Fields of influence
CHEMISTS ARE used to harnessing all sorts of subtle and not-so-subtle tools to choreograph the dance of molecules; from lasers to microwaves to plain old heating and stirring. But now, in a few labs around the world, an unusual new idea is crackling and sparking into life: chemists are starting to explore whether electric fields can be used to control reactions too.
At first blush, electric fields might seem like an untameable partner; could such a diffuse force really be used to influence the making and breaking of individual bonds? But a stunning experiment conducted early in 2017 showed for the first time that this is precisely what can be done. Set things up just right, and these fields can conjure chemistry in supercharged style. Now the race is on to see where this control could take us.
The spark for this revolution came from Sason Shaik in 1974, when he was sitting in a small, dim lecture hall at the University of Washington in Seattle, US. The lecturer was a man who had a habit of waving his arms and hands around to act out the motions of atoms and molecules. ‘This was very vivid, so I always listened attentively,’ says Shaik. On this particular day, the lecturer was describing a catalyst: a molecule that can speed up the rate of a reaction without itself getting used up. But not any old catalyst; this one sped up a reaction a million times. ‘I was pretty impressed,’ says Shaik, who is now at the Hebrew University in Jerusalem, Israel. ‘I thought: this is like the best of the best.’
What Shaik had heard about was a reaction involving tertiary butyl chloride. Dissolved in ether, only a tiny fraction of the molecules will split at the carbon-chlorine bond. But add a high concentration (5.5M) of a simple salt, lithium perchlorate, and the rate of bond-breaking goes up a million fold.
It’s not such a useful reaction in itself but this simple salt catalyst did an almost unbelievably good job of speeding it up. Shaik wanted to know how. He soon realised that at such high concentrations, each catalyst molecule could only have about two solvent molecules around it. In other words, it was dominating the whole set up, and he suspected it could be setting up a liquid crystal-like matrix and perhaps introducing an electric field into the solution. It could be that electric field which drives the catalysis, he thought.
Shaik never got to the bottom of exactly how the lithium perchlorate catalysis works; his focus was on building a research career studying reactivity using valence bond theory. But the problem did stick in his mind and he began to think that electric field catalysis wasn’t such an outlandish idea.
Read the rest of this feature at Chemistry World here (subscription required).
Picture credit: Tjflex2, flickr