SolutionsFormylation of Aromatic Rings
1. The intermediate of the Reimer-Tiemann reaction
What is the electrophilic species of the Reimer-Tiemann reaction and how is it formed?
It is dichlorocarbene, :CCl2. Hydroxide removes the proton of chloroform, which is acidic because of the electron-withdrawing effect of the three chlorines, and the CCl3− anion loses a chloride. The electron-deficient carbene is attacked by the highly activated phenoxide ring, mainly at the ortho position.
2. Link with the hydrolysis of dihalides
After the attack of phenoxide on the carbene, how is the aldehyde reached?
A dichloromethyl group (–CHCl2) attached to the ring is obtained, that is, a geminal dihalide at a benzylic position. As in the hydrolysis of geminal dihalides, the basic medium replaces the chlorines and the CHO group forms. The final product, after acidification, is salicylaldehyde (2-hydroxybenzaldehyde).