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AMINES

AMINES. Classification. Primary amine. Secondary amine. Tertiary amine. Quaternary ammonium compound. Aliphatic amines. Aromatic amines. Examples of nomenclature. Cyclic amines. Structure and bonding in amines. sp 3. C-N-C angle 108 ° C-N bond length 1.47 Å.

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AMINES

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  1. AMINES

  2. Classification Primary amine Secondary amine Tertiary amine

  3. Quaternary ammonium compound

  4. Aliphatic amines Aromatic amines

  5. Examples of nomenclature

  6. Cyclic amines

  7. Structure and bonding in amines sp3 C-N-C angle 108° C-N bond length 1.47Å Trimethylamine

  8. Structure and bonding in amines Chiral carbon Chiral nitrogen?

  9. Pyramidal inversion in amines fast sp3 sp3 sp2 (planar) Energy barrier: 6 kcal/mol (25 kJ/mol) at room temp.

  10. Physical properties of some amines

  11. Hydrogen bonding of amines Not possible for tertiary amines Hydrogen bonds are also formed with water Amines with fewer than 5 carbons are water-soluble

  12. Basicity of amines Because of nitrogen lone pair amines are both basic and nucleophilic An amine (a Lewis base) An acid A salt Amines are much more basic than alcohols, ethers, or water.

  13. Basicity of amines Deprotonation of amine salt by water is used as measure of amine basicity Stronger acid (lower pKa value) Weaker conjugated base Weaker acid (higher pKa value) Stronger conjugated base pKa = -log Ka Ka = Keq[H2O] = [H3O+][RNH2]/[RNH3+]

  14. Basicity of some alkylamines

  15. Note the diference in basicity of amine and amide nitrogen Amides are completely nonbasic Resonance stabilization of amide

  16. After amide protonation No resonance stabilization Inductive destabilization of the positive charge

  17. Energy profiles for amine and amide protonation Energy RCONH3+ RNH3+ RNH2 RCONH2 Reaction progress

  18. Aromatic amines Resonance structures of aniline Resonance structures after protonation of aniline pKa for aniline = 4.63 Arylamines are less basic than alkylamines

  19. Comparison of basicity – arylamines vs. alkylamines Energy RNH3+ G0 alkylamine ArNH3+ RNH2 + H2O G0 arylamine Resonance stabilization ArNH2+ H2O Reaction progress

  20. Basicity of para-substituted anilines Y pKa Stronger base -NH2 6.15 -OCH3 5.34 -CH3 5.08 -H 4.63 -Cl 3.98 -Br 3.86 -CN 1.74 -NO2 1.00 EDG (activating ring in electrophilic substitution) Stabilize protonated amino group EWG (deactivating ring in electrophilic substitution) Stabilize non- protonated amino group Weaker base

  21. Energy profiles for protonation of para-substituted anilines Energy Y = EWG G0 Y = EDG G0 Reaction progress

  22. => Amine Salts • Ionic solids with high melting points • Soluble in water • No fishy odor

  23. Separation and purification of amine component from a mixture Amine + neutral compound Dissolve in ether, add aq. HCl Ether layer (neutral compound) Aqueous layer (RNH3+Cl-; amine salt) Add NaOH, ether Ether layer (amine) Aqueous layer (NaCl)

  24. Preparation of amines SN2 reaction of alkyl halides

  25. Preparation of amines Azide synthesis (SN2 reaction)

  26. Preparation of amines Gabriel synthesis (SN2 reaction) benzylamine

  27. Preparation of amines Reduction of nitriles and amides

  28. Preparation of amines Reductive amination of ketones and aldehydes

  29. Preparation of amines Reductive amination of ketones and aldehydes Primary amine Secondary amine Tertiary amine

  30. Preparation of amines Hofmann rearrangement

  31. Preparation of amines Curtius rearrangement azide

  32. Preparation of arylamines Two-step sequence: nitration, reduction 90% yield

  33. Reactions of amines Alkylation

  34. Reactions of amines Acylation (with acid chlorides, anhydrides or esters) Tertiary aminesdo not reactwith carboxylic acids derivatives

  35. Reactions of amines Hofmann elimination

  36. Reactions of amines Reaction of alkylamines with nitrous acid Unstable, decomposes immediately after formation with evolution of nitrogen gas

  37. Reactions of arylamines Reaction of arylamines with nitrous acid (diazotization) Primary arylamine Arenediazonium salt Stable < 5 C

  38. Reactions of arylamines Diazonio replacement reactions CuBr NaI -N2 -N2 CuCl CuCN -N2 -N2 H3O+ heating H3PO2 -N2 -N2

  39. Reactions of arylamines Diazonium coupling reactions An azo compound Where Y = -OH (phenol) or -NR2 (tertiary arylamine) Y – strong electron donating group

  40. Reactions of arylamines Example of diazonium coupling reactions

  41. Quaternary ammonium salts in Phase Transfer Catalysis

  42. Quaternary ammonium salts in Phase Transfer Catalysis How it works? H2O + Na+ HO- R4N+ Cl- Aqueous phase H2O + Na+ HO- + Cl- + R4N+ CHCl3 + cyclohexene CHCl3 + cyclohexene + R4N+ HO- Organic phase

  43. Quaternary ammonium salts in Phase Transfer Catalysis Examples:

  44. Naturally Occurring Amines Alkaloids Cinchona flower Quinine (antimalarial)

  45. Naturally Occurring Amines Alkaloids Reserpine (antihypertensive) Rauwolfia serpentina

  46. Naturally Occurring Amines Alkaloids Morphine (an analgesic) Papaver somniferum

  47. Morphine Alkaloids Heroin – not found in nature

  48. Morphine derivatives Codeine – found in nature (analgesic, antitussive) Nalorphine – synthetic analgesic, morphine antagonist

  49. „Morphine Rule” (Structural requirements necessary for biological activity) Quaternary carbon linked to phenyl ring, and two carbon chain bondedtotertiary amino group QSAR –quantitative structure-activity relationship

  50. Synthetic analgesics Meperidine - pain killer

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