Chapter 3 - Synthesis and Purification at Low Temperature

Abstract

Common cold baths and dry ice bath can attain low temperature. Mixing of crushed ice with salt (use ice mill to mill it) gives low temperatures. Dry ice bath is also commonly used for creating low temperature. Its sublimation temperature is 78.5 ºC. When it is used, inert solvents such as acetone, alcohol, and chloroform should always be added to improve the thermal conduction. This type of low temperature bath can maintain constant temperature. For example, in CS2 case 111.6 ºC can be obtained. This temperature is the solid-liquid equilibrium point (i.e., melting point) for carbon disulfide under standard atmospheric pressure. This is an important route for synthesizing many compounds of rare-gas such as HXY molecules (X = Kr, Xe, Ar; Y = halides CN, SH) and many volatile inorganic compounds. Vacuum technique is a very important experimental method in inorganic synthesis. The synthesis or separation of many volatile compounds and those sensitive to oxygen, air, and water vapor needs to be carried out under vacuum conditions. Some precision measurements such as LEED (Low-Energy Electron Diffraction), AES (Auger Electron Spectroscopy), and ISS (Ion Scattering Spectroscopy) also need to be operated under ultrahigh vacuum of 10-9Pa. The most common thermometers in laboratory for measuring low and ultra low temperature are: thermal resistance thermometer, thermocouple, and thermistor.