Triphenylmethane
The pKa of the hydrogen on the central carbon is around 31. The trityl anion absorbs strongly in the visible region, making it red. This colour can be used as an indicator when maintaining anhydrous conditions with calcium hydride; the hydride reagent reacts with water to form solid calcium hydroxide, while it is also a strong enough base to generate the trityl anion. If the hydride is used up then the solution will turn colourless. The sodium salt can be prepared also from the chloride.
Before the popularization of butyllithium and related strong bases, trityl sodium was often used as a strong, non-nucleophilic base.in the lab, in small scale reaction, triphenylmethane can be used to indicate excess n-Buli or LDA.
Wednesday, August 13, 2008
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2 comments:
That's really useful. Have you run reactions with the trityl cation present as an indicator? I would imagine that the methane would be reasonably unreactive (sort of like using mesitylene as an internal standard in GC).
How much triphenylmethane would you recommend using per every 10 mL solvent? I'd guess ~1 drop to see the color change.
tank you for your comment.
yes, I did use triphenylmethane as indicator several times. I add only 1 mg,that is enough to make the solution (10 ml THF) red when you add n-buli.
the material is white solid, quite easy to handle.
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