Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: asa029 on April 09, 2011, 03:20:32 AM
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One of my reactions calls for a cold bath of -91 degrees celsius. This can (per theory, at least!) be achieved using a slurry bath consting of heptane and liquid nitrogen. I tried doing this, but did not achieve the requisite slurry, only heptane lumps in a steaming heptane bath (which was kind of dissapointing).
Do anyone have any tips or tricks to make the slurry? I was thinking using a mechanical stirrer next time (I only used a huge magnet). Maybe this will help?
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Bear in mind that if heptane freezes at -91, the bath will solidify and you won't have a slurry. For a slush the freezing point needs to be a bit lower than that. https://www2.bc.edu/~hoveyda/cool.html (https://www2.bc.edu/~hoveyda/cool.html) has a good list of cooling baths, pick a liquid nitrogen one that is below the required temp like acetone.
I generally half fill the dewar with solvent, pour in about 1/2 the volume of solvent of liquid nitrogen and mix until constant temperature with a large spatula. Add liquid nitrogen portionwise until you hit the required temp.
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Diethylether / liquid nitrogen worked out good for me. At least down to -95°C.