REIMER TIEMANN REACTION

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1)Reimer Tiemann reaction:

An aldehyde group is generally introduced  at ortho to the -OH group,  when the phenol is treated  with chloroform and sodium hydroxide solution.For example Phenol react with Chloroform and sodiumhydroxide to give o-hydroxybenzaldehyde as follow-
Aspirin

Mechanism:

It involves  electrophilic substitution of the aromatic nucleus, the electrophile being dichlorocarbene :CCl2, form by the action of strong alkali on chloroform shown as bellow

Reaction of aldehyde 
The small amount of the P-hydroxybenzaldehyde also produced at the same time, can be separated by steam distillation. The O-isomer,which is capable of undergoing chelation by intramolecular hydrogen  bond would obviously be more volatile. 

Similarly, Carbon tetrachloride in the presence of alkali reacts with phenol to give O-and P-hydroxy benzoic acid show as bellow

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