It’s one thing you can use, especially if you’re a fan of Dexter, but back in the real world we already control the actual precursor Methylphosphonyl difluoride. If you take sodium cyanide and drop it into H2SO4 and water, you get poison gas. If you want to stop that, control the production and export of cyanide, not the water or sulphuric acid!

Isopropyl alcohol is not a chemical weapon precursor, just like water isn’t a cyanide gas precursor.