Organic nitrogen compounds: Amines, Amides, A.A, proteins

Organic nitrogen compounds: Amines, Amides, A.A, proteins

1. Preparation of Amines

   • Ammonia heated under pressure with halogenoalkane
     • 1-3 H substituted by an aryl or alkyl group
   • Reduction of aromatic nitro-compounds to form aryl amines *
     • Reduction of Nitrobenzene using tin and HCl under reflux: -NO2 → NH2
       • Cool, +NaOH → redissolve tin(IV) hydroxide
         • Steam distillation
           • Separate phenylamine and water
           • Salting out
             • Solvent extraction
               • Drying agent: Potassium hydroxide
                 • Final distillation

2. Properties

   • Aryl amines
     • Less volatile, usually liquid
     • Dissolve in organic solvents, only slightly in water
   • Alkyl amines
     • H-bond → higher m.p
     • Lower members are gases or volatile liquids
   • Strong Bases: lone pair on N
     • e- shift from alkyl group → primary alkyl amines better that ammonia
     • aryl amine: e- on N interact with delocalised pi e- → weaker base than NH3

3. Reactions

   • NS: With Halogenoalkanes → substituted ammine
   • A-E: With AC → N substituted amides
     • Condensation polymers: polyamides
   • Amines form complex ions in similar way to NH3
   • ES of phenylamine → 4-aminobenzenesulfonamide
     • Sulfonamides destroy bacteria

4. Amino Acids

   • Contain NH2 and COOH and R group
   • Acidic and basic properties
     • In alkaline soln: acid
     • In acidic son: base
     • In neutral soln: zwitterion formed
       • aa can exist as zwitterions in solid state → high mp, dissolve in water. Don't dissolve in organic solvent
   • 20
   • Peptide bond C-N in condensation reaction
   • Proteins made up of particular sequence of aa
     • Can determine structure of protein, e.g. Insulin by Frederick Sanger
     • Difficult for chemists to synthesise proteins
       • Longer chain = more difficult
   • Hydrolysis of proteins
     • Reflux with d.HCl
       • aa neutralised
         • aa separated by paper chromatography
           • Invisible, so spray with ninhydrin in fume cupboard and dry → purple spots
             • Rf value to identify aa
           • Sometimes electrophoresis is used
   • Optical activity
     • Most aa form optical isomers
     • aa in living organisms are L enentiomers
     • Laboratory synthesis of aa tends to produce racemic mixture of L and D enantiomers

5. Ecstasy (an amine) causes release of serotonin and dopamine in the brain

6. Paracetamol

   • Phenol is nitrated using H2SO4 and Sodium nitrate
     • 2-nitrophenol and 4-nitrophenol
     • Fractional distillation
       • 4-nitrophenol is reduced → 4-aminophenol
         • Using Sodium tetrahydridoborate(III) in alkaline soln
         • + ethanoic anhydride →paracetamol
       • 4-nitrophenol ↑bp
   • No chiral centres → simpler

7. Azodyes

   • Phenylamine + nitrous acid (made in situ) +HCl
     • <5 degrees
     • benzenediazonium chloride + water
       • Diazonium compound reactions
         • NS: N evolved
         • Is strong electrophile
           • Coupling → strong coloured compounds, no N produced
             • Diazo-compounds are extremely stable and unreactive
             • Extensive delocalised e- system → bright colours
               • Dye

8. Polymers

   • Nylon
     • Wallace Hume Carothers
     • Made from 2 monomers
       • Hexanedioic acid + 1,6-diaminohexane → nylon-6,6
       • Obtained via phenol or cyclohexane
     • Uses: tights, carpets, ropes
   • Kevlar
     • 1st used in 1970s as a replacement for steel in racing car tyres
     • Resists high temp, low thermal conductivity, high tensile strength, flame, chemical and cut resistant
     • Uses: cables, tyres, bullet proof vests, ropes, adhesives
   • Addition polymerisation
     • 2-propanamide → Poly(propanamide)
       • Crossed linked → gel which absorbs water → soft contact lenses
       • Non-cross-linked → thickener and filler in facial surgery
     • Ester exchange: Poly(ethylethanoate) + methanol → poly(ethanol) + methylethanoate
       • Solubility varies
       • uses: disposable laundry bags (bags dissolve in wash cycle), viscoelastic gel
     • Properties of polyamides
       • Links vulnerable to attack under acidic or alkaline conditions
       • Addition polymers of just C and H are difficult to break down → pollution