Amines

Question 1

What is an amine

Answer 1

-derived from ammonia
-all contain an N atom
-hydrogens are replaced with an organic group
-primary amine: 1 organic group, e.g. methylamine
-secondary amine: 2 organic groups, e.g. dimethylamine
-tertiary amine: 3 organic groups, e.g. trimethylamine
-quaternary ion: 4 organic groups, e.g. tetramethylamine ion (typically has coordinate bond)

Question 2

Cationic surfactants

Answer 2

-quaternary ammonium salts are used ti make cleaning products
-e.g. shampoo, washing up liquids
-made from positive end and are attracted to negative ions
-long hydrocarbon tail = cationic surfactants
-non-polar tail is attracted to oil/grease
-polar head is attracted to water

-can also be used as hair conditioner or fabric softener
-positive ammonium ion is attracted to negatively charged hair or fibres

Question 3

Why do amines act as a base? What affects the strength?

Answer 3

-have a lone pair of electrons
-hence accept proton, forming coordinate bond
-higher electron density = more readily available electrons = more strong base
-electron density on N depends on the type of group attached to it

Question 4

Which amines are the weakest base and why?

Answer 4

-aromatic amines
-benzene is an electron withdrawing group
-pulls electrons away from N into ring structure
-electron density of N atom is reduced
-hence lone pair of electrons are less available

Question 5

Which amines are the strongest base and why?

Answer 5

-primary amines (aliphatic)
-alkyl groups push electrons towards N atom
-electron density at N increases
-lone pair of electrons are more available

Question 6

Order of base strength, starting from the weakest base

Answer 6

Aromatic amines

Ammonia

Primary aliphatic amines

Secondary aliphatic amines

Question 7

How to make aliphatic amines

Answer 7

Reacting haloalkane and excess ammonia
-ammonia is a nucleophile, attacks C atom
-alkylammonium salt is formed as an intermediate (N+ and Cl-)
-second ammonia acts as a base, proton acceptor
-primary amine and ammonium halide salt is produced

Cons:
-secondary, tertiary and quaternary salts may also be produced
-hence impure product
-primary amines still have a lone electron pair
-can act as a nucleophile on remaining haloalkane

Reducing Nitriles (catalytic hydrogenation):
-nickel/platinum catalyst and hydrogen gas
-high pressure and temperature
-cheapest method
-only primary amine produced so pure product is made
-RCH2CN + 2H2 —> RCH2CH2NH2

-LiAlH4 is expensive but can be used too (plus dilute acid)
-[H] is dissolved in non-aqueous solvent, e.g. dry ether
-RCH2CN + 4[H] —> RCH2CH2NH2

Question 8

How to make aromatic amines

Answer 8

-used to make dye stuffs and pharmaceuticals
-made by reducing nitro compounds
-nitrobenzene is heated under reflux with conc HCl and tin
-forms salt, C6H5NH3+Cl-
-salt reacts with alkali, NaOH
-water and phenylamine is produced

Question 9

What are amides and N-substituted amide

Answer 9

-derivatives of carboxylic acids
-have -CONH2 functional group
-like carboxylic acid but OH is replaced by NH2
-N-substituted amide = 1 H atom is replaced with an alkyl group