(1) Slowly add 2,4-dihydroxybenzoic acid to an alkaline aqueous solution of sodium hydroxide, keeping the temperature below 30°C. After all the 2,4-dihydroxybenzoic acid has been added and dissolved, lower the temperature to 20°C and slowly add dimethyl sulfate dropwise, keeping the temperature below 40°C. After the addition is complete, maintain the temperature at 30-40°C for 6 hours. After the reaction is complete, raise the temperature to 60°C and stir for 30 minutes to completely decompose any unreacted dimethyl sulfate. Then lower the temperature to room temperature and adjust the pH to 1 with 10% hydrochloric acid. A large amount of white solid precipitates out. Centrifuge, wash thoroughly with deionized water, and dry to obtain crude 4-methoxysalicylic acid;
(2) Add the crude 4-methoxysalicylic acid to deionized water, heat to 80°C, stir for 0.5 hours, filter while hot, and dry to obtain pure 4-methoxysalicylic acid;
(3) In a deionized aqueous solution of potassium carbonate, heat to 50°C, slowly add 4-methoxysalicylic acid, adjust pH to 7, stop adding 4-methoxysalicylic acid, stir for 30 minutes, start recovering the solvent, cool down to crystallize, filter, and obtain crude potassium 2-hydroxy-4-methoxybenzoate;
(4) Dissolve the crude potassium 2-hydroxy-4-methoxybenzoate in a 50% ethanol solution, decolorize with activated carbon for 40 minutes, filter, cool down to crystallize, and vacuum dry to obtain pure potassium 2-hydroxy-4-methoxybenzoate.
4MSK (Potassium 2-hydroxy-4-methoxybenzoate) inhibits the activity of the enzyme tyrosinase, which is needed for melanin production. It can be used to lighten and balance skin tone, and reducing dark spots or age spots.
