Chapter 23 The 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 23.1 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

Aromatic amines are named as derivatives of aniline Common Nomenclature Aromatic amines are named as derivatives of aniline 23.1 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 23.1 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

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

Substitutive Nomenclature Heterocyclic amines

Problems Name the following compounds:

Draw the following molecules 2-propen-1-amine N-methyl-N’-propyl-1,4-butanediamine p-aminophenol

Most amines undergo rapid inversion at N Structure of Amines Bond length: Most amines undergo rapid inversion at N 23.2 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 Diethylamine, MW = 71.1 amu bp = 56.3°C Pentane, MW = 72.1 amu bp = 36.1°C

Basicity of Amines Amines react with acids to form ammonium salts

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)

Quaternary Salts Quaternary ammonium and phosphonium salts are compounds in which all four groups around the N and P are alkyl or aryl 23.6 Quaternary Ammonium and Phosphonium Salts

Phase-Transfer Catalysis

Synthesis of Amines

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 23.11 Synthesis of Amines

Hydrolysis of the phthalimide frees the amine 23.11 Synthesis of Amines

Reduction of Nitro Compounds Catalytic hydrogenation: Reduction with finely divided metal powders: 23.11 Synthesis of Amines

Reduction of Nitro Compounds LiAlH4 and NaBH4 fail to provide the amine 23.11 Synthesis of Amines

Reductive Amination

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 23.7 Alkylation and Acylation Reactions of Amines