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Air-free techniques refer to a range of manipulations in the chemistry laboratory for the handling of compounds that are air-sensitive. These techniques prevent the compounds from reacting with components of air, usually water and oxygen; less commonly carbon dioxide and nitrogen. A common theme among these techniques is the use of a high vacuum to remove air, and the use of an inert gas: preferably argon, but often nitrogen. The two most common types of air-free technique involve the use of a glovebox and a Schlenk line. In both methods, glassware (often Schlenk tubes) are pre-dried in ovens prior to use. They may be flame-dried to remove adsorbed water. Prior to coming into an inert atmosphere, vessels are further dried by ''purge-and-refill'' — the vessel is subjected to a vacuum to remove gases and water, and then refilled with inert gas. This cycle is usually repeated three times or the vacuum is applied for an extended period of time. One of the differences between the use of a glovebox and a Schlenk line is where the ''purge-and-refill'' cycle is applied. When using a glovebox the ''purge-and-refill'' is applied to an airlock attached to the glovebox, commonly called the "port" or "ante-chamber". In contrast when using a Schlenk line the ''purge-and-refill'' is applied directly to the reaction vessel through a hose or ground glass joint that is connected to the manifold.〔Duward F. Shriver and M. A. Drezdzon "The Manipulation of Air-Sensitive Compounds" 1986, J. Wiley and Sons: New York. ISBN 0-471-86773-X.〕 ==Glovebox== The most straightforward type of air-free technique is the use of a glovebox. A glove bag uses the same idea, but is usually a poorer substitute because it is more difficult to purge, and less well sealed. Inventive ways of accessing items beyond the reach of the gloves exist, such as the use of tongs and strings. The main drawbacks to using a glovebox are the cost of the glovebox itself, and limited dexterity wearing the gloves. In the glovebox, conventional laboratory equipment can often be set up and manipulated, despite the need to handle the apparatus with the gloves. By providing a sealed but recirculating atmosphere of the inert gas, the glove box necessitates few other precautions. Cross contamination of samples due to poor technique is also problematic, especially where a glovebox is shared between workers using differing reagents, volatile ones in particular. Two styles have evolved in the use of gloveboxes for synthetic chemistry. In a more conservative mode, they are used solely to store, weigh, and transfer air-sensitive reagents. Reactions are thereafter carried out using Schlenk techniques. The gloveboxes are thus only used for the most air-sensitive stages in an experiment. In their more liberal use, gloveboxes are used for the entire synthetic operations including reactions in solvents, work-up, and preparation of samples for spectroscopy. Not all reagents and solvents are acceptable for use in the glovebox, although again, different laboratories adopt different cultures. The "box atmosphere" is usually continuously deoxygenated over a copper catalyst. Certain volatile chemicals such as halogenated compounds and especially strongly coordinating species such as phosphines and thiols can be problematic because they irreversibly poison the copper catalyst. Because of this problem, many experimentalists choose to handle such compounds using Schlenk techniques. In the more liberal use of gloveboxes, it is accepted that the copper catalyst will require more frequent replacement but this cost is considered to be an acceptable trade-off for the efficiency of conducting an entire synthesis within a protected environment 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Air-free technique」の詳細全文を読む スポンサード リンク
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