Saturday, May 19, 2007

You want the Chemistry? ... You can't handle the Chemistry!

OK I guess I need to provide some detail. I was a graduate student in an inorganic fluorine chemistry research group. We were investigating Main Group compounds that had inorganic pi systems created by oxidizing electron rich molecules using Arsenic pentafluoride in liquid sulphur dioxide.

The graduate student ahead of me discovered reaction 1. S4N4 is a contact explosive prepared from one of those classic fire from God reactions that were popular in the late 19th century. So you prepare the explosive and then grind it to a fine powder (grind gently because I was in a lab in England where a small beaker of the stuff spontaneously exploded and split a lab bench from end to end). You put the fine powder and some sulphur in a vessel with lots of sulphur dioxide as solvent and then add lashings of AsF5. About a week of recrystallizations later gets you to SNSAsF6 which contains the dithianotronium cation [SNS]+ (think ONO+).

Now SNS+ is a lot of fun but I discovered rxn 2. It turns out that SNS+ does not react like ONO+. SNS+ is a propargyl-allenyl 1,3-dipole favouring reverse electron demand cycloaddition reactions with pi bonds. Thus the reaction with alkynes gives the derivatives of CAT in high yield.

The hero of this story is the 4,5-bis(trifluoromethyl)-1,3,2-dithiazolium cation. I discovered that the reduction of this cation by sodium dithionite in liquid sulphur dioxide gives the blue gas radical in reasonable yield but the reaction works the best because the products are the radical, insoluble NaAsF6 and the solvent SO2. Laborious fractional distillation of the reaction volatiles give the black liquid referred to in the previous post. And I always wondered why the preparation wasn't repeated more often.
Thanks for the interest in the chemistry.

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For a while it was all about research and then it was all about teaching and now it's all about trying to find a balance while teaching at a small liberal arts and science university.