amines Flashcards
(23 cards)
what’s dif bw aliphatic amines + aromatic amines
aliphatic = bonded to C chain
aromatic = bonded to benzen/C ring
why do primary aliphatic amines act as bronsted-lowry bases
lone pair of e- on N is readily available for forming a dative covalent bond with a H+ and so accepting a proton.
why r primary aliphatic amines only weak bases
only a low concentration of hydroxide ions is produced.
eqn for reaction w primary aliphatic amine w water
CH3NH2 +H2O ⇌ CH3NH3+ +OH-
why are primary aliphatic amines stronger than ammonia
the alkyl groups are electron releasing and push electrons towards the nitrogen atom and so making the lone pair of electrons on the nitrogen more readily available to accept protons.
why are 2ndary amines stronger bases that 1’ amines
they have more alkyl groups that are substituted onto the N atom in place of H atoms. Therefore more electron density is pushed onto the N atom (as the inductive effect of alkyl groups is greater than that of H atoms), so making the lone pair of electrons on the nitrogen more readily available.
why r 3’ amines weaker bases that 2’ amines
The tertiary amines and corresponding ammonium salts are less soluble in water and this makes them less strong bases than the secondary amines.
why do 1’ aromatic amines not form basic solns
because the lone pair of electrons on the nitrogen delocalise with the ring of electrons in the benzene ring. This means the lone pair on the N is less able to accept protons.
Overall order of base strength
Weaker bases Aromatic amines < ammonia< primary amines< tertiary amines< secondary amines Stronger bases
what do amines react w acids to form
ammonium salts
how to convert ammonium salt back to amine
Addition of NaOH
are the ammonium salts soluble
YES BC IONIC
if water evaporated what happens to ammonium salts
These ionic salts will be solid crystals, if the water is evaporated, because of the strong ionic interactions.
how to make buffer soln from amine
weak base with a salt of that weak base
e.g.Ammonia and ammonium chloride
Methylamine and methylammonium chloride
Ethylamine and ethylammonium chloride
why can NS of halogenoalkane w ammonia lead to a successive series of reactions
Primary amines can be formed by the nucleophilic substitution reaction between halogenoalkanes and ammonia in a one step reaction. However, as the lone pair of electrons is still available on the N in the amine formed, the primary amine can react in the same nucleophilic way w the halogenoalkane in a successive series of reactions forming secondary, tertiary amines and quaternary ammonium salts.
how to limit successive reaction
Using an excess of ammonia can limit the further subsequent reactions and will maximise the amount of primary amine formed
what will happen if excess of halogenoalkane used
quaternary ammonium salt
use of quaternary ammonium salt
cationic surfactants
what do surfactants do
Surfactants reduce the surface tension of liquids.
The positive nitrogen is attracted toward negatively charged surfaces such as glass, hair, fibres and plastics. This helps in their uses as fabric softeners, hair conditioners and sewage flocculants.
how to prepare amines from NITRILES in 2 step reaction
Step 1. convert halogenoalkane to nitrile by using KCN in aqueous ethanol (heat under reflux)
CH3CH2Br + CN- CH3CH2CN + Br -
Step 2. reduce nitrile to amine by using LiAlH4 in ether or by reducing with H2 using a Ni catalyst
CH3CH2CN + 4[H] CH3CH2CH2NH2
2 disadvantage of 2 step reaction
KCN produced = toxic
2 step so may have low yield
disadvantage of reacting halogenoalkanes and ammonia to form 1’ amine
not an efficient method for preparing a high yield of the primary amine because of the further substitution reactions that occur.
Reducing nitroarenes to aromatic amines 2 ways
- nitrobenzene + 6[H] -> phenylamine + 2H2O
Reagent: Sn and HCl or Fe and HCl
Conditions: Heating
Mechanism: Reduction
- catalytic hydrogenation (H2 using a Ni catalyst)
