Organic Synthesis (Cambridge (CIE) A Level Chemistry): Exam Questions

Ibuprofen and paracetamol are pain-relief drugs.

Fig. 1.1

Ibuprofen and paracetamol both contain the aryl (benzene) functional group.

State the other functional groups present in each molecule.

ibuprofen .........................................................................

paracetamol ...................................................................

Ibuprofen contains a chiral centre and has two enantiomers.

i) State one similarity and one difference in the physical or chemical properties between the two enantiomers.

similarity.......................................

difference.....................................

[1]

ii) Explain what is meant by racemic mixture.

[1]

Paracetamol reacts separately with the two reagents shown in the table.

Complete Table 1.1 by:

• drawing the structures of the organic products formed,

• stating the types of reaction.

Table 1.1

One of the steps in the manufacture of ibuprofen is shown in Fig. 1.2.

Fig. 1.2

i) Write an equation to show how AlCl₃ generates the electrophile for the conversion of X into Y.

[1]

ii) Draw the mechanism for the conversion of X into Y. Include all necessary curly arrows and charges.

[3]

iii) Write an equation to show how the AlCl₃ is regenerated.

[1]

Cuminyl alcohol can be synthesised from benzene by the following route shown in Fig. 2.1.

Fig. 2.1

Suggest reagents and conditions for steps 1–4.

step 1 ...................................................

step 2 ...................................................

step 3 ...................................................

step 4 ...................................................

Name the mechanism of step 2 and state the type of reaction in step 4.

Mechanism of step 2 ..........................................................................................................

Type of reaction in step 4 ....................................................................................................

Draw the reaction mechanism for step 2.

Deduce the number of peaks that would be present in the ¹³C NMR spectrum of cuminyl alcohol.

Outline how ethanal can be synthesised from ethane in three steps.

ethane $\stackrel{\mathrm{step}1}{\to }$ chloroethane $\stackrel{\mathrm{step}2}{\to }$ ethanol $\stackrel{\mathrm{step}3}{\to }$ ethanal

State the reaction conditions and reagents and name the type of reaction taking place.

i) Step 1

Reagents ..........................................................................................................

Conditions .........................................................................................................

Reaction type ....................................................................................................

[3]

ii) Step 2

Reagents ..........................................................................................................

Conditions .........................................................................................................

Reaction type ....................................................................................................

[3]

iii) Step 3

Reagents ..........................................................................................................

Conditions .........................................................................................................

Reaction type ....................................................................................................

[3]

The following reaction pathway in Fig. 3.1 is used to produce compounds A and B, which when reacted together, form a branched ester molecule, compound C.

Suggest suitable reagents and conditions for the synthesis of compound A via step 1 and give the name for this type of reaction.

Fig. 3.1

The ketone in part (a) must be converted to compound B to produce the ester.

i) Name the molecule that is produced from step 2

[1]

ii) Name the type of reaction that is involved in step 2 and suggest suitable reagents and conditions for this step.

[2]

Draw the skeletal formula of the ester formed from the reaction scheme.

Noradrenaline shown in Fig. 4.1 is a hormone and neurotransmitter, which is released during stress to stimulate the heart and increase blood pressure.

Fig. 4.1

State the names of three functional groups in the noradrenaline molecule.

Consider the following two-step synthesis of noradrenaline from dihydroxybenzaldehyde in Fig. 4.2.

Fig. 4.2

Draw the structure of the intermediate Z in the box.

Suggest reagents for steps 1 and 2.

step 1 ..................................................................................................................................

step 2 ..................................................................................................................................

Dihydroxybenzaldehyde reacts with Br₂(aq).

• Describe what you would see during this reaction

• Draw the structure of the product

Compound G is a naturally occurring aromatic compound that is present in raspberries.

Identify the functional groups present in compound G.

Complete Table 5.1 with information about the reactions of the three stated reagents with compound G.

Table 5.1

The dye H can be made from compound G by the route shown below in Fig. 5.1.

Fig. 5.1

i) Draw the structures of the amine J and the intermediate K in the boxes above.

[2]

ii) Suggest reagents and conditions for

step 1 ........................................................................................................................

step 2 ........................................................................................................................

[3]

Explain why dye H is very stable.

Benzocaine is an ester based compound that is used medicinally as a local anaesthetic in pain relievers and cough drops. One of the first industrial processes to manufacture benzocaine was the five-step reaction shown in Fig. 1.1.

Fig. 1.1

State the systematic name of benzocaine.

Step 1 involves the reaction of benzene with bromomethane.

i) State a suitable catalyst for step 1.

[1]

ii) Draw a mechanism for step 1. Include all necessary curly arrows, charges and the structure of A.

[3]

Concentrated sulphuric acid and concentrated nitric acid are used to form the ion required for step 2.

The following equilibrium is the first step in the formation of the ion:

H₂SO₄ + HNO₃ ⇋ HSO₄^- + H₂NO₃⁺

i) State the roles of each acid in this reaction.

[2]

ii) Use your answer to part (i) to suggest the relative strengths of the acids.

[1]

iii) Different isomers with the molecular formula C₇H₇NO₂ can be formed during step 2.

Draw the structure of the isomer B. Explain your answer.

[2]

Suggest reagents and conditions for steps 3–5 of the synthesis.

step 3 ................................................................................

step 4 ................................................................................

step 5 ................................................................................

Fig. 1.2 shows an alternative reaction scheme for the production of benzocaine.

Fig. 1.2

i) Suggest why this reaction scheme is an improvement.

[1]

ii) Suggest why this reaction scheme may not work.

[1]

Propanone can be synthesised from 2-bromopropane according to the reaction scheme shown in Fig. 2.1.

Fig. 2.1

Step 1 is not completed in acidic conditions.

Suggest reagents and conditions for each of steps 1 to 3.

step 1 ................................................................................

step 2 ................................................................................

step 3 ................................................................................

Suggest one reaction, including reagents and conditions, to replace steps 1 and 2.

Using structural formulae, construct an equation for the reaction of compound B with an oxidising agent, [O], to form propanone.

Ethene is used in the radical-free synthesis of 1-aminopropane as shown.

ethene $\stackrel{\mathrm{step}1}{\to }$ compound A $\stackrel{\mathrm{step}2}{\to }$ compound B $\stackrel{\mathrm{step}3}{\to }$ propylamine

Identify which step of the reaction scheme could use potassium cyanide dissolved in ethanol. Explain your answer.

Draw the skeletal structure of compound A and state the reagents required for its formation.

The final step of the reaction scheme forms 1-aminopropane from compound B.

Name compound B and identify the type of reaction that compound B undergoes to form propylamine. Explain your answer.

Sudan II is an azo dye that was used as a colourant in chilli powder until it was banned due to its links to an increased risk of cancer.  It can be synthesised from 1,3-dimethylbenzene by the route shown in Fig. 4.1

Fig. 4.1

Draw the structures of the organic compounds A, B, C and D in the boxes.

i) Write an equation to show the formation of an appropriate reactive species to react with 1,3-dimethylbenzene to form compound A.

[1]

ii) Draw the mechanism for this reaction. Include all necessary curly arrows and charges.

[3]

Two other structural isomers of compound A could have been formed from the mononitration of 1,3-dimethylbenzene, as shown in Fig.4.2.

Fig. 4.2

Suggest, with the aid of suitable diagrams, why 1,3-dimethyl-2-nitrobenzene is likely to be the more abundant product.