3.11- Amines Flashcards
What sort of bases are primary amines
They are bronsted lowry bases because the lone pair of electrons on the nitrogen is readily available for forming a dative covalent bond with a H+ , they are only weak bases as only a low concentration of hydroxide ions are present
Why is the base strength of amines go Secondary amines> Tertiary amines > Primary amines > ammonia > aromatic amines
Secondary amines are the strongest because they have more alkyl groyps that are subsituted onto the N atom in place of the H atoms, there is more electron density pushed on to the N atom, this is because the inductive effect of alkyl groups is greater than that of H atoms,
Tertiary amines are not as strong as secondary becuase they are less soluble in water and this makes them weaker bases than secondary amines
Primary amines are still strong due to the alkyl group
Ammonia is stronger than aromatic because the phenylamine do not form basic solution becuase the long pair of electrons on the nitrogen delocalise with the ring of electrons in the benzene ring, this measn the N is less able to accept protons, hence ammnonia will be a stronger base
What are the reaction with acids for amines
They react with acids to form ammonium salts
How do you convert an ammonium salt back into an amine
If you add NaOH to an ammonium salt this will convert it back to an amine, these ionic salts will be solid crystals if the water is evaporated because of the strong ionic intercations
How do you make a basic buffer from an amine
Basic buffers can be made if you combine a weak base with a salt of that weak base
Explain the issues of trying to synthesis a amine using a halogenoalkane and ammonia
Primary amines can be formed via nucleophillic subsitution in a one step reaction, however as the lone pair of elecrons is still available on the N it can keep reacting with halogenoalkanes until it forms a quaternary ammounium salt, this means it isnt ideal for making a primary amine becuase of the further reaction it would mean that the desired product would have to be seperated from the other products
What will using excess of ammonia or halogenoalkane give you respectively
Excess ammonia will give you more amount of primary amine that is formed, and using an excess of halogenolakane will give you more of the quaternary ammounium salt
What can quaternary ammonium salts be used for
They can be used as cationic sufractants, these reduce the surface tension of liquids, the positive nitrogen is attracted to the negative charged surfaces such as glass, hair, fibres and plastics. This helps in their uses as fabric softeners, hair conditioners and sewage flocculants
How do you prepare amines from nitriles
Step 1-
Convert the halogenoalknanes into nitrile by using KCN in aqueous ethanol
Step 2-
Reduce the nitril to amine by using LiALH4 in ether or by reducing with H2 using an Ni catalyst
The disadvantage is that becuase it is a two step reaction it may have a low yield also KCN is a toxic compoundf
