An organic compound A (C₆H₆O) gives dark green colouration with ferric chloride. On treatment with CHCl₃ and KOH, followed by acidification gives compound B. Compound B can also be obtained from compound C on reaction with pyridinium chlorochromate (PCC). Identify A, B and C.

Solution

Chemistry ma’am · 4 steps

C₆H₆O is phenol, Reimer–Tiemann puts CHO ortho, and PCC makes that aldehyde from an alcohol.

1. Find A. C₆H₆O is C₆H₅OH, which is phenol. The coloured complex with neutral FeCl₃ confirms a phenolic –OH, so A is phenol.
2. Reimer–Tiemann gives B. CHCl₃ with KOH forms dichlorocarbene, :CCl₂. It attacks the phenoxide ion mainly at the ortho position, and acidification leaves a –CHO there. So B is salicylaldehyde (2-hydroxybenzaldehyde).
3. Work back to C. PCC is a mild oxidant: it turns a primary alcohol into an aldehyde and stops there. To give salicylaldehyde, C must carry a -CH₂OH where B has the –CHO, so C is 2-hydroxybenzyl alcohol (salicyl alcohol).
4. So. A is phenol, B is salicylaldehyde and C is 2-hydroxybenzyl alcohol, which is exactly the set in option (a).

The idea to keep. Read every reagent as a direction. Reimer–Tiemann puts a CHO ortho to a phenolic OH. PCC only goes uphill, from alcohol to aldehyde, so the compound it acts on must be the alcohol.

Answer from the NTA final answer key. Solution by PrepWiser.