[kalos]

Hi all,
I'm running a reaction at -78°C under Argon in a Schlenk flask. I really have to keep the water out in this one. I'd like to monitor the reaction, though. When I started this for the first time, I always ruined my reaction. Since I don't monitor anymore, the reaction runs well. I'd like to monitor nonetheless for optimization purposes. How do you do that kind of stuff? The way I did it:
- let argon flow in
- prick the septum with a small syringe needle for the argon flow
- and a long one for getting a sample (heated beforehand to remove water, but I have to let it cool down, so I'm not sure how effective that is anyways) and push the long needle down into the solution,
- put my finger on top of the opening of the needle,
- pull needle out and collect solution in an eppendorf tube.
From there I quench and do my TLC.
So, how do I do this without hydrolyzing everything, because apparently that's exactly what happens all the time.
I also tried a variant in which I had a super thin capillary that I pushed through the big needle, so that only the capillary would get into the solution. Alas, to no effect.

Grateful for any comments on this!

[willug]

Using a capillary through a needle is the normal way of doing it. What do you mean 'to no effect'? Nothing was drawn up though your capillary?

[PhDoc]

Kalos, what you're saying is unclear. Typical TLC procedure for inert atmosphere reactions is to draw out a capillary spotter, then place the "thin end" into the reaction mixture via a syringe needle under positive flow of argon or dry nitrogen.

I'm uncertain what part of your procedure is not working. Sometimes, when viscosity of the reaction medium is high, fluid will not flow up the capillary. Under such conditions, it's often necessary to take a small aliquot under inert dry conditions, via syringe, and transfer to purified THF in a receiving flask under inert conditions. This has the effect of reducing viscosity permitting flow into your spotter.

Is this what you're talking about?

[kalos]

Thanks for the responses. Sorry for not being entirely clear. The problem with the capilary is that I still get hydrolysis. Viscosity is not a problem.

[orgopete]

I think I may not understand this problem. If the reaction is not monitored, the product can be assayed by TLC, or that is implied. If the reaction is monitored by hydrolyzing an aliquot, TLC fails. I think I'd use a GC to monitor the reaction.