Phenols

This question is about aromatic compounds.

The diagrams show the Kekulé and delocalised models of benzene.

Kekulé Delocalised

One piece of evidence for the delocalised model is that benzene does not decolourise aqueous bromine.

Suggest two other pieces of evidence which support the delocalised model of benzene.

A student investigates the reactions of benzene and phenol with excess bromine.

The student’s observations are given in Table 20.1.

Table 20.1

Explain the difference in the relative reactivities of benzene and phenol with bromine.

The white precipitate has a relative molecular mass of 330.7.

Construct an equation for the reaction of phenol with excess bromine shown in Table 20.1.

Show the structure of the organic species.

Compound G is an organic compound used in the production of pesticides.

Compound G can be synthesised from benzene in the two-stage process shown.

Synthesis 1

Benzene
Methylbenzene
Compound G

Suggest a reagent and halogen carrier that could be used in Stage 1 of Synthesis 1.

Stage 2 of Synthesis 1 is the conversion of methylbenzene to compound G.

Outline the mechanism for the reaction in Stage 2.

Show the role of H₂SO₄ as a catalyst.

A student suggested an alternative two-stage synthesis of compound G from benzene.

Synthesis 2

Benzene
Nitrobenzene
Compound G

When Synthesis 2 is attempted, the synthesis is not successful and a different organic compound from compound G is produced.

• Suggest why Synthesis 1 is successful but Synthesis 2 is not successful.

• Suggest the structure of the different organic compound that is formed in Synthesis 2.

In the production of a pesticide, compound G is reduced to amine H.

Suggest suitable reagents and complete the equation for this reduction.

Reagents........

Equation:

Compound G
Amine H

This question is about different compounds that each contain O and H atoms covalently bonded together.

The alcohol 2,3‑dimethylhexan‑1‑ol has the molecular formula C₈H₁₈O.

Draw the skeletal formula of 2,3‑dimethylhexan‑1‑ol.

What is the number of H atoms in 8.45 g of 2,3‑dimethylhexan‑1‑ol?

Give your answer to 3 significant figures and in standard form.

Why does paracetamol not react with Na₂CO₃(aq)?

The student uses the reaction of nuromol tablets with Na₂CO₃(aq) to determine the mass of ibuprofen and the mass of paracetomol in one nuromol tablet.

The student’s method is outlined below.

• Weigh four nuromol tablets.

• Add the tablets to an excess of aqueous sodium carbonate.

• Collect the gas produced and measure its volume.

Results Mass of four nuromol tablets = 2.80 g Volume of gas collected at RTP = 48.0 cm³

Assume that ibuprofen is the only compound in nuromol tablets that reacts with Na₂CO₃(aq).

Determine the mass of ibuprofen and the mass of paracetomol, in mg, in one nuromol tablet.

Barium hydroxide, Ba(OH)₂, is an alkali. A student is supplied with a solution of Ba(OH)₂ with a concentration of 46.80 g dm^–3 at 25 °C.

The student dilutes 20.0 cm³ of this solution of Ba(OH)₂ with water and the solution is made up to 100.0 cm³ at 25 °C.

Calculate the pH of the diluted solution of Ba(OH)₂ at 25 °C.

Give your answer to 2 decimal places.

This question is about aromatic compounds.

Ethylbenzene, C₆H₅CH₂CH₃, can be prepared by reacting benzene with chloroethane, CH₃CH₂Cl, in the presence of Al Cl₃. The Al Cl₃ acts as a halogen carrier.

Ethylbenzene

In the mechanism, chloroethane reacts with the halogen carrier to form a carbocation, which acts as the electrophile.

What is meant by the term electrophile ?

Outline the mechanism for this reaction, including the role of Al Cl₃ as a halogen carrier.

The table shows directing effects for different groups in the electrophilic substitution of aromatic compounds.

The reactions of C₆H₅NH₂ are similar to the reactions of phenol.

Write an equation for the tri-substitution of C₆H₅NH₂ with chlorine.

Explain why chlorine reacts much more readily with C₆H₅NH₂ than with benzene.

Oil of wintergreen is a liquid used in medicine to relieve muscle pain.

Compound H is a component in oil of wintergreen and can be synthesised from compound G, as shown below. The boiling point and density of compound H are stated.

Compound G
Compound H boiling point = 222 °C density = 1.174 g cm⁻³

A student prepares a sample of compound H by the method below.

Step 1 Reflux 8.97 g of compound G for 30 minutes with an excess of methanol in the presence of a small amount of sulfuric acid as a catalyst.

Step 2 Add an excess of aqueous sodium carbonate, Na₂CO₃(aq). Two layers are obtained.

Step 3 Purify the impure compound H that forms from the resulting mixture.

The student follows this method and obtains 5.32 g of pure compound H.

Why does the student use reflux in Step 1 ?

In Step 2, Na₂CO₃(aq) removes the sulfuric acid catalyst and any unreacted compound G from the mixture.

Write equations for this removal.

Removal of sulfuric acid

Removal of unreacted compound G

Compound G

Another student suggests that adding aqueous sodium hydroxide would be more effective in removing the sulfuric acid catalyst than Na₂CO₃(aq).

Comment on whether the student’s suggestion is an improvement for the preparation of compound H.

Calculate the percentage yield of compound H.

Give your answer to three significant figures.

Describe how to purify the impure compound H from the two layers in Step 2.

This question is about aromatic compounds containing the –COOH and –OH functional groups.

Salicylic acid, shown below, is used in the manufacture of some important medicines.

Salicylic acid

Complete the flowchart for reactions of salicylic acid, by adding the organic products in each

PAS, shown below, is an antibiotic used to treat several diseases including tuberculosis (TB).

A student predicts that PAS could polymerise to form a polymer containing both ester and amide linkages.

Draw a section of this polymer.

The section should contain one amide and one ester linkage, which should be displayed.

For the treatment of TB, the maximum daily dosage of PAS that should be prescribed is 300 mg per kg of body mass.

A child weighs 20.0 kg.

Calculate the number of PAS molecules in the maximum daily dosage of PAS for this child.

Aspirin tablets are used for pain relief.

The structure of aspirin is shown below.

A student uses the reaction of aspirin with cold NaOH(aq) to determine the mass of aspirin in one tablet.

In this reaction, 1 mol of aspirin reacts with 1 mol of cold NaOH(aq).

The student’s method is outlined below.

Step 1 The student reacts three aspirin tablets with 100 cm³ of 0.500 mol dm^–3 NaOH(aq). The NaOH is in excess. A colourless solution forms.

Step 2 The colourless solution from Step 1 is made up to 250.0 cm³ with distilled water.

Step 3 A 25.00 cm³ sample of the diluted solution from Step 2 is titrated with 0.200 mol dm^–3 HCl(aq) in the burette.

The HC l (aq) reacts with excess NaOH(aq) that remains in Step 1:

The student repeats the titration to obtain concordant (consistent) titres.

Titration results The trial titre has been omitted.

The burette readings have been read to the nearest 0.05 cm³.

Analysis of results From the results, the student can determine the following.

1. The amount, in mol, of excess NaOH(aq) that remains after the reaction of aspirin with NaOH(aq).

2. The amount, in mol, of NaOH(aq) that reacted with the aspirin.

Use the results to determine the mass, in mg, of aspirin in one aspirin tablet.

Aspirin reacts with hot NaOH(aq), under reflux.

Draw a labelled diagram of suitable apparatus for reflux.

In this reaction, 1 mol of aspirin reacts with 3 mol of hot NaOH(aq).

Complete the equation for the reaction of aspirin with an excess of hot NaOH(aq).

Show structures for organic compounds.

This question is about the chemistry of aromatic compounds.

What chemical test(s) could be used to confirm the presence of the phenol group in compounds K and L ?

A student thought that¹³C NMR spectroscopy could be used to distinguish between compounds J, K and L.

Explain, with reasoning, whether the student is correct.

Compound J is substituted at the 2-and 4-positions by chlorine in the presence of a catalyst.

Outline the mechanism for the 4 substitution of compound J by chlorine in the presence of a catalyst.

Show the role of the catalyst.

Compounds K and L react with chlorine much more readily than compound J.

Explain why.

Compound J, C₆H₅CH₂CH₂OH, is reacted with acidified potassium dichromate(VI) under reflux to form organic product M.

Write an equation for this reaction.

Use [O] to represent the oxidising agent and show the structure of M.

A two-stage synthesis of an amine from compound J is shown below.

Add the reagents for each stage of this synthesis.

Compound J

Compounds 1, 2 and 3 are heated with NaOH(aq).

Which compound(s) react(s)?

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

This question is about reactions of phenol.

Complete the mechanism below for Stage 1 and Stage 2.

Show curly arrows, the structure of the intermediate and the missing formulae on the dotted lines.

Two molecules of salicylic acid can react together in the presence of an acid catalyst to form compound B.

Compound B has three rings and a molecular formula of C₁₄H₈O₄.

Write the equation for this reaction showing the structures of organic compounds.

A student reacts phenol with nitric acid and sulfuric acid at 100 °C to form impure crystals of an organic compound, C. The student purifies the crystals by recrystallisation.

Describe how the student could recrystallise the impure crystals to obtain a pure sample of C.

The pure sample of C is analysed to give the following results.

Percentage composition by mass: C, 31.44%; H, 1.31%; N, 18.34%; O, 48.91%.

The mass spectrum of C shows a molecular ion peak at m / z = 229.0

The¹³C NMR spectrum of C is shown below.

The table shows directing effects for different groups in the electrophilic substitution of aromatic compounds.

Analyse all the information to suggest the structure for C.

Show all your reasoning.

compound C

Which one of the following reacts with ethanoic acid and with phenol?

A Aqueous potassium hydroxide

B Bromine

C Calcium carbonate

D Methanol and an acid catalyst

Phenol reacts with bromine.

Which is the least likely organic product?

Which chemical(s) can react with phenol?

1 Potassium hydroxide

2 Ethanoyl chloride

3 Nitric acid

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

This question is about aromatic compounds.

Phenol undergoes nitration more readily than benzene.

A student carries out the nitration of phenol with dilute nitric acid to produce 2-nitrophenol and 4-nitrophenol.

A small amount of 3-nitrophenol is also produced.

2-nitrophenol 3-nitrophenol 4-nitrophenol

The student thought that¹³C NMR spectroscopy could be used to distinguish between these three nitrophenols.

Explain whether the student is correct.

Explain why phenol is nitrated more readily than benzene.

Methylbenzene reacts with sulfur trioxide, SO₃, to form D, shown below.

The electrophile in this reaction is SO₃.

Complete the mechanism for the formation of D. Show curly arrows and the structure of the intermediate.

This question is about aromatic carboxylic acids and their derivatives.

The concentration of ester K in the cosmetic product is 9.13 × 10⁻² g dm⁻³.

Using the results, calculate the concentration, in mol dm⁻³, of ester M in the cosmetic product.

Give your answer to two significant figures.

concentration of ester M =........ mol dm⁻³

This question is about the chemistry of aromatic compounds.

Benzoic acid can be nitrated by concentrated nitric acid in the presence of concentrated sulfuric acid as a catalyst, as shown in Equation 17.1.

The organic product of this reaction is 3-nitrobenzoic acid.

Outline the mechanism for this nitration of benzoic acid.

Show how H₂SO₄ behaves as a catalyst.

* A chemist carries out the reaction in Equation 17.1 using 4.97 g of benzoic acid.

The chemist obtains 3-nitrobenzoic acid as an impure solid.

The chemist purifies the solid to obtain 4.85 g of 3-nitrobenzoic acid.

Describe a method to obtain a pure sample of 3-nitrobenzoic acid from the impure solid, determine the percentage yield and check its purity.

A student investigates the relative ease of nitration of phenol, benzene, and benzoic acid.

The student finds that the conditions required for the nitration of each compound are different, as shown in Table 17.1.

State the trend in the relative ease of nitration of phenol, benzene, and benzoic acid.

Apply your knowledge of the bonding in arenes to explain the trend in part (b)(i).

A student synthesises 3-bromophenylamine, shown below, starting from nitrobenzene.

Complete the flowchart showing the structure of the intermediate and the formulae the reagents for each stage.

Another student attempts the same synthesis but carries out reduction before bromination. The student was surprised to find that two structural isomers of 3-bromophenylamine had been formed instead of the desired organic product.

Explain this result and suggest the structures of the two isomers that formed.

Explanation........

Structures