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Created by Professor William Tam & Dr. Phillis Chang Ch. 20 - 1 Chapter 20 Amines.

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Presentation on theme: "Created by Professor William Tam & Dr. Phillis Chang Ch. 20 - 1 Chapter 20 Amines."— Presentation transcript:

1 Created by Professor William Tam & Dr. Phillis Chang Ch Chapter 20 Amines

2 Ch Nomenclature  1 o Amines  2 o Amines

3 Ch  3 o Amines

4 Ch A.Arylamines

5 Ch B.Heterocyclic Amines

6 Ch Physical Properties and Structure of Amines 2A.Physical Properties

7 Ch B.Structure of Amines  N: sp 3 hybridized  Trigonal pyramidal  Bond angles close to o

8 Ch  3 o Amines with three different groups ●The two enantiomeric forms interconvert rapidly:  Impossible to resolve enantiomers. ●Pyramidal or nitrogen inversion:  Barrier ~ 25 kJ/mol.  Enough to occur rapidly at room temperature.

9 Ch  Ammonium salts with four different groups. enantiomers can be resolved

10 Ch Basicity of Amines: Amine Salts

11 Ch  The aminium ion of a more basic amine will have a larger pK a than the aminium ion of a less basic amine

12 Ch >> By releasing electrons, R— stabilizes the alkylaminium ion through dispersal of charge >

13 Ch Basicity of amines:

14 Ch A.Basicity of Arylamines Compare cyclohexylamine with arylamines.

15 Ch ●Five resonance structures Aniline

16 Ch ●Only two resonance structures

17 Ch

18 Ch B.Basicity of Heterocyclic Amines

19 Ch

20 Ch C.Amines versus Amides  Amides are far less basic than amines (even less basic than arylamines). The pK a of the conjugate acid of a typical amide is about zero Larger resonance stabilization Smaller resonance stabilization

21 Ch < >

22 Ch D.Aminium Salts and Quaternary Ammonium Salts However, R 4 N ⊕ ⊖ OH are strong bases (as strong as NaOH) Cannot act as bases

23 Ch E.Solubility of Amines in Aqueous Acids

24 Ch F.Amines as Resolving Agents  Enantiomerically pure amines are often used to resolve racemic forms of acidic compounds by the formation of diastereomeric salts.

25 Ch

26 Ch Preparation of Amines 4A.Through Nucleophilic Substitution Reactions  Alkylation of ammonia

27 Ch

28 Ch  Alkylation of azide ion and reduction

29 Ch  The Gabriel synthesis

30 Ch  Alkylation of 3 o amines

31 Ch B.Preparation of Aromatic Amines through Reduction of Nitro Compounds

32 Ch C.Preparation of Primary, Secondary, and Tertiary Amines through Reductive Amination

33 Ch  Mechanism Sodium cyanoborohydride, NABH 3 CN, is often used to reduce the imine.

34 Ch  Examples

35 Ch D. Preparation of Primary, Secondary, or Tertiary Amines through Reduction of Nitriles, Oximes, and Amides

36 Ch  Examples

37 Ch  Examples

38 Ch D.Preparation of Primary Amines through the Hofmann and Curtius Rearrangements  Hofmann rearrangement:

39 Ch  Examples

40 Ch  Mechanism

41 Ch  Curtius rearrangement:

42 Ch Reactions of Amines  Acid-base reactions  Alkylation

43 Ch  Acylation

44 Ch  Electrophilic aromatic substitution NH 2 :powerful activating group, ortho-para director

45 Ch A.Oxidation of 3 o Amines

46 Ch Reactions of Amines with Nitrous Acid  Nitrous acid (HONO) is a weak, unstable acid

47 Ch A.Reactions of Primary Aliphatic Amines with Nitrous Acid 1 o aliphatic amine (aliphatic diazonium salt) (highly unstable)

48 Ch B.Reactions of Primary Arylamines with Nitrous Acid (arenediazonium salt) (stable at <5 o C)

49 Ch  Mechanism

50 Ch  Mechanism (Cont'd) diazonium ion

51 Ch C.Reactions of Secondary Amines with Nitrous Acid N-Nitroso- amines

52 Ch D.Reactions of Tertiary Amines with Nitrous Acid

53 Ch Replacement Reactions of Arenediazonium Salts

54 Ch A.Syntheses Using Diazonium Salts

55 Ch B.The Sandmeyer Reaction: Replacement of the Diazonium Group by -Cl, -Br, or -CN The Sandmeyer reactions use a copper containing reagent.

56 Ch A Sandmeyer reaction.

57 Ch A Sandmeyer reaction.

58 Ch C.Replacement by —I

59 Ch D.Replacement by —F

60 Ch E.Replacement by —OH

61 Ch F.Replacement by Hydrogen: Deamination by Diazotization

62 Ch Coupling Reactions of Arenediazonium Salts

63 Ch  Examples

64 Ch  Examples

65 Ch  Examples

66 Ch Reactions of Amines with Sulfonyl Chlorides A sulfonamide

67 Ch A.The Hinsberg Test  Sulfonamide formation is the basis for a chemical test, called the Hinsberg test, that can be used to demonstrate whether an amine is primary, secondary, or tertiary.

68 Ch  Hinsberg with a 1 o Amine

69 Ch  Hinsberg with a 2 o Amine

70 Ch  Hinsberg with a 3 o Amine

71 Ch Synthesis of Sulfa Drugs

72 Ch Analysis saltsof Amines 11A.Chemical Analysis  They dissolve in dilute aqueous acid  Moist pH paper is  basic  Hinsberg test for 1 o, 2 o and 3 o.  1 o aromatic amines form diazo salts.  azo dye formation with 2-naphthol

73 Ch B.Spectroscopic Analysis  IR ●1 o amines  3300 – 3555 cm -1 (N–H)  two bands. ●2 o amines  3300 – 3555 cm -1 (N–H)  one band only. ●3 o amines  No bands at 3300 – 3555 cm -1 region.

74 Ch ●Aliphatic amines  1020 – 1220 cm -1 (C–N) ●Aromatic amines  1250 – 1360 cm -1 (C–N)

75 Ch  1 H NMR spectra ●1 o and 2 o amines  N–H  (0.5 – 5 ppm), usually broad, exact position depends on the solvent, concentration, purity and temperature. ●N–H protons are not usually coupled to protons on adjacent carbons. ●Protons on the  carbon of an aliphatic amine are deshielded by the electron- withdrawing effect of the nitrogen and absorb typically in the  2.2–2.9 region.

76 Ch ●Protons on the  carbon are not deshielded as much and absorb in the range  1.0–1.7

77 Ch  13 C NMR spectra C NMR chemical shifts (  )

78 Ch  Mass spectra ●The molecular ion in the mass spectrum of an amine has an odd number mass (unless there is an even number of nitrogen atoms in the molecule). ●The peak for the molecular ion is usually strong for aromatic and cyclic aliphatic amines but weak for acyclic aliphatic amines. ●Cleavage between the  and  carbons of aliphatic amines is a common mode of fragmentation.

79 Ch Eliminations Involving Ammonium Compounds 12A.The Hofmann Elimination

80 Ch Preparation of the 4 o ammonium hydroxide

81 Ch  Although most eliminations involving neutral substrates tend to follow the Zaitsev rule, eliminations with charged substrates tend to follow what is called the Hofmann rule and yield mainly the least substituted alkene

82 Ch An anti mechanism

83 Ch B.The Cope Elimination A syn mechanism Prep of amine oxide, see slide 45.

84 Ch Summary of Preparations and Reactions of Amines  Preparation of amines

85 Ch

86 Ch  Reactions of amines

87 Ch

88 Ch

89 Ch  END OF CHAPTER 20 


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