Chapter 23The Chemistry of Amines

Amines

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Classification of Amines

• Amines are organic derivatives of ammonia

• Note how amines are classified differently from that of alcohols

423.1 Nomenclature of Amines

Common Nomenclature

• For simple amines, add “amine” to the name of the alkyl group

• When alkyl groups differ, name the amine as an N-substituted amine

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Common Nomenclature

• Aromatic amines are named as derivatives of aniline

623.1 Nomenclature of Amines

Substitutive Nomenclature

• Amines are named in a similar fashion to the their analogous alcohols– Remove the “-e” and replace it with “-amine”

• If there is more than one amino group, use Greek prefixes to indicate how many and numbers to indicate location on the alkyl chain

723.1 Nomenclature of Amines

• When alkyl groups differ, use the N-substitution system

• When there is more than one substituted amine, use N and N’ to differentiate

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• Name the amino group as a substituent when there is a higher priority principal group

• Recall:

Substitutive Nomenclature

• Heterocyclic amines

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Problems

1) Name the following compounds:

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2) Draw the following molecules• 2-propen-1-amine

• N-methyl-N’-propyl-1,4-butanediamine

• p-aminophenol

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Structure of Amines

• Bond length:

• Most amines undergo rapid inversion at N

1323.2 Structure of Amines

Physical Properties of Amines• H-bonding ability increases boiling point

• Low molecular weight amines tend to be water soluble whether they are primary, secondary or tertiary

• Fewer than 5 carbons usually = solubility in water

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Diethylamine, MW = 71.1 amubp = 56.3°C

Pentane, MW = 72.1 amubp = 36.1°C

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Basicity of Amines

• Amines react with acids to form ammonium salts

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Separations Using Amine Basicity• Ammonium salts are ionic compounds which imparts a high

degree of water-solubility• This property can be useful in separation of amines from

other compounds

Acidity of Amines• NH3, RNH2, and R2NH are amphoteric: they may act as bases

and acids• They are very weakly acidic

– Will give up H+ to a very strong base• The conjugate base of an amine is called an amide (do not

confuse with amide derivatives of carboxylic acids)

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Quaternary Salts

• Quaternary ammonium and phosphonium salts are compounds in which all four groups around the N and P are alkyl or aryl

1923.6 Quaternary Ammonium and Phosphonium Salts

Phase-Transfer Catalysis

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Synthesis of Amines

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Direct Alkylation of Amines

• Further alkylations can take place to give complex mixtures

Gabriel Synthesis of Primary Amines

• Direct alkylation is not a good method for the preparation of primary amines

• The Gabriel synthesis allows for controlled preparation

2323.11 Synthesis of Amines

• Hydrolysis of the phthalimide frees the amine

2423.11 Synthesis of Amines

Reduction of Nitro Compounds

• Catalytic hydrogenation:

• Reduction with finely divided metal powders:

2523.11 Synthesis of Amines

Reduction of Nitro Compounds

• LiAlH4 and NaBH4 fail to provide the amine

2623.11 Synthesis of Amines

Reductive Amination

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• Formaldehyde can be used to introduce methyl groups

• Neither an imine nor an enamine can be an intermediate in the reaction of a secondary amine and formaldehyde

3023.7 Alkylation and Acylation Reactions of Amines