1 post tagged “janus”
Published in CHEMTECH June 1999 as "The Janus Element"
Books I wish had never been written: No. 1 The Periodic Table (Il Tavolo Periodico) by Primo Levi. That’s about it, really. Not that it is a bad book - quite the reverse. I regard it as the best book ever written by a chemist. If you have never read it, you must. No, my problem is that I wish I had written something similar myself, first.
Levi was an Italian Jew whose career spanned the war. His book is autobiographical, and each chapter, named after an element, relates a period of his life and how that element impinged on it.
A super idea, something that every chemist should emulate. But the lay public is probably not ready for thousands of “Periodic Tables”, so we will have to write for each other, in columns such as this, or via an internet discussion group. (Does anyone know if such a group exists already?).
The element that has haunted me most throughout my career, flickering into my consciousness like the will-of-the wisps it causes, is phosphorus. I see it as a Janus element, along with nitrogen and chlorine, a bringer of life and death, essential but much abused. Regular readers of this column will know that the burning red allotrope impinged on me quite literally in the sixth form, and inorganic phosphates caused me no end of frustration while I was working for my D Phil, but I want to concentrate here on neurotoxins.
The chain of thoughts that led me back to Levi’s book, and to my own phosphorus “chapter”, began Proust-like with an apparently unrelated, trivial incident. I needed to send some flammable adhesives across the Atlantic, and therefore needed to encase them in United Nations approved packages. This eminently reasonable interference by an international body in chemical commerce brought to mind a more irritating example from my previous job working with polyurethane foams. Dimethyl methylphosphonate (dmmp) was a marvellous, innocuous additive for foam formulations, reducing viscosities and improving fire retardance without any loss of performance.
Unfortunately, it can also be a precursor for much nastier materials, so the UN declared it a controlled substance, and our supplier withdrew it. Sensible, perhaps? Well, not really. It’s no harder to make dmmp than it is to react it further. Anyone with the ability to synthesise the toxins could easily make the raw material. But whatever the merits of the case, the recollection established in my mind the link between beneficial phosphorus compounds and their lethal derivatives.
My mental rewind then took me back to a previous stage in my career, to when I was working with acrylic fibres. Phosphorus in various forms is often used to reduce the flammability of synthetic fibres. It was already known that polymers based on trimethylolpropane (tmp) caused problems in fires if there was phosphorus around. Bizarrely, the beautiful, innocent-looking by-product molecule
is intensely toxic, interfering with the function of acetylcholine. But that shouldn’t have been a problem - there were no traces of tmp in our acrylic fibres. We merely wanted to copolymerise a few percent of a vinylphosphonate with the main constituent, acrylonitrile. We were carrying out the reactions in concentrated aqueous sodium thiocyanate, a good solvent for polyacrylonitrile. Things were going well - the expected level of phosphorous was being incorporated in the fibre, the fibres were showing the expected improvements in limiting oxygen index. But the solutions had an unpleasant mustardy smell. Head space analysis showed that for the diethyl vinylphosphonate we were making traces of either ethyl thiocyanate (Toxic) or ethyl isothiocyanate - an early nerve gas. The phosphonate ester was acting as an alkylating agent. When we used bis-beta chloroethyl vinylphosphonate
CH2=CH-PO(OCH2CH2Cl)2
the solutions smelled even worse, but we couldn’t detect anything. Heaven knows what we were making - we didn’t wait to find out, but closed the project immediately.
Typical of phosphorus. It has been an untrustworthy friend to humanity since the beginnings of the industrial revolution, since match workers started to develop “Phossy jaw”. But also typical of the fascination of chemistry. We think we understand our subject, but there are surprises around every corner. Delightful surprises most of the time, but we never know when we’re going to wake a Balrog. So the incident is also a reminder of the dangers of hubris. Industrial chemists and their managers aren’t bad people, but an arrogant faith in our control over the elements has brought much misery, sick operatives and sterile rivers. The chemical industry has a poor reputation, a public perception of a corporate cavalier attitude to employee safety and the environment, a perception shamefully accurate until relatively recently. We need to remember that our subject is two-faced. Will-of-the wisps are bewitching phenomena. They have led people to their deaths.
