I did a lithiation of bihiophene( a thiophene with 3 - alkoxy chain, another thiophene with 3-alkyl chain, 2 side are connected each other and I wanna add trimethyltin at 5 position each.) But when I added n-BuLi(2.5M in Hxn) at -78C (2.2eq), color changed clear yellow to yellowish dark brown while i dropwised the BuLi. at -78C, dropwise the buLi and left that temp for an hour, warm up to rt for an hour and then cooled down to -78C, drop the trimethyltin chloride(1M solution).
Usually, when buLi added, color changed clear yellow i experimented before. I wanna know why color change dark.
* n-BuLi showed no white powder(LiOH), and reagent opened at march, stored it in refridge.
I thought its butyllithium's problem(my product show clear peak at NMR)
Dear Yina Avery Kim , if your butyllithium solution was still clear, I think that the intermediate brown coloration is not a problem associated with butyllithium. The question is: Did the brown color lighten up / disappear after the addition of trimethyltin chloride?
Kim
You did the reaction
Added n-BuLi(2.5M in Hxn) at -78C (2.2eq), color changed clear yellow to yellowish dark brown while i dropwised the BuLi. at -78C, dropwise the buLi and left that temp for an hour (I think 5-10 min is enough) add your reactant then (do not warm up your solution) and keep stirring while monitoring your reaction with tlc (it may take couple of hrs). Work up your reaction mix. and check with NMR. Changing color may be due to the formation of bianion !!!!
let me know the result, I may be able to help
Good Luck
Dear Yina Avery Kim, I fully agree with Adel Amer's answer. It is quite likely that the intermediate brown color is due to the formation of a dilithiated intermediate. Did you finish the experiment already?
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