The present Invention relates to a process for the preparation substantially pure propane- 1 -sulfonicacid- { 3 -[5 -(4-chiorophenyI)-1 H-pyrrolo [2,3-b]pyridine-3 -carbonyl]-2,4-difluoro-phenyl} -amide or Vemurafenib of Formula (1), The present invention further relates to a process for the preparation substantially pure propane- 1 -sulfonic acid- { 3 - [5-(4-chlorophenyi)-1H-pyrrolo [2,3-b]pyridine-3 -carbonyl] -2,4-difluoro-phenyl} -amide trifluoro methane sulfonic acid salt or Vemurafenib triflate of Formula (VII).