VX, IUPAC name
O-ethyl
S-[2-(diisopropylamino)ethyl] methylphosphonothioate, is an extremely toxic substance whose only application is in
chemical warfareChemical warfare involves using the toxic properties of chemical substances as weapons. This type of warfare is distinct from Nuclear warfare and Biological warfare, which together make up NBC, the military acronym for Nuclear, Biological, and Chemical...
as a
nerve agentNerve agents are a class of phosphorus-containing organic chemicals that disrupt the mechanism by which nerves transfer messages to organs...
. As a chemical weapon, it is classified as a weapon of mass destruction by the
United NationsThe United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...
in UN Resolution 687. The production and stockpiling of VX was outlawed by the
Chemical Weapons ConventionThe Chemical Weapons Convention is an arms control agreement which outlaws the production, stockpiling and use of chemical weapons. Its full name is the Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction...
of 1993.
The VX
nerve agentNerve agents are a class of phosphorus-containing organic chemicals that disrupt the mechanism by which nerves transfer messages to organs...
is the most well-known of the V-series of nerve agents and is considered an area denial weapon due to its physical properties.
Discovery
Dr. Ranajit Ghosh, a chemist at the Plant Protection Laboratories of
Imperial Chemical IndustriesImperial Chemical Industries was a British chemical company, taken over by AkzoNobel, a Dutch conglomerate, one of the largest chemical producers in the world. In its heyday, ICI was the largest manufacturing company in the British Empire, and commonly regarded as a "bellwether of the British...
based in the
United KingdomThe United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
was investigating a class of
organophosphateAn organophosphate is the general name for esters of phosphoric acid. Phosphates are probably the most pervasive organophosphorus compounds. Many of the most important biochemicals are organophosphates, including DNA and RNA as well as many cofactors that are essential for life...
compounds (organophosphate esters of substituted aminoethanethiols). Like
Gerhard SchraderDr. Gerhard Schrader was a German chemist specializing in the discovery of new insecticides, hoping to make progress in the fight against hunger in the world. However, Dr...
, an earlier investigator of organophosphates, Dr. Ghosh found that they were quite effective
pesticidePesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...
s. In 1954, ICI put one of them on the market under the trade name Amiton. It was subsequently withdrawn, as it was too toxic for safe use. The toxicity did not go unnoticed, and samples of it had been sent to the British Armed Forces research facility at
Porton DownPorton Down is a United Kingdom government and military science park. It is situated slightly northeast of Porton near Salisbury in Wiltshire, England. To the northwest lies the MoD Boscombe Down test range facility which is operated by QinetiQ...
for evaluation. After the evaluation was complete, several members of this class of compounds became a new group of nerve agents, the V agents. The best known of these is probably VX, assigned the UK Rainbow Code
Purple Possum, with the
Russian V-AgentVR is a "V-series" nerve agent closely related to the better-known VX nerve agent....
coming a close second (Amiton is largely forgotten as VG). This class of compounds is also sometimes known as Tammelin's esters, after
Lars-Erik TammelinLars-Erik Tammelin, born 1923, died 1991, was a Swedish chemist, defence researcher and civil servant.Tammelin, who was an organic chemist, was recruited to the Swedish Defence Research Establishment in 1950 for research on nerve gas and nerve gas countermeasures...
of the Swedish Institute of Defense Research. Dr. Tammelin was also conducting research on this class of compounds in 1952, but did not publicize his work widely.
Chemical characteristics
With its high
viscosityViscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
and low
volatilityIn chemistry and physics, volatility is the tendency of a substance to vaporize. Volatility is directly related to a substance's vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure.The term is primarily...
, VX has the texture and feel of motor oil. This makes it especially dangerous, as it has a high persistence in the environment. It is odorless and tasteless, and can be distributed as a liquid, both pure and as a mixture with a polymer in the form of thickened agent, or as an aerosol. It works as a nerve agent by blocking the function of the
enzymeEnzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
acetylcholinesterase"Acetylcholinesterase, also known as AChE or acetylcholine acetylhydrolase, is an enzyme that degrades the neurotransmitter acetylcholine, producing choline and an acetate group. It is mainly found at neuromuscular junctions and cholinergic nervous system, where its activity serves to terminate...
. Normally, an electric nerve pulse would cause the release of
acetylcholineThe chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
over a
synapseIn the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...
that would stimulate muscle contraction. The acetylcholine is then broken down to non-reactive substances (
acetic acidAcetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
and
cholineCholine is a water-soluble essential nutrient. It is usually grouped within the B-complex vitamins. Choline generally refers to the various quaternary ammonium salts containing the N,N,N-trimethylethanolammonium cation....
) by the acetylcholinesterase enzyme. If more muscle tension is needed the nerve must release more acetylcholine. VX blocks the action of acetylcholinesterase, thus resulting in initial violent contractions, followed by sustained supercontraction restricted to the subjunctional endplate sarcoplasm and prolonged depolarizing neuromuscular blockade, the latter resulting in flaccid paralysis of all the muscles in the body. Sustained paralysis of the diaphragm muscle causes death by asphyxiation.
Synthesis
VX is produced via the "transester process". This entails a series of steps whereby
phosphorus trichloridePhosphorus trichloride is a chemical compound of phosphorus and chlorine, having chemical formula PCl3. Its shape is trigonal pyramidal. It is the most important of the three phosphorus chlorides. It is an important industrial chemical, being used for the manufacture of organophosphorus compounds...
is methylated to produce methyl phosphonous dichloride. The resulting material is reacted with
ethanolEthanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
to form a diester. This is then
transesterifiedIn organic chemistry, transesterification is the process of exchanging the organic group R″ of an ester with the organic group R′ of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst...
with N',N'-diisopropylaminoethanol to produce the mixed
phosphonitePhosphonites are organophosphorus compounds with the formula P2R. They are derivivatives of phosphonous acid.- See also :*Phosphine - PR3*Phosphine oxide - OPR3*Phosphinite - PR2*Phosphinate - OPR2...
. Finally, this immediate precursor is reacted with sulfur to form VX.
VX can also be delivered in binary chemical weapons which mix in-flight to form the agent prior to release. Binary VX is referred to as VX2, and is created by mixing aO-(2-diisopropylaminoethyl) O'-ethyl methylphosphonite (
Agent QLIsopropyl aminoethylmethyl phosphonite , also known as O- O'-ethyl methylphosphonite, is a precursor chemical to the nerve agent VX.-Uses in chemical warfare:...
) with elemental sulfur (Agent NE) as is done in the
Bigeye aerial chemical bombThe Bigeye bomb was a proposed U.S. binary chemical weapon. The Bigeye was a glide bomb designed under the auspices of the U.S. Navy. Initially approved by the Carter administration, the program persisted into the early 1990s.-Background:...
. It may also be produced by mixing with sulfur compounds, as with the liquid dimethyl polysulfide mixture (Agent NM) in the canceled XM-768 8-inch binary projectile program.
Solvolysis
Like other
organophosphorusOrganophosphorus compounds are degradable organic compounds containing carbon–phosphorus bonds , used primarily in pest control as an alternative to chlorinated hydrocarbons that persist in the environment...
nerve agents, VX may be destroyed by reaction with strong nucleophiles such as
pralidoximePralidoxime or 2-PAM, usually as the chloride or methiodide salts, belongs to a family of compounds called oximes that bind to organophosphate-inactivated acetylcholinesterase. It is used to combat poisoning by organophosphates or acetylcholinesterase inhibitors , in conjunction with atropine and ...
. The reaction of VX with concentrated aqueous sodium hydroxide results in competing cleavage of the P-O and P-S esters, with P-S cleavage dominating. This is somewhat problematic, since the product of P-O bond cleavage (named EA 2192) remains toxic. In contrast, reaction with the anion of hydrogen peroxide (hydroperoxidolysis) leads to exclusive cleavage of the P-S bond.,
 |
P-S cleavage
NaOH(aq) reacts with VX in two ways. It can cleave VX's P-S bond, yielding two relatively nontoxic products... |
 |
P-O cleavage
...or it can cleave VX's P-O bond, forming ethanol and EA 2192 (shown in red), which has similar toxicity to VX itself |
Biological effects
VX is the most toxic nerve agent ever synthesized for which activity has been independently confirmed. The median lethal dose (LD
50) for humans is estimated to be about 10 milligrams through skin contact and the LCt
50 for inhalation is estimated to be 30–50 mg·min/m³.
Early symptoms of percutaneous exposure (skin contact) may be local muscular twitching or sweating at the area of exposure followed by nausea or vomiting. Some of the early symptoms of a VX vapor exposure to nerve agent may be rhinorrhea (runny nose) and/or tightness in the chest with shortness of breath (bronchial constriction).
MiosisMiosis is the constriction of the pupil of the eye to two millimeters or less...
(pinpointing of the pupils) may be an early sign of agent exposure but is not usually used as the only indicator of exposure.
Treatment
Primary consideration should be given to removal of the liquid agent from the skin before removal of the individual to an uncontaminated area or atmosphere. After removal from the contaminated area, the casualty will be decontaminated by washing the contaminated areas with household bleach and flushing with clean water. After decontamination, the contaminated clothing is removed and skin contamination washed away. If possible, decontamination is completed before the casualty is taken for further medical treatment.
An individual who has received a known nerve-agent exposure or who exhibits definite signs or symptoms of nerve-agent exposure should immediately have the nerve agent antidote drugs
atropineAtropine is a naturally occurring tropane alkaloid extracted from deadly nightshade , Jimson weed , mandrake and other plants of the family Solanaceae. It is a secondary metabolite of these plants and serves as a drug with a wide variety of effects...
,
pralidoximePralidoxime or 2-PAM, usually as the chloride or methiodide salts, belongs to a family of compounds called oximes that bind to organophosphate-inactivated acetylcholinesterase. It is used to combat poisoning by organophosphates or acetylcholinesterase inhibitors , in conjunction with atropine and ...
(2-PAM), and a sedative/antiepileptic such as
diazepamDiazepam , first marketed as Valium by Hoffmann-La Roche is a benzodiazepine drug. Diazepam is also marketed in Australia as Antenex. It is commonly used for treating anxiety, insomnia, seizures including status epilepticus, muscle spasms , restless legs syndrome, alcohol withdrawal,...
injected. In several nations the nerve agent antidotes are issued for military personnel in the form of an
autoinjectorAn autoinjector is a medical device designed to deliver a single dose of a particular drug....
such as the United States military
Mark I NAAKThe Mark I NAAK, or MARK I Kit, is United States military nomenclature for the "Nerve Agent Antidote Kit". It is a dual-chamber autoinjector: Two anti-nerve agent drugs — atropine sulfate and pralidoxime chloride — each in injectable form, constitute the kit. The kits are only effective against the...
.
Atropine works by binding and blocking a subset of acetylcholine receptors (known as
muscarinic acetylcholine receptorMuscarinic receptors, or mAChRs, are acetylcholine receptors that form G protein-coupled in the plasma membranes of certain neurons and other cells...
, mAchR), so that the build up of acetylcholine produced by loss of the acetylcholinesterase function can no longer affect their target. The injection of pralidoxime regenerates bound acetylcholinesterase.
Diagnostic tests
Controlled studies in humans have shown that minimally toxic doses cause 70-75% depression of erythrocyte cholinesterase within several hours of exposure. The serum level of ethyl methylphosphonic acid (EMPA), a VX hydrolysis product, was measured to confirm exposure in one poisoning victim.
History
- For an in-depth discussion, see main article on nerve agent history
The chemists Ranajit Ghosh and J.F. Newman discovered the V-series nerve agents at
ICIImperial Chemical Industries was a British chemical company, taken over by AkzoNobel, a Dutch conglomerate, one of the largest chemical producers in the world. In its heyday, ICI was the largest manufacturing company in the British Empire, and commonly regarded as a "bellwether of the British...
in 1952, patenting diethyl S-2-diethylaminoethyl phosphono- thioate (
agent VGVG is a "V-series" nerve agent chemically similar to the better-known VX nerve agent. Tetram is the common Russian name for the substance...
) in November, 1952. Further commercial research on similar compounds ceased in 1955 when its lethality to humans was discovered. Information on the substance was passed to
Porton DownPorton Down is a United Kingdom government and military science park. It is situated slightly northeast of Porton near Salisbury in Wiltshire, England. To the northwest lies the MoD Boscombe Down test range facility which is operated by QinetiQ...
in 1954 and research there led to VX within a year. This was traded to the United States as the British passed over VX in favor of continuing with
sarinSarin, or GB, is an organophosphorus compound with the formula [2CHO]CH3PF. It is a colorless, odorless liquid, which is used as a chemical weapon. It has been classified as a weapon of mass destruction in UN Resolution 687...
as the UK chemical weapon of choice. The reasoning behind the decision is unclear, although the then recent completion of a sarin production facility at Nancekuke may have played a part.
The US then went into production of large amounts of VX in 1961 at
Newport Chemical DepotThe Newport Chemical Depot, previously known as the Wabash River Ordinance Works and the Newport Army Ammunition Plant, was a bulk chemical storage and destruction facility in west central Indiana, thirty miles north of Terre Haute operated by the United States Army...
.
IraqIraq ; officially the Republic of Iraq is a country in Western Asia spanning most of the northwestern end of the Zagros mountain range, the eastern part of the Syrian Desert and the northern part of the Arabian Desert....
under
Saddam HusseinSaddam Hussein Abd al-Majid al-Tikriti was the fifth President of Iraq, serving in this capacity from 16 July 1979 until 9 April 2003...
admitted to UNSCOM that it had researched VX, but had failed to weaponize the agent due to production failure. After U.S. and allied forces had invaded Iraq, no proof of weaponized VX was found.
In December 1994 and January 1995, Masami Tsuchiya of
Aum ShinrikyoAum Shinrikyo was a Japanese new religious movement. The group was founded by Shoko Asahara in 1984. The group gained international notoriety in 1995, when it carried out the Sarin gas attack on the Tokyo subway....
synthesized 100 to 200 grams of VX which was used to attack three persons. Two persons were injured and one 28-year-old man died, who is believed to be the only victim of VX ever documented in the world. The VX victim, whom
Shoko Asahara, born on March 2, 1955, is a founder of the controversial Japanese new religious group Aum Shinrikyo. He was convicted of masterminding the 1995 sarin gas attack on the Tokyo subway and several other crimes, for which he was sentenced to death...
had suspected as a spy, was attacked at 7:00 am on December 12, 1994 on the street in Osaka by
Tomomitsu Niimiis a former Aum Shinrikyo member indicted for participation in the Sarin gas attack on the Tokyo subway and a number of other crimes. He was Aum's minister of internal affairs....
and another AUM member, who sprinkled the nerve agent on his neck. He chased them for about 100 yards (90 metres) before collapsing, dying 10 days later without ever coming out of a deep coma. Doctors in the hospital suspected at the time he had been poisoned with an organophosphate pesticide. But the cause of death was pinned down only after cult members arrested for the
subway attackThe Sarin attack on the Tokyo subway, usually referred to in the Japanese media as the , was an act of domestic terrorism perpetrated by members of Aum Shinrikyo on March 20, 1995....
confessed to the killing. Ethyl methylphosphonate, methylphosphonic acid and diisopropyl-2-(methylthio) ethylamine were later found in the body of the victim. Unlike the cases for
sarinSarin, or GB, is an organophosphorus compound with the formula [2CHO]CH3PF. It is a colorless, odorless liquid, which is used as a chemical weapon. It has been classified as a weapon of mass destruction in UN Resolution 687...
(
Matsumoto incidentThe Matsumoto incident was an act of domestic terrorism perpetrated by members of Aum Shinrikyo in Matsumoto, Japan, in Nagano prefecture, on the evening of June 27 and the morning of June 28, 1994....
and
Sarin gas attack on the Tokyo subwayThe Sarin attack on the Tokyo subway, usually referred to in the Japanese media as the , was an act of domestic terrorism perpetrated by members of Aum Shinrikyo on March 20, 1995....
), VX was not used for mass murder.
The only countries known to possess VX are the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
and
RussiaRussia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
. A
SudanSudan , officially the Republic of the Sudan , is a country in North Africa, sometimes considered part of the Middle East politically. It is bordered by Egypt to the north, the Red Sea to the northeast, Eritrea and Ethiopia to the east, South Sudan to the south, the Central African Republic to the...
ese
pharmaceutical facilityThe Al-Shifa pharmaceutical factory in Khartoum North, Sudan, was constructed between 1992 and 1996 with components imported from the United States, Sweden, Italy, Switzerland, Germany, India, and Thailand....
was bombed by the U.S. in 1998 acting on information that it used VX and that the origin of the agent was associated with both Iraq and Al Qaeda. The chemical in question was later identified as O-ethyl hydrogen methylphosphonothioate (EMPTA), used as a precursor in the production of VX. It is also used to treat seeds and turf grasses.
US VX stockpile elimination
In the late 1960s, the US canceled its chemical weapons programs and began the destruction of its stockpiles of agents by a variety of methods. Early disposal included the US Army's
CHASEOperation CHASE was a United States Department of Defense program that involved the disposal of unwanted munitions at sea from May 1964 into the early 1970s....
(Cut Holes And Sink 'Em) program, in which old ships were filled with chemical weapons stockpiles and then
scuttledScuttling is the act of deliberately sinking a ship by allowing water to flow into the hull.This can be achieved in several ways—valves or hatches can be opened to the sea, or holes may be ripped into the hull with brute force or with explosives...
. CHASE 8 was conducted on June 15, 1967, in which the S.S.
Cpl. Eric G. Gibson was filled with 7,380 VX rockets and scuttled in 7200 feet (2,194.6 m) of water, off the coast of
Atlantic City, New JerseyAtlantic City is a city in Atlantic County, New Jersey, United States, and a nationally renowned resort city for gambling, shopping and fine dining. The city also served as the inspiration for the American version of the board game Monopoly. Atlantic City is located on Absecon Island on the coast...
.
As of FY2008 the US Department of Defense reported dumping at least 124 tons of VX into the Atlantic Ocean off the coasts of New York/New Jersey and Florida. This material consisted of nearly 22,000
M55 rocketThe M55 rocket was a chemical weapon developed by the United States in the 1950s. The United States Army produced both Sarin and VX unitary warheads for the M55.-History:...
s, 19 bulk containers holding 1400 pounds (635 kg) each, and one
M23 chemical landmineThe M23 is a U.S. steel cased chemical landmine. The mine was developed in the late 1950s and early 1960s and approximately 100,000 were produced. The U.S...
.
IncinerationIncineration is a waste treatment process that involves the combustion of organic substances contained in waste materials. Incineration and other high temperature waste treatment systems are described as "thermal treatment". Incineration of waste materials converts the waste into ash, flue gas, and...
was used for VX stockpile destruction starting in 1990 with
Johnston Atoll Chemical Agent Disposal SystemJohnston Atoll Chemical Agent Disposal System was the U.S. Army's first chemical munitions disposal facility. It was located on Johnston Island, at Johnston Atoll and completed its mission and ceased operation in 2000.-Background:...
in the North Pacific with other incineration plants following at
Deseret Chemical DepotThe Deseret Chemical Depot is a U.S. Army chemical weapon storage area located in Utah, 60 miles southwest of Salt Lake City. It is related to the Tooele Chemical Agent Disposal Facility.-History:...
,
Pine Bluff ArsenalThe Pine Bluff Arsenal is a US Army installation located in Jefferson County, Arkansas, just northwest of the city of Pine Bluff. PBA is one of the six Army installations in the United States that store chemical weapons...
,
Umatilla Chemical DepotThe Umatilla Chemical Depot, based in Umatilla, Oregon, was a U.S. Army installations in the United States that stored chemical weapons. The chemical weapons originally stored at the depot consisted of various munitions and ton containers containing GB and VX nerve agents and HD blister agent...
and
Anniston Army DepotAnniston Army Depot is a major United States Army facility fulfilling various depot operations. Primary missions are the repair of tracked vehicles and storage of chemical weapons . The depot is located in Bynum, Alabama....
with the last of the VX inventory destroyed on December 24, 2008.
The
Newport Chemical DepotThe Newport Chemical Depot, previously known as the Wabash River Ordinance Works and the Newport Army Ammunition Plant, was a bulk chemical storage and destruction facility in west central Indiana, thirty miles north of Terre Haute operated by the United States Army...
began VX stockpile elimination using chemical neutralization in 2005. VX was hydrolyzed to much less toxic byproducts by using concentrated caustic solution, and the resulting waste was then shipped off-site for further processing. Technical and political issues regarding this secondary byproduct resulted in delays, but the depot completed their VX stockpile destruction in August, 2008.
Worldwide VX stockpile elimination
Worldwide, VX disposal has continued since 1997 under the mandate of the
Chemical Weapons ConventionThe Chemical Weapons Convention is an arms control agreement which outlaws the production, stockpiling and use of chemical weapons. Its full name is the Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction...
.
In Russia, the US is providing support for these destruction activities with the Nunn-Lugar program. The Nunn-Lugar program has been able to convert a former chemical weapons depot at
ShchuchyeShchuchye is a town and the administrative center of Shchuchansky District of Kurgan Oblast, Russia, located on Lake Shchuchye, west of Kurgan...
,
Kurgan OblastKurgan Oblast is a federal subject of Russia . Its administrative center is the city of Kurgan. Population: -History:The oblast was formed on February 6, 1943, just when the Soviet Army decisively defeated Hitler's forces near Stalingrad...
, into a facility to destroy those chemical weapons. The new facility, which opened in May 2009, has been working on eliminating the nearly 5,950 tons of nerve agents held at the former storage complex. However, this facility only holds about 14% of Russian chemical weapons that are stored throughout seven sites.
Another such destruction plant for Russia, built for €140 million and paid for by Germany, is to open at Potshep,
Bryansk OblastBryansk Oblast is a federal subject of Russia . Its administrative center is the city of Bryansk. Population: 1,278,087 .-History:...
, in 2009.
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