Sciencemadness Discussion Board

Pinacol Synthesis Variations

TheChemiKid - 7-3-2014 at 04:19

I am interested in attempting the synthesis of Pinacol from Acetone.

550px-Pinacol_coupling_of_acetone.png - 14kB

It entails using Magnesium and Mercuric Chloride, then water to react with Acetone to form Pinacol. I was wondering if anything could replace the Mercuric Chloride, such as Gallium?

I don't know why the picture isn't working, if you press on it, you can see it.

Dr.Bob - 7-3-2014 at 06:13

Try searching google for "catalyst pinacol acetone", I found lots of catalysts:

http://www.chemtube3d.com/RAD-pinacolcoupling.html

http://www.organic-chemistry.org/namedreactions/pinacol-coup...

http://www.arkat-usa.org/get-file/42209/

http://chem.ccnu.edu.cn/klpcb/www/wuanxin/UpLoad/20079101882...

http://books.google.com/books?id=NYYMD-KYZb4C&pg=PA284&a...

TheChemiKid - 7-3-2014 at 06:23

Thank you so much!

I would presume the Magnesium would need the surface cleaned for this reaction. Would Iodine work for that?

Dr.Bob - 10-3-2014 at 10:31

Depends on the conditions used. I prefer to just grind up the Mg fillings in a mortar and pestle just before use, and then maybe even wash them with ether once. If they are freshly ground up some, they often work well. Just don't try to grind them in a blender, that can lead to bad fires.

TheChemiKid - 10-3-2014 at 14:50

Thanks for that.
I have one more question. In the chemtube procedure, it specifies to use benzene. I have very limited amounts of benzene, so I was wondering whether toluene or xylene could be used in its place.

Electra - 10-3-2014 at 23:20

Never done this particular reaction myself but in my research into Vanadium I remember frequently running into it being used as a Pinacol coupling catalyst in the VCl3 form.

http://www.ncbi.nlm.nih.gov/pubmed/16209617

Dr.Bob - 11-3-2014 at 13:11

Quote: Originally posted by TheChemiKid  
In the chemtube procedure, it specifies to use benzene. I have very limited amounts of benzene, so I was wondering whether toluene or xylene could be used in its place.


I almost any reaction, toluene or xylene can be used as the solvent, as long as they are non-reactive (which they should be in an aldol reaction), and the BP will change, so the temperature of reflux will go up, which may speed up the reaction. There are some few cases where they cannot be interchanged, but in most cases that works fine.

I rarely use benzene now, the only case I found where it was absolutely necessary was in purifying a compound by chromatography, where the Rf difference between two aromatic compounds was much larger in benzene than in toluene, likely due to benzene's symmetry making it slightly less polar than toluene, which has a larger dielectric constant. Toluene also forms different azeotropes than benzene, but that can often be dealt with proper selection of solvents.

TheChemiKid - 12-3-2014 at 07:29

Thank you, when I have tried this reaction, I will post a detailed writeup, though it may also be put in prepublication. If so, I will post a link.