Reactions

Reactions

1. Alkanes

   • Combustion
     • Exothermic
     • Non-Toxic Products
     • Example...
       • C3H8 + 5O2 ===> 3CO2 + 4H2O
   • Halogenation
     • Under UV Radiation
     • Free Radical Mechanism
       • Propagation
       • Initiation
       • Termination
     • Mixture of Products
     • Example...
       • CH4 +CL2 =UV=> CH3CL + HCL CH3CL+CL2 =UV=> CH2CL2 +HCL etc...

2. Alkenes

   • Combustion
     • Exothermic
     • Smoky Flame
     • Example...
       • 2C3H6 + 9O2 ===> 6CO2+6H2O
   • Electrophilic Addition
     • Bromination
       • With Bromine
         • Example...
           • H2C=CH2 + Br2  ===>              Br-H2C-CH2-Br (dibromoalkane)
       • With Bromine Water
         • Example...
           • H2C=CH2 + Br2 + H2O ===>      Br-H2C-CH2-OH + HBr (bromoalcohol)
         • Test for alkene
           • Decolourises
       • Can be in dark
     • Hydrobromination
       • Example...
         • H3C-CH=CH2 + HBR ===>
         • Major Product
           • H3C-CH(Br)-CH3
         • Minor Product
           • H3C-CH2-CH2-Br
   • Catalytic Addition
     • Hydrogenation
       • Example...
         • H2C=CH2 + H2 =Pt, High Temp, High Pressure=>H3C-CH3 
     • Hydration
       • Ethanol Manufacture
       • Example...
         • H2C=CH2(g) + H2O(g) =H3PO4, High Pressure, 300C=>           H3C-CH2-OH
   • Oxidative Addition
     • Test for alkenes
     • Example...
       • H2C=CH2 + [O] + H2O             [O]=KMnO4, Acid/Alkali=> HO-H2C-CH2-OH (diol) If acid, purple is decolourised.      If alkali, purple goes green 
   • Addition Polymerisation
     • Free Radical Mechanism
     • Example...
       • n H2C=CH2 =catalyst, pressure=> -(-H2C-CH2-)-n poly(ethene)

3. Halogenoalkanes

   • With Ammonia
     • Example...
       • R-X + NH3 =xs NH3, pressure, closed vessel=> R-NH2 + HX (primary amine) An additional mole of ammonia is required to react with HX formed. PTO for competing reaction...
       • R-X + R-NH2 ===> R2NH + HX (secondary amine)
   • With Aqueous KOH
     • Test For R-X
       • Neutralise with HNO3 Add AgNO3
       • White Precipitate:- R-Cl
       • Cream Precipitate:- R-Br
       • Yellow Precipitate:- R-I
     • Example...
       • R-X + OH^- =aqueous KOH=>   R-OH + X^-
     • Rate
       • R-I > R-Br > R-Cl
       • Tert. > Secd. > Pri.
   • With Ethanolic KOH
     • Elimination of HX
     • Example...
       • H3C-CH2X + OH^- =ethanolic KOH=> H2C=CH2 + H2O + X^-

4. Alcohols

   • With Sodium
     • Example...
       • 2C3H7OH +2Na ===>   2C3H7O^-Na^+ H2 (sodium propoxide)
   • Dehydration
     • Example...
       • C3H7OH =conc. H2SO4=>     H3C-HC=CH2 + H2O (alkene)
   • Halogenation
     • With Phosphorous trihalides
       • Examples...
         • For chloroalkane... 3C3H7OH + PCl3 ==>         3C3H7Cl +H3PO3
         • For bromoalkane... 3C3H7OH + P + 1.5Br2 =heat under reflux=> 3C3H7Br +H3PO3
         • For iodoalkane... 3C3H7OH + P + 1.5I2 =heat under reflux=> 3C3H7I +H3PO3
     • With PCl5
       • Test For OH Group
       • Example...
         • C3H7OH + PCl5 ==>         C3H7Cl + POCl3 + HCl (steamy fumes, turn damp litmus paper red) 
     • With Thionyl Chloride
       • Makes For Easily Purifiable Halogenoalkanes
       • Example...
         • C3H7OH + SOCl2 ==>     C3H7Cl + SO2(g) + HCl(g)
     • With Hydrogen Halides
       • Examples...
         • For chloroalkane...(CH3)3C-OH + HCl =conc. HCl=> C3H7Cl + H2O (only with tertiary alcohols)
         • For bromoalkane...C3H7OH + HBr =NaBr, conc. H2SO4, distill product=> C3H7Br +H2O
         • For iodoalkane... C3H7OH +HI =KI, conc. H3PO4, distill product=> C3H7I + H2O
   • Oxidation
     • Primary
       • R-CH2-OH + [O] =distilling=> R-C(=O)(-H) (aldehyde) [O] = K2Cr2O7 PTO if not distilled...
       • R-CH2-OH + 2[O] =boil under reflux=> R-C(=O)(-OH) (carboxylic acid)
     • Secondary
       • R2CH-OH + [O] ==> R-C(=O)(-R) (ketone)
     • Tertiary
       • R3C-OH + [O] ==> no reaction