VX – What is it?

Over this last month or so, the nerve agent VX has hit the headlines for all the wrong reasons but I did think it was worth looking at the chemistry of this molecule in this moths blog post.

The obvious question is what is it?

VX, or, to use the full IUPAC name is actually Ethyl ({2-[bis(propan-2-yl)amino]ethyl}sulfanyl)(methyl)phosphinate. It is referred to as VX as it is a ‘V’ series of nerve agents (‘V’ stands for venom) and was first syntheiszed in the UK in 1952.

The substance itself is very viscous and has a low volatility – it’s texture is said to resemble oil and it belongs to the group of compunds known as organophosphates. Now, organophosphates are found in very important biological compounds, for example DNA and RNA. As well as being used as nerve agents, they are also the basis for many insectidices, herbicides, solvents and plasticizers.

By Ben Mills – Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3735896

The substance itself is tasteless and odourless and a 10mg does, absorbed through the skin is thought to be enough to kill somebody.

It works by blocking the enzyme acetylcholinesterase. This enzyme helps with neurotransmission (the process that allows two neurons to communicate with each other). The blocked enzyme is rendered useless which results in the build-up of a neurotransmitter between the synapses of neurons, ultimately leading to uncontrolled muscle contractions and seizures. Symptoms appear after a couple of minutes – so it is fast acting.

Amazingly, there are antidotes to it, these being atropine and pralidoxime but if not given soon enough, it will be too late to reverse the effects.

Chemically, it is possible to destroy VX by reacting it with strong nucleophiles (eg, concentrated aqueous sodium hydroxide). This will lead to the cleavage of the phosphorous – oxygen and phosphorous – sulfur bonds. This is not as good as it sounds though, as at least one of the products is also toxic!

I hope this blog post hasn’t alarmed you – VX is difficult to manufacture, it is not the sort of chemical you will be able to make one Saturday afternoon in your shed. And at a larger, governmental level, it is classified as a weapon of mass destruction and banned, although some countries are allowed to keep it for research purposes.

It will be interesting to see how the new stories develop over the coming months and if any more details of its use are released.

Do you have any questions about the chemistry of VX? If so, please post them below and I will do my best to answer them!