Chemistry 11 (HL)
Unit 7 / IB Topics 10.6 and 20.5
Organic Chemistry 10: Reaction Pathways
Chemists in a variety of industries need to design reactions to
make certain organic compounds. Many organic compounds are
derived from crude oil products – alkanes or alkenes.
The individual reactions you have looked can be linked together to
make a particular product from a particular reactant, via a reaction
pathway.
USE THE ORGANIC CHEMISTRY ROAD MAP to help you
determine reaction pathways.
EXAMPLE 1:
You are asked to convert 1-chlorobutane into butanoic acid.
Describe the steps you would use, giving reagents, conditions and equations for each stage.
1-chlorobutane  butanoic acid
halogenoalkane  carboxylic acid
Step 1: 1-chlorobutane  butan-1-ol
reagent: dilute aqueous NaOH
conditions: room temperature
reaction type / mechanism: SN2
–
equation: CH3CH2CH2CH2Cl + OH  CH3CH2CH2CH2OH + Cl
–
You should be able to draw the two steps for the SN2 mechanism.
st
1 step:
nd
2 step:
–
CH3CH2CH2CH2Cl + OH  transition state
–
transition state  CH3CH2CH2CH2OH + Cl
Step 2: butan-1-ol  butanoic acid (this can occur in one step under reflux conditions)
+
2–
reagent: acidified potassium dichromate (H /Cr2O7 )
condtions: heat under REFLUX
reaction type: oxidation
equation (simplified):
CH3CH2CH2CH2OH + [O]  CH3CH2CH2COOH
Chemistry 11 (HL)
Unit 7 / IB Topics 10.6 and 20.5
EXAMPLE 2:
You want to synthesize pineapple flavouring. You decided to prepare ethyl butanoate, starting with an
alkene and a primary alcohol. Describe the steps involved, giving reagents, conditions and equations
for each. State any mechanisms involved
FIRST: Deduce the type of compound you want, and which reactants are required to produce it.
ethyl butanoate = ESTER = alcohol + carboxylic acid
SECOND: Identify the starting materials needed to synthesize ethanol and butanoic acid, and
then the ester.
Here is ONE option:
Chemistry 11 (HL)
Unit 7 / IB Topics 10.6 and 20.5
THIRD: Put it all together:
Step 1: Synthesize ethanol using ethene:
reagent: water (or steam)
condtions: high temperature (>100ºC)
reaction type: addition (hydration)
equation:
CH2CH2 + H2O  CH3CH2OH
Step 2: Synthesize butanoic acid using 1-chlorobutane (or 1-bromobutane):
Step 2a: 1-chlorobutane  butan-1-ol
reagent: dilute aqueous NaOH
condtions: room temperature
reaction type: nucleophilic substitution (SN2)
equation:
–
CH3CH2CH2CH2Cl + OH  CH3CH2CH2CH2OH + Cl
–
Step 2b: butan-1-ol  butanoic acid
+
2–
reagent: acidified potassium dichromate (H / Cr2O7 )
condtions: heat under REFLUX
reaction type: oxidation
equation (simplified):
CH3CH2CH2CH2OH + [O]  CH3CH2CH2COOH
Step 3: Synthesize the ester ethyl butanoate using ethanol and butanoic acid
reagents: ethanol and butanoic acid
condtions: heat and sulfuric acid catalyst
reaction type: condensation
equation:
CH3CH2CH2CH2OH + CH3CH2OH  CH3CH2CH2COOCH2CH3 + H2O