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Attending the lectures of the Cambridge notables: Harry Emeléus


Making boron trifluoride
Norman Greenwood Scientist
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Well, meanwhile of course, other things were going on in the lab, and I clearly had to think of a theme which would be big enough to allow me to use this first month's results, but which would not interfere with other work that was going on in the lab, on interhalogen compounds. And I chanced on the idea that a catalytic agent that was well known was boron trifluoride, like aluminium chloride, it is good at what was called Friedel-Crafts catalysts. And there were some fashionable theories at the time which said that was due to ionic intermediates, and I thought, well, if there are ions there I should be able to find them with my techniques of working under vacuum, high resistivity, but if there is a conductivity, I can measure it, and study it. So I thought that was a good thing, and Emmy approved of that, and typically with Emmy, he said, 'Do you know how to make boron trifluoride?' And so I said, 'Well, not off the top of my head', and he said, 'Well, look it up'. And so... he didn't say it quite so bluntly, but I looked it up, and it was not a difficult prep, but would mean making a bit of apparatus, and handling fluorine, but that was off because I didn't want to handle fluorine; that is a very aggressive thing. So there were other things, of using chlorides and calcium fluoride and things like fluoroborates, which would give the required product.

And so I built this apparatus, and made some of it, and... that is a gas, I might say, at room temperature, is boron trifluoride. And when I'd done this, he said, 'Well done, that didn't take you long. Here's a cylinder of the stuff'. And I wasn't best pleased, I have to say, but looking back on it, of course, it was Emmy's way; if you're going to use a compound, know how to make it. And if you've made it well, okay, don't waste time on it, you're not going to learn anything by making litres and litres of this gas, I have some here. Because he was a consultant with a particular firm which was making fluorine and was making boron trifluoride also, down at Avonmouth near Bristol, and he gave me that. So that was let off the hook, and we can continue the boron trifluoride story later.

Norman Greenwood (1925-2012) was born in Australia and graduated from Melbourne University before going to Cambridge. His wide-ranging research in inorganic and structural chemistry made major advances in the chemistry of boron hydrides and other main-group element compounds. He also pioneered the application of Mössbauer spectroscopy to problems in chemistry. He was a prolific writer and inspirational lecturer on chemical and educational themes, and held numerous visiting professorships throughout the world.

Listeners: Brian Johnson

Professor Brian FG Johnson FRS, FRSE, FRS Chem, FAcad Eu, FAS. Professor of Inorganic Chemistry University of Edinburgh 1991-1995, Professor of Inorganic Chemistry University of Cambridge 1995-2005, Master Fitzwilliam College Cambridge 1999-2005. Research interests include studies of transition metal carbonyls, organometallic chemistry, nano- particles and homogeneous catalysis. Professor Johnson is the author of over 1000 research articles and papers.

Tags: Avonmouth, Bristol, Harry Emeléus

Duration: 2 minutes, 59 seconds

Date story recorded: May 2011

Date story went live: 25 November 2011