Synthesis (1) combines 2, 4? Dihydroxybenzoic acid is slowly added to an alkaline aqueous solution of sodium hydroxide, with a temperature controlled below 30 ℃. When 2, 4? After all the dihydroxybenzoic acid is added and dissolved, cool it down to 20 ℃, slowly add dimethyl sulfate dropwise, and control the temperature below 40 ℃. After the dropwise addition, keep it at 30-40 ℃ for 6 hours. After the reaction is completed, heat it up to 60 ℃, stir for 30 minutes, and allow the unreacted dimethyl sulfate to completely decompose. Then, cool it down to room temperature, adjust the pH to 1 with 10% hydrochloric acid, and a large amount of white solid material will precipitate. Centrifuge it, rinse it with deionized water, dry it, and obtain 4? Methoxysalicylic acid crude product; (2) Will 4? Add crude methoxysalicylic acid to deionized water, heat to 80 ℃, stir for 0.5 hours, filter while hot, and dry to obtain 4? Methoxysalicylic acid pure product; (3) In a deionized aqueous solution of potassium carbonate, heat up to 50 ℃ and slowly add 4? When adjusting the pH of methoxyChemicalbook based salicylic acid to 7, stop adding 4? Methoxysalicylic acid, stir for 30 minutes, start solvent recovery, cool and crystallize, and filter to obtain 4? Potassium methoxysalicylate crude product; (4) Will 4? Dissolve the crude potassium methoxysalicylate in a 50% ethanol solution, decolorize with activated carbon for 40 minutes, filter, cool and crystallize, and vacuum dry to obtain 4? Potassium methoxysalicylate pure product. 4-Methoxysalicylate potassium (4-Methoxysalicylate potassium) has a structure similar to salicylic acid and is a new type of medicinal whitening ingredient. It is used in cosmetics to have a whitening effect and is an effective ingredient in cosmetics. Potassium 4-methoxysalicylate can coordinate keratin metabolism, correct abnormal epidermal growth, promote the discharge of melanin, and achieve smooth and whitening skin; It can also block the source of melanin production and enhance self-healing ability. When used in combination with various types of whitening products, it can improve the whitening effect and has good development prospects.