Identify the correct statements from the given below:
(A) Alcohols are less basic than amines.
(B) Aromatic primary amines can be prepared by Gabriel phthalimide synthesis.
(C) Primary amines have higher boiling points than tertiary amines.
(D) Carbylamine test can be used as a test for both primary aliphatic and aromatic amines
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (C) and (D) only
The four statements test the basicity, preparation, boiling points and the test for amines. Each follows from the lone pair on nitrogen and the N–H bonds of the amine.
(A) Alcohols are less basic than amines. — Correct. Nitrogen is less electronegative than oxygen, so it holds its lone pair less tightly and gives it to a proton more readily. Amines form salts with acids and turn red litmus blue; alcohols are only very feebly basic.
(B) Aromatic primary amines can be prepared by Gabriel phthalimide synthesis. — Incorrect. In Gabriel synthesis the phthalimide anion must displace a halide from the halide by nucleophilic substitution. Aryl halides do not undergo this substitution, so the method gives only aliphatic primary amines:
\( \displaystyle \ce{C6H4(CO)2N^-K+} \xrightarrow{\ce{R-X}} \ce{C6H4(CO)2N-R} \xrightarrow{\ce{NaOH(aq)}} \ce{R-NH2 + C6H4(COO^-Na+)2} \)
(C) Primary amines have higher boiling points than tertiary amines. — Correct. A primary amine has two hydrogen atoms on nitrogen and forms intermolecular hydrogen bonds; a tertiary amine has no N–H bond and cannot. Among the isomers of \( \ce{C3H9N} \), propan-1-amine boils at about 321 K, but trimethylamine at about 276 K.
(D) Carbylamine test can be used as a test for both primary aliphatic and aromatic amines — Correct. Any primary amine, aliphatic or aromatic, heated with chloroform and ethanolic KOH gives a foul smelling isocyanide; secondary and tertiary amines do not:
\( \displaystyle \ce{R-NH2 + CHCl3 + 3KOH} \xrightarrow{\text{heat}} \ce{R-NC + 3KCl + 3H2O} \)