Reactions of Halogenoalkanes
Halogenoalkanes can undergo nucleophilic substitution due to the electron deficient carbon atom.
Therefore, it can also under hydrolysis when reacted with an aqeous solution of hot OH- ions.
Mechanism:
The hydroxide ion has a lone pair which is attracted to the carbon and donates itself to it. This forms a new covalent bond between the OH- and the carbon and breaks the C-Halogen bond by heterolytic fission. Therefore a Halide ion is formed.
· Lone pair attracts and donates itself to C atom
· New covalent forms between OH and C
· C and halogen bond breaks by heterolytic fission
· Halide ion and alcohol formed
Rate of Hydrolysis:
The rate of hydrolysis depends on two things: bond enthalpy & polarity
The more polar a bond is, the more the carbon atom is able to attract the nucleophile and react quicker.
The higher the bond enthalpy, the harder the bond can be broken.
However, bond enthalpy is more important than bond polarity. Therefore, the rate of reaction decreases on going down the group as the bond enthalpies do.
Halogen-containing polymers
PTFT aka Teflon: A polymer of tetrafluoroethene.
Carbon-fluorine bonds are very strong because of the high bond enthalpy. Therefore, the PTFE is inert and resistant to chemical attack. Therefore this is why it is able to be non-stick and heat resistant.
PVC aka Poly(vinylchlorine): A polymer of chloroethene
PVC is used for drainpipes, plastic window frames. Sports equipments etc.
Chlorofluorocarbons, CFCS:
CFCs were used as blowing agents in expanded polystyrene foam, refrigerants and solvents for dry cleaning. However, they were found to have lead to the depletion of the Ozone layer due to the Chlorine radicals CFCs can break down into. Therefore, they have been replaced with alternatives.
e.g. HFCs- hydrofluoroalkanes or HCFCs- hydrofluorohydrocarbons. However, these too can deplete the ozone layer but at a tenth of that of CFCs.












