Amines
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AMINES
Amines are organic Compounds Containing Nitrogen
Classification of Amines
- primary (1°) - one C attached to N
- secondary (2°) - two C attached to N
- tertiary (3°) - three C attached to N
- quaternary (4°) - four C attached to N (and a positive charge)
NOTE: Tthe difference from other functional groups, which are classified according to the Carbon atom to which the functional group is attached
Nomenclature of Amines
- IUPAC: amino- substituent
- common: alkyl amine
- Chemical Abstracts: alkanamine
Structure of Amines
Sp3 (tetrahedral) nitrogen including the lone pair
Tertiary amines usually cannot be isolated as separate enantiomers
Basicity of Amines, Acidity of Ammonium Ions
N lone pair relatively easily protonated
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water solubility of amines can be easily changed with pH
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aromatic amines are water-soluble (protonated) below pH 4
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aliphatic amines are water-soluble (protonated) below pH 9
Basicity Trends
1. Aromatic amines are less basic due to resonance delocalization of the N lone pair
2. Amides are nonbasic due to strong delocalization of the N lone pair
3. Electron withdrawing effects decrease basicity
because the N lone pair is less available for bonding to a proton
Preparations of Amines
1. substitution reactions:
SN2 reaction of ammonia on alkyl halides
but the amine product is still nucleophilic and further substitution often results
primary amines can be made by using a great excess of NH3 to avoid further substitution
2. Reduction reactions:
Reactions of Amines
1. substitution reactions:
SN2 reactions on alkyl halides, but over substitution is a problem, except for making quaternary ammonium ions
- acyl substitutions to make amides (usually from acid chlorides)
2. Diazonium Salts
Secondary amines react with HNO2 (nitrous acid) to make N-nitrosoamines
Primary amines react with HNO2 to form a diazonium ion (diazotization reaction)
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aliphatic diazonium ions are unstable, give carbocations
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possible products include rearrangements, eliminations, nucleophilic substitution
Aryl diazonium ions are relatively stable and can be replaced by many nucleophiles this method provides a good way to attach nucleophiles to aromatic rings
Sandmeyer reactions : CuX as catalyst to convert diazonium ion to ArX
3. Elimination Reactions
- Hoffmann elimination - from a quaternary ammonium hydroxide
- Cope elimination - from a tertiary amine oxide
Pyrrole
- pyrrole is even more reactive than benzene in electrophilic aromatic substitution
- the porphine ring system is a tetrapyrrole - found in heme, chlorophyll, etc.
Pyridine
- pyridine is less reactive than benzene in electrophilic aromatic substitution
Alkaloids
Naturally occurring amines, such as morphine. The alkaloid name comes from their basic (alkaline) properties