Electrophilic substitution

This question is about making the explosive 2-methyl-1,3,5-trinitrobenzene, commonly known as TNT.

TNT can be made by reacting methylbenzene with concentrated nitric acid in the presence of concentrated sulfuric acid.

Give the overall equation for the reaction between methylbenzene and nitric acid.

The yield of TNT in this reaction is 42.5%.

Calculate the mass, in g, of TNT (M_r = 227.0) obtained from

Methylbenzene has density = 0.867 g cm^–3 and M_r = 92.0

In the mechanism for this reaction, concentrated nitric acid reacts with concentrated sulfuric acid to produce the nitronium ion O₂N⁺

Give an equation for the reaction to produce the nitronium ion.

State the role of the nitronium ion in the reaction with methylbenzene.

Outline the mechanism for the reaction of the nitronium ion with methylbenzene to give 2-methyl-1-nitrobenzene.

Equation

Role of nitronium ion

Mechanism

Figure 5 shows enthalpy of hydrogenation data for cyclohexene and benzene.

It also shows predicted data for the theoretical molecule cyclohexa-1,3,5-triene.

Compare benzene and the theoretical molecule cyclohexa-1,3,5-triene in terms of:

• stability

• shape

• carbon–carbon bond lengths.

For each of these properties, suggest reasons for any differences.

Use data from Figure 5 in your answer.

Two steps in the synthesis of an aromatic amine are shown.

State the two reagents needed for Step 1.

Give an equation to show the formation of the reactive intermediate from these two reagents.

Equation

State the reagent(s) needed for Step 2.

State a possible use for the amine formed in Step 2.

This question is about intermediates in reaction mechanisms.

Figure 3 shows an intermediate formed in the first step of a nucleophilic addition–elimination mechanism.

Figure 3

Complete Figure 3 to show the structures of the two reactant species with curly arrows and relevant lone pairs of electrons involved in the formation of the intermediate.

Draw curly arrows and relevant lone pairs of electrons on the intermediate to show how the final products are formed.

Figure 4 shows an intermediate formed in the first step of a reaction mechanism of methylbenzene.

Complete Figure 4 to show the reactant species and any curly arrows involved in the formation of the intermediate.

Draw a curly arrow on the intermediate to show how the product is formed.

Give the name of the reaction mechanism.

Name of mechanism

Figure 5 shows the reactant species involved in the first step of a mechanism.

Figure 5

Complete Figure 5 to show the structure of the intermediate formed with curly arrows involved in its formation.

Give the name of the reaction mechanism.

Name of mechanism

Benzene reacts with methanoyl chloride (HCOC l) in the presence of a catalyst.

Give an equation for the overall reaction when benzene reacts with methanoyl chloride.

Name the organic product.

Identify the catalyst needed in this reaction.

Give an equation to show how the catalyst is used to form the electrophile, [HCO]⁺

Outline the mechanism for the reaction of benzene with the electrophile, [HCO]⁺

This question is about the reaction scheme shown.

State the reagents needed for step 1 and the reagents needed for step 2.

Give the name of the mechanism for the reaction in step 3.

Name the reagent for step 4.

State a necessary condition for step 4.

Amine A is formed in step 2 and amine B is formed in step 5.

Explain why the yield of B in step 5 is less than the yield of A in step 2.

Explain why amine B is a stronger base than amine A.

Which type of reaction is not involved in this reaction sequence?

Use Figure 3 and the data shown in Table 1 to calculate ΔH₂

A mixture of concentrated nitric acid and concentrated sulfuric acid reacts with benzene.

Figure 4 shows the incomplete mechanism for this reaction.

Name the mechanism.

Complete the mechanism in Figure 4 by adding

• any lone pairs of electrons involved in each step

• two curly arrows in step 1

• a curly arrow in step 2

• a curly arrow in step 3

• a curly arrow in step 4.

Name of mechanism

State the type of reaction in step 1.

Identify the reagent(s) and conditions needed for step 1.

State the name of the mechanism for the reaction in step 2.

Identify the inorganic reagent needed for step 2.

Name the organic product of step 2.

Name of mechanism

Name of organic product

The organic product of step 2 is reacted with concentrated sulfuric acid in step 3.

Outline the mechanism for step 3.

Draw the repeating unit of polystyrene.

Paracetamol is a medicine commonly used to relieve mild pain. Traditionally, paracetamol has been made industrially in a three-step synthesis from

Name the mechanism of the reaction in Step 1.

Complete the equation for the reaction in Step 2.

In theory, either ethanoyl chloride or ethanoic anhydride could be used in Step 3.

Complete the mechanism for the reaction of 4-aminophenol with ethanoyl chloride. RNH₂ is used to represent 4-aminophenol in this mechanism.

In practice, ethanoic anhydride is used in the industrial synthesis rather than ethanoyl chloride.

Give one reason why ethanoyl chloride is not used in the industrial synthesis.

In Step 3 other aromatic products are formed as well as paracetamol.

Draw the structure of one of these other aromatic products.

Chemists have recently developed a two-step process to produce paracetamol from phenol. In the first step, phenol is oxidised to hydroquinone.

In the second step, hydroquinone reacts with ammonium ethanoate to form paracetamol.

Complete the equation for this second step.

Calculate the mass, in kg, of hydroquinone (M_r = 110.0) needed to produce 250 kg of paracetamol.

Methylbenzene reacts with a mixture of concentrated nitric acid and concentrated sulfuric acid.

What is the name of the mechanism for this reaction?

The reaction between propanoyl chloride and benzene is an example of acylation.

Which is a correct representation of part of the mechanism of this reaction?

The nitration of benzene uses a nitrating mixture of concentrated nitric acid and concentrated sulfuric acid.

Which statement is correct?

Nitrobenzene reacts when heated with a mixture of concentrated nitric acid and concentrated sulfuric acid to form a mixture of three isomeric dinitrobenzenes.

Write an equation for the reaction of concentrated nitric acid with concentrated sulfuric acid to form the species that reacts with nitrobenzene.

Name and outline a mechanism for the reaction of this species with nitrobenzene to form 1,3-dinitrobenzene.

Name of mechanism

Mechanism

The dinitrobenzenes shown were investigated by thin layer chromatography

In an experiment, carried out in a fume cupboard, a concentrated solution of pure 1,4-dinitrobenzene was spotted on a TLC plate coated with a solid that contains polar bonds. Hexane was used as the solvent in a beaker with a lid.

The start line, drawn in pencil, the final position of the spot and the final solvent front are shown on the chromatogram in Figure 3

Use the chromatogram in Figure 3 to deduce the R_f value of 1,4-dinitrobenzene in this experiment.

Tick (✓) one box.

State in general terms what determines the distance travelled by a spot in TLC.

To obtain the chromatogram, the TLC plate was held by the edges and placed in the solvent in the beaker in the fume cupboard. The lid was then replaced on the beaker.

Give one other practical requirement when placing the plate in the beaker.

A second TLC experiment was carried out using 1,2-dinitrobenzene and 1,4-dinitrobenzene. An identical plate to that in Question 8.3 was used under the same conditions with the same solvent. In this experiment, the R_f value of 1,4-dinitrobenzene was found to be greater than that of 1,2-dinitrobenzene.

Deduce the relative polarities of the 1,2-dinitrobenzene and 1,4-dinitrobenzene and explain why 1,4-dinitrobenzene has the greater R_f value.

Relative polarities

Explanation

A third TLC experiment was carried out using 1,2-dinitrobenzene. An identical plate to that in Question 8.3 was used under the same conditions, but the solvent used contained a mixture of hexane and ethyl ethanoate.

A student stated that the R_f value of 1,2-dinitrobenzene in this third experiment would be greater than that of 1,2-dinitrobenzene in the experiment in Question 8.6

Is the student correct? Justify your answer.