Amines

• Amines?can be thought of as derivates of ammonia, in which one or more of the hydrogens is replaced by an alkyl or aryl group
• The number of substituted hydrogens is the basis of classifying amines

Classification of amines

• Notice the classification is not the same as in alcohols and haloalkanes, where the designation primary, secondary and tertiary is based on the substituents on the?carbon?atom rather than the?nitrogen?atom
• If the R group is an alkyl group (methyl, ethyl, etc) then then it is an?aliphatic amine;?if it is an aryl group (benzene ring or phenyl) then it is an?aromatic amine
• Aliphatic and aromatic amines share similar chemical reactions and the aryl group can strongly influence the chemistry and reactivity of the amine group

Naming Amines

• Amines can be named using common names or IUPAC systematic names
• The common way to name amines is to use the alkyl (or aryl) prefix followed by?-amine
• The IUPAC systematic name uses the numbered prefix?amino-?followed by the alkane (or aromatic) stem

Nomenclature of aliphatic and aromatic amines table

Preparing Amines

• Primary amines can be prepared from different reactions including:
  • The reaction of halogenoalkanes with ammonia
  • The reduction of nitriles

   

Reaction of halogenoalkanes with ammonia

• This is a?nucleophilic substitution?reaction in which the nitrogen lone pair in ammonia acts as a?nucleophile?and?replaces?the halogen in the halogenoalkane
• When a halogenoalkane is reacted with?excess, hot ethanolic ammonia under pressure?a?primary amine?is formed

Formation of primary amine

Reduction of nitriles

• Nitriles contain a -CN functional group which can be?reduced?to an -NH2?group
• The nitrile vapour and?hydrogen gas?are passed over a?nickel catalyst?or?LiAlH4?in?dry ether?can be used to form a?primary amine

Nitriles can be reduced with LiAlH4?or H2?and Ni catalyst

• Phenylamine?is an organic compound consisting of a benzene ring and an?amine?(NH2) functional group
• It can be produced in a?three-step synthesis?reaction followed by the separation of phenylamine from the reaction mixture
  • Step 1-?Benzene undergoes?nitration?with concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4) at 25 to 60?oC to form?nitrobenzene
  • Step 2 -?Nitrobenzene is?reduced?with?hot tin?(Sn) and?concentrated hydrochloric acid?(HCl)?under reflux?to form an acidic mixture that contains the organic product C6H5N+H3
  • Step 3?- Sodium hydroxide (NaOH) is added to the acidic reaction mixture to form?phenylamine
  • Step 4 -?The phenylamine is separated from the reaction mixture by?steam distillation

   

The overall reaction of formation of phenylamine from benzene

Multi-step synthesis of phenylamine from benzene

Dye Manufacture

• Aromatic amines are used to make a class of synthetic dyes called?azo dyes
• Azo dyes contain an azo functional group,?R-N=N-R, in which the R groups can be alkyl, aryl or a mixture of both

• The synthesis takes place in three steps, beginning with the creation of nitrous acid?in situ
  • In situ literally means on site and is a term used to describe reagents that are made in the reaction vessel, usually because they are too unstable to exist outside of the reaction conditions

   

• The nitrous acid reacts with the phenylamine to create the intermediate?benzenediazonium ion
• The third step is called the?coupling reaction?where the benzenediazonium ion reacts with another aromatic compound to produce an azo dye
• By carefully varying the aromatic compound it is possible to make a wide variety of azo dyes

Summary table showing the steps in azo dye production