Why does LDA solution gradually turn dark brown?

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.


