Soman (or GD, EA 1210, Zoman, PFMP, A-255, systematic name: O-pinacolyl methylphosphonofluoridate)[1] is an extremely toxic chemical substance. It is a nerve agent, interfering with normal functioning of the mammalian nervous system by inhibiting the enzyme cholinesterase. It is an inhibitor of both acetylcholinesterase and butyrylcholinesterase.[2] As a chemical weapon, it is classified as a weapon of mass destruction by the United Nations according to UN Resolution 687. Its production is strictly controlled, and stockpiling is outlawed by the Chemical Weapons Convention of 1993 where it is classified as a Schedule 1 substance. Soman was the third of the so-called G-series nerve agents to be discovered along with GA (tabun), GB (sarin), and GF (cyclosarin).
When pure, soman is a volatile, corrosive, and colorless liquid with a faint odor like that of mothballs or rotten fruit.[3] More commonly, it is a yellow to brown color and has a strong odor described as similar to camphor. The LCt50 for soman is 70 mg·min/m3 in humans.
GD can be thickened for use as a chemical spray using an acryloid copolymer. It can also be deployed as a binary chemical weapon; its precursor chemicals are methylphosphonyl difluoride and a mixture of pinacolyl alcohol and an amine.[3][failed verification]
After World War I, during which mustard gas and phosgene were used as chemical warfare agents, the 1925 Geneva Protocol was signed in an attempt to ban chemical warfare. Nevertheless, research into chemical warfare agents and the use of them continued. In 1936 a new, more dangerous chemical agent was discovered when Gerhard Schrader of IG Farben in Germany isolated tabun (named GA for German Agent A by the United States), the first nerve agent, while developing new insecticides. This discovery was followed by the isolation of sarin (designated GB by the United States) in 1938, also discovered by Schrader.
During World War II, research into nerve agents continued in the United States and Germany. In summer 1944, soman, a colorless liquid with a camphor odor (designated GD by the United States), was developed by the Germans. Soman proved to be even more toxic than tabun and sarin. Nobel Laureate Richard Kuhn together with Konrad Henkel discovered soman during research into the pharmacology of tabun and sarin at the Kaiser Wilhelm Institute for Medical Research at Heidelberg.[4] This research was commissioned by the German Army. Soman was produced in small quantities at a pilot plant at the IG Farben factory in Ludwigshafen. It was never used in World War II.[5]
Producing or stockpiling soman was banned by the 1993 Chemical Weapons Convention. When the convention entered force, the parties declared worldwide stockpiles of 9,057 tonnes of soman. As of December 2015, 84% of the stockpiles had been destroyed.[6]