Organic Synthesis (A Level only) (AQA A Level Chemistry)

A reaction pathway is set out below in Figure 1. Use this pathway to answer all of the following questions. 

Figure 1

Concentrated sulfuric acid, H₂SO₄, is used in Reaction 2 of Figure 1. Outline the mechanism for the dehydration of the alcohol. 

Compound D reacts with ammonia, NH₃, to produce a primary amine. Name and give the structural formula of the product from this reaction.

Compound C can undergo polymerisation. Draw the polymer produced and name the type of polymerisation that this compound undergoes.

The following reaction pathway, outlined in Figure 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 process.

Figure 1

In order for the ester to be produced, the ketone in Figure 1 must be converted to another compound.

The aldehyde molecule in Figure 1 can react with aqueous potassium cyanide, KCN(aq) in the presence of sulphuric acid, H₂SO₄. Outline the mechanism for the nucleophilic addition reaction and give the name of the product.

Explain why the reaction in part (c) produces a racemic mixture.

A reaction profile for the production of 2-chlorobutane from butanone in three steps is shown below in Figure 1.

Figure 1

Name suitable reagents for Steps 1 and 2 and give the type of reaction that is occurring in Step 2.

Name and outline the mechanism for Step 3 of Figure 1. 

Outline the chemical test and observation that would distinguish butane, C₄H₁₀, from Compound Y in Figure 1.

A large excess of 2-chlorobutane, CH₃CHClCH₂CH₃, reacts with ammonia to produce a solid product. Give the name and use of the type of compound formed by this reaction.

Consider the following reaction sequence shown in Figure 1.

Figure 1

Explain what is meant by the terms electrophile and substitution reaction.

Step 1 in the reaction scheme shows the preparation of compound A from methylbenzene.

Identify suitable reagents for Step 1 outlined in Figure 1.

Give the name or formula of the electrophile involved in Step 1 and write one equation to show its formation.

Outline the mechanism for Step 1.

For Step 2, give the reagents and write an equation for this reaction using [H] to represent the reducing agent. 

Give the m/z value of a major peak which could appear in the mass spectrum of methylbenzene, but would not appear in the spectrum of Compounds A and B.

Justify your answer.

The reaction pathway for the formation of an N-substituted amide is shown in a three step synthesis in Figure 1. In Step 1, the major product of the reaction is formed.

Figure 1

Give the IUPAC names of Compounds W and X.

Give a suitable reagent and reaction equation for Step 2 given in Figure 1.

Step 3 produces an N-substituted amide. Name and outline the mechanism for Step 3 using propanoyl chloride as a reagent. Give the structure of the N-substituted amide formed during the reaction.

5.0g of Compound W was used to produce Compound X. The percentage yield was 64%.

Ethyl 4-aminobenzoate, shown in Figure 1, is more commonly known as benzocaine. It is an ester based compound that is used medicinally as a local anaesthetic in pain relievers and cough drops.

Figure 1

One of the first industrial processes to manufacture benzocaine was the multi-step reaction shown in Figure 2.

Figure 2

The current cost of >99.7% pure benzene is around £10.00 per litre compared to > 99.5% pure methylbenzene at a cost of around £7.00 per litre.

Explain why it would be beneficial to start from methylbenzene instead of benzene in the manufacture of benzocaine. Your answer should not include economic considerations. 

Concentrated sulphuric acid and concentrated nitric acid are used to form the nitronium ion required for step 2 of the reaction scheme, in part (a).

The following equilibrium is the first step in the formation of the nitronium ion.

H₂SO₄ + HNO₃ ⇋ HSO₄^- + H₂NO₃⁺ 

Give the reagents and conditions necessary for steps 4 and 5 of the reaction scheme shown in part (a).

A student suggests the reaction scheme shown in Figure 3 as an alternative to the original industrial reaction scheme shown in part (a) for the production of benzocaine.

Figure 3

A student is asked to prepare a sample of propyl propanoate using propanal.

Suggest a reaction scheme, using displayed formulae, that the student could use to prepare their sample of propyl propanoate.

Conditions and reagents are not required.

Use your answer from part (a) to help answer this question.

One of the intermediates in the reaction scheme, from part (a), has a molecular mass of 74.0 g mol^-1.

Propanal and the intermediate (M_r = 74.0) in the reaction scheme, from part (a), are to be separated by distillation.

Explain which chemical will distill first.

Use your answer from part (a) to help answer this question.

One of the intermediates in the reaction scheme, from part (a), has a molecular mass of 60.0 g mol^-1.

Propanone can be synthesised from 2-bromopropane according to the reaction scheme shown in Figure 1.

Figure 1

Step 1 is not completed in acidic conditions.

Give the reagents and conditions for steps 2 and 3 of the reaction scheme in part (a).

Suggest one reaction to replace steps 1 and 2 in the part (a) reaction scheme.

To prepare a sample of ethanal, a student adapts the reaction scheme from part (a). The student’s adapted reaction scheme is shown in Figure 2.

Figure 2

Explain one improvement the student should make to their adapted reaction scheme.

State four factors that should be considered when designing a reaction scheme for the synthesis of a target compound in industry.

Propylamine, shown in Figure 1, can be synthesised from ethene.

Figure 1

A student suggests that ethene should be reacted with hydrogen cyanide to produce propylamine.

Figure 2 shows the outline of a reaction scheme to convert ethene into propylamine.

Figure 2 

                                       Step 1                           Step 2                            Step 3

                        Ethene      →     Compound A     →     Compound B     →    Propylamine

 Identify which step of the reaction scheme could use the student’s suggestion of hydrogen cyanide. Justify your answer.

Draw the skeletal structure of compound A, from part (b), and state the reagents required for its formation.

The final step of the reaction scheme will form the desired amine.

Thyroxine, shown in Figure 1, is a biologically active hormone that is partially responsible for the body's metabolic rate. Deficiencies can lead to obesity while an excess can lead to weight loss.

Figure 1 

Complete Table 1 to describe possible chemical tests that prove the presence of the functional groups in thyroxine. Your answer should include the chemical formula and state of any reagents and the expected result.

Table 1

Butan-2-yl propanoate, shown in Figure 2, is heated under reflux with dilute hydrochloric acid.

Figure 2

Name the two organic products formed from the described reaction of butan-2-yl propanoate.

Suggest an alternative set of reagents to improve the yield of the two organic products identified in part (i).   

In terms of the carboxylic acid produced, calculate the percentage atom economy for the acid and alkaline hydrolysis of ethyl ethanoate.

Suggest why the alkaline hydrolysis of esters may be preferred over acid hydrolysis despite having a lower percentage atom economy.