Halogenoalkanes Flashcards
What is hydrolysis of halogenoalkanes
When halogenoalkanes are reacted with hot aqueous sodium hydroxide ions to make alcohols by nucleophilic substitution reaction.
It is done under reflux.
What are halogenoalkanes?
Halogenoalkanes are compounds in which a halogen atom has replaced at least one of the hydrogen atoms in an alkene chain.
Describe the steps to nucleophilic substitution reaction of a halogenoalkane
A hydroxide ion (or any nucleophile) will have an electron pair.
This will be attracted to an electron deficient carbon atom. The carbon atom is electron deficient because of the halogen being more electronegative.
The donation of the electron pair to carbon forms a covalent bond between the oxygen and carbon atom.
This means that the carbon-halogen bond must break, and this happens through heterolytic fission. Which means that the halogen gets both the electrons making it a halogen ion.
What is a nucleophile?
An atom or group of atoms that are attracted to an electron deficient centre or atom where it donates a pair of electrons.
What is the reaction to measure rate of hydrolysis for halogenoalkanes?
Halogenoalkanes are reacted with aqueous silver nitrate and ethanol is also added.
The water is the nucleophile and ethanol is the common solvent.
Halide ions form because of nucleophilic substitution.
The halide ions react with Ag to make AgCl which would be a precipitate.
What is the colour of the silver halogens precipitate?
AgCl White
AgBr Cream
AgI Yellow
What’s the most important factor in the hydrolysis of halogenoalkanes?
Bond enthalpy because of the strength of the carbon-halogen bond
How are tetrafluoroethene made in to PTFE?
Through polymerisation
What is made when chloro ethene is polymerised?
PVC
what are the uses of PTFE and why
PTFE are used on non stick pans, nail polish and on metal surfaces
The strength of the carbon-halogen bond means that is is resistant to chemical attack
What are the uses of PVC
Children’s toys, drain pipes and plastic window panes and also sports equipment
What were CFCs used for and why?
Air conditioning, refrigerators, propellants and aerosols
Non flammable properties as well as it being non toxic and very unreactive
What harm do CFCs cause?
CFCs remain stable until they reach the stratosphere where they break down because of ultraviolet radiation and form chlorine radicals.
Chlorine radicals deplete the ozone layer which means that harmful UV radiation can reach the earths surface and cause skin cancer
What are the replacement of CFCS?
HCFCs or HFCs are now used because they are less harmful however they do still deplete the ozone just not as much
