Isopropyl aminoethylmethyl phosphonite (NATO designation QL), also known as O-(2-diisopropylaminoethyl) O′-ethyl methylphosphonite, is a precursor chemical to the nerve agent VX and VR-56.

It is a colorless liquid with a strong fishy odor, and is slightly soluble in water.

[2] QL is a component in binary chemical weapons, mainly VX nerve agent.

[3] It, along with methylphosphonyl difluoride (DF), was developed during the 1980s in order to replace an aging stockpile of unitary chemical weapons.

[5] However, when reacting with sulfur, the corresponding sulfide of QL isomerizes into the highly toxic VX molecule.