A method for preparing semicarbazone comprising the steps of adding 3-fluoro isocyanate to S-(3,5-di-tert-butyl-4-hydroxybenzyl) thioglycolic acid hydrazide in toluene to form a first mixture; stirring the first mixture under nitrogen gas until a precipitate is formed; collecting the precipitate by filtration; washing the collected precipitate with boiled solvent to obtain a product; drying the obtained product; recrystallizing the dried product using alcohol to obtain a solid; adding aldehyde to the solid in alcohol to obtain a second mixture; adding a few drops of strong acid to the second mixture to obtain a third mixture; stirring and refluxing the third mixture; cooling the stirred and refluxed third mixture to obtain crystals; filtering and washing the obtained crystals thoroughly; and drying the filtered and washed crystals under vacuum to obtain 2-(2-(3,5-di-tert-butyl-4-hydroxybenzylthio) acetyl)-N-(3- fluorophenyl) hydrazinecarboxamide.