Q.Write short notes on the following: a) Sandmeyer's reaction b) Reimer-Tiemann reaction c) Finkelstein reaction.
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Start your 14-day free trial to unlock the full solution →These are three classic named reactions from organic chemistry: one converts a diazonium salt to an aryl halide/nitrile, one formylates phenol, and one exchanges a halogen for iodine.
a) Sandmeyer's reaction:
An aromatic primary amine is first converted to its diazonium salt (Ar-N2+) by treatment with NaNO2/HCl at 0-5 degrees C. This diazonium salt is then treated with a cuprous (Cu+) salt - CuCl, CuBr, or CuCN - together with the corresponding halogen acid, which replaces the -N2+ group with -Cl, -Br, or -CN respectively, releasing N2 gas:
Ar-N2+ Cl- --(CuCl/HCl)--> Ar-Cl + N2
This is a key method for introducing a halogen (or nitrile group) onto an aromatic ring at a position that is otherwise hard to functionalise directly.
b) Reimer-Tiemann reaction:
Phenol is treated with chloroform (CHCl3) and concentrated aqueous NaOH, followed by acid hydrolysis. Under basic conditions, chloroform is converted to a highly reactive electrophilic species called dichlorocarbene (:CCl2), which attacks the electron-rich phenoxide ring ortho to the -OH, and after hydrolysis of the resulting intermediate, a -CHO group is installed at the ortho position, giving salicylaldehyde (2-hydroxybenzaldehyde):
C6H5OH --(CHCl3, NaOH; then H3O+)--> 2-hydroxybenzaldehyde (salicylaldehyde)
c) Finkelstein reaction: …
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