess water. Acetals as protecting groups Acetals are stable in basic solution

  21. (a) Protection of carbonyl group (b) Reduction of the ester group (c) Unmasking of the carbonyl group

  22. Primary amine Aldehyde or ketone Carbinoamine （氨基甲醇） 12.4.4 The addition of amines（胺） 1. Reaction with primary amines: imides(亚胺) Aldehydes and ketones react with primary amines to yield imides N-Substituted imides: Schiff’s bases (西佛碱) Step 1. Nucleophlic addition Step 2. Elimination Imide （亚胺）

  23. Careful control of pH! The reactions are accelerated by acid-catalysis (a) Protonation of carbonyl group (b) Nucleophile attacks carbonyl group pH: 4~5 (c) Elimination with acid-catalysis

  24. N-Cyclohexylide- Isobutylamine （N-亚环己基异丙胺） Cyclo- hexanone Isobutylamine （异丙胺） Hydroxylamine （羟胺） An oxime （肟） Hydrazine （肼） A hydrazone （腙） Reaction with derivatives of ammonia

  25. 2,4-Dinitrophenyl Hydrazine （2,4-二硝基苯肼） 2,4-dinitrophenyl hydrazone (腙) Semicarbazone （缩氨基脲） （半卡巴腙） Semicarbazine （氨基脲） The products are insoluble and have sharp characteristic melting point. The reaction are often used to identify unknown aldehydes and ketones.

  26. N-(1-Cyclopentenyl) Pyrrodine [N-(1-环戊烯基)吡咯烷] Cyclopentanone （环戊酮） Pyrrolidine （吡咯烷） Reactions with secondary amines Aldehydes and ketones react with secondary amine (R2NH), to form enamines （烯胺）

  27. Dimethyl sulfoxide （二甲亚砜） 12. 5The Addition of Ylides: the Wittig Reaction Aldehydes and ketones react with phosphorous ylides to yield alkenes and triphenyl phosphine oxide （三苯基氧膦） Solvents: THF, DMSO The characteristics of Wittig reaction: Regioselectivity

  28. 14.5.1 Ylides and the Preparation of Phosphorous Ylides Ch.P346(己) Ylides (叶立德): Molecules with two oppositely charged atoms A hybrid of the two resonance structures Preparation of phosphorous ylides: Step1 Alkyl halides Triphenyphosphine SN2 reaction Substrates: 1°, 2°Alkyl halides

  29. Triphenyl phosphonium yelid Aldehyde or ketone Step 2 An acid-base reaction The strong base: Alkyllithiun or phenyllithium 12.5.2Mechanism of the Wittig reaction (内膦盐) Oxaphosphetane （氧膦烷） A betaine (甜菜碱)

  30. Triphenlphosphine Oxaide(三苯基氧膦） 12.5.3 Synthesis of alkenes by Wittig reactions

  31. Furfural （糠醛） Furoic acid （糠酸）(75%) Synthesis of β-Carotene （β-胡萝卜 素） Georg F. K. Wittig received the Nobel Prize in Chemistry in 1979. 12.6 Oxidation of Aldehydes and ketones The strong oxidizing reagents: K2Cr2O7 / H+, KMnO4 / OH-; The mild oxidizing reagent: Ag2O/OH-. P287 9.5 Tollens reagent

  32. German chemist whose method of synthesizing olefins (alkenes) from carbonyl compounds is a reaction often termed the Wittig synthesis. For this achievement he shared the 1979 Nobel Prize for Chemistry. Wittig was born in Berlin and studied at Kassel and Marburg. He was professor at Freiburg 1937-44, Tubingen 1944-56, and Heidelberg 1956-67.In the Wittig reaction, which he first demonstrated 1954, a carbonyl compound (aldehyde or ketone) reacts with an organic phosphorus compound, an alkylidene- triphenylphosphorane, (C6H5)3P=CR2, where R is a hydrogen atom or an organic radical. The alkylidene group (=CR2) of the reagent reacts with the oxygen atom of the carbonyl group to form a hydrocarbon with a double bond, an olefin (alkene). In general:(C6H5)3P=CR2 + R2'CO (C6H5)3PO + R2C=CR2The reaction is widely used in organic synthesis, for example to make squalene (the synthetic precursor of cholesterol) and vitamin D3 Georg Wittig 1/2 of the prize University of Heidelberg Heidelberg, Federal Republic of Germany b. 1897d. 1987

  33. Bernhard Tollens Was born in Hamburg, Germany, received His Ph.D. at University of Göttingen,and then became professor at the same institution. Bernhard Tollens (1841-1918)

  34. 12.6.2 Baeyer-Villiger oxidation of ketones Ketones react with peroxy acides to give esters: The oxygen atom is inserted between the carbonyl group and the larger of two groups attached to it. The migratory aptitude of groups: H > phenyl > 3°alkyl > 2°alkyl > 1°alkyl > methyl (67%)

  35. Mechanism of the Baeyer-Villiger oxidation: Babiturate (巴比妥) Adolf von Baeyer was awarded the Nobel Prize in Chemistry in 1905.

  36. A great German organic chemist of his time, he received the 1905 Nobel Prize in Chemistry for his researches on organic dyes and hydroaromatic compounds. Most famous were his researches on the constitution and synthesis of the plant pigment indigo (1883), the discovery of barbituric acid (1863) phenolphthalein and fluorescein (1871), and the "strain theory" of triple bonds and small carbon rings.Three of his students (E. Fischer, E. Büchner, R. Willstätter) received Nobel prizes. Johann Friedrich Wilhelm Adolf von Baeyer Germany Munich University b. 1835d. 1917

  37. RCHO ~1730 cm-1 RCOR 1705 ~1720 cm-1 ArCHO 1695 ~1715 cm-1 ArCOR 1680 ~1700 cm-1 1680~1690 cm-1 1665~1690cm-1 2820, 2720 cm -1 (m) Stretching vibration 1717 1715 1690 1700 σ / cm -1 12.7Spectroscopic analysis of aldehydes and ketones Ch.P336 (四) Stretching vibration 1665 ~ 1780 cm -1 (s) When the carbonyl groups conjugate with carbon-carbon double bond, the location of the pick shifts to the direction of lower frequency （低频）

  38. –CHO IR Spectrum of octyl aldehyde

  39. IR Spectrum of Acetophenone Strentching vibration of C = O : 1683 cm -1

  40. The characteristic absorption of aldehydic proton: 1H NMR, δ: 9 ~ 10 ppm 1H NMR spectrum of acetaldehyde

  41. 1H NMR Spectrum of Butanone 1H NMR δ：2.2 ppm δ：2.5 ppm

  42. CH2 CH2 CH3 190-220 ppm CH2 CH2 CH3 200 180 160 140 120 100 80 60 40 20 0 Chemical shift (δ, ppm) 13C NMR : The signal for the carbon of C=O in aldehydes And ketones appears at very low field:

  43. Problems to Chapter 12 9.41(b),(c) 9.44 9.45 9.48* 9.49 9.50 9.51 P303 9.21(b),(e),(f),(g),(h) 9.25(b),(c),(e) 9.29(b)~(d) 9.32(a),(b) 9.34((b),(d) 9.36(c) 9.38(b) 9.39(c) 9.40(b) Ch.P363 (十四) (十五) (十六)(B)

  44. Additional Problems: • Show how the Wittig reaction might • be used to prepare the following alkene. • Identify the alkyl halide and the carbonyl • components that would be used.

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