Reactions With Alkenes
Organic Reactions
** ALKENES **
General Formula: CnH2n
Reactivity:
* Non-polar molecules with Van Der Waals intermolecular forces, so not soluble in water
* Volatile (4 first alkenes are all gaseous at room temperature)
* Unsaturated (C=C), so more reactive than alkanes:
- second bond weaker, so easily broken
- C=C rich in electrons (4e) attracts electrophiles groups
Main Reactions
Addition Reactions + Polymerization
ADDITION (Halogenation)
Alkene + Halogen (F2, Cl2, Br2, I2) → Dihaloalkane
Halogenation:
Addition of a halogen yields to dihaloalkanes
Example:
C2H4 + Cl2 → C2H4Cl2
Uses:
*Makes starting material for PVC and indication of alkenes
* Bromine dissolves in dichloromethane is used to distinguish between alkanes and alkenes. If reddish-brown color of Br2 disappears when added to unknown, the unknown has alkenes in it.
Addition (Hydrogenation)
Alkene + Hydrogen → Platinum or Palladium Catalyst
(also called Reduction)
Hydrogenation:
Addition of Hydrogen with Pt or Pd catalyst yields to Alkanes
Example:
C2H4 + H2 → C2H6
(PtO2/Pd)
Uses:
Hydrogenation of oil for margarine
Addition (Hydrogen Hallides)
Alkene + Acid Hallide (HF, HCl, HBr, HI) → Haloalkane
Addition of Hydrogen Hallides yield to Haloalkane
Example:
C2H4 + HCl → C2H5Cl
Uses:
Haloalkanes are useful starting materials for organic syntheses.
Addition (Hydration)
Alkene + Water → Alcohol
Hydration:
Addition of water in acidic condition yields to alcohols.
Example:
C3H6 + H2O → C3H8O
(acid)
Uses:
Commercial manufacture of ethanol.
Polymerization
a. Two kinds of polyethylene
HDPE = gallon milk cartons (more rigid)
LDPE = plastic bags, squeeze bottles (more flexible)
b. Reaction
nCH2=CH2 → [-CH2-CH2-]n
c. Monomer
Ethylene
CH2=CH2
d. Conditions
Temp: 200 C
Pressure: 2000 atm
Initiator: O2