A LevelChemistryCambridge (CIE)Exam Questions34. Nitrogen CompoundsPhenylamine & Azo Compounds

Phenylamine & Azo Compounds (Cambridge (CIE) A Level Chemistry): Exam Questions

Exam code: 9701

41 mins4 questions
Medium
Hard
1a
5 marks

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

Three amine molecules: ammonia (NH3), phenylamine (C6H5NH2), and N-methylethanamine (CH3CH2NHCH3), shown as structural diagrams

Fig. 1.1

i) State the relative order of basicity of the three amine molecules shown in Fig. 1.1.

least basic ......................... < ......................... < ......................... most basic

[1]

ii) Explain your answer to part (i).

[4]

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1b
3 marks

Phenylamine, C6H5NH2, can be produced from nitrobenzene, C6H5NO2.

State the name of the type of reaction and the reagents and conditions required for this conversion.

type of reaction ...............................................................

reagents ...............................................................

conditions ...............................................................

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1c
2 marks

Phenylamine, C6H5NH2, can be used in the manufacture of azo dyes. In the first step, phenylamine reacts with hydrochloric acid and nitrous acid, HNO2, to form a diazonium salt.

C6H5NH2 + HCl + HNO2 → C6H5N2+Cl− + 2H2O

In the second step, the diazonium salt solution is added to an alkaline solution of a phenol coupling agent to form the azo dye.

i) The diazonium salt, C6H5N2+Cl−, is unstable. State the essential temperature condition required to prevent the diazonium salt from decomposing during this reaction.

[1]

ii) Draw the structure of the diazonium salt formed in this reaction. The nitrogen-containing group must be shown fully displayed.

[1]

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1d
2 marks

In the second step of azo dye production, the diazonium salt reacts with an alkaline solution of a phenol coupling agent.

Draw the skeletal formula of the azo dye formed if the coupling agent used is 2,6-dimethylphenol.

[2]

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2a
1 mark

4-methylphenylamine can be manufactured from methylbenzene in two steps.

Draw the skeletal formula of the intermediate organic compound formed in step 1.

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2b
2 marks

State the reagents and conditions required for step 1.

reagents ...............................................................

conditions ...............................................................

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2c
2 marks

Step 2 involves heating the intermediate under reflux with tin and concentrated hydrochloric acid.

Explain why aqueous sodium hydroxide must also be added to obtain 4-methylphenylamine.

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3a
3 marks

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

Reaction scheme for the synthesis of 4-hydroxyazobenzene from phenylamine: phenylamine reacts in step 1 to form benzenediazonium chloride, which undergoes coupling in step 2 to form 4-hydroxyazobenzene

Fig. 3.1

Step 1 requires nitrous acid, HNO2, which is generated in situ.

i) State the reagents and conditions required for step 1.

reagents ...............................................................

conditions ...............................................................

[2]

ii) Construct an equation for the reaction that takes place in step 1.

[1]

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3b
1 mark

Step 2 is a coupling reaction.

State the name of the organic reagent required to react with benzenediazonium chloride to form 4-hydroxyazobenzene.

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3c
1 mark

Fig. 3.2 shows the structure of another azo dye.

Structure of a methyl orange analogue azo dye, showing two aromatic rings connected by an N=N azo linkage with an N-methylphenylamine fragment on one ring

Fig. 3.2

State the systematic name of the secondary amine used to form the structure shown in Fig. 3.2.

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1a
5 marks

The acid-base indicator methyl red is an azo dye synthesised from 2-nitrobenzaldehyde and phenylamine. Fig. 1.1 shows the first stages of this synthesis.

Synthesis scheme for methyl red showing: 2-nitrobenzaldehyde undergoes step 1 (oxidation) to give 2-nitrobenzoic acid, then step 2 (reduction) to give compound A (2-aminobenzoic acid), which undergoes step 3 (diazotization) and coupling with phenylamine to give methyl red

Fig. 1.1

i) State the reagents and conditions for steps 1 and 2 of the synthesis.

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

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

[3]

ii) Draw the structural formula of compound A in the box provided. The nitrogen-containing group must be shown fully displayed.

[2]

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1b
6 marks

When heated, phenylamine reacts with iodomethane to form compound B, N-methylphenylamine.

i) Describe the mechanism for the formation of the N-methylphenylammonium iodide salt from the reaction of phenylamine and iodomethane. Include all relevant curly arrows, lone pairs, and dipoles.

[3]

ii) A further reaction occurs with an excess of iodomethane to form compound C, N,N-dimethylphenylamine.

Explain what this implies about the relative basicity of phenylamine and compound B.

[3]

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1c
2 marks

Explain why the temperature used in step 3 must be kept between 0 °C and 10 °C.

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1d
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4 marks

Fig. 1.2 shows the structure of indigotin. It can be synthesised from 2-nitrobenzaldehyde and propanone in aqueous sodium hydroxide.

Structural formula of indigotin, a blue dye with a symmetric bicyclic structure containing two indole units connected by a C=C double bond, with NH and C=O groups
Skeletal formula of indigotin showing the two fused ring systems connected by a central C=C bond

Fig. 1.2

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

Incomplete equation for the synthesis of indigotin from 2-nitrobenzaldehyde and propanone in aqueous NaOH, with blank spaces for balancing coefficients and products

Fig. 1.3

[1]

ii) Calculate the mass of 2-nitrobenzaldehyde required to produce 12.0 g of indigotin from this reaction. The percentage yield is 82.0%. Show your working.

[3]

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1e
2 marks

Fig. 1.4 shows the structure of Coumarin 440.

Reaction scheme showing the structure of Coumarin 440 with blank boxes for the structures of compounds D and E
Reaction scheme for Coumarin 440 transformations showing labelled blank product boxes for D and E

Fig. 1.4

Coumarin 440 is hydrolysed with excess aqueous sodium hydroxide to form organic compound D.

Coumarin 440 reacts with ethanoyl chloride to form organic compound E.

Draw the skeletal formulae of compounds D and E in the boxes provided.

[2]

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