In the commercial method of manufacturing picric acid from phenol the intermediate formed is

Direct nitration of phenol using conc. HNO3 gives a very poor yield of picric acid.Conc. HNO3 being a very strong oxidant and thus oxidation products dominate nitration productIndirect nitration is used in commercial preparation of picric acid. On sulphonation of phenol we get –SO3H group is bulky and deactivating. Thus reactivity decreases. Thus the intermediate, on nitration gives a very good yield of picric acid.