The effects of ligands on clean synthesis of adipic acid via direct oxidation of cyclohexene with 30% H 2O 2 catalyzed by Na 2WO 4·2H 2O were studied. In most cases, the yield of target product adipic acid is high if the acidity of ligand is strong. Although the acidity of some phenolic ligands, L(+)ascorbic acid and 8 quinolinol is weak, the yield of adipic acid is still high. It is demonstrated that the acidic effect and the coordination effect of ligand play the same important role in oxidaton ...