1. Nucleophilic Elimination
Halogenoalkanes

2. Starter
Draw the mechanism for the nucleophilic substitution the occurs in the following reaction:
Chloroethane + Sodium hydroxide  Ethanol + Sodium Chloride

3. Testing For HalogenoAlkanes
Steps:
Add sodium hydroxide (NaOH) to perform a nucleophilic substitution reaction.
Add dilute nitric acid (HNO3) to neutralise the mixture
Add silver nitrate (AgNO3) to create a precipitate
A further test can be done with ammonia (NH3) to be completely sure.
Halogen in halogenoalkane
Addition of Ag+(aq)
Addition of NH3 (aq) to precipitate formed
Chlorine
White precipitate
Dissolves in dilute NH3
Bromine
Cream precipitate
Dissolves in conc NH3
Iodine
Yellow precipitate
Does not dissolve in NH3

4. Nucleophilic elimination
Nucleophilic elimination definition: An electron rich species (nucleophile) attacks an electron deficient atom, causing the loss of a small molecule and the production of a double bond.
CH3 H C Br
CH3 H C Br - OH -
H2O

5. Reflux The reaction mixture in the round bottomed flask is heated.
As reactants and products evaporate the cold water passing through the outer layer of the condenser causes the gasses to condense.
This ensures no product is lost.

6. - - Elimination of HBr from 2-bromopropane CH3CHBrCH3 + OH-
CH3CH=CH2 + H2O + Br-
(in ethanol)
CH3 H C Br
CH3 H C
propene Br - OH -
H OH
acting as a base

7. Conditions Substitution Elimination
Sodium hydroxide dissolved in water (aqueous).
OH- acts as nucleophile.
Reflux
Product is an alcohol and halide.
Sodium hydroxide dissolved in ethanol and heated under reflux.
OH- acts as base.
Product is an alkene and hydrogen halide is lost.

8. Knowledge Check
1. Draw the mechanism and name the products formed for the following reactions:
Chloroethane + Sodium hydroxide (in ethanol)
1-bromopropane + Sodium hydroxide (in ethanol)
2. Predict the type of reaction mechanism the following reactions will undergo:
Chloroethane + Sodium hydroxide (in water)
2-Bromopropane + Aqueous Sodium hydroxide
Iodoethane + Sodium hydroxide (in ethanol)

9. Knowledge Check
When 2-bromobutane reacts with hydroxide ions there are two possible outcomes.
Draw the mechanism for the reaction that would form an alkene.
Draw the mechanism for the reaction that would form an alcohol.
Give the additional conditions needed for each mechanism.