LDA (lithium diisopropylamide) solution in THF/hexane gradually turns red-brown liquid. Especially commercially available one is extremely dark red-brown. What makes it brown?

I've searched online journals, but I couldn't find possible theories. When I synthesize LDA, at first LDA solution in THF/hexane is light yellow. Of course, I keep it under nitrogen/0-10 degrees celsius but it gradually turns brown.

Does LDA react THF or the THF stabilizer BHT? Do they make LDA solution brown? Please give me any plausible explanations.

  • $\begingroup$ BHT is a phenol. It would be deprotonated and unlikely to be in the solution. Butyllithium reacts with THF to form ethylene and the enolate of acetaldehyde. Perhaps LDA does this slowly. Traces of moisture could protonate some of the enolate leading to base catalyzed condensation products that are brown from oxidation. $\endgroup$ – user55119 Dec 5 '18 at 2:58
  • $\begingroup$ It seems to be plausible. Thank you for your kindness! $\endgroup$ – Zen Dec 27 '18 at 13:55

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