Which of the following gives a positive FeCl3 test ?
(A) Phenol
(B) o-Cresol
(C) Quinol
(D) Ethanol
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B) and (C) only
The neutral FeCl3 test is a test for the phenolic –OH group, an –OH attached directly to a benzene ring. Phenols react with iron(III) chloride to form coloured iron–phenoxide complexes (violet, blue or green):
\( \displaystyle \ce{6C6H5OH + Fe^3+ -> [Fe(OC6H5)6]^3- + 6H^+} \)
Alcohols, whose –OH group is attached to an sp3 carbon, do not give this colour.
(A) Phenol — Correct. It gives a violet colour with neutral \( \ce{FeCl3} \).
(B) o-Cresol — Correct. 2-Methylphenol has an –OH group on the ring, so it is a phenol and gives a coloured complex.
(C) Quinol — Correct. Quinol (hydroquinone, benzene-1,4-diol) has two phenolic –OH groups and also responds.
(D) Ethanol — Incorrect. Ethanol is an alcohol, not a phenol, so it gives no colour.
Note: The question is from beyond the NCERT textbook.