2-(3-Oxoisobenzofuran-1(3H)-ylidene)-2-phenyl-d5-acetic Acid (E/Z Mixture) is a labeled derivative of Phthalic Anhydride (P384485), an important industrial chemical commonly used in large-scale production of plasticizers for plastics. Recent research have also evaluated Phthalic Anhydride as potential antibacterial agent.