Write the ionization reaction of a. aniline, C6H5NH2 in glacial acetic acid and identify the conjugate acid of aniline. b. phenol, C6H5OH in ethylene diamine, NH2CH2CH2NH2 and identify the conjugate base of phenol.
The Correct Answer and Explanation is :
a. Ionization of Aniline (C₆H₅NH₂) in Glacial Acetic Acid:
The ionization reaction of aniline in glacial acetic acid can be represented as:
C₆H₅NH₂ (aniline) + CH₃COOH (acetic acid) ⇌ C₆H₅NH₃⁺ (anilinium ion) + CH₃COO⁻ (acetate ion)
Conjugate Acid of Aniline:
The conjugate acid of aniline is the anilinium ion (C₆H₅NH₃⁺). When aniline, which is a weak base, reacts with the weak acid acetic acid, it accepts a proton (H⁺) from acetic acid. This protonation leads to the formation of the anilinium ion, which is the conjugate acid of aniline. Aniline itself has a basic nitrogen atom, which can accept a proton, leading to this conjugate acid.
Explanation:
Aniline is a weak base, and glacial acetic acid is a weak acid. When they react, the nitrogen atom in aniline, with its lone pair of electrons, attracts a proton (H⁺) from acetic acid. This results in the formation of the anilinium ion (C₆H₅NH₃⁺), where the nitrogen now has a positive charge due to the added proton. The remaining acetate ion (CH₃COO⁻) is the conjugate base of acetic acid. This reaction is reversible, depending on the relative acid strengths of acetic acid and aniline.
b. Ionization of Phenol (C₆H₅OH) in Ethylene Diamine (NH₂CH₂CH₂NH₂):
The ionization reaction of phenol in ethylene diamine (which acts as a base) can be represented as:
C₆H₅OH (phenol) + NH₂CH₂CH₂NH₂ (ethylene diamine) ⇌ C₆H₅O⁻ (phenoxide ion) + NH₃⁺ (protonated ethylene diamine)
Conjugate Base of Phenol:
The conjugate base of phenol is the phenoxide ion (C₆H₅O⁻). When phenol reacts with ethylene diamine, a basic nitrogen atom in ethylene diamine abstracts a proton from the hydroxyl group of phenol, leaving behind the phenoxide ion.
Explanation:
Phenol has a hydroxyl group (-OH) attached to a benzene ring. The oxygen in this hydroxyl group is electronegative and can donate a lone pair to form a bond with a proton. Ethylene diamine, being a stronger base than phenol, can abstract this proton from the hydroxyl group, resulting in the formation of the phenoxide ion (C₆H₅O⁻) and a protonated form of ethylene diamine. The phenoxide ion is the conjugate base of phenol. It is stabilized by the delocalization of the negative charge onto the aromatic ring, making phenol a weak acid.
In summary, the conjugate acid of aniline is the anilinium ion, and the conjugate base of phenol is the phenoxide ion.