In a nitrogen atmosphere, 270 mL of tetrahydrofuran was added to 13.0 g (0.33 mol) of 60% sodium hydride under cooling with ice; to the mixture, 94.5 g (0.32 mol) of 5-acetoxy-4,6-di-tert-butyl-2-hydroxybenzaldehyde in 200 mL of tetrahydrofuran was added dropwise and the mixture was stirred for 1 hour at room temperature. Thereafter, the Grignard reagent prepared in Example 6 was added dropwise to the mixture, which was subjected to reaction for 1 hour at room temperature. Under cooling with ice, 1000 mL of a saturated aqueous solution of ammonium chloride was added and the mixture was extracted twice with 1000 mL of ethyl acetate. The organic layer was washed with 1000 mL of a saturated aqueous solution of sodium chloride and dried over anhydrous magnesium sulfate. After filtering off the magnesium sulfate, the filtrate was concentrated and the concentrate was dissolved in 1000 mL of hexane under heating. Thereafter, the solution was slowly cooled down to 0° C. for crystallization and the crystal was separated and dried to give 85.6 g of 4-acetoxy-3,5-di-tert-butyl-2-(1-hydroxy-2-pentylheptyl)phenol.
