[harini_5]

I’ve learnt about the modification of Riemer Tieman reaction in which carbon tetra chloride is added to phenol to get aromatic acids. What is the electrophile attacking phenol? 

[macman104]

Are you saying that phenol would create benzoic acid, or it would it create 2 (or 4)-hydroxybenzoic acid?  As it stands, I'm not entirely sure about this mechanism.  You learned about this in your course, or you read it, or...

[harini_5]

Sorry for not stating clearly  What I meant was when carbon tetrachloride is added to phenol we get p-hydroxy benzoic acid as the major product.

[Yarr]

Phenol can be not only O-alkylated but also C-alkylated, with the para position being the most reactive. This introduces a -CCl3 group in para position, which on hydrolysis gives the -COOH group.