amines (3.3.11)
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how are amines classified?
as primary, secondary or tertiary: * primary = 1 C atom bonded to N atom * secondary = 2 C atoms bonded to N atom * tertiary = 3 C atoms bonded to N atom (can also be quarternary ammonium salts which have 4 C atoms bonded to N atom)
what are the rules to remember when naming amines?
• the suffix arises from the longest carbon chain bonded to the N atom • the name should start with the classification • the position of the amine group needs to be recognised • if the N atom is within the structure (N-substituted amine) the name must start with N- • any prefixes are arranged in alphabetical order • if there are two amine groups an e is needed in the suffix • eg. 3^0, N-ethyl-N-methylbutan-1-amine
what are amines?
nucleophiles (N atom has a lone pair)
what reactions do ammonia and amines undergo?
nucleophilic substitution reactions with halogenoalkanes to form primary, secondary and tertiary amines and quarternary ammonium salts
what reactions do ammonia and primary amines undergo?
nucleophilic addition-elimination reactions with acyl chlorides and acid anhydrides
why do multiple nucleophilic substitution reactions occur when ammonia/amines and halogenoalkanes react?
• there is a lone pair on the N atom of the nitrogen-containing product produced in each reaction so it can react with another molecule of the halogenoalkane (if it is in excess) • this continues until the quarternary ammonium salt is produced
how are quarternary ammonium salts structured?
a positive N atom will be in the middle and 3 of the groups it is bonded to will be based on the halogenoalkane while one will be based on the amine, and the negative halide ion will be next to it
how are quarternary ammonium salts used?
as cationic surfactants
how can primary aliphatic amines be prepared?
by the reaction of ammonia with halogenoalkanes and the reduction of nitriles
what are the conditions for the production of a primary aliphatic amine by nucleophilic substitution between ammonia and a halogenoalkane?
excess concentrated ammonia
what happens when excess ammonia is used in the reaction between ammonia and a halogenoalkane?
the primary amine is produced
what happens when excess halogenoalkane is used in the reaction between ammonia and a halogenoalkane?
the quarternary ammonium salt is produced
what are the 2 stages in the production of a primary aliphatic amine by the reduction of nitriles?
• a halogenoalkane is refluxed with potassium cyanide (KCN) in the prescence of aqueous ethanol • reduction to the primary amine using H2 with a nickel catalyst occurs
what is the advantage of producing primary amines by the reduction of nitriles?
the primary amine is the only product, so further substitution reactions are avoided
what is the disadvantage of producing primary amines by the reduction of nitriles?
• potassium cyanide is highly toxic • hydrogen is highly flammable
what would the equation be for the production of butylamine by the reaction of ammonia with a halogenoalkane?
CH3CH2CH2CH2Br + 2 NH3 -> CH3CH2CH2CH2NH2 + NH4Br
what would the equations be for the production of butylamine by the reduction of a nitrile?
1 - CH3CH2CH2Br + KCN -> CH3CH2CH2CN + KBr 2 - CH3CH2CH2CN + 4 [H] -> CH3CH2CH2CH2NH2
how are aromatic amines prepared?
by the reduction of nitro compounds
what are the two stages in the production of an aromatic amine?
1 - benzene undergoes nitration with concentrated HNO3 and concentrated H2SO4 to form C6H5NO2 2 - C6H5NO2 reacts with hydrochloric acid (reducing agent) and tin (catalyst) to form phenylamine -> C6H5NO2 + 6 [H] -> C6H5NH2 + 2 H2O
what are aromatic amines used in?
the manufacture of dyes
what are amines (apart from nucleophiles)?
weak bases
what does the base strength of an amine depend on?
the availability of the lone pair on the N atom to accept a proton (stronger base = greater availability of N atom to accept proton)
what is the order of base strength for ammonia, primary aliphatic amines and primary aromatic amines (from strongest to weakest)?
strongest - primary aliphatic amines ammonia weakest - primary aromatic amines
why are primary aliphatic amines eg. methylamine the strongest bases?
• the N atom is bonded to an alkyl group which is electron-donating (positive inductive effect), so the electron density is pushed onto the N atom • this means the lone pair on the N atom is more available to accept the proton