2012: Advent Chemistry: Cyanide

by on December 12, 2012

The cyanide ion consists of one carbon, triple-bonded to one nitrogen, with a negative charge on the carbon. And it is, as I’m sure you’re aware, a deadly poison.

The thing is, though, that it’s only the cyanide ion that’s poisonous. The functional group of carbon-triple bond-nitrogen isn’t deadly at all. It’s just another functional group. If a compound doesn’t actually release the cyanide ion then it can contain as much ‘cyanide’ as you like and still be harmless.
Odds are that you’ve worn cyanide – it’s a major component of acrylic fibers. Acrylic is mostly made up of the polymer of acrylonitrile, and the ‘nitrile’ functional group is what cyanide is called in that part of chemistry.

I do hope none of you are panicking about acrylic all of a sudden. The point I’m trying to make isn’t that deadly-chemicals-are-all-around-us-oh-no-help-help. The point I’m making is that chemicals aren’t deadly. They’re just stuff. All the stuff in the world is made of chemicals. Every time one sort of stuff becomes another, a chemical reaction takes place. Acrylonitrile is safe. Acrylic cloth is safe. The CN group is only dangerous in very specialised circumstances, just as the NO2 and aromatic components of TNT are only explosive in exactly the right combination.

Don’t be frightened of things that have chemical names. Every day, the cells in your body manufacture tens of kilograms of adenosine triphosphate – it’s a vital part of energy transfer. You need it to live, just as you need sugar (dextrose monohydrate) and vitamin C (ascorbic acid) and haemoglobin (a metalloprotein) to live. You’re made of stuff, and stuff is chemicals.

I don’t have a picture for you today, because I couldn’t find one of the chemical I wanted to show you. But I do have a molecule to tell you about. In hydrogen cyanide and potassium cyanide, cyanide is deathly poisonous. But in the food additive E538, calcium hexaferrocyanide, six cyanide ions are bound up with one iron and one calcium ion. They’re so tightly bound that it’s inert, unreactive, safe. It’s so safe, that it’s used as an anti-caking agent in table salt.

Chemical names don’t make a thing dangerous. Looking a bit like a dangerous thing doesn’t make a thing dangerous. Containing something that would be dangerous in other circumstances doesn’t make a thing dangerous. If you don’t worry about petrol when it’s in a car, but you do when it’s in a bomb, you understand this already.

Leave a Reply