page_title: Desiccant
section_title: Drying of solvents
hierarchical_section_title: Desiccant / Drying of solvents
caption_attribution_description: English: Toluene is refluxed in sodium-benzophenone to remove oxygen and water, before being distilled. Photo taken 4 Sep 2006. Keywords: reflux, toluene, sodium, benzophenone, distillation, desiccation Gallery A bottle of benzophenone by Lancaster. Toluene is refluxed with sodium and benzophenone to produce dry, oxygen-free toluene. The mixture is still not blue yet indicating that the reaction is not complete. The intense blue coloration due to the benzophenone ketyl radical shows that the toluene is considered free of air and moisture. After the toluene has been thoroughly dried by the sodium and benzophenone, it is distilled at atmospheric pressure under a slight positive pressure of nitrogen to prevent contamination by air into the receiving Schlenk flask. Category:desiccants Category:distillation
context_page_description: A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness in its vicinity; it is the opposite of a humectant. Commonly encountered pre-packaged desiccants are solids that absorb water. Desiccants for specialized purposes may be in forms other than solid, and may work through other principles, such as chemical bonding of water molecules. They are commonly encountered in foods to retain crispness. Industrially, desiccants are widely used to control the level of water in gas streams.
context_section_description: Desiccants are also used to remove water from solvents, typically required by chemical reactions that do not tolerate water, e.g., the Grignard reaction. The method generally, though not always, involves mixing the solvent with the solid desiccant.  Studies show that molecular sieves are superior as desiccants relative to chemical drying reagents such as sodium-benzophenone.  Sieves offer the advantages of being safe in air and recyclable.
caption: Toluene is heated under reflux with sodium and benzophenone to produce dry, oxygen-free toluene. The toluene is dry and oxygen free when the intense blue coloration from the benzophenone ketyl radical is observed.
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