Cooling bath

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A cooling bath is a mixture used in a laboratory when low temperatures are needed. The simplest and cheapest cooling bath is an ice/water mixture, which maintains a temperature of 0 °C. For lower temperatures, three main types of cooling baths are typical:

  • ice / inorganic salts mixtures which can go down to -55 °C
  • dry ice (CO2(s)) in organic solvents can go down to -78 °C
  • liquid nitrogen, neat or in organic solvents can go down to -196 °C

Below is a table of the most common cooling baths used in the lab.

Cooling Baths

The following table lists different cooling baths and their respective temperature.

Temperature (°C) Mixture
13 p-Xylene / CO2(s)
12 1,4-Dioxane / CO2(s)
6 Cyclohexane / CO2(s)
5 Benzene / CO2(s)
2 Formamide / CO2(s)
0 Water / Ice
-12 Cycloheptane / CO2(s)
-13 Ethylene Glycol / CO2(s)
-15 Benzyl alcohol / CO2(s)
-15 25 g NH4Cl / 100 g Ice
-20 33 g NaCl / 100 g Ice
-22 Tetrachloroethylene / CO2(s)
-23 Carbon Tetrachloride / CO2(s)
-25 1,3-Dichlorobenezene / CO2(s)
-26 o-Xylene / CO2(s)
-28 67 g NaBr / 100 g Ice
-30 m-Toluidine / CO2(s)
-34 85 g MgCl2∙6H2O / 100 g Ice
-40 123 g CaCl2∙6H2O / 100 g Ice
-41 Acetonitrile / CO2(s)
-42 Pyridine / CO2(s)
-48 m-Xylene / CO2(s)
-55 143 g CaCl2∙6H2O / 100 g Ice
-56 n-Octane / CO2(s)
-60 Isopropyl Ether / CO2(s)
-63 Chloroform / CO2(s)
-78 Acetone / CO2(s)*
-84 Ethyl Acetate / N2(l)
-89 n-Butanol / N2(l)
-93 Toluene / N2(l)
-94 Acetone / N2(l)
-95 n-Hexane / N2(l)
-98 Methanol / N2(l)
-104 Cyclohexene / N2(l)
-114 Ethanol / N2(l)
-116 Diethyl Ether / N2(l)
-130 n-Pentane / N2(l)
-160 Isopentane / N2(l)
-196 N2(l)

*Some people recommend isopropanol over acetone for dry ice traps because it is less flammable, less volatile and fizzes less.

N.B. You will find a lot of websites which give erroneous data for cooling baths. Most notably is the dry ice/ether one which is very often reported as going to -100 °C. CO2 has a mp of -78 °C, which means that if you add it to a solvent with a mp below that temperature, you will only be able to get it down to -78 °C. Therefore, adding dry ice to any solvent listed below Acetone / CO2(s) will still give you -78 °C. Acetone is used just because it is the cheapest of all.