amines Flashcards
what kind of base do amines act as
bronsted-lowry bases
why are primary amines able to act as bases
Primary aliphatic amines act as Bronsted-Lowry Bases because the
lone pair of electrons on the nitrogen is readily available for forming a
dative covalent bond with a H+ and so accepting a proton. They are
weak bases as only a low concentration of hydroxide ions is
produced.
why are primary amines better bases than ammonia
Primary aliphatic amines are stronger bases than ammonia as the
alkyl groups are electron releasing and push electrons towards the
nitrogen atom and so make it a stronger base.
why are secondary amines better bases than primary amines
Secondary amines are stronger bases than primary amines because 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)
why are aromatic amines weak bases
Primary aromatic amines such as phenylamine do not form basic solutions because the
lone pair of electrons on the nitrogen delocalise with the ring of electrons in the benzene
ring. This means the N is less able to accept protons.
order of basic strength
Aromatic amines < ammonia< primary amines< secondary amines
what is formed when amines react with acids
ammonium salts
amine + acid equation using HCL and methylamine
CH3NH2 (aq) +HCl (aq) = CH3NH3+Cl-
aq) (methylammonium chloride
how to convert ammonium salt back to amine
add NaOH
what is true about ammonium salts and solubility
good solubility in water because of ionic character
how to make primary amine in one step reaction and name mechanism, conditions, reactants and products
add ammonia to halogenoalkane
nucleophilic substitution reaction
ethanol dissolved
bromoethane into primary amine equation and name
CH3CH2Br + 2NH3 = CH3CH2NH2 + NH4Br
bromoethane + ammonia = ethylamine
what is the problem with nucleophilic substitution in forming primary amines
the product has a lone pair and thus further reactions can occur to form secondary and tertiary amines or quaternary ammonium salts
how to make yield of primary amine higher in nuc sub reaction
Using an excess of ammonia can limit the further
subsequent reactions and will maximise the amount
of primary amine
how to promote the formation of quaternary ammonium salt from nuc sub reaction
use excess halogenoalkane
use of quaternary salt and why
cationic surfactants
reduce 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
other better way to make amines
reduction of nitriles
step 1 of making amines from nitriles reagents and conditions
convert halogenoalkane into nitrile using KCN in ethanol and heat under reflux
step 1 making amines from nitriles equation using bromoethane and KCN
CH3CH2Br + CN- = CH3CH2CN + Br -
step 2 of making amines from nitriles reagents and conditions
reduce nitrile to amine
use LiAlH4 in ether OR H2 and Ni catalyst
step 2 making amines equation using bromoethane
CH3CH2CN + 4[H] = CH3CH2CH2NH2
disadvantages of making amines by reducing nitriles
2 step so may be lower yield and takes longer
KCN is toxic
reagents, conditions, mechanism to form aromatic amine from nitroarine
Sn and HCl OR Fe and HCl
Heating
Reduction
what must be done after reducing nitroarine to make the aromatic amine
add NaOH to the ammonium salt formed due to the HCl to form aromatic amine
how else can you recude nitroarine reagents and conditions
catalytic hydrogenation (H2 using Ni catalyst)
what can primary amines react with to form secondary amides and what kind of mechanism
acyl chlorides or acid anhydrides
nucleophilic addition elimination mechanism
