4.2.2 haloalkanes Flashcards
what conditions are needed for nucleophilic substitution of haloalkanes
aqueous solution and reflux
define hydrolysis
splitting of a molecule by a reaction with water
what conditions are needed for hydrolysis of haloalkanes
reflux, addition of AgNO3
why can flouroalkanes not undergo hydrolysis
the c-f bond is too strong
give three properties of CFC’s
low reactivity, high volatility and non-toxicity
give an alternative of CFC’s
HFC’s
what is the ozone layer made of
naturally reoccurring O3 in the upper stratosphere that filters out much of the sun’s harmful UV radiation
how is ozone formed
oxygen molecules decompose in UV light and then oxygen radicals react with oxygen molecules to form ozone
when is the amount of ozone constant
- formation=depletion
* uv light absorbed=damaging uv rays
what can increased UV on earth cause
skin cancer and crop mutation by preventing UV rays from penetrating Earth
how do CFC’s catalyse ozone depletion
uv radiation caused c-cl bonds to break CFC molecules in the upper atmosphere and cl radicals are produced that catalyse the breakdown of ozone
why are cfc’s still a concern
they have a long lifetime in the atmosphere and are released from disused items
what are NO’s
a pollutant formed from thunderstorms and combustion engines
how does NO break down ozone
acts as a catalyst to break down ozone
what is the general equation for a reaction of alcohols to form a haloalkane
ROH + HX –> RX + H2O
How can HBr and HI be made
-by adding H2SO4 to NaBr/NaI
eg NaBr + H2SO4 –> NaHSO4 + HBr
what is the reagent when alcohols are substituted to make haloalkanes
sodium halide in sulfuric acid
what is the general equation when alcohols are substituted to make haloalkanes
ROH + HX –> RX + H2O
what type of mechanism is used when alcohols are substituted to make haloalkanes
electrophilic addition
what is nucleophilic substitution in haloalkanes
when a nucleophile replaces a halogen atom for another atom or group of atoms
what are the reagents when making alcohols from a haloalkane
potassium/sodium hydroxide
what type of mechanism does making alcohols from a haloalkane use
nucleophilic substitution
describe hydrolysis of haloalkanes
- water is a poor nucleophile and reacts slowly with haloalkanes so reflux is required
- aqueous silver nitrate is added
- halide ion will react with silver ions to form a precipitate
what is the general equation for hydrolysis if haloalkanes
RX + H2O –> ROH + H-X
state the reactivity of the halogens in hydrolysis and why
fastest
I
Br
Cl
slowest
the lower the bond enthalpy the weaker the bond, Cl has the strongest bonds and I has the weakestwhat are 2 alternative to CFC’s and why are they less damaging
- HFC’s can be used as they do not contain the C-Cl bond for example in refrigerators
- CO2 is used as a blowing agent for producing expanded polymers
what were CFC’s used for and why
- used for aerosols, refrigerators and air-conditioning
- because they have low-reactivity, high volatility and non-toxicity
