For the same alkyl group, all the three primary, secondary and tertiary amines are more basic than ammonia in aqueous solutions. Their relative basicity, however, depends upon a combination of three factors: +I-effect of alkyl groups, the stability of the ammonium cation (formed after accepting a proton) due to H-bonding with water molecules and the steric effect of the alkyl groups which tend to reduce the extent of H-bonding. All these three factors are favourable for secondary amines thereby making them the strongest bases. If, however, the alkyl group is bigger than the methyl group, +I-effect of the alkyl group outweighs stability of the ammonium cation due to H-bonding thereby making tertiary amines more basic than the primary amines. Due to delocalization of lone pair of electrons of the nitrogen atom on the benzene ring, aniline is a weaker base than ammonia. The basic strength of the substituted anilines, however, depends upon the nature of the substituent. Whereas electron-donating groups tend to increase, electron-withdrawing groups tend to decrease the basic strength.
Consider the following statements about the basic character of amines.
(A) Amine salts on treatment with a base like NaOH regenerate the parent amine.
(B) Amine salts are soluble in water but insoluble in organic solvents like ether.
(C) In the gaseous phase, the order of basicity of amines is: tertiary amine > secondary amine > primary amine > NH3.
(D) Amines, being basic in nature, react with alkalis to form salts.
Which of the statements given above are correct? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (B) and (C) only
Amines are bases: the unshared electron pair on nitrogen takes up a proton from an acid, and an ammonium salt is formed. A stronger base can take the proton back and set the amine free.
(A) Amine salts on treatment with a base like NaOH regenerate the parent amine. — True. The hydroxide ion removes the proton from the ammonium ion:
\( \displaystyle \ce{R-NH3^+X^- + OH^- -> R-NH2 + H2O + X^-} \)
(B) Amine salts are soluble in water but insoluble in organic solvents like ether. — True. Being ionic, the salts dissolve in water.
This is used to separate amines from non-basic organic compounds that do not dissolve in water.
(C) In the gaseous phase, the order of basicity of amines is: tertiary amine > secondary amine > primary amine > NH3. — True. With no water to solvate the ions, only the +I effect of the alkyl groups counts, so basicity rises with the number of alkyl groups.
(D) Amines, being basic in nature, react with alkalis to form salts. — False. Being bases, amines react with acids to form salts; an alkali, being a base itself, sets the amine free from its salt instead.
\( \displaystyle \ce{R-NH2 + HX -> R-NH3^+X^-} \)
NCERT (2026-27 edition):
9.6 Chemical Reactions – “1. Basic character of amines: Amines, being basic in nature, react with acids to form salts.”
“Amine salts on treatment with a base like NaOH, regenerate the parent amine.”
“Amine salts are soluble in water but insoluble in organic solvents like ether. This reaction is the basis for the separation of amines from the non basic organic compounds insoluble in water.”
“…This trend is followed in the gaseous phase. The order of basicity of amines in the gaseous phase follows the expected order: tertiary amine > secondary amine > primary amine > NH3.”