Methylphosphonyl difluoride (DF), also known as EA-1251^[2] or difluoro,^[3] is a chemical weapon precursor. Its chemical formula is CH₃POF₂. It is a Schedule 1 substance under the Chemical Weapons Convention. It is used for production of sarin and soman as a component of binary chemical weapons; an example is the M687 artillery shell, where it is used together with a mixture of isopropyl alcohol and isopropyl amine, producing sarin.

Methylphosphonyl difluoride can be prepared by reacting methylphosphonyl dichloride with hydrogen fluoride (HF) or sodium fluoride (NaF).

Methylphosphonyl difluoride is both reactive and corrosive. It is absorbed through skin and causes burns and mild nerve agent symptoms. It reacts with water, producing HF fumes and methylphosphonic acid as a result. It is also capable of corroding glass.

In 2013–2014, the stockpile of chemicals covered by the CWC was removed from Syria and destroyed. Of the stockpile, 581 tons (over 96%) of the stockpile was DF. It was destroyed by the U.S. Army on the MV Cape Ray by hydrolysis.^[4][5]