Methylphosphonyl difluoride (DF), also known as EA-1251[2] or difluoro,[3] is a chemical weapon precursor.

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.

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.

In 2013–2014, the stockpile of chemicals covered by the CWC was removed from Syria and destroyed.