[yxmsoccer]

I was trying to do a reaction at -10C, so I checked the cooling bath list and decided to use ethylene glycol and dry ice. But when I added a little bit more dry ice, the temperature started to drop until around -40C. It is quite different from acetone/dry ice mixture which can always stay around -75C. I was wondering if there is any stiochiometric relationship between ml of ethylene glycol and g of dry ice you need to make -10C. Thank you!

[Honclbrif]

Jensen. C. M. Dry-Ice Bath Based on Ethylene Glycol Mixtures. J. Chem. Ed. 2000, 77, 629
 
http://www.che.psu.edu/faculty/rioux/group/group_info/references/dry_ice_bath_based_on_ethylene_glycol_mixtures.pdf

[yxmsoccer]

Just tried. Working perfectly. Thanks a lot!

[opsomath]

Dude. Salt, ice, go. This is way too complicated.

[Honclbrif]

Opsomath does have a pretty good point there. For -10 salt and ice is perfectly sufficient. The EtOH/glycol mixtures are really only useful if you have to maintain an intermediate temp. Another problem with them is they have a tendency to freeze solid, so don't immerse your flasks above the equator...

[yxmsoccer]

Got it! Do you also have any ways to keep it overnight? What if I have a automatic cooling bath machine in my lab!

[Honclbrif]

If you have an automatic cooling bath with a thermostat it should take care of itself, as long as it can reach the temp range you need.

[Halogenator]

I was trying to do a reaction at -10C, so I checked the cooling bath list and decided to use ethylene glycol and dry ice. But when I added a little bit more dry ice, the temperature started to drop until around -40C. It is quite different from acetone/dry ice mixture which can always stay around -75C. I was wondering if there is any stiochiometric relationship between ml of ethylene glycol and g of dry ice you need to make -10C. Thank you!

You added too much dry ice. Ethylene glycol freezes at -13C. Any CO2/solvent bath must have liquid and frozen solvent in equilibrium for proper temperature control, otherwise it will approach -78ish.

Opsomath does have a pretty good point there. For -10 salt and ice is perfectly sufficient. The EtOH/glycol mixtures are really only useful if you have to maintain an intermediate temp. Another problem with them is they have a tendency to freeze solid, so don't immerse your flasks above the equator...

Except salt and ice gives you about -20 unless heat transfer is lousy which it frequently is because salt/ice freezes solid. If I want -20 I use dry ice/brine.
If I want -10 I use the automatic cooling bath with ethylene glycol/H20 for the bath fluid.

[Honclbrif]

Every time I've done salt + ice I've gotten -10C, with a healthy amt of salt well mixed.