[hairygorillaz]

Hi guys,

I have a problem with a reaction I'm running. I am using MeI, but the reaction temperature is 95 °C (give or take 5 °C or so). Even though the reaction is run in toluene and I have a reflux condenser at -20 °C, the reaction "stops" because I have no more MeI even though I use a large excess (around 20 equivalents). I have to constantly add more for the reaction to go to completion. Also, the reaction is set up under inert conditions, connected to a nitrogen line.

Any tips on how to keep low BP reactants in the reaction vessel?

Thanks in advance!

[wildfyr]

Use a sealed pressure flask like this (https://www.sigmaaldrich.com/catalog/product/aldrich/z567191?lang=en&region=US). A note: This is obviously somewhat dangerous, but still pretty standard. Do not fill it more than apporx 1/3 of the way. You are using toluene so the pressure won't be too high, but its still volatile. Put it behind blast shield. Heat it up slowly. Make sure you screw the cap and o-ring on right or else it will leak.

I've seen people do THF reactions at 120°C in these bad boys (and also make them explode when pushed further) so they are pretty tough. I specifically used methyl iodide to quaternize polyamines at 95°C in them, so I know it works.

You can screw it down in a box with strong nitrogen or argon pressure flowing to get "mostly" inert conditions but I don't have a method to truly exclude oxygen and water except to add reagents and assemble the flask in a glovebox. My reaction wasn't sensitive.

[pgk]

Another option is to add diluted MeI dropwise (≈ 1-2 drops/sec) and work at lower temperature (say 70-75oC). This will significantly delay the reaction but it will probably work.

[hairygorillaz]

Use a sealed pressure flask like this (https://www.sigmaaldrich.com/catalog/product/aldrich/z567191?lang=en&region=US). A note: This is obviously somewhat dangerous, but still pretty standard. Do not fill it more than apporx 1/3 of the way. You are using toluene so the pressure won't be too high, but its still volatile. Put it behind blast shield. Heat it up slowly. Make sure you screw the cap and o-ring on right or else it will leak.

I've seen people do THF reactions at 120°C in these bad boys (and also make them explode when pushed further) so they are pretty tough. I specifically used methyl iodide to quaternize polyamines at 95°C in them, so I know it works.

You can screw it down in a box with strong nitrogen or argon pressure flowing to get "mostly" inert conditions but I don't have a method to truly exclude oxygen and water except to add reagents and assemble the flask in a glovebox. My reaction wasn't sensitive.

I don't think the reaction is THAT sensitive, so I think this may be a solution. Thanks a lot! I'll give it a go.

[hairygorillaz]

Another option is to add diluted MeI dropwise (≈ 1-2 drops/sec) and work at lower temperature (say 70-75oC). This will significantly delay the reaction but it will probably work.

The reaction already takes about 24 hours at 95 °C. So I think this may not be too feasible, but thanks a lot. No harm trying

[rolnor]

You could use methyl triflate wich is much more reactive then MeI and you can run at lower temperature.

[opsomath]

Methyl tosylate is also an option, safer and easier to handle than MeI and certainly MeOTf.

[rolnor]

Methyl tosylate is far less reactive than methyl triflate but higher boiling of course.

[hairygorillaz]

Thanks guys. Couldn't change it to a triflate or tosylate, because the iodide was incorporated into the final molecule, but the sealed tube did the trick