Question

(i) How would you obtain chlorobenzene from diazonium salt and aniline from chlorobenzene? (Write only chemical equation.) (2)
(ii) Write the increasing order of basicity of the following compounds: NH₃, (CH₃)₃N, CH₃NH₂, (CH₃)₂NH. (1)
(iii) What are the main sources of protein? (1)

Hint:

Chlorobenzene from a diazonium salt is the Sandmeyer reaction (Cu₂Cl₂/HCl); aniline from chlorobenzene needs NH₃ with Cu₂O at high T and P. Remember the aqueous basicity order (CH₃)₂NH > CH₃NH₂ > (CH₃)₃N > NH₃.

Answer 1

Part (i): Chemical equations
Step 1 (Chlorobenzene from a diazonium salt - Sandmeyer reaction): Benzene diazonium chloride is warmed with cuprous chloride dissolved in HCl; the -N₂⁺ group is replaced by -Cl and nitrogen gas escapes.
C₆H₅N₂⁺Cl^- \( \xrightarrow{\text{Cu}_2\text{Cl}_2 / \text{HCl}} \) C₆H₅Cl + N₂
Step 2 (Aniline from chlorobenzene): Chlorobenzene is heated with ammonia at high temperature and pressure using a cuprous oxide catalyst; the chlorine is replaced by the -NH₂ group.
C₆H₅Cl + 2NH₃ \( \xrightarrow[\text{475 K, high pressure}]{\text{Cu}_2\text{O}} \) C₆H₅NH₂ + NH₄Cl

Part (ii): Increasing order of basicity
Step 1 (Concept): In aqueous solution the basic strength of amines depends on the combined effect of the electron-releasing (+I) effect of alkyl groups, solvation (stabilisation of the protonated cation by water) and steric hindrance. Adding methyl groups increases +I but reduces solvation and adds crowding, so the trend is not simply increasing.
Step 2 (Order): For methylamines in water the observed order of basic strength is (CH₃)₂NH > CH₃NH₂ > (CH₃)₃N > NH₃. Hence in increasing order:
\[ \text{NH}_3 < (\text{CH}_3)_3\text{N} < \text{CH}_3\text{NH}_2 < (\text{CH}_3)_2\text{NH} \]

Part (iii): Main sources of protein
Step 1: Proteins come from both animal and plant foods.
• Animal sources: milk, eggs, cheese, meat and fish.
• Plant sources: pulses and legumes (gram, beans, peas), soybean and nuts.