Cooling baths are used to remove heat from reactions. This may be in order to safely dissipate heat from exothermic reactions, slow rates of reaction, or exhibit kinetic control of a process to alter the distribution of products formed.

Ice baths

By far the most common cooling baths used are ice-baths. these offer easy cooling to around 0 °C, however, with ice alone, thermal transfer may be poor. Addition of water to the ice-bath usually aids the dispersion of heat.

Many additives can be used with ice-baths to alter the temperature. Sodium chloride is the most common additive, lowering the temperature below zero.

Water baths

These are generally better at dispersing heat than just ice-baths as the thermal transfer tends to be better. However, they offer less cooling, and are more awkward to maintain at an exact temperature, unless using external heating or cooling sources (eg a Peltier pump unit).

Cryogenic baths

Largely cryogenic baths fall into two categories:

• Dry ice / solvent

• Liquid nitrogen / solvent

A whole range of temperatures can be acheived by varying the coolant and the solvent. These tend to be stable temperatures, as providing there is excess coolant (e.g. visible dry ice pellets) in the solvent, then the temperature should be as specified.

By far the most commonly used cryo-bath is dry-ice/acetone, providing a –78 °C temperature.

The choice of solvent is important, not just for the temperature. Safety issues applied to many solvents, such as flammability and toxicity.