CAIE A-Level Chemistry 34.2 Phenylamine and Azo Compounds

Practise phenylamine synthesis, basicity, diazotisation and azo coupling through conditions and structures.

Exam points

select reagents and temperatures for preparing phenylamine, forming a diazonium salt and coupling it
compare phenylamine basicity by deciding whether the nitrogen lone pair is available to accept H+
draw diazonium, phenol or azo products while retaining other substituents shown in a synthesis route

Covered syllabus points

34.2.1—Preparation of phenylamine via the nitration 34.2.2—Describe 34.2.3—Basicities of aq. ammonia, ethylamine 34.2.4—About azo compounds

[Maximum number: 4]

Potassium iodide, KI, is used as a reagent in both inorganic and organic chemistry.

(a)

$\quad \mathrm{KI}$ is used as a source of $\mathrm{I}^{-}$ ions in organic synthesis.

One example of this is shown in the synthetic route in Fig. 1.1.

Fig. 1.1

[ 4 ]

(i)

Identify the reagents required for steps 1 and 2 .
step 1
step 2

[ 2 ]

reaction 1 concentrated $\mathrm{HNO}_{3}$ AND concentrated $\mathrm{H}_{2} \mathrm{SO}_{4}$ (concentrated seen once)

reaction 2 Sn AND (concentrated) HCl

(ii)

Step 3 occurs in two stages.
stage I $\mathrm{NaNO}_{2}$ and HCl undergo an acid-base reaction to produce $\mathrm{HNO}_{2}$ .
stage II $\mathrm{HNO}_{2}$ reacts with $\mathbf{C}, \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}$ , to produce $\mathbf{D}, \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~N}_{2}{ }^{+}$ .
Complete the equations for stage I and for stage II.

$stage I $\mathrm{NaNO}_{2}+\mathrm{HCl} \rightarrow$$

stage II

[ 2 ]

step $1 \quad \mathrm{NaNO}_{2}+\mathrm{HCl} \rightarrow \mathrm{HNO}_{2}+\mathrm{NaCl}$

step $2 \quad \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}+\mathrm{HNO}_{2}+\mathrm{H}^{+} \rightarrow \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~N}_{2}+2 \mathrm{H}_{2} \mathrm{O}$

[Maximum number: 8]

(a)

Benzene can be used as a starting material to produce phenylamine by a two-step synthesis.

Figure for Question (a) — CAIE A-Level Chemistry A2

[ 2 ]

(i)

Give reagents and conditions for the production of phenylamine from nitrobenzene in step 2.

[ 2 ]

tin and $\mathrm{HCl}[1]$

conc and heat / boil / reflux [1]

(b)

Phenylamine reacts with $\mathrm{Br}_{2}(\mathrm{aq})$ .

[ 3 ]

(i)

Write an equation for this reaction. You may use structural or displayed formulae.

[ 1 ]

$\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}+3 \mathrm{Br}_{2} \rightarrow \mathrm{C}_{6} \mathrm{H}_{2} \mathrm{Br}_{3} \mathrm{NH}_{2}+3 \mathrm{HBr}[1]$

(ii)

Name the organic product of this reaction.

[ 1 ]

(iii)

Describe two observations that can be seen when phenylamine reacts with $\mathrm{Br}_{2}(\mathrm{aq})$ . observation 1 observation 2

[ 1 ]

(c)

Describe the relative basicities of ammonia, ethylamine and phenylamine, starting with the least basic.
Explain your answer in terms of their structures. < <
least basic
most basic

[ 3 ]

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Covered syllabus points

34.2 Phenylamine and azo compounds question 1

Question (a)

Question (i)

Question (ii)

34.2 Phenylamine and azo compounds question 2

Question (a)

Question (i)

Question (b)

Question (i)

Question (ii)

Question (iii)

Question (c)