3.3.11 Amines Flashcards
Name the mechanism to prepare amines from halogenoalkanes.
Nucleophilic Substitution
What are the reagents and conditions to form amines via halogenoalkanes?
-Excess ammonia (NH₃)
-Ethanolic solution
-Warm under reflux
Draw out the mechansim to form a primary amine from a halogenoalkane
-2 steps/1 intermediate
-4 curly arrows overall
-NH4Br formed
How can you maximise the yield of primary amine formed?
Use excess ammonia to reduce further substitution.
How can you promote the formation of the quaternary salts?
Using an excess of halogenoalkane
How can amines be prepared from nitriles (2 ways)?
Reduction
-LiAlH₄ in dry ether
OR
-H₂ with a Ni catalyst
What is the disadvantage of reducing nitriles to form amines?
Two step reaction - have to form nitrile then amine
KCN is toxic (used in nucleophilic sub. of halogenoalkane)
What is the reaction for the preperation of aromatic amines from nitroarenes?
Reduction
Name the reagents and condition for to form aromatic amines from nitroamines.
Sn and Hcl
Heat
Write the equation for the formation of an aromatic amine from a nitroamine.
nitrobezene + 6[H] —>
phenylamine + H₂O
Why are amines considered bases?
They have a lone pair of electrons on nitrogen, which can accept a proton (H⁺), forming a dative covalent bond.
Compare the base strength of different types of amines & ammonia
Aromatic amines
<NH₃
<1° amines
<3° amines
<2° amines
Why are primary aliphatic amines stronger bases than NH₃?
The alkyl groups on amines are electron releaseing and push electrons towards the N atom
Making the lone pair on the N more readily available to accept protons
Why are secondary amines stronger bases than primary amines?
More alkyl groups in secondary amines (that are substituted onto the N atom in place of H atom)
More electron density pushed onto the N atom
Inductive effect of alkyl groups is greater than that of H atoms
Why do primary aromatic amines not form basic solutions?
The lone pair on nitrogen delocalises with the reing of electrons in the benzene ring.
Therefore, the lone pair on the N is less able to accept protons.
What happens when amines react with acids?
They form ammonium salts (soluble in water).
Write an equation for the reaction between methylamine and hyrochloric acid & name the salt formed.
CH₃NH₂ + HCl → CH₃NH₃⁺Cl⁻
methylammonium chloride
How are basic buffers made?
Combining a weak base with the salt of that weak base.
What can be added to methylamine to produce a basic buffer?
Methylammonium chloride
What are quaternary ammonium salts?
Positively charged ions formed when a tertiary amine reacts with a halogenoalkane.
What are quaternary ammonium salts used for?
Cationic surfactants
Used in fabric softeners & conditioners
Reduce surface tension of liquids
Positive N is attracted towards negatively charged surfaces such as hair, glass and plastics.
