Method for preparing 3-methoxy-4-hydroxybenzaldehyde

The invention discloses a method for preparing 3-methoxy-4-hydroxybenzaldehyde. The method comprises the following steps of firstly processing guaiacol and glyoxylic acid by sodium hydroxide to obtain guaiacol sodium and sodium glyoxylate, dropwise adding a sodium glyoxylate solution into a guaiacol sodium solution while controlling the dropwise addition speed, reacting for 4-7 hours, adjusting the pH value, and adding a certain amount of mesoporous copper oxide, by reasonably controlling the pressure, intensity of pressure, temperature, the pH value of a reaction medium, and the molar ratio of MHPA to CuO of an oxidation reaction, reacting to obtain a reaction liquid, decarboxylating the reaction liquid with 50% sulfuric acid, removing an over-oxidized product with saturated sodium hydrogen carbonate, extracting and separating to obtain 3-methoxy-4-hydroxybenzaldehyde. By the advantage that mesoporous copper oxide has large specific surface area, the usage amount of a catalyst is greatly decreased; since ethyl acetate is adopted during the processing process and clean oxygen is adopted as an oxidant, the environmental pollution caused by organic solvents such as toluene is avoided and the catalyst is easily separated and recycled and is stable in performance.