Amines and Amides


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Chapter 15 in General, Organic, and Biological Chemistry, 7th Edition, Denniston

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  • tertiary, primary, secondarytertiary, secondary
  • Tertiary amines have no hydrogen attached to the nitrogen; this is what prevents them from forming hydrogen bonds among themselves. Just as a bit of review: Hydrogen bonding can only happen when there is a hydrogen atom attached to nitrogen, oxygen, or fluorine. One important point is that these three atoms have much higher electronegativities than the hydrogen, so they pull the electrons in the bond away from hydrogen, leaving it with a partial positive charge. The other important point is that these three atoms have unshared pairs of electrons with a partial negative charge that can attract a partially positive hydrogen atom from an adjacent molecule.
  • 1-butanamine2-pentanamineethanol1-propanaminewaterN-methylethanamine
  • 2-butanamine cyclopentanamine N-methylethanamine3-hexanamine N-ethyl-N-methylpropanamine
  • The amine accepts a proton from the acid, forming an alkylammonium ion. This ion is then associated with the anion “left over” from the acid, forming the alkylammonium salt.
  • N-methylethanamonium ion and hydroxide ionmethanammonium bromide
  • propanamide N,N-dimethylethanamide 3-bromo-N,N-dimethylbenzanamide
  • Note that the reaction is shown in two steps. In the first step, an amide and a carboxylic acid salt are formed. In the second step, the carboxylic acid salt reacts with itself (so to speak) to form another amide and a water molecule.
  • Amines and Amides

    1. 1. 1Chapter 15Amines and Amides
    2. 2. 2IntroductionAmines and amides contain one or more nitrogen atoms.Amines have an amino group.Amides are the product of reaction between an amine and acarboxylic acid derivative.
    3. 3. 31. Amines: structure and propertiesAmines are organic derivatives of ammonia.They are basic, like ammonia.They are ammonia molecules with one or more of the hydrogensreplaced by an organic group.The amine structure is pyramidal, as is ammonia.R may be a hydrogen or an aliphatic or aromatic organic group.
    4. 4. 41. Amines: structure and properties
    5. 5. 51. Amines: structure and propertiesAmines are classified by the number of carbons directlybonded to the nitrogen atom:A primary amine has one: RNH2 = 1oA secondary amine has two: R2NH = 2oA tertiary amine has three: R3N = 3oVideo
    6. 6. 61. Amines: structure and propertiesDetermine the classification of each of the followingamines.pencast
    7. 7. 71. Amines: structure and propertiesAmines are more polar than hydrocarbons and less polarthan alcohols.Because N is less polar than O, solubility and boiling points arelower than corresponding alcoholsH-bonds are formed, but not as strongly as with –OH.
    8. 8. 81. Amines: structure and propertiesAmine boiling points Alcohol boiling pointsmethanamine-6 oCmethanol65.0 oCethanamine16.6 oCethanol78.5 oCpropanamine47.8 oCpropanol97.4 oC
    9. 9. 91. Amines: structure and propertiesHydrogen bonding between primary amine molecules
    10. 10. 101. Amines: structure and propertiesOnly primary and secondary amines can formintermolecular hydrogen bonds with themselves.Boiling points for comparable molecular weight 1o, 2o,and 3o amines confirm this.Video
    11. 11. 111. Amines: structure and propertiesPredict which compound in each pair will have the higherboiling point.pentane or 1-butanaminecyclohexane or 2-pentanamineethanamine or ethanolbutane or 1-propanaminemethanamine or waterN-methylethanamine or butanepencast
    12. 12. 121. Amines: nomenclaturePrimary aliphatic aminesFind the longest continuous carbon chain containing the aminegroup to get the parent compound.Drop the final –e of the parent name and add the suffix -amine.Number the parent chain to give the amine carbon the lowestpossible number.Name and number all substituents as usual.Secondary and tertiary aliphatic aminesAdd the prefix N-alkyl to the name of the parent for 2o and 3oamines.
    13. 13. 131. Amines: nomenclatureName each of the following amines.pencast
    14. 14. 141. Amines: nomenclatureDraw structures for the following amines.3-decanamineN,N-dipropylbutanamineN-ethylcyclohexanamine2-methyl-2-pentanamineN-ethyl-2-heptanaminepencast
    15. 15. 151. Amines: nomenclatureThe simplest aromatic amine is benzenamine, also calledaniline.Substituents on the ring are numbered.Groups attached to the nitrogen are labelled N-.4-chlorobenzenamineN,N-diethylbenzenamine
    16. 16. 161. Amines: reactionsPreparation of aliphatic amines is by reduction of amides.Recall that reduction involves decreasing the number of bondsto oxygen and increasing the number of bonds to hydrogen.amide amine
    17. 17. 171. Amines: reactionsIf R’ = R’’ = H, a primary amine is produced.If R’ = H and R’’ = organic group, a secondary amine isproduced.If R’ = R’’ = organic group, a tertiary amine is produced.
    18. 18. 181. Amines: reactionsPreparation of primary aromatic amines is by reductionof nitro compounds.nitrobenzene aniline
    19. 19. 191. Amines: reactionsAmines react as weak bases in aqueous solution.“Weak” means only partially dissociated in solution.“Base” means proton (H+) acceptor.Water acts as the proton donor (acid).amine water alkylammoniumionhydroxide ion
    20. 20. 201. Amines: reactionsWhen an amine (a base) is neutralized by an acid, analkylammonium salt is produced.alkylammonium saltamine acid
    21. 21. 211. Amines: reactionsNaming alkylammonium saltsStart with the name of the amine.Replace the suffix –amine with –ammonium.Add the name of the anion.3-hexanamine 3-hexanammonium chloride
    22. 22. 221. Amines: reactionsWhat are the products of the following reactions?CH3CH2NHCH3 + H2O CH3NH2 + HBr pencast
    23. 23. 231. Amines: reactionsAn alkylammonium salt is the conjugate acid of thecorresponding amine. Therefore, alkylammonium saltswill react with hydroxide ions to produce the amine andwater.The salt is quite soluble in water because of the charged ions.The amine is only somewhat soluble in water.Video
    24. 24. 241. Amines: reactionsCocaineNon-water-soluble amine (“crack”)Water-soluble ammonium saltCrack cocaine, powder cocaine, and the lawCrack cocaine sentencing reform: the battle continues
    25. 25. 251. Amines: quaternary ammonium saltsAlkylammonium salts can be prepared from 1o, 2o, or 3oamines.The nitrogen atom is bonded to three, two, or one hydrogen(s),respectively.In quaternary ammonium salts, the nitrogen is bonded tofour organic groups.
    26. 26. 262. Heterocyclic aminesA cyclic compound with at least one nitrogen within aring structure is called a heterocyclic amine.Many heterocyclic amines are biologically important, orbiologically active.DNA, RNA, myoglobin, chlorophyllLSD, cocaine, nicotine, strychnine
    27. 27. 272. Heterocyclic aminesTheobromine (3,7-dimethylpurine-2,6-dione )Caffeine (1,3,7-trimethyl-1H-purine-2,6(3H,7H)-dione-3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione)
    28. 28. 282. Heterocyclic aminesNicotine (3-[(2S)-1-methylpyrrolidin-2-yl]pyridine)LSD (9,10-didehydro-N,N-diethyl-6-methylergoline-8β-carboxamide)
    29. 29. 293. AmidesIn amides, an amino group (–NH2) replaces the –OHgroup of carboxylic acids.ethanamideethanoic acid ethanamineLINKS:
    30. 30. 303. AmidesAmides are (mainly) solids at room temperature and havevery high boiling points.Molecules are polar and can hydrogen bond with each other.Simple amides are soluble in water.Molecules are polar and can hydrogen bond with water.Amides do not behave like bases.
    31. 31. 313. Amides
    32. 32. 323. AmidesVideo
    33. 33. 333. AmidesAmides are named asalkanamides.Name the carboxylic acid.Replace the –oic acidending with –amide.Alkyl groups attached tothe nitrogen are namedN-alkyl as a prefix.
    34. 34. 343. AmidesName the following compounds.pencast
    35. 35. 353. AmidesDraw structures for the following compounds.N-methylpropanamideN,N-diethylbenzamide3-bromo-4-methylhexanamidepencast
    36. 36. 363. AmidesAspartame is an amide (among other things!):3-amino-3-[(1-methoxycarbonyl-2-phenyl-ethyl)carbamoyl]propanoic acidModel
    37. 37. 373. AmidesAcetaminophen is an amide (among other things!):N-(4-hydroxyphenyl)ethanamideModel
    38. 38. 383. AmidesPrimary and secondary amines react with acidanhydrides to produce amides.acid anhydride amine amide carboxylic acid saltcarboxylic acid salt amide water2
    39. 39. 393. AmidesPrimary and secondary amines react with acid chloridesto produce amides.2acid chloride amine amide alkylammonium chloride
    40. 40. 403. AmidesBoth reactions for preparation of amides involve an acylgroup transfer.22Video
    41. 41. 413. AmidesAspartame(3S)-3-amino-4-[[(2S)-1-methoxy-1-oxo-3-phenylpropan-2-yl]amino]-4-oxobutanoic acidModel
    42. 42. 423. AmidesNeotame(3R)-3-(3,3-Dimethylbutylamino)-4-[[(1R)-2-methoxy-2-oxo-1-(phenylmethyl)ethyl]amino]-4-oxobutanoic acid
    43. 43. 433. AmidesComparison of I.U.P.A.C. names for aspartame andneotame(3R)-3-(3,3-Dimethylbutylamino)-4-[[(1R)-2-methoxy-2-oxo-1-(phenylmethyl)ethyl]amino]-4-oxobutanoic acid(3S)-3-amino-4-[[(2S)-1-methoxy-1-oxo-3-phenylpropan-2-yl]amino]-4-oxobutanoic acid
    44. 44. 443. AmidesAlthough the amide bond is difficult to break, hydrolysisof an amide is possible with heating in the presence ofeither a strong acid or a strong base.In strong acid: carboxylic acid + alkylammonium ionIn strong base: carboxylic acid salt + amine
    45. 45. 453. AmidesIn strong acid: carboxylic acid + alkylammonium ion
    46. 46. 463. AmidesIn strong base: carboxylic acid salt + amine
    47. 47. 474. Amino acidsAn amino acid is a combination of an amino group and acarboxyl group.Proteins are polymers of amino acids (chains of amides).amino group carboxyl grouppeptide bond (amide bond)