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

(i) Same conversions, described stepwise.
Step 1: A diazonium salt, C₆H₅N₂⁺Cl^-, is very reactive because -N₂⁺ is an excellent leaving group (it leaves as inert N₂). Treating it with Cu₂Cl₂/HCl (Sandmeyer conditions) substitutes chlorine on the ring:
C₆H₅N₂⁺Cl^- \(\xrightarrow{\text{Cu}_2\text{Cl}_2/\text{HCl}}\) C₆H₅Cl + N₂.
Step 2: The reverse direction (ring Cl to ring NH₂) needs forcing conditions because aryl C-Cl is strong. Ammonia at about 475 K and high pressure over Cu₂O gives aniline:
C₆H₅Cl + 2NH₃ \(\xrightarrow[\text{475 K, pressure}]{\text{Cu}_2\text{O}}\) C₆H₅NH₂ + NH₄Cl.

(ii) Basicity, reasoned the other way round. A stronger base holds the extra proton more firmly, i.e. the more stable its conjugate acid (the ammonium cation) the more basic the amine. Ammonia has no alkyl group and no +I help, so it is weakest. Trimethylamine has maximum +I but its cation is poorly hydrated and crowded, so it slips below the primary and secondary amines in water. Dimethylamine is the best compromise of +I plus adequate solvation, so it is strongest. Increasing order: NH₃ \(<\) (CH₃)₃N \(<\) CH₃NH₂ \(<\) (CH₃)₂NH.

(iii) Protein sources, grouped by diet. Non-vegetarian foods rich in protein include egg, fish, meat and milk products such as cheese. For vegetarians the chief sources are pulses (dal), soybean, beans, peas and nuts. Thus a mixed diet of these supplies the amino acids the body needs.