To a beaker add 20 g of menthol powder and 20 g of 85% formic acid then slowly with vigorous stirring add 1 mL of conc. sulfuric acid, stir for 3h and let the solution stand for 5 days in dark occasionally stirring. Pour the solution into 100 mL of water and add 10 g of sodium bicarbonate, discard the bottom layer and wash the organic layer twice with 50 mL of water. Dry the crude product with some anhydrous magnesium sulfate and distill in a vacuum ( 50mm Hg) at 131°C.
The two layers after 5 days
Collecting and washing the organic layer
Pure menthyl formate