3.3.11 Amines Flashcards
What are amines
derived from ammonia molecules which all contain a nitrogen atom where hydrogens are replaced with an organic group
How many different types of amines are there, what are they and how can they be separated into 2 categories?
5
Primary, secondary, tertiary, quaternary ion, aromatic amine (phenylamine)
2 categories:
Aromatic amines
Non-aromatic amines are ALIPHATIC AMINES
When there are 4 organic groups joined to a nitrogen a quaternary ion with a positive charge is formed, what can this be used for and how?
Quaternary ammonium salts are used to make cleaning products and conditioner e.g shampoo and washing up liquid
- they have long hydrocarbon tail called CATIONIC SURFACTANTS
- non-polar tail is attracted to oil/grease whilst the polar head is attracted to water,
- this allows water and oil to mix and remove grease from clothing, skin etc
- cationic surfactants with the positive ammonium ion is attracted to negatively charges fibres and hair, this removes static so used in fabric softener and hair conditioner
When there are 4 organic groups joined to a nitrogen a quaternary ion with a positive charge is formed, what can this be used for and how?
Quaternary ammonium salts are used to make cleaning products and conditioner e.g shampoo and washing up liquid
- they have long hydrocarbon tail called CATIONIC SURFACTANTS
- non-polar tail is attracted to oil/grease whilst the polar head is attracted to water,
- this allows water and oil to mix and remove grease from clothing, skin etc
- cationic surfactants with the positive ammonium ion is attracted to negatively charges fibres and hair, this removes static so used in fabric softener and hair conditioner
How do amines act as a base?
Amines have a lone pair of electrons that allow them to ACCEPT a proton and hence they act as a base
What does the strength of the base of amines depend on
- the availability of the lone pair of electrons on the nitrogen
-the higher the electron density (depends on type of group attached to nitrogen) the more readily available the electrons are
What does the strength of the base of amines depend on
- the availability of the lone pair of electrons on the nitrogen
-the higher the electron density (depends on type of group attached to nitrogen) the more readily available the electrons are
What are the orders of strength of amines as bases and why ?
aromatic amines : weakest
(benzene ring pulls e-‘s away from nitrogen into ring structure, decreasing e-density at nitrogen reduces lone pair availability)
ammonia : mid
primary aliphatic amines : strongest
(alkyl groups are electron pushing groups so they push e-‘s towards nitrogen. electron density at nitrogen increases so lone pair availability is increased)
what are the 2 ways you can form an aliphatic amine
- reacting a halogenoalkane with excess ammonia
- reducing a nitrile
Explain the process of reacting a halogenoalkane with excess ammonia
- nucleophilic substitution
- excess ammonia acts as base and nucleophile
- ammonia nucleophile attacks delta positive carbon
- halogen is released and intermediate of R-NH3+ is formed
- a second ammonia gives up a lone pair to a hydrogen (acts as base and accepts proton /H)
-N-H bond electrons go to the carbonated N atom and the H is released to the base ammonia
-this forms the aliphatic amine, ammonium (NH4+) and negative halogen
What is the down side to using halogenoalkane and excess ammonia to form primary amines?
because amines still have a lone pair of electrons, it can act as a nucleophile
so with any remaining halogenoalkane, the primary amine can continue reacting to produce secondary amine, tertiary amine and quaternary salts
so this reaction can easily produce an impure product
THE MECHANISM FOR MAKING EACH AMINE IS SIMILAR, INSTEAD OF 2 AMMONIA MOLECULES WE USE 2 AMINES
what are the 2 ways aliphatic aminescan be made by reducing nitriles, what are the reagents and conditions? compare the pros and cons of either
1: - via catalytic hydrogenation (adding hydrogen)
- use hydrogen gas and a nickel/platinum catalyst
- high temp and high pressure
– its a cheaper process
- only primary amines are formed so a pure product is made
2: - reduction with a strong reducing agent
- LiAlH4 (strong reducing agent) and dilute acid
- LiAlH4 is dissolved in non-aqueous solvent such as dry ether
- LiAlH4 is expensive so not used in industry
How do you make aromatic amines, reagents
- reducing of nitrocompounds e.g nitrobenzene
- reagents = CONCENTRATED HCL, TIN CATALYST, NaOH
- heat nitro compound under REFLUX with conc HCL and tin catalyst to form salt e.g C6H5NH3+Cl-
- salt formed in step one is reacted with alkali (NaOH) to make aromatic amine e.g phenylamine
Why do we need 6[H] to reduce nitrobenzene into phenylamine?
2 [H] is required to substitute onto the benzene ring to form NH2 and 4[H] is needed to form water with the o2 that has been released (2H20 forms)
