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22.15 Nitrosation of Alkylamines

22.15 Nitrosation of Alkylamines. +. H. –. ••. ••. ••. ••. ••. ••. O. O. N. O. N. O. H. • •. • •. • •. ••. ••. +. H. H. H. +. ••. ••. ••. ••. +. O. N. O. O. N. O. • •. • •. • •. • •. • •. +. H. H. Nitrite Ion, Nitrous Acid, and Nitrosyl Cation. ••.

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22.15 Nitrosation of Alkylamines

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  1. 22.15Nitrosation of Alkylamines

  2. + H – •• •• •• •• •• •• O O N O N O H •• •• •• •• •• + H H H + •• •• •• •• + O N O O N O •• •• •• •• •• + H H Nitrite Ion, Nitrous Acid, and Nitrosyl Cation

  3. •• •• N O •• + Nitrosyl Cation and Nitrosation

  4. + •• •• N N O •• •• •• N N O •• •• + Nitrosyl Cation and Nitrosation +

  5. + •• •• •• •• N N N O N O •• •• •• + H + H •• •• + N N O •• •• + H Nitrosation of Secondary Alkylamines • Nitrosation of secondary amines gives an N-nitroso amine.

  6. •• •• •• N O (CH3)2NH (CH3)2N •• Example NaNO2, HCl •• H2O (88-90%)

  7. N-nitrosodimethylamine(leather tanning) N O (CH3)2N N N N N N O O N-nitrosopyrrolidine(nitrite-cured bacon) N-nitrosonornicotine(tobacco smoke) Some N-Nitroso Amines

  8. R R H + •• •• •• •• N N N O N O •• •• •• + H H + H R H •• •• N N O •• •• + H Nitrosation of Primary Alkylamines • Analogous to nitrosation of secondary amines to this point. +

  9. R + H •• •• •• •• + N N N O N O •• •• •• H H R R H + H •• •• •• N N N O N O •• •• •• •• + H H + H Nitrosation of Primary Alkylamines R • This species reacts further. H

  10. H + + O N N R •• •• •• H R H •• N N O •• •• + H Nitrosation of Primary Alkylamines • Nitrosation of a primary alkylamine gives an alkyl diazonium ion. • Process is called diazotization.

  11. + + N N N R R N •• •• •• Alkyl Diazonium Ions • Alkyl diazonium ions readily lose N2 to give carbocations. +

  12. + HONO N N NH2 – N2 OH H2O + (80%) + (3%) (2%) Example: Nitrosation of 1,1-Dimethylpropylamine Mechanism 22.1

  13. R R R R + •• •• N N N O •• •• R R Nitrosation of Tertiary Alkylamines • There is no useful chemistry associated with the nitrosation of tertiary alkylamines.

  14. 22.16Nitrosation of Arylamines

  15. N(CH2CH3)2 N(CH2CH3)2 1. NaNO2, HCl, H2O, 8°C 2. HO– N O (95%) Nitrosation of Tertiary Arylamines • Reaction that occurs is electrophilic aromatic substitution.

  16. N O NHCH3 NCH3 (87-93%) Nitrosation of N-Alkylarylamines • Similar to secondary alkylamines; • Gives N-nitroso amines NaNO2, HCl,H2O, 10°C

  17. + fast + + R N2 RN N + slow + + N ArN Ar N2 Nitrosation of Primary Arylamines • Gives aryl diazonium ions. • Aryl diazonium ions are much more stable thanalkyl diazonium ions. • Most aryl diazonium ions are stable under the conditions of their formation (0-10°C).

  18. NH2 (CH3)2CH NaNO2, H2SO4 H2O, 0-5°C + N (CH3)2CH N Example: HSO4–

  19. H Ar NO2 Ar NH2 Ar + N N Ar Synthetic Origin of Aryl Diazonium Salts

  20. 22.17Synthetic Transformationsof Aryl Diazonium Salts

  21. Cl Br Ar Ar F Ar CN Ar + N N Ar H I Ar Ar OH Ar Transformations of Aryl Diazonium Salts

  22. + N N Ar OH Ar Preparation of Phenols H2O, heat

  23. NH2 (CH3)2CH OH (CH3)2CH Example 1. NaNO2, H2SO4 H2O, 0-5°C 2. H2O, heat (73%)

  24. Cl Br Ar Ar F Ar CN Ar + N N Ar H I Ar Ar OH Ar Transformations of Aryl Diazonium Salts

  25. + N N Ar I Ar Preparation of Aryl Iodides • Reaction of an aryl diazonium salt with potassium iodide: KI

  26. NH2 Br Example I 1. NaNO2, HCl H2O, 0-5°C Br 2. KI, room temp. (72-83%)

  27. Cl Br Ar Ar F Ar CN Ar + N N Ar H I Ar Ar OH Ar Transformations of Aryl Diazonium Salts

  28. F Ar + N N Ar Preparation of Aryl Fluorides • Heat the tetrafluoroborate salt of a diazonium ion; • process is called the Schiemann reaction.

  29. NH2 F CCH2CH3 CCH2CH3 O O Example 1. NaNO2, HCl, H2O, 0-5°C 2. HBF4 3. heat (68%)

  30. Cl Br Ar Ar F Ar CN Ar + N N Ar H I Ar Ar OH Ar Transformations of Aryl Diazonium Salts

  31. Cl Br Ar Ar + N N Ar Preparation of Aryl Chlorides and Bromides • Aryl chlorides and aryl bromides are prepared by heating a diazonium salt with copper(I) chloride or bromide. • Substitutions of diazonium salts that use copper(I) halides are called Sandmeyerreactions.

  32. Example NH2 Cl 1. NaNO2, HCl, H2O, 0-5°C 2. CuCl, heat NO2 NO2 (68-71%)

  33. NH2 Cl Example 1. NaNO2, HBr, H2O, 0-10°C Br Cl 2. CuBr, heat (89-95%)

  34. Cl Br Ar Ar F Ar CN Ar + N N Ar H I Ar Ar OH Ar Transformations of Aryl Diazonium Salts

  35. CN Ar + N N Ar Preparation of Aryl Nitriles • Aryl nitriles are prepared by heating a diazonium salt with copper(I) cyanide. • This is another type of Sandmeyer reaction.

  36. NH2 CH3 Example 1. NaNO2, HCl, H2O, 0°C CN CH3 2. CuCN, heat (64-70%)

  37. Cl Br Ar Ar F Ar CN Ar + N N Ar H I Ar Ar OH Ar Transformations of Aryl Diazonium Salts

  38. + N N Ar H Ar Transformations of Aryl Diazonium Salts • Hypophosphorous acid (H3PO2) reduces diazonium salts; ethanol does the same thing. • This is called reductive deamination.

  39. NH2 CH3 CH3 Example NaNO2, H2SO4, H3PO2 (70-75%)

  40. Value of Diazonium Salts • 1) Allows introduction of substituents such as OH, F, I, and CN on the ring. • 2) Allows preparation of otherwise difficultly accessible substitution patterns.

  41. NH2 NH2 NaNO2, H2SO4,H2O, CH3CH2OH Br Br Br2 H2O Br Br Br (100%) Br (74-77%) Example

  42. 22.18Azo Coupling

  43. + + H N N N N Ar' Ar Ar Ar' an azo compound Ar' must bear a strongly electron-releasing group such as OH, OR, or NR2. Azo Coupling • Diazonium salts are weak electrophiles. • React with strongly activated aromatic compounds by electrophilic aromatic substitution.

  44. OH + N C6H5N OH N NC6H5 Example + Cl–

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