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Cooling baths

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Cooling baths are used extensively in organic chemistry for a variety of reasons. The low temperature of these baths is determined both by the appropriate use of solvent as well as a cryogenic agent such as liquid nitrogen, dry ice (CO2) or ice. Most of these methods require continuous monitoring to ensure the temperature remains steady. For longer or unmonitored reactions, it may be best to invest in a cryocooler.

Temperature Mixture Composition
0 °C Ice
-20 °C Equal amounts of ice and NaCl. The actual temperature obtained will depend on how finely crushed and well mixed the components are, and could be as high as -10°. A dewar is recomended.  Brine/ dry ice produces an identical mixture.
-40 °C Acetonitrile/dry ice. Put the acetonitrile into the Dewar with your thermocouple, slowly add dry ice until you hit your desired temperature. Don't add too much dry ice or you'll freeze the MeCN solid.
-78 °C Dry ice/acetone:  Slowly adding acetone to dry ice will minimize the amount of dry ice you need to handle.  Alternatively, you must slowly add dry ice to the acetone or the large volumes of carbon dioxide produced will cause rapid bubbling.
-98 °C liquid nitrogen/methanol
-131 °C liquid nitrogen/n-pentane

Temperatures between -20 and -80° can be obtained using varied mixtures of ethylene glycol and ethanol over dry ice. A little more detailed list taken from the Hoveyda group website at Boston College.

Temperature   Mixture Composition
13 °C p-Xylene/ dry ice
12 °C Dioxane/ dry ice
6 °C Cyclohexane/ dry ice
5 °C Benzene/ dry ice
2 °C Formamide/ dry ice
0 °C Crushed Ice
-5 -> -20 °C Ice/Salt
-10.5 °C Ethylene Glycol/ dry ice
-12 °C Cycloheptane/ dry ice
-15 °C Benzyl alcohol/ dry ice
-22 °C Tetrachloroethylene/ dry ice
-22.8 °C Carbon Tetrachloride/ dry ice
-25°C 1,3-Dichlorobenezene/ dry ice
-29 °C o-Xylene/ dry ice
-32 °C m-Toluidine/ dry ice
-41 °C Acetonitrile/ dry ice
-42 °C Pyridine/ dry ice
-47 °C m-Xylene/ dry ice
-56 °C n-Octane/ dry ice
-60 °C Isopropyl Ether/ dry ice
-77 °C Acetone/ dry ice
-77 °C Butyl Acetate/ dry ice
-83 °C Propyl Amine/ dry ice
-83.6 °C Ethyl Acetate/Liq N2
-89 °C n-Butanol/Liq N2
-94 °C Hexane/Liq N2
-94.6 °C Acetone/Liq N2
-95.1 °C Toluene/Liq N2
-98 °C Methanol/Liq N2
-100 °C Ethyl Ether/dry ice
-104 °C Cyclohexane/Liq N2
-116 °C Ethanol/Liq N2
-116 °C Ethyl Ether/Liq N2
-131 °C n-Pentane/Liq N2
-160 °C Isopentane/Liq N2
-196 °C Liq N2


  • Chemotoplex, Burk, Kiwi
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Last Modified
09:02, 18 Feb 2014

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