• Home
  • About
  • Chemistry
    • Solvent of the Week
    • Compound of the Week
    • Reagent of the week
    • Publications
    • Translations
    • Glassware designs
    • Advanced Preparative Separation
    • Videos
    • A day in a mineral lab
    • A day in a wine lab
    • A day in a polyurethane lab
  • Philosophy
    • Poor Matthew
    • On Australian coins
    • On global warming
    • On aluminium cans
    • Questions to ask potential housemates
    • Why chemistry skills are now less valued than they were
    • Tribute to Mr John Clarke
    • Theory on Covid-19
  • Photos
  • Blog
MJLPHD

On the use and handling of Titanium tetrachloride

19/2/2014

0 Comments

 
PictureTitanium tetrachloride
Titanium tetrachloride (also called titanium (IV) chloride or TiCl4) is a strong Lewis acid. It is highly oxophilic and reacts instantly with water to form TiO2 and HCl vapours. It is a clear, colourless liquid at RT. Less pure samples may have a colour or solid particulates but it can be re-purified by distillation. It is not compatible with ethereal solvents as it is known to form crystalline diether complexes. It is non-polar and is soluble in/compatible with benzene and chlorinated solvents. I recently used TiCl4 in an attempt to catalyze a reaction.
It is a bit tricky to use, but does not require strict anhydrous conditions to the point of using a syringe or cannula. I was able to remove it from the bottle using a Pasteur pipette. Further I was able to comfortably monitor the result by C-NMR by placing my compound in CDCl3 and then adding TiCl4 before transfer to an NMR tube. I was concerned about HCl escaping from the solution in the NMR tube so I sealed the top with para-film but this proved not to be a problem. I thought a TiO2 precipitate might form which could interfere with the NMR by disturbing the homogeneity but this too turned out to be not a problem and I was able to view the signals of my start material and the product.

PictureTiCl4 before addition to compound/solvent in flask. The white fumes are TiO2 and HCl.
I felt that the reaction had not worked cleanly enough. Given the oxophilicity of TiCl4, this could be due to a methoxy or a nitro group (both of which were present on my compound but on the other half of the molecule to where I aimed for the reaction). TiCl4 is known to reduce nitro groups and in my case it looked like mine had been replaced with an amino and an alkene.

PictureYellow Ti(IV)Cl4 complexed with nitrile(s)
I decided to try with a homologue compound that contained a nitrile group in the place of the methoxy. I ran this reaction in a flask in 1,2-DCE (above) instead of an NMR tube in CDCl3. With the first compound, the mixture instantly looked like brown gunk. However, with this second compound, a beautiful bright yellow precipitate was formed (right). The start material was white so I think that this yellow precipitate was a Ti(IV)Cl4 complex where the nitrile group has acted as either one or two ligands. When I worked up this reaction by addition of water, the yellow vanished. Rotavapping the organic layer returned over 80% of my start material as a pure white solid and it was possible to make the yellow complex again from the recovered product. This yellow colour seems to be from delocalization of d-orbital electrons in the Ti(IV), rather than freely moving conjugated electrons in the organic compound. It therefore seems that TiCl4 prefers to coordinate with nitriles groups more than methoxy groups, which in a sense can 'protect' the rest of the molecule from the oxophilic attack of TiCl4.
The Ti(IV)Cl4 complex might be breaking up by the action of water, or it may be the HCl produced by the addition of water which removes the ligands from the Ti(IV). If I could suck off the 1,2-DCE/TiCl4 in a vacuum trap I could run a crystal structure on the yellow product and determine its configuration. While I have not so far had the resources to follow this up, it may be useful to other workers.

0 Comments

Your comment will be posted after it is approved.


Leave a Reply.

    Matthew's Chemistry blog.

    A chronicle of tips, tricks & stories

    Contributions from readers are welcome and should be emailed to matthew.leonard742@gmail.com

    Archives

    September 2016
    December 2015
    September 2015
    July 2015
    June 2015
    May 2015
    April 2015
    March 2015
    February 2015
    January 2015
    December 2014
    November 2014
    October 2014
    September 2014
    August 2014
    July 2014
    May 2014
    March 2014
    February 2014
    January 2014
    December 2013
    November 2013
    October 2013

Powered by Create your own unique website with customizable templates.