How will you convert phenol to benzoic acid?

(i) How will you convert phenol to benzoic acid?
ii) An organic compound A having molecular formula gives a characteristic colour with aqueous solution. A on treatment with NaOH at 400 K under pressure gives B which on acidification gives a compound C. The compound C reacts with acetyl chloride to give D which is a popular pain killer. Deduce the structure of A, B, C and D.