It was reported in 1993 that BP Chemical, a US company, had a process that it was ready to license to the Iranians, who said they wanted it to produce acrylics. But the plant would also have produced hydrogen cyanide as a by-product, and that was a poison gas. The White House had stopped the deal.
Strict export controls are necessary to block deliberate export of equipment and chemicals needed to manufacture gases for chemical warfare.
Even though some of the chemicals are not particularly dangerous, they should not be sold to countries that are working on chemical weapons.
Many of the substances sold to countries with chemical weapons programmes are of "dual use", meaning they can have legitimate applications in pesticides, dyes or even ink for ballpoint pens. Developing countries have sometimes portrayed the calls for export controls as "colonialism" by Western countries and advocate instead a worldwide ban on chemical weapons.
Hydrogen cyanide is one of the least effective gas weapons – among other things, it is lighter than air – and in any case there are much cheaper ways to make it than as a by-product of acrylics production.