Dimethyl carbonate is referred to as DMC. It is a colorless, transparent liquid with a pungent odor at room temperature. Its relative density (d204) is 1.0694, its melting point is 4℃, its boiling point is 90.3℃, its flash point is 21.7℃ (open) and 16.7℃ (closed), its refractive index (nd20) is 1.3687, and it is flammable and non-toxic. It can be mixed with almost all organic solvents such as alcohols, ketones, and esters in any proportion and is slightly soluble in water. It can be used as a methylation agent. Compared with other methylation agents, such as iodomethane and dimethyl sulfate, dimethyl carbonate is less toxic and can be biodegraded. The previous method of using phosgene as a raw material to prepare dimethyl carbonate is no longer commonly used. Instead, it is prepared by catalytic oxidation carbonylation of methanol in the presence of oxygen, which is more environmentally friendly than the previous method. Dimethyl carbonate can methylate aniline, phenol and carboxylic acid, but many reactions require high pressure. DBU can be added during the refluxing of DMC to catalyze the methylation of dimethyl carbonate to carboxylic acid: