Radon and your lungs

Dear Reader,

I suspect that the next post is going to make people hopping mad with me, it is about the idea of using radon-222 as a medical treatment. Now before we go any further I would like to point out that I have no vested interest in the radon industry. Nor do I have a personal grudge against the radon therapy industry.

Now we will begin, I come from a school of thought that holds the view that radon-222 is horrible, this school of thought is the vast collection of people in the radioactivity business who live to hate radium-226 and its daughters. Rather than being a nice playful radioisotope radium-226 is considered to be a nasty so and so. It is an alpha emitter which forms a volatile daughter which also emits an alpha and then attaches its self to dust and smoke particles. In this way it creates a horror of sticky alpha active bits which stick in the lungs and do you a lot of harm.

By comparison plutonium-239 is a much nicer radioisotope to work with, it will not diffuse through gloves or fly through the air with great ease.

Some time ago a student (Hanna) at Chalmers was starting a PhD in radium chemistry, and she had a problem. She needed to work in a glove box. The state regulator were not willing to license the work unless it could be shown that the radon was trapped rather than being dumped up the stack. As an inorganic chemist I got involved, I applied what I know about zeolites and xenon to the problem and I then told the young lady of the joys of silver exchanged zeolite. This then resulted in a paper on radon and silver (Hanna Hedström, Mark Foreman, Christian Ekberg  and Henrik Ramebäck, Radiochimica Acta, 2012, 100(6), 395). We will keep the radon and silver story for another day, back to radon.

I checked the yearly intake limit for radon-222 and for inhalation it is 10 mCi when it is pure, but it is normally encountered with the daughters present. The limit when the daughters are present is 100 μCi (0.1 mCi). For comparison polonium-210 (half life 140 days) has a limit which is lower at 600 nCi per year, I would reason that the longer effective half life of the polonium in a human is likely to be responsible (at least in part) for this difference.

So I went and looked for a short lived noble gas, so I looked at the limit for xenon-133 (5.2 day half life), while there is no ALI for this isotope there is a DAC of 100 nCi (0.1 μCi) per litre. The DAC is a derived air concentration which is the limit for the air which you can breathe for 40 hours a week for one year.

I checked the DAC for radon-222 and it was much lower at 0.00003 μCi per litre (when the daughters are present), which works out as 0.03 nCi per litre or 3 pCi per litre. Now it should be clear to you that the USA’s goverment (NRC) hold the view that radon is very much worse for your health than xenon-133 is.

Even if we use their DAC for radon when the daughters are absent (400 pCi per litre) it is a lot worse than the xenon. We need to ask ourselves why.

Lets start by considering the decay energy, the xenon isotope is a mixed beta / gamma emitter which has an average beta energy of 100 keV. If we ignore skin exposure for a moment and only consider the beta dose to the lungs then 100 nCi (3700 Bq) of xenon-133 in air will deliver 370 MeV of energy into your lungs per second.

The alpha decay energy of the radon is 5489.52 keV, 14.8 Bq (400 pCi) of radon-222 will deliver 81.244896 MeV of energy into your lungs (call that 81.2 MeV) which is less energy. But alpha (α) is a high LET radiation which is considered (on the basis of energy delivered) to be 20 times more harmful to your cells than beta (β) or gamma (γ) radiation. So the effect of the radon on the lungs at the limit will be 4.4 times as harmful as the effect of the beta decay of the xenon.

The biggest problem with the radon is that it forms solid radioactive daughters which emit alpha particles, these daughters can lodge in the lungs where they continue to deliver radiation to the lung tissue. The atoms of radon are likely to come out of you when your breath out (some will diffuse into your blood and then go into the fatty tissues). So as a result you can imagine that radon is considered to be a grave threat to the lungs, it is worst when smoke or dust is present.

I recently spoke with a medical doctor from the Czech republic who runs a radon bath treatment site. He told me that in the Czech Republic that inhalation therapy was banned, he told me that one reason was worker safety. He told me that a patient is immersed in a bath of water (circa 5 kBq per litre) in a air conditioned room. The person is kept very still in the bath, I imagine that by avoiding splashing and stirring of the bath that the rate at which the radon is transferred into the air is reduced.

I also imagine that the Czech treatment room is a damp place which should reduce the number of dust particles per litre of air, this dampness will reduce the likelihood of radioactive dust entering a person’s lungs. I think that a bad environment for radon is always a dry and dusty place, the addition of smoke to radon containing air will always make it even worse. I have horrible visions of a uranium miner having a smoke in the mine while driving a poorly maintained diesel truck in the mine. Both the diesel and the tobacco smoke will increase the harm which the radon will do to his lungs.

A better situation would be the same miner now wearing a dust mask driving a well maintained truck in the mine. While I hold the view that it would be best if the miner gave up smoking totally, if he (or she) abstains from smoking in the mine then it would very good for the worker’s health.

So at least in the Czech Republic some steps have been taken to reduce the amount of lung damage.

Now from what I have read so far it is clear that radon therapy does bring with it a risk. I am sure that the supporters of radon treatment and others will point out that no medical treatment is totally without risk. I agree fully on this point, I have never heard of a medical procedure which is perfectly risk free.

But for a medical procedure to be justified, the benefits must out weigh the risks and costs. I will move onto benefit vs cost later.

Bhopal cleanup

Dear Reader,

I was glad to read that something is being done about the Bhopal site, I have held the view for a long time that the Bhopal event is a horrible industrial accident which could have been prevented or at least mitigated with great ease. But due to cost cutting at the plant a horrible toxic gas leak occurred which had on off site effect which was far more horrible than Chernobyl.

I may write more about the event later.

If you think that Chernobyl was ugly, then take a look at the Bhopal event ! The reason I think that the Indian accident was worse was that the death toll (general public) was far higher. Chernobyl can not be proven to have killed any member of the general public, while the Bhopal pesticide factory accident gassed to death thousands of local people.

I think that care needs to be taken to make sure that the clean up is done in a careful way which does not create a new threat to either the health / safety of the local people (+ workers) or a new threat to the environment.

Alternative blankets for fusion reactors

Dear Reader,

While reading about fusion reactors, I noticed that an alternative molten salt can be used, this is a 1:1:1 mixture of LiF, NaF and BeF2. I expect that this will be rather similar to Li2BeF4 but I could not resist having a look in the crystallography database. I found that a report exists of Na3Li.2[BeF4] (J. Vicat, Duc Tran Qui, S. Aleonard and P. Richard, Acta Crystallographica B, 1974, 30(11), 2678-2682).

This is a more complex solid that the Li2BeF4, the lithium is five coordinate (distorted trigonal based pyramidal).

A view of the coordination environment of the lithium. The lithium in orchid, the sodium is in yellow, the flourine in green and the beryllium in blue.

Two of the sodiums has a distorted square based pyramidal geometry. (Na1 and Na2). While Na3 is six coordinate the geometry is so distorted away from octahedral that I can not tell what it is. Here is a picture of Na1′s coordination environment.

The coordination environment of Na1

One of the berylliums (Be1) is has a nice and regular looking tetrahedral environment. I think that the important thing is that with the Be:F ratio of 1:4 we have the nice tetrahedrons.

The coordination environment of Be1

The other (Be2) has a distorted tetrahedral environment (one bond is longer than the others, this is the bond to the flourine bonding to the sodium and the lithium).

Coordination environment of Be2

Also a report exists of a Na2LiBeF7 by G. Brunton, Materials Research Bulletin, 1972, 7, 641-646. I will get onto that one in the next post on Be chemistry.

Toad juice II

Dear Reader,

I have already written a little about one of the toxins which some toads make, now we should think about the ring at the top right of the molecule. I think it will be aromatic, because of the fact that we have a flat unsaturated ring which has six pi electrons in it. Here is a picture of the two main resonance forms.

Resonance forms for the aromatic ring in the toad toxin

It is important to note that the toxins in toads do vary a lot from one species to another.

Is fusion safe ? and beryllium chemistry

Dear Reader,

I imagine that you have seen the suggestions by fusion experts that nuclear fusion will give us a cheap, safe, clean and green source of energy which will provide power for the world’s needs. I am currently thinking about how green is fusion, right now I have contacted a fusion expert who I know and I am awaiting his views on the matter.

While we are waiting I think it is important to ask the question of what was is the typical cause of a nuclear accident. Is it a issue with management, an “act of god“ or was it a technical failure ?

In the case of the Windscale fire I have seen suggestions that it was human error, poor design of the reactor or mismanagement of the project. I know that before the 1999 Tokaimura that a criticality accident at the JCO site was considered to be a was considered to “be an unrealistic scenario” according to the UN report on the accident.

I have to ask the question, did a failure in a regulatory body (either the external state regulator or the companies own internal regulation) cause the first step to be taken which lead to the accident in 1999.

One model of how accidents occur is the Swiss cheese model, the idea is that a weakness in a system is like a void in a lump of cheese. Due to some event a void can appear in the organisation, this void can grow in size, shrink, vanish or move around. As long as some solid cheese exists which prevents a path existing from one side of the block of cheese to the other then everyone is “safe”.

But when a series of holes align themselves to create a path through the cheese block then an accident occurs and then the airplane crashes, the core melts or some other horrible outcome occurs. In some ways the most important step is for the plant owner or the management is to recognise that a given type of accident is possible.

This first step of admitting that a given accident type is at least a theoretical possibility enables the company to start to take steps to prevent it occurring. For example the understanding that someone could get a body part caught in the moving parts of a machine lead to the idea of the 19th century UK law which requires where possible all moving parts of machines to be fenced off or guarded.

While it is impossible to fence off some moving parts such as the chain of a chain saw or all the parts of a handheld electric drill, this law does improve safety by greatly reducing the number of moving parts which can cause injury to factory workers. In the same way if a fusion reactor is going to be built we need a good understanding of the possible threats which it poses.

One is the beryllium used in the heat transfer fluid in some designs, I was reading recently about fusion reactor safety and I saw that a mixed lithium / beryllium fluoride has been proposed as a tritium breeding layer and as a heat transfer layer. I can tell you that beryllium is a very nasty element, in some ways it is worse than some of the radioactive elements. As a result special care will be needed if beryllium or its compounds are used in fusion reactors.

I have looked at the crystal structure of Li2BeF4 (J.H. Burns and E.K. Gordon, Acta Crystallographica, 1967, 1, 1948-1923), this is an interesting looking 3D network. But before we get stuck into it we should look at some organic salts of “H2BeF4″. L.A.Gerrard and M.T.Weller (Acta Crystallogr.,Sect.C:Cryst.Struct.Commun., 2002, 58, m407) report a nice and simple tetrahedral BeF4 unit which has protonated DABCO as the counterion. Those of you who know VSEPR should have predicted that one OK. Here is a picture of the anion in the solid.

The tetrahedral BeF4 dianion

If we have less fluorides per beryllium centre (to make the Be:F ratio 2:7) then we need to use one of the fluorides as a bridging ligand to give us four electron pairs (eight electrons) around all the metal centres. Then we get the following dinuclear complex. See S. Aleonard and M.-F. Gorius (C.R.Seances Acad.Sci.,Ser.II, 1989, 309, 683)

The BeF7 trianion

If we go a little further and have a Be:F ratio of 1:3 then we will end up with a dinuclear complex which has two bridging flourides. This is shown below. (B. Neumuller and K. Dehnicke, Z.Anorg.Allg.Chem., 2005,631, 2535)

The Be2F6 dianion, note the SiF6 dianion in the right of the picture

And now for something completely different (sorry no monty python for you today) if we mix lithium and beryllium fluorides with an salt of an amine fluoride to give us Li2Be4F14 in the unit cell (L.A. Gerrard and M.T. Weller, Chem.Commun., 2003, 716 ). This network will have a charge of -4 and it will form long strips of metal atoms which are in a 1D coordination polymer. Here is the picture for you of the metal atoms and flouride anions in the unit cell.

The metal and flourine atoms in one unit cell

How here are two strips of metal atoms side by side.

Two strips side by side, note that there are no interconnections between the strips

Now here is four strips viewed from a different angle.

Four strips viewed from a different angle, note that they do not touch each other

Now if we look at Li2BeF4 we will see it is a complex solid, I have looked and all the metal atoms have tetrahedral environments, here are a series of views of the unit cell to show you what the solid looks like. This is going to be hard, it is a 3D coordination polymer. These 3D coordination polymers can turn out to be what I call “atomic fog” but this one is not too bad, I have seen much worse in my time.

Side view of Li2BeF4 cell showing the bonds going in one dirrection

Now after turning by 10 degrees

Now the end view.

One last thing in case any of my readers are thinking of doing beryllium chemistry, my short answer is “do not do it !“. Beryllium is the most toxic non radioactive element, some forms of it are almost as bad gram for gram as Pu-239. In some ways I would like John Hunt (the voice of the UK’s AIDS advert) to dispense advice to you about beryllium chemistry using the voice of doom, but you just have me right now.

I would suggest that if any chemistry students do not want to turn back and do something else then I suggest they talk to your local friendly radiochemist  and learn how to work with gram amounts of plutonium. Then do the beryllium chemistry in the same way using negative pressure boxes and all the other safety precautions which you would use for large scale Pu work.

Clay again

Dear Reader,

Again we are turning out attention to clay, clay is a wonderful substance on which we play tennis on, make pots from and create art with. Clay is also important when cesium gets into our soil. I recently wrote a little on the subject of the clay minerals in the soils in Japan. Here is a useful set of lecture notes on silicate minerals, most clays seem to be silicates.

I have recently read that the soil from Japan holds tightly onto cesium, when soil which was contaminated by the Fukushima event was soaked in 1 M ammonium chloride solution (at 25 oC) only about 20 % of the cesium radioactivity was liberated from the soil. Then when this soil was treated with 1 M acetic acid only about 10 % more of the cesium was liberated from the soil.

It was also found that treatment with 1 milimole per litre sulphuric acid only was able to liberate less than 1 % of the radioactivity while 1 mole per litre sulphuric acid was able to liberate about half the cesium.

These findings suggest it will be hard to wash the cesium out of the soil, but if the soil is washed with ammonium chloride then the remaining cesium will be hard to transfer to plants. I suspect that as time goes on that the amount of cesium which can be transferred to the plants will become less and less as the cesium becomes more and more fixed to the minerals in the soil.

Update on your new best friend

Dear Reader,

Slightly more than one year ago I wrote about the new best friend of the Japanese people. Rather than a person who will go out and go for a karaoke session with you, drink beer with you or go for a walk in the park with you this new friend is one who can clean up your drinking water and keep your fruit and veg safe. Also this friend can help keep the milk healthy. Now you might ask what sort of super nice person can do all these things, or what sort of imp or kappa is able to do all these things.

The identity of this new friend is a bit more humble sounding, it is the clay in the soil. I have seen a recent paper by Naofumi Kozai, Toshihiko Ohnuki, Makoto Arisaka, Masayuki Watanabe, Fuminori Sakamoto, Shinya Yamasaki and Mingyu Jiang (Journal of Nuclear Science and Technology, 2012, 49(5), pages 473 to 478) in which the cesium behaviour in the soil is reported.

In this paper the soil was examined with X-ray diffraction. This found smectite, mica, hornblende, kaolinite, quartz, orthoclose, cistobalite, feldspar, stishovite, gibbsite, sodalite, olivine and sorosilicate minerals in the soils.

The smectite clay is rather similar to the illite clay which I showed a picture of recently. The two clays are related, I have seen a thesis which explains how the smectite clay transforms into illite clay. For your information the thesis is here. The difference between these two layered clays is in the anionic bread layers between the potassium jam. The smectite and the illite have slightly different layers.

A smectite clay, the oxygens are in orange red, the potassium ions in blue, the aluminium/silicon atoms are in sea green. Note that layers of potassium ions which look like slices of bread.

I think that both the smectite and illite are formed from mica, so I would say that the more mica in the rocks which formed the soil the better when you are considering cesium in soil. The mica is very similar to the two clays, again it is a layered solid.

Many of us know mica, it is a mineral which can be made into thin sheets. We will soon see why it is possible to split mica into thin sheets. It is easy to separate the mica by peeling apart the layers.

Here is a view of a mica (Muscovite) which was studied some time ago. (O.V. Sidorenko, B.B. Zvyagin and S.V. Soboleva, Kristallografiya, 1975, 20, 543-549). Should should see again that the solid is layered, the potassiums (blue) have anionic layers of alumo-magnesium silicate between them. I have shown all the non oxygen atoms in the layers as green.

Mica showing the layers of potassium ions between the anionic layers

The important thing about the mica is that the aluminium atoms are randomly mixed with magnesium and silicon atoms in the two layers. The authors of the paper I am working from expressed the view that one of the types of layers (the middle layer in the trilayer anionic layer) has 20 % magnesium and 80 % aluminium. While the two outer layers of the anionic trilayer have 28.4 % aluminium and 71.6 % silicon. The mica also contains some hydroxyl anions which I have been unable to locate in that solid. I have made a new drawing of the mica which shows the mixed aluminium/silicon and aluminium/magnesium layers in different colours to show you how the solid fits together.

Diagram of mica. The potassium ions are in blue. The mixed aluminium/magnesium sites are in grey. The mixed aluminium/silicon sites are in green. The oxygens are in a rather fetching shade of orange.

It is important to note that the green aluminium/silicon sites have a tetrahedral arrangement of oxygen atoms around the central atoms while the grey mixed magnesium/aluminium sites have a distorted octahedral arrangement of oxygens around the central atoms.

The hornblende clay is a very different mineral, I have looked at the crystal structure and it looks in some ways like a SBA-15 or MCM-41 to me. It has tube like holes which pass in one direction through the clay. These tubes are then filled with sodium and potassium cations. As the clay is so different, I suspect that it may behave differently to the layered clays which I showed you.

The mica based minerals can change the spacing between the anionic layers to suit a new cation which has a larger diameter than the potassium. In this way the larger cesium ions can be held in the solid. But in the case of the hornblende, I do not think it will be so easy to add a larger cation. I think that the holes will get plugged up and blocked by the larger cations.

Here is a view of several unit cells of the hornblende clay, the solid is a little disordered. It has a mixture of sodium (yellow) and potassium (blue) cations in the solid. Also note that it has grey calcium ions in the alumosilicate layers. The aluminiums are purple, the silicons are sea green and the iron atoms in the clay are orange. The oxygen is in a rather fetching orange/red as before.

A view of hornblende clay showing the holes in which the potassium/sodium ions go.

I will try and give you an update soon on the clay and the cesium.

Aftonbladet and chernobyl

Dear Reader,

It has come to my attention that a woman called Natalia Kazmierska has seen fit to comment on the Chernobyl event recently. This has made me think about the way in which the general public think about radiation biology.

I doubt if I will be attending a showing of the film “The Chernobyl Diaries”. Frankly I have better things to do  and I think that watching 28 days later gave me all the frights about zombies that I need for the next decade or so. I would like to point out that regarding radiation it is a case that what “everyone knows” is not right. While the general public expect a large number of mutant babies and deformed wildlife (overgrown rats, dogs with snake heads, snakes with dog’s bodies and what ever else you can imagine), I have to disappoint many people and point out that many of these wild (and far fetched mutants) are impossible.

In an adult mammal (and almost all other warm blooded animals) the cells are already differentiated and it is impossible to change an organ by altering a cell as

1. The organ has many cells

2. It is impossible to change the DNA of all the cells in the organ in the same way using radiation.

If we consider the eye as an example, somewhere in your genome is a genetic code which determines your eye colour. If you want to change your eye colour (and you do not want to use fancy contact lenses) then you would need to change the DNA in all the cells which are currently part of the section of the eye which gives the iris its colour. This is a very tall order which I think is currently impossible.

When you were an unborn baby at an early stage there would have been one eye which would have been destined to become your eye, if you had altered the DNA of this cell then you could alter the eye colour. But unless you also changed the cell which was destined to become your naughty bits (opps I mean reproductive organs) then this mutation can not be passed onto the next generation. So it is not possible to mutate adult humans or even human babies (for the purpose of this bit of biology they already have their organs locked in this way).

I know that newspapers would love to be able to report a “real life mutant associate prof who marks his students work using psychic powers to read student’s minds before writing the results down using a biro held using his tentacles”, but I have to tell you that such a story is totally impossible. If you want to print such a thing then I think other than vanity publication or writing in a novel/comic book your only chance would be to write it for the “Sunday sport“. For those of my readers who do not know, the Sunday sport is a comic like news paper which is packed with wild tales about sexual matters, sport, showbiz gossip and plainly silly things such as world war two bomber found on moon, aliens going on drinking binge in a UK pub and a monkey landing an airplane.

I think that the main reason why radiation is so bad at mutating humans (and most animals) is that the likelihood on inducing a mutation in the reproductive organs which can be passed onto your children is only 1 % per sievert (Sv). It is important to distinguish between a mutation which can be passed onto your children and the case of a child which does not develop normally due to irradiation in utero. Most of the horror pictures which people may have shown you are likely to be either fetuses which were deformed for some reason which is unrelated to radiation or a child which developed in an abnormal way due to the action of some agent such as (alcohol or radiation) on the unborn child.

It is important to bear in mind that the chance of inducing cancer in a human (typical adult over 16 or 18) is also low, it is widely accepted as being at 5 % per sievert, as a dose of about 4 sievert delivered over a short time is likely to send a person to the other side (assuming no specialist medical care) it is very hard to mutate a person’s gametes to enable them to have abnormal children let alone children with superpowers.

For example if we consider the associate prof with two superpowers (mind reading) and the tentacles which he can write with then it should be clear to most of my readers that such differences are a long way removed from what is the norm. I imagine that to get either of these “superpowers” would require a long series of mutations, this long series of mutations would require a large number of genetic changes to occur which are very unlikely to occur in the lifetime of one human. A typical mutation which could occur in a human would be a change in a gene which stops a person making a protein or some other biomolecule which is needed for normal life, this would include hemophilia appearing in a family which never had it before.

An alternative would be for the genetic code for the mutant prof to already be common in the human genome but to have a single gene which switches off this weird stuff. We can quickly discount this as if this was the case then every now and then we would see a person born who could read minds and had the extra limbs. As I have never heard of such a human then either the authorities are doing a good job of hushing it all up or more likely it has never occurred. I hold the view that it is very hard to keep something wild and exciting secret for a long time, a secrete organisation is only as strong as the weakest member so it is likely that a secret organisation will within decades become a publicly known one.

So I think we can discount the likelihood of an associate prof who mind reads and can write using extra organs appearing by mutating a “normal” human.

I would like to point out that the nuclear industry is one of the few which has worked out a method for isolating the worst forms of its waste from humans / the environment until it is no longer a threat. Wastes from other sectors will stay nasty and horrible forever. For example asbestos waste will remain hazardous forever and so will heavy metal waste from electrical batteries (NiCd cells). I would like to suggest that Natalia that she should consider this issue.

I would also like to point out that the worst accidents I can think of in the energy sector have been outside the nuclear industry, for example back in the 1960s a spoil heap at a Welsh coal mine slide down a hill and killed almost every last child in a primary school (Aberfan). If society or Natalia wants to have a debate on the safety of the nuclear sector that is fine by me, but we need to consider the whole of the energy sector rather than cherry picking the parts we want to discuss or be opposed to. I will be blogging on this in greater detail in the near future.

Toad juice

Dear Reader,

I was informed by one of my PhD students that a place in Sweden is sponsoring toads, the idea is that you pay a fee to support a toad. As a result the nuclear chemistry and industrial materials recycling sections of the department of chemical and biological engineering are considering if they should have a whip round and then sponsor a toad.

Now before we get going toads have had a bit of a raw deal, they get a bad press which they frankly do not deserve (at least not always). For example they get blamed for giving people warts, and toxic mushrooms are called “toadstools” (why can they not have sofas or armchairs ?) and why are driving test examiners compared with toads ? You might argue that this web page is biased against toads and is an example of hate speech against toads.

But I would say that the cane toad is a nasty little so and so who needs to be put in his/her place, maybe the other toads should take the cane toad behind the potting shed and reeducate it a little.

It is important to note that all the toads have toxin which protect them, one of the toxins which the common european toad has is a cardiotoxic steroid. This is an interesting molecule called bufotalin which has been isolated from a range of different toads. One paper (A.Kalman, V.Fulop, G.Argay, B.Ribar, D.Lazar, D.Zivanov-Stakic, D.Vladimirov, Acta Cryst., 1988, C44, 1634-1638) used the Chinese toad Ch’an Su as a source of the toxin. The molecule is a steroid which has an additional six membered ring group attached. The additional group is an aromatic ring which is in disguise. Here is a molecule of bufotalin.

Bufotalin a toxin from a toad

I will write more about the “toad toxin” later

Carbon tetrachloride

Dear Reader,

I saw a chemistry world blog article about carbon tetrachloride so now I feel compelled to write to you about an organic solvent from yesteryear, it is carbon tetrachloride or more correctly tetrachloromethane. This is the substance which sent Margo Jones to the other side when her carpet was dry cleaned with it, it also almost sent a friend of mine to the same place years ago. An old chemist who I know used to mouth pipette everything, one day he mouth pipetted solutions of things in carbon tetrachloride (I think he was measuring distribution ratios) and he told that hours later he started to vomit. He told me that he continued to puke for about three days and he suspects that he had a lucky escape (He recovered and then went onto have a productive life).

Top tip of the day : Never mouth pipette anything !

The thing which interests me most about carbon tetrachloride is the free radical chemistry of this molecule. I strongly suspect that the trichloromethyl radical is a very stable radical which contributes to some of the chemistry of carbon tet. I know many years ago both the Soviets and the Americans built PUREX plants using carbon tetrachloride as the diluent. The nice thing about carbon tet is it gives a very good quality uranium and plutonium product, also it is easy to purify the process solvent to recover pure carbon tet, it is non flammable and the phase separation is easy. But it had a horrible sting in its tail, when you irradiate carbon tetrachloride you form chloride anions. I suspect that the solvated electrons are captured by the LUMO of the carbon tetrachloride and then it splits up to form anionic chloride ions and trichloromethyl radicals. The chloride impurity in the PUREX plants quickly formed aqua regia with the nitric acid used in the PUREX process. The resulting corrosion soon caused both plants to be shut down.

I will get onto the free radical chemistry which occurs in flames later, but an interesting bit of free radical chemistry using carbon tetrachloride is used in the production of cypermethrin. This is a insect killing agent which I have bought at Ica and used to kill creepy crawlies in my house. A key step in the production of cypermethrin is the formation of the cyclopropane ring. The synthesis starts with a pericyclic reaction (Claisen rearrangement) which uses an allylic alcohol and triethyl orthoacetate to form γ,δ unsaturated ester. This ester it then reacted with carbon tetrachloride in a free radical reaction. Treatment with two bases then forms the cyclopropane ring which makes up a key part of the carboxylic acid part of the insect killing agent.