Questions on Synthetic routes
1. Starting with 2-methylpropane deduce a synthetic pathway to make 2-methylpropanoic acid.
CH3CH(CH3)CH3 → CH3CH(CH3)COOH
For each step specify the reagents and any necessary conditions and write an equation for each step.
2. Design a synthetic route to make butanone starting with but-1-ene.
CH3CH2CHCH2 → CH3CH2COCH3
Knowing that the first step involves the addition of hydrogen bromide to but-1-ene state the name of
the mechanism for the first two steps.
3. You are provided with ethanal and any inorganic reagents and laboratory equipment you require but
no other organic compounds. Design a method to synthesise ethylethanoate from ethanal.
CH3CHO → CH3COOC2H5
For each step specify the reagents and any necessary conditions.
4. Show how phenylamine can be synthesised from benzene.
5. Propyl ethanoate is used as a solvent and has the characteristic smell of pears.
Design a synthetic route to make propyl ethanoate starting from 1-chloropropan and chloroethane as
the only organic compounds available.
Answers
1. Step 1: React with chlorine in ultra violet light and separate 1-chloro-2-methylpropane from any other
chlorinated products.
CH3CH(CH3)CH3 + Cl2 → CH3CH(CH3)CH2Cl
Step 2: React 1-chloro-2-methylpropane with warm dilute aqueous sodium hydroxide solution to give 2methylpropan-1-ol.
CH3CH(CH3)CH2Cl + NaOH → CH3CH(CH3)CH2OH + NaCl
Step 3: Oxidize 2-methylpropan-1-ol by refluxing with acidified potassium dichromate(VI) solution to
give the required product
(via 2-methylpropanal).
CH3CH(CH3)CH2OH + H2O + 4e− → CH3CH(CH3)COOH + 4H+
2. Step 1: React but-1-ene with hydrogen bromide to form 2-bromobutane (formed in preference to 1bromobutane according to Markovnikov’s rule). Mechanism: Electrophilic addition.
Step 2: React 2-bromobutane with warm dilute aqueous sodium hydroxide solution to give butan-2-ol.
Mechanism: a mixture of SN1 and SN2.
Step 3: Oxidize butan-2-ol by refluxing with acidified potassium dichromate(VI) solution to give
butanone.
3. Step 1: Oxidize some of the ethanal by refluxing with acidified potassium dichromate(VI) solution to
give ethanoic acid.
Step 2: Reduce the rest of the ethanal with sodium borohydride (or lithium aluminium hydride) to give
ethanol.
Step 3: Warm the ethanol and the ethanoic acid formed in Steps 1 and 2 in the presence of
concentrated sulfuric acid to produce the desired ester.
4. Step 1: Covert benzene into nitrobenzene by warming (keep below 50 oC) with a mixture of
concentrated nitric acid and concentrated sulfuric acid.
Step 2: Reduce nitrobenzene to phenylamine by using tin and concentrated hydrochloric acid then react
the phenylammonium chloride intermediate with sodium hydroxide solution.
5. Step 1: React 1-chloropropane with warm dilute aqueous sodium hydroxide solution to give propan-1ol.
Step 2: React chloroethane with warm dilute aqueous sodium hydroxide solution to give ethanol.
Step 3: Oxidize the ethanol obtained in Step 2 by refluxing with acidified potassium dichromate(VI)
solution to ethanoic acid.
Step 4: React the ethanoic acid with the propan-1-ol obtained from Step 1 by warming in the presence
of concentrated sulfuric acid to give the ester.