[asa029]

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?

[democanarchis]

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 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.

[OC pro]

Diethylether / liquid nitrogen worked out good for me. At least down to -95°C.