A LevelChemistryCIEExam Questions34. Nitrogen Compounds (AL)34.2 Phenylamine & Azo Compounds

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First teaching 2023

First exams 2025

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Phenylamine & Azo Compounds (CIE A Level Chemistry)

Exam Questions

42 mins4 questions
Medium
Hard
1a7 marks

Three nitrogen containing molecules, ammonia, NH3, phenylamine, C6H5NH2 and N-methylethylamine, CH3CH2NHCH3, are drawn below respectively in Fig. 1.1.

7-6-1a-m-three-amine-molecules

Fig. 1.1

i)
List the three amine molecules drawn in Fig. 1.1 in order of increasing base strength.

[1]

ii)
Explain your answer to part (b) (i).

[6]

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1b3 marks

Phenylamine, C6H5NH2 shown in Fig. 1.1 in part (a) can be produced from nitrobenzene, C6H5NO2. 

Name the type of reaction and suggest suitable reagents and conditions for this conversion.

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1c2 marks

Azo dyes are organic compounds, which are largely used in the treatment of textiles and leather products, as well as in food. Phenylamine, C6H5NH2, can be used in the manufacture of azo dyes. 

The manufacturing process is outlined below.

Step 1

Phenylamine is dissolved in HCl to produce a diazonium salt. A diazonium salt contains two nitrogen atoms joined together by a triple bond. The reaction for this process is as follows:

C6H5NH2  +  HCl   +  HNO2   →    C6H5N2+Cl-    +   2H2O
Step 2

This solution is then slowly added to an alkaline solution of a phenol coupling agent to form the dye. 

i)
The diazonium salt, C6H5N2+Cl-, is an unstable compound. Suggest a condition that could be added to ensure that the salt would not break down during the reaction.

[1]

ii)
Draw the structure of the diazonium salt formed in Step 1, showing the displayed formula of the nitrogen containing group.

[1]

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1d2 marks

Phenol, C6H5OH, is an aromatic organic compound which is also crucial in the manufacture of azo dyes.

The final step of the azo dye production involves pairing up the diazonium salt with a phenol compound as a coupling agent. 

Suggest a structure for the azo dye if the coupling agent used is 2,6-dimethylphenol. 

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2a1 mark

4-methylphenylamine is a useful compound in the manufacture of azo dyes. It can be manufactured from methylbenzene in two stages.

Draw the structure of the intermediate required to manufacture 4-methylphenylamine.

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2b2 marks

State the reagents and conditions required to manufacture the intermediate in part (a).

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2c2 marks

The final stage for the preparation of 4-methylphenylamine involves the intermediate being heated under reflux in the presence of concentrated hydrochloric acid and a tin catalyst.

Explain why sodium hydroxide is also required in this step.

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3a2 marks

The azo dye 4-hydroxyazobenzene, C12H10N2O, can be produced from phenylamine as shown in Fig. 3.1.

4-hydroxyazobenzene-reaction-scheme

Fig. 3.1

Step 1 involves nitric(III) acid.

i)
Give the reagents and conditions for the formation of nitric(III) acid.
 
[2]
 
ii)
Write an equation for the reaction that takes place in step 1.
 
[1]

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3b1 mark

Step 2 is the coupling reaction of benzenediazonium chloride to form 4-hydroxyazobenzene.

Identify the other reagent involved in this coupling reaction.

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3c1 mark

An analogue of the azo dye methyl orange is shown in Fig. 3.2. It is an azo dye formed by a similar reaction to 4-hydroxyazobenzene.

yz19t5B3_methyl-orange-analogue-structure

Fig. 3.2

Give the name of the secondary amine used to form the structure in Fig. 3.2.

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1a5 marks

Organic molecules are an important source of colour both in the natural world and in a wide range of industrial applications.

Azo dyes are synthetic compounds that do not occur naturally. They can be used to colour textiles such as cotton.

The acid‐base indicator methyl red is an azo dye that can be produced from 2‐nitrobenzaldehyde and phenylamine as shown in Fig. 1.1.

Z4Ps_8RN_methyl-red-synthesis-2-cie-ial7-6-nitrogen-compounds-a-level-only-methyl-red-synthesis-2-cie-ial

Fig. 1.1

i)
Suggest reagents and conditions for steps 1 and 2 of the synthesis.
 
step 1 ................................................................................
 
step 2 ................................................................................
 
[3]
 
ii)
Draw the structure of compound A in the box.
 
[2]

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1b5 marks

When heated, phenylamine can react with iodomethane to form compounds B and C. 

i)
Draw a mechanism for the formation of the N-methylphenylamine iodide salt of compound B from the reaction of phenylamine and iodomethane. Include all necessary curly arrows and charges.
 
[2]
 
ii)
Compound C requires an excess of iodomethane to form.
 
Suggest what this condition means in terms of the basicity of phenylamine and compound B. Explain your answer.
 
[3]

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1c2 marks

Suggest why the temperature used in steps 2 and 3 should be kept as close to 5 °C as possible. 

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1d
Sme Calculator4 marks

Indigotin, shown in Fig. 1.2 is a naturally occurring compound that is used to dye denim a blue colour.

indigotin7-6-1d-h-indigotin

Fig. 1.2

It can be synthesised from 2‐nitrobenzaldehyde and propanone in aqueous sodium hydroxide.

i)
Complete the equation for this reaction, shown in Fig. 1.3.
 

q21e-i-paper-5-oct-2021-edexcel-ial-chemistry

Fig. 1.3
 
[1]
 
ii)
Calculate the mass of 2‐nitrobenzaldehyde required to make 12.0 g of indigotin from this reaction with a percentage yield of 82.0%.
 
[3]

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1e3 marks

Coumarin 440 is a dye that occurs naturally in plants but can be synthesised in the laboratory. It is used to generate blue light in lasers.

Coumarin 440 is hydrolysed with excess sodium hydroxide to form the organic compound D in Fig.1.4.

Coumarin 440 is condensed with ethanol chloride to form the organic compound E in Fig.1.4.

Fo6aSPD7_coumarin-440-reaction-scheme-blank7-6-1-e-h-coumarin-440-reaction-scheme-blank1

Fig. 1.4

Draw the structures of compounds D and E in the boxes.

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