Preperation of Amines
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What is an aliphatic amine?
An amine with no aromatic ring
2 ways of producing an aliphatic amine
Halogenoalkanes and ammonia reacting Reduction of nitriles
How to produce an aromatic amine
Prepared by reducing nitro compounds
Reaction of ammonia with halogenoalkane ->
Ammonia 2NH3 + Halogenoalkane RCH2Cl -> Primary amine RCH2NH2 + Ammonium halide salt [NH4]+Cl-
Condition of ammonia when reacting witha halogenalkane
Excess ammonia or else the amide will act as a nucleophile and reactions will occur to form secondary and tertiary amides.
Mechanism of ammonia with halogenoalkane
Nucleophilic substitution
Reaction when nitriles are reduced
Nitrile RCN -> RCH2NH2 Amine
2 methods when reducing nitriles
Laboratory method Industrial method
Reagents and conditions of the laboratory method
Reagent: LiAlH4 Condition: Dry ether (anhydrous solvent)
Reagents and conditions of the industrial method
Reagents: H2 gas + Nickel catalyst Conditions: High pressure and temperature
Equation of reduction of nitriles
RCN + 4[H] -> RCH2NH2
Advantages of reduction of nitriles over ammonia + halogenoalkanes
Produces only one product so yield is only primary amine Extend carbon chain by one
Reagents and conditions when reducing nitro compounds
Reagents: Tin + Conc HCl Conditions: Heat under reflux
Reaction of reducing nitro compounds
RNO2 + 6[H] -> RNH2 + 2H2O
Final step of reducing amines
NaOH added to neutralise exces HCl to obtain the free amine
Uses of aromatic amines
Dye synthesis Making pharmaceuticals
Suggest why ethanol (aq) is a suitable solvent when heating oil with KOH. Give a safety precaution used when heating the mixture. Justify why? [3]
[1] Reason: Allow to dissolve both oil and KOH [2] Safety precaution: Precaution must be linked to heating e.g. Use a water bath for heating mixture [3] Justification: Prevents risk of fire / Ethanol is flammable
1,6-Diaminohexane can also be formed in a two-stage synthesis starting from 1,4-dibromobutane. Suggest the reagent and a condition for each stage in this alternative synthesis. [3]
[1] Stage 1 reagent KCN [2] Stage 1 condition aqueous alcohol [3] Stage 2 reagent & condition H2 and Ni
Justify the statement that it is better to prepare primary amines from nitriles rather than from halogenoalkanes. [2]
[1] further reaction (of primary amines) OR Impure product/mixture of products/lower atom economy [2] No further reaction OR Single product / higher atom economy
A student dissolves a few drops of propylamine in 1 cm3 of water in a test tube. Give an equation for the reaction that occurs. [1]
[1] CH3CH2CH2NH2 + H2O ⇌ CH3CH2CH2NH3+ + OH–
Amine F can be prepared in a three-step synthesis starting from methylbenzene. Suggest the structures of the two intermediate compounds. For each step, give reagents and conditions only. Equations and mechanisms are not required. [5]
[1] Product of step 1 C6H5CH1Cl [2] Product of step 2 C6H5CH2CN [3] Step 1 Cl2 & UV [4] Step 2 KCN alcoholic & aq [5] Step 3 H2 / Ni