Re: ORGLIST: TLC help - monitoring a reaction

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From: Mark Cunningham (markacunningham$##$msn.com)
Date: Sun Feb 04 2007 - 10:22:01 EST


Ken,
 
  It's surprising that you can't use GC to monitor this reaction by GC or MS, where normally, in both of these methods, the goal is to get compounds in the gas phase. Methyl methacrylate has a boiling point of 101 oC, so it should not be super volatile. Make sure the GC splitting ratio is not to high or that your septum at the injector port is not leaking. Or, make sure you are not losing the sample, in for example, the solvent cut, before it reaches the column. Another possible method, though it takes more work, is to monitor methyl methacrylate (the starting material) by NMR. You'll have to collect a small sample of the reaction mixture, quench it the way you ordinarily would when the reaction is complete. All of this should be done on small scale in a test tube. First, run an NMR control of pure methyl methacrylate, and monitor and compare peak areas, for example, the double bond peaks of the control to those of methyl methacrylate in the reaction mixture. Hopefully that gave you a few ideas,
Mark

> From: esprcorn$##$hotmail.com> To: everybody$##$orglist.net> Date: Fri, 2 Feb 2007 00:16:09 -0500> Subject: ORGLIST: TLC help - monitoring a reaction> > Ok, easy one again for ya guys...> > Again, I'm a 1st year grad student so I'm still struggling with some of the > basics...> > I'm running a reaction where I'm supposed to monitor the disappearance of > the starting material (methyl methacrylate) by TLC. I'm using a reaction > scheme/protocol from another paper. But methy methacrylate appears to be > very limitedly UV active and very volatile. So I can't really see the spot > and even if I could it evaporates before it can elute. I think...> > Before realizing this I tried monitoring on GC in the lab, but I didn't get > anything.. Again, likely due to the volatility of methyl methacrylate....> > Is there another way I can monitor the consumption of the methyl > methacrylate? Or will I have to settle for monitoring the product possibly? > Or just give it 24 hours and work it up crossing my fingers?> > In the paper where I got the reaction, their substrates are all UV active > and non-volatile so this was not an issue for them.> > This is fun stuff... but I'm stumped...> > Thanks!!> > Ken> > _________________________________________________________________> Get in the mood for Valentine's Day. View photos, recipes and more on your > Live.com page. > http://www.live.com/?addTemplate=ValentinesDay&ocid=T001MSN30A0701> > _______________________________________________> ORGLIST - Organic Chemistry Mailing List> Website / Archive / FAQ: http://www.orglist.net> To post a message (TO EVERYBODY) send to everybody$##$orglist.net> To unsubscribe, send to everybody-request$##$orglist.net the message: unsubscribe your_orglist_password your_address


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