• Blog Stats

    • 82,806 hits
  • Archives

  • Enter your email address to subscribe to this blog and receive notifications of new posts by email.

    Join 158 other followers

  • Copyright notice

    This blog entry and all other text on this blog is copyrighted, you are free to read it, discuss it with friends, co-workers and anyone else who will pay attention.

    If you want to cite this blog article or quote from it in a not for profit website or blog then please feel free to do so as long as you provide a link back to this blog article.

    If as a school teacher or university teacher you wish to use content from my blog for the education of students then you may do so as long as the teaching materials produced from my blogged writings are not distributed for profit to others. Also at University level I ask that you provide a link to my blog to the students.

    If you want to quote from this blog in an academic paper published in an academic journal then please contact me before you submit your paper to enable us to discuss the matter.

    If you wish to reuse my text in a way where you will be making a profit (however small) please contact me before you do so, and we can discuss the licensing of the content.

    If you want to contact me then please do so by e-mailing me at Chalmers University of Technology, I am quite easy to find there as I am the only person with the surname “foreman” working at Chalmers. An alternative method of contacting me is to leave a comment on a blog article. If you do not know which one to comment on then just pick one at random, please include your email in the comment so I can contact you.

  • Advertisements

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.


Go on, Have your say !

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: