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Chapter 24. Amines

Chapter 24. Amines. Based on McMurry’s Organic Chemistry , 6 th edition. 24.1 Naming Amines. Alkyl-substituted (alkylamines) or aryl-substituted (arylamines) Classified: 1 ° (RNH 2 ), methyl (CH 3 NH 2 ), 2 ° (R 2 NH), 3 ° (R 3 N). IUPAC Names – Simple Amines.

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Chapter 24. Amines

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  1. Chapter 24. Amines Based on McMurry’s Organic Chemistry, 6th edition

  2. 24.1 Naming Amines • Alkyl-substituted (alkylamines) or aryl-substituted (arylamines) • Classified: 1° (RNH2), methyl (CH3NH2), 2° (R2NH), 3° (R3N)

  3. IUPAC Names – Simple Amines • For simple amines, the suffix -amine is added to the name of the alkyl substituent

  4. IUPAC Names – Amines With More Than One Functional Group • Consider the NH2 as an amino substituent on the parent molecule

  5. IUPAC Names – Multiple Alkyl Groups • Symmetrical secondary and tertiary amines are named by adding the prefix di- or tri- to the alkyl group

  6. IUPAC Names – Multiple, Different Alkyl Groups • Named as N-substituted primary amines • Largest alkyl group is the parent name, and other alkyl groups are considered N-substituents

  7. Common Names • Simple arylamines have common names

  8. Common Names of Heterocyclic Amines • If the nitrogen atom occurs as part of a ring, the compound is designated as being heterocyclic • Each ring system has its own parent name

  9. 24.4 Basicity of Amines • The lone pair of electrons on nitrogen makes amines basic and nucleophilic • They react with acids to form acid–base salts and they react with electrophiles

  10. Amines as Acids • Loss of the N–H proton requires a very strong base

  11. 24.6 Synthesis of Amines • Reduction of nitriles and amides (review)

  12. Reduction Aryl Nitro Compounds • Arylamines are prepared from nitration of an aromatic compound and reduction of the nitro group • Reduction by catalytic hydrogenation over platinum is suitable if no other groups can be reduced • Iron, zinc, tin, and tin(II) chloride are effective in acidic solution

  13. SN2 Reactions of Alkyl Halides • Ammonia and other amines are good nucleophiles

  14. Gabriel Synthesis of Primary Amines • A phthalimide alkylation for preparing a primary amine from an alkyl halide • The N-H in imides (CONHCO) can be removed by KOH followed by alkylation and hydrolysis

  15. Reductive Amination of Aldehydes and Ketones • Treatment of an aldehyde or ketone with ammonia or an amine in the presence of a reducing agent

  16. Reductive Amination Is Versatile • Ammonia, primary amines, and secondary amines yield primary, secondary, and tertiary amines, respectively

  17. Mechanism of Reductive Amination • Imine is intermediate

  18. Hofmann and Curtius Rearrangements • Carboxylic acid derivatives can be converted into primary amines with loss of one carbon atom by both the Hofmann rearrangement and the Curtius rearrangement

  19. Hofmann Rearrangement • RCONH2 reacts with Br2 and base • Gives high yields of arylamines and alkylamines

  20. Curtius Rearrangement • Heating an acyl azide prepared from substitution an acid chloride • Migration of R from C=O to the neighboring nitrogen with simultaneous loss of a leaving group

  21. Reactions of Amines • Alkylation and acylation have already been presented

  22. Arylamines Are Not Useful for Friedel-Crafts Reactions • The amino group forms a Lewis acid–base complex with the AlCl3 catalyst, preventing further reaction • Therefore we use the corresponding amide

  23. Diazonium Salts: The Sandmeyer Reaction • Primary arylamines react with HNO2, yielding stable arenediazonium salts

  24. Uses of Arenediazonium Salts • The N2 group can be replaced by a nucleophile

  25. Diverse Reactions of Arenediazonium Salts • Sequence of (1) nitration, (2) reduction, (3) diazotization, and (4) nucleophilic substitution leads to many different products

  26. Preparation of Aryl Halides • Reaction of an arenediazonium salt with CuCl or CuBr gives aryl halides (Sandmeyer Reaction) • Aryl iodides form from reaction with NaI without a copper(I) salt

  27. Aryl Nitriles and Carboxylic Acids • An arenediazonium salt and CuCN yield the nitrile, ArCN, which can be hydrolyzed to ArCOOH

  28. Formation of Phenols (ArOH) • From reaction of the arenediazonium salt with copper(I) oxide in an aqueous solution of copper(II) nitrate

  29. Reduction to a Hydrocarbon • By treatment of a diazonium salt with hypophosphorous acid, H3PO2

  30. Mechanism of Diazonium Replacement • Through radical (rather than polar or ionic) pathways

  31. Diazonium Coupling Reactions • Arenediazonium salts undergo a coupling reaction with activated aromatic rings, such as phenols and arylamines, to yield brightly colored azo compounds, ArN=NAr

  32. How Diazonium Coupling Occurs • The electophilic diazonium ion reacts with the electron-rich ring of a phenol or arylamine • Usually occurs at the para position but goes ortho if para is blocked

  33. Azo Dyes • Azo-coupled products have extended  conjugation that lead to low energy electronic transitions that occur in visible light (dyes)

  34. Nuclear Magnetic Resonance Spectroscopy • N–H hydrogens appear as broad signals without clear-cut coupling to neighboring C–H hydrogens • In D2O exchange of N–D for N–H occurs, and the N–H signal disappears

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