Haloalkanes
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Write the word equation for the preparation of Chloroethane from an alkane
Ethane + Chlorine→chloroethane
What are the conditions under which chloroethane is made from an alkane?
• Room temperature and pressure • in the presence of UV radiation
What is the equation for the formation of chloroethane from an alkane?
CH3CH3 + Cl2→CH3CH2Cl + HCl
What is the mechanism for the formation of chloroethane from an alkane?
Free radical substitution
What are the reagents needed to make chloroethane from an alkene?
Ethene and HCl
What are the conditions needed to make chloroethane from an alkene?
Room temperature and pressure
What is the mechanism by which chloroethane can be made from an alkene?
Electrophilic addition
What is the chemical equation for the reaction of ethene and HCl to produce chloroethane?
H2C=CH2 + HCl →CH3CH2Cl
What is the atom economy for the reaction needed to make chloroethane from an alkene?
100%
Why are haloalkanes generally more reactive than alkanes?
• The strength of Carbon-Halogen bonds is lower than Carbon-hydrogen bonds • So the Carbon-halogen bonds break more easily and allow the haloalkanes to react
What is the exception to haloalkanes being more reactive than alkanes? Why?
Fluroalkanes • Carbon-fluorine bonds have a higher bond enthalpy than Carbon-Hydrogen bonds • so require more energy to break
Are Carbon-Halogen bonds polar?
Yes
Why are Carbon-Halogen bonds polar?
Halogens have a higher electronegativity than Carbon
Define hydrolysis
A chemical reaction involving water or an aqueous solution of a hydroxide that causes the breaking of a bond in a molecule
What are the reagents needed to prepare an alcohol from a haloalkane by hydrolysis?
Haloalkane and NaOH(aq) or water
What are the conditions to prepare an alcohol from a haloalkane by hydrolysis?
Heat under reflux
What is the mechanism to prepare an alcohol from a haloalkane by hydrolysis?
Nucleophilic substitution
Give an equation for the reaction of bromoethane and water to produce an alcohol
CH3CH2Br + H2O —> CH3CH2OH + HBr
Define nucleophile
A species capable of donating a pair of electrons
Give 3 examples of nucleophiles
NH3(aq), H2O, OH-(aq)
What do most nucleophiles have in common?
They have lone pairs
How do you test for the rate of hydrolysis of haloalkanes?
Place the test tube with haloalkane in a hot water bath, add ethanol and then AgNO3 (aq)
Why is the experiment to test the rate of hydrolysis of haloalkanes conducted in a hot water bath?
To speed up the rate of reaction
Why does the experiment to test the rate of hydrolysis of haloalkanes use ethanol?
Ethanol acts as a cosolvent as both water and the haloalkane dissolve in ethanol so the reactants can mix