The alkylation in the steel salt of 2-hydroxy-5-methoxy benzaldehyde with dimethylsulfate is often done in almost any solvent or blend of solvents by which the metallic salt has ample solubility and the dimethylsulfate has superior security. By way of example, appropriate solvents include reduced molecular body weight alcohols for example https://citychems.com/product/buy-2c-e-4-ethyl-25-dimethoxy/