Topic B6: Amines
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What reactants are required for preparing a primary amine?
-haloalkane -excess ammonia -ethanol (excess sodium hydroxide/ excess ammonia - base generates amine from ammonium salt)
Preparing primary amine: Why does ammonia need to be in excess?
reduces further substitutions of amine group to form secondary and tertiary amines
Preparing primary amine: Why is ethanol used as a solvent?
prevents the formation of alcohol from haloalkane and water
Aromatic amine are prepared from the reduction of…
nitrobenzene
What reactants are required for the preparation of an aromatic amine?
-tin catalyst -concentrated hydrochloric acid (low pH conditions) -sodium hydroxide (in excess)
What is the method for preparing an aromatic amine?
-place nitrobenzene in a flask -add tin (catalyst) -heat under reflux -add excess sodium hydroxide -heat and distil off the aromatic amine product
Preparing primary amine: What are the 2 stages of reaction?
Haloalkane + Ammonia —> Ammonium salt Ammonium salt + Alkali —> Primary amine + salt + water
How do amines act as bases?
lone pair of electrons on nitrogen can accept H+ (to form a dative covalent bond)
Preparing primary amine: Method
-heat haloalkane in a sealed tube -add excess ammonia dissolved in ethanol -add excess alkali (sodium hydroxide) -heat and distil off the primary amine
What is a tertiary quaternary ion?
Central Nitrogen atom is bonded to 4 groups Overall positive charge
Nitrogen with 4 ethyl groups attached is called….
tetraethylammonium ion
Why are quaternary ammonium ions not bases?
-they have no lone pair -as lone pair has already formed a dative bond with alkyl/ organic group
Is ammonia more or less basic than methylamine?
Less basic
Why is methylamine more basic than ammonia?
-alkyl chains in methyl amine donate electrons towards nitrogen -this makes the lone pair of electrons on nitrogen more available to accept H+ Hence, more basic (as base = H+ acceptor)
Why is diphenylamine less basic than ammonia?
-aromatic rings pull electrons away from the nitrogen into the delocalised system of electrons -this means electrons are less available for donation
Amine + Water —>
Tetra-alkylammonium ion + OH-
Amine + Acid —> (Propylamine + HCl)
salt (propylammonium chloride)