Oxygen difluoride as a commercial reagent.

[NNadir]

Oxygen difluoride holds a very special place in the history of chemistry in my view, owing to the fact that its existence stimulated the great chemist Neil Bartlett, at UC Berkeley, to develop the chemistry of the noble gases.

Recognizing that the ionization potential of oxygen and xenon were very close, Barlett surmised that xenon should have chemistry: Until that time it was thought that all of the noble gases, helium, neon, argon, krypton and xenon (and to be complete, radon) were unable to form chemical compounds. Bartlett recognized that if oxygen could form a cationic compound with fluorine, then it was very likely that xenon could do so well.

Bartlett then synthesized Xe⁺(PtF₆^-), the very first stable chemically bonded compound of a noble gas. Later many other noble gas compounds were identified, such as xenon hexafluoride, xenon difluoride, krypton difluoride (about which I'll say a little more below).

Maybe Bartlett's noble work deserved a Nobel, but for some reason, he didn't win it.

Xenon hexafluoride is an interesting and somewhat dangerous compound inasmuch as if it gets wet it is rapidly hydrolyzed to give HF and XeO₃ (in equilibrium with "xenic acid," which is if it is allowed to dry, can and does spontaneously explode, leaving not a trace of its existence. (This is why xenon headlights should be banned, for their terrorist potential, but no, let's not go there.)

Anyway, about oxygen difluoride: I have always thought of it as a laboratory curiosity of no practical significance until now.

On another website where I read and write sometimes, I was recently discussing the fluorination of molten salts from the MSRE, the molten salt reactor experiment, where uranium was decontaminated from fission products in a matter of hours by distillation in a stream of fluorine gas.

I have always assumed that the plutonium was carried with the uranium, at least partially, but apparently according to those who have delved into the particular ORNL documents more than I have, this was not true.

The problem is that while PuF₆ is stable in a stream of fluorine gas, it is only slowly formed from PuF₄ by direct fluorination. This made a problem for the ORNL guys in removing the plutonium from their molten salt mixture.

Not to worry though. I checked back through my files and found a paper out of Los Alamos by Mills and Reese touching on this point, Journal of Alloys and Compounds, 213/214 (1994) 360-362 "Separation of plutonium and americium by low-temperature fluorination"

The fluorinating agent in this case is well, oxygen difluoride, which is made by direct reaction using a cryogenic trap, between fluorine and oxygen. When the oxygen fluoride gas is allowed to boil off on to plutonium tetrafluoride, the volatile plutonium hexafluoride gas.

This is considered an excellent way to remove plutonium from americium (and curium), since americium and curium both are more "lanthanide like" than plutonium, even if americium has a well defined +5 oxidation state. (Separations of curium and americium are more difficult, by the way.)

Thus in a modern pyroprocessing system, avoiding the limitations of solvent based extraction systems, which suffer limited stability in high radiation fields. (This is not true, by the way of so called "ionic liquids" in which it is possible to form plutonium electride salts in high radiation fields.) This sort of thing will become increasingly important should humanity seriously attempt to address climate change. Interestingly this chemistry should be very clean, resulting only in HF and plutonium oxide with no residual solvents. HF is easily neutralized with calcium carbonate to give insoluble CaF₂, the mineral fluorite from which most fluorine is currently mined and carbon dioxide.

Another paper that touches on exotic compounds being used to make plutonium hexafluoride is work by Yu. V. Drobyshevskii, V. N. Prusakov and V. F. Serik out of the I. V. Kurchatov Institute of Atomic Energy, out of so called "classified abstracts." These scientists observed PuF₄ in equilibrium with very low temperature KrF₂ and found that there was a solid phase reaction at the interface between the two solids to give gaseous PuF₆.

Esoteric I guess, but cool nonetheless.

[Orrex]

1. I'm sorry to admit that I always had trouble with chemistry

Inasmuch as this layman knows anything about any branch of science, chemistry has always been my weakest subject.

Still, this does indeed sound very cool, esoteric or not.

Thanks for the post!

[seeviewonder]

2. Are you a chem major or have a chem degree by any chance?

I'm working on a B.S. in chemistry right now and should have it finished within the next two semesters. Just wondering!

[NNadir]

3. Thanks for thinking I'm young.

Welcome to the field.

Chemistry is the most critical science, but it's been sort of an ugly stepchild in the public imagination.

In your career I hope you will join the ACS and take part in ACS life.

The American Chemical Society and the Democratic Party are the only things of which I remain a member, and the benefits of the first have been enormous.

If you really, really, really, really want to do so something cool, get a Ph.D. in nuclear chemistry. You'll never be out of a job.

[seeviewonder]

4. I actually have a textbook on Radiochemistry/Nuclear Chemsitry

co-authored by Jan Rydberg. I originally wanted to go into that specialized field instead of biochemistry or organic since that seemed to be the way everyone else was going at the time I entered school. Also, a lot of universities did not offer a specialty in that sub-field. I would absolutely love to get into that specialized field but it doesn't look like I'll be able to anytime soon. Also, I am an ACS Student Affiliate already and I intend on becoming a full-fledged member once I am finished with my degree and in the industry.

[NNadir]

5. Well, it is true that nuclear science has been under assault by people who don't, um,

know anything at all about, um, nuclear science.

As a result funding has been cut for nuclear chemistry programs.

Nevertheless, there is a nuclear chemistry section at ACS, and there are many fascinating talks at the meetings. You can still find programs if you look.

You should know that among nuclear chemistry graduate students, only a small percentage have ever taken a course purely devoted to the field as undergraduates.

A good solid understanding of basic chemical concepts are all you really need. Every thing you see in inorganic and organic chemistry is involved, with the added excitement of changing the nature of the matter in the reaction system, and a flux of very interesting forms of energy.

In nuclear science one can see the existance of cesium metal in the presence of halogens like iodine and bromine, in nuclear science, the wave functions of electrons call for relativistic corrections in shielding coefficients.

I'm biased of course, but I cannot think of a more exciting science.

The former President of the ACS and, for my money, the most outstanding chemist of the twentieth century, in a nation that produced Woodward, Hoffman, Corey and many others, Glenn Seaborg was a nuclear chemist.

These are great giant shoulders to stand on.