zeolite2008 - 14-11-2007 at 14:23
I am trying synthesis of 1,3,5-Tris-(4-carboxyphenyl)benzene according to literature:
a. 1,3,5-Tris-(4-bromophenyl)benzene (5 g, 9.2 mmol) was dissolved in dry THF (70 ml) under atmosphere of argon.
b. The stirred solution was cooled to -60 oC and Bu-Li in hexane (19.1 ml, 27.6 mol) was added. then a green precipitate of organyl lithium compoud
was formed.
c. then gaseous CO2 was passed into the mixture to give a colourless precipitate of the lithium salt. then acidified with acetic acid and water added
to cause white precipitate.
I do as above, but for step b, i did not get green precipitate or first green then turned to white colour, finally i got just white with a little
light red precipitate,
for step c, when passed into CO2, the precipitate mixture was still white with a little light red color. after i added into acetic acid, the
precipitate disappeared, and turned into yellow solution, then i added water, just got yellow precipitate.
I donot know why? what is the key step should be paid more attention!
Please help! thanks!
JohnWW - 14-11-2007 at 22:39
"According to literature"? Can you give the references, or, better still, attach here PDF copies of the journal articles that you are using, please?
jam640 - 15-11-2007 at 02:59
Probably according to Journal of the American Chemical Society, 126(3), 884-890; 2004.
1. Is your inert atmosphere purrrfect?
2. Do you have the same molarity of your butyl lithium (you never know, people have made that mistake before when following published procedure
straight of the paper)?
3. Is your CO2 dry?
Nicodem - 15-11-2007 at 11:19
4. Is your THF really dry? Was it distilled from sodium benzophenone ketyl, like it should be?
5. How old is your BuLi? BuLi usually deteriorates in less then a year even if stored in a refrigerator.
6. How does the 1H NMR of the product look like? How many TLC spots does it give? Surely you didn't just conclude the reaction failed just because you
did not get any green color!
zeolite2008 - 15-11-2007 at 13:33
many thanks for all the suggestions.
the paper is J. Chem. Soc. Perkin trans, 1988, 1251.
the THF was dried by adding some 3A molecular sieve
the CO2 was UHP grade, so i did not further dry the CO2
maybe trace of water will lead to the diffrent phenomenon?
jam640 - 15-11-2007 at 14:01
Yes, organolithiums tend to be _very_ sensitive to oxygen/water contant and slightest impurity may fail the reaction completely and or change the
apperance of products to a great extent (for example completely different coloration). Drying your THF with molecular sieves is probably not good
enough.