How haloalkanes react - OZ Flashcards
What are the 2 ways in which th C-X bond breaks in a haloalkane
in the stratosphere where high energy uv from the sun arrives, the bond breaks by homolytic fission giving radicals
but more usually haloalkanes do substitution involving heterolytic fission of the C-X bond
Is the C-Halogen bond in a haloalkane polar or not and why
it is polar because the halogen atoms are move electronegative than carbon atoms
Nucleophile definition
a species with a lone pair of electrons, which it donates to a partially positive carbon forming a new covalent bond
What charge is a nucleophile
negatively charged anion or partially negative atom with a lone pair
What is the mechanism of nucleophilic substitution using bromoethane and hydroxide
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What happens during the mechanism of nucleophilic substitution
the nucleophile forms a new bond to the partially positive carbon of the haloalkane. Carbons only have 4 bonds so one of the current bonds has to break, this will be the C-halogen bond and it breaks by heterolytic fission
What occurs during substitution reactions
one atom or group in a molecule gets replaces by another atom or group
Haloalkanes react by
nucleophilic substitution
Reaction of haloalkane with hydroxide ion - Reagents and conditions
Reagents - NaOH (aq) provides the OH- ions
Conditions - heat under reflux
Reflux definition
liquid reaction mixture is boiled in a flask connected to vertical condenser, this is used when the mixture needs heating for a while as prevents loss of reactants and products as vapour. The compounds continuously evaporate and then condense and drip back into the flask
Reflux diagram
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When a haloalkane reacts with the nucleophile OH- what organic molecule will be produced
alcohol
When 2-bromopropane is reacted with sodium hydroxide under reflux e what is the products given
propane-2-ol and sodium bromide
When 1,3-dichlorobutane is reacted with sodium hydroxide under reflux and what is the products given
butane-1,3-diol and sodium chloride
What reactions occur with haloalkanes
reaction with hydroxides, water and ammonia
How do haloalkanes react with water
water can act as a nucleophile as the oxygen has a lone pair it can donate and is partially negative. But is is a worse nucleophile than hydroxide ions as water does not have a full negative charge. So the reaction is very slow
What is produced when a haloalkane reacts with water
alcohol and hydrogen halide
Mechanism of haloalkane reaction with water
https://cdn.savemyexams.com/uploads/2023/07/nucleophilic-substitution-involving-water.webp
(with curly arrow in 2nd step going from the OH bond to the O)
Overall reaction of bromopropane with water
CH3CH2Br + H20 -> CH3CH2OH + HBr
How do haloalkanes react with ammonia and reagents and conditions
ammonia is another nucleophile without a full minus charge, so vigorous conditions are needed for this reaction
Reagents - conc ammonia solution
Conditions - heat in a sealed tube
Mechanism of haloalkane reaction with ammonia
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Overall reaction of bromopropane with ammonia
CH3CH2Br + NH3 -> CH3CH2NH2 + HBr
What is produced when a haloalkane reacts with ammonia
amine and hydrogen halide
Can a alcohol be used to make a haloalkane and why
yes, because the alcohols have polar bonds too, so they can react in a similar way to haloalkanes. But like the C-F bond the C-O bond is very strong and the reaction would be very slow/ To make the reaction work best it is carried out in acid (which provides H+). This protonates the oxygen
What happens during the process of making a haloalkane from an alcohol
the positive oxygen pulls the bonding electrons even more strongly weakening the C-O bond and making the carbon very δ+. The δ+ C is now more readily attacked by the nucleophile (halide ion) and the C-O bond breaks more readily.
Mechanism of making haloalkanes
Look at notes
How to make 1-bromobutane from butan-1-ol
nucleophile needed in Br- and acid conditions so HBr is used. The reaction is refluxed but the haloalkane is likely to be liquid so it would be washed in a separating funnel with various solutions to remove impurities then dried using a suitable drying agent (anhydrous sodium sulphate). For final purification is would be distilled
