Topic 18 Flashcards
Bromination of benzene
Reactants: benzene, bromine
Reagents: FeBr3 or AlCl3 catalyst
Conditions:
Products: bromobenzene, HBr
Observations: orange to colourless
HBr + ammonia = white solid
Reaction: Electrophilic substitutionNitration of benzene
Reactants: benzene, nitric acid Reagents: concentrated sulfuric acid Conditions: 50°C Products: nitrobenzene, water Observations: nitrobenzene is yellow and oily Reaction: Electrophilic substitution
Friedel-Crafts alkylation of benzene
Reactants: benzene, halogenoalkane Reagents: AlCl3 catalyst Conditions: anhydrous, heat under reflux Products: eg. methyl benzene, HCl Observations: HCl = misty fumes Reaction: Electrophilic substitution
Friedel-Crafts acylation of benzene
Reactants: benzene, acyl chloride Reagents: AlCl3 catalyst Conditions: anhydrous, heat under reflux Products: phenyl ketone, HCl Observations: HCl = misty fumes Reaction: Electrophilic substitution
Phenol + sodium hydroxide
Sodium phenoxide and water
Acting as an acid
Bromination of phenol
Reactants: phenol, bromine Reagents: no catalyst needed Conditions: room temp Products: 2,4,6 tribromophenol, HBr Observations: orange to colourless, white ppt, misty fumes Reaction: Electrophilic substitution
Making amines from halogenoalkanes
Reactants: halogenoalkane, ammonia Reagents: Conditions: heat in a sealed tube Products: 1° amine, HCl Observations: HCl = misty fumes Reaction: Nucleophilic substitution
Note: 1° amine reacts with halogenoalkane forming 2° amine and HCl etc.
Making amines from nitriles
Reactants: eg. ethanenitrile Reagents: LiAlH4 Conditions: mix in dry ether Products: 1° amine Observations: Reaction: reduction of nitrile
Making aromatic amines
Reactants: nitrobenzene Reagents: tin metal mixed with conc. hydrochloric acid (reducing agent, 6Hs) Conditions: heat under reflux Products: phenylamine and 2 water Observations: Reaction: reduction of nitrobenzene
Making amides
Reactants: acyl chloride or carboxylic acid, amine
Reagents:
Conditions:
Products: N-substituted amide, HCl or water
Observations: amine also reacts with HCl formed = white smoke
Reaction: condensation
Order of basicity of amines
Least basic
Aromatic amines- The lone pair on the N atom in phenylamine merges with the delocalised electrons in the pi bond, making them less available for donating.
Ammonia
1°/2°/3° amines- The ethyl group is electron releasing, so the N atom has a higher electron density, so the lone pair is more available.
Reaction of 1° amine with water
RNH₂ + H₂O ⇌ RNH₃⁺+ OH‾
Reaction of 1° amine with acid
RNH₂ + HCl ⇌ RNH₃⁺Cl‾ (white smoke)
Reaction of 1° amine with acid
RNH₂ + HCl (g) ⇌ RNH₃⁺Cl‾ (white smoke)
Reaction of 1° amine with copper (II) ions
2RNH₂ + [Cu(H₂O)₆]²⁺ ⇌ [Cu(H₂O)₄(OH)₂] + 2 RNH₃⁺
Pale blue precipitate
4RNH₂ + [Cu(H₂O)₄(OH)₂] ⇌ [Cu(RNH₂)₄(H₂O)₂]²⁺ + 2H₂O + 2OH‾
Deep blue solution
Reaction of 1° amine with acyl chloride
Acyl chloride + primary amine → N-substituted amide + HCl
then HCl + RNH₂ (primary amine) → RNH₃⁺Cl‾ (salt)
Reaction of 1° amine with halogenoalkane
1° amine + halogenoalkane → 2° amine + HCl
2° amine + halogenoalkane → 3° amine + HCl
3° amine + halogenoalkane → 4° amine⁺ Cl‾
Why are amino acids soluble?
They form zwitter ions, which interact with the water
Why do solid amino acids have a high melting point?
They form zwitter ions with strong ionic bonds
Why is phenol more reactive than benzene with bromine?
The lone pair of electrons on the oxygen merges with the delocalised system
Increases the electron density of the ring
Increases the susceptibility to attack by the electrophile
Why heat under reflux
Speed up rate of reaction
Prevent loss of volatile reactants and products
What do alcohols, phenols and carboxylic acids react with as acids?
Alcohol- metal
Phenol- metal and hydroxides
Carboxylic acid- metal, hydroxides and carbonates
Describe the structure of benzene and compare it to the kekule structure.
P orbitals overlap sideways forming a pi bond above and below the plane of C atoms.
The pi bond electrons are delocalised around the ring.
Bonding more stable.
What is the trend in boiling points of primary to tertiary amines?
1- highest
2- lower, N atom in middle of chain, dipole attractions less
3- no H atoms bonded to N atoms, no H bonds!
Define zwitterion
A molecule containing positive and negative charges but has no overall charge
What is the isoelectronic point?
The pH of a an aqueous solution at which it is electrically neutral.
Hydrolysis of dipeptides
Reactants: Dipeptide and water
Conditions: Heat with conc. HCl
Products: 2 amino acids
Observations: forms protonated version of amino acids
