Dimethyl phthalate is an organic compound with molecular formula (C2H3O2)2C6H4. The methyl ester of phthalic acid, it is a colorless liquid that is soluble in organic solvents. Dimethyl phthalate is an organic compound with molecular formula (C2H3O2)2C6H4. The methyl ester of phthalic acid, it is a colorless liquid that is soluble in organic solvents. Dimethyl phthalate is used as an insect repellent for mosquitoes and flies. It is also an ectoparasiticide and has many other uses, including in solid rocket propellants, and plastics. Its LD50 is 8200 mg/kg (rats, oral).