Chem 1140; Techniques forHandling Air-Sensitive Compounds• Introduction• The Glove Box• Schlenk Techniques• Drying and Degassing SolventsMaterials which oxidize, decompose or even explode under the influence ofoxygen or moisture.• Pyrophoric CompoundsMetal alkyls and aryls e.g. RMgX, RLi, RNa,R3Al, R2ZnMetal carbonyls e.g. Ni(CO)4, Fe(CO)5, Co2(CO)8Alkali metals e.g. Na, K, CsMetal powders e.g. Al, Co, Fe, Mg, Pd, Pt, ZnMetal hydrides e.g. NaH, KH, LiAlH4Hydrides e.g. B2H6, PH3, AsH3Boranes, phosphines, arsenes, etc. e.g. Et3B, R3P, R3As• Chemicals which react violently with waterMetal hydrides, metal amides (NaNH2), metal alkyls and aryls, metals, metal powders, hydrides, many main group halides (BCl3, BF3, AlCl3, PCl3, SiCl4), inorganic acid halides (POCl3, SOCl2), low molecular weight organic acid halides and anhydrides.Glove boxes and Schlenk techniques do NOT protect from explosive orshock sensitive materials or mixtures!!! Also, they only provide limitedprotection from toxic compounds.What are Air-Sensitive Compounds?P. Wipf 1 Chem 1140The Glove Box• The best way to keep things away from atmospheric oxygen and water isto work in a fully enclosed “bench top,” containing an “inert atmosphere,”which one could reach into with gloves. Such a device is called a “glovebox” or a “dry box”. There are also cheap “glove bags”, bags you can fillwith inert gas and reach into with attached gloves.A glove box has four important components:1. The actual “box” is a large aluminum chamber with a plastic front windowand two impressive looking gloves. This is the working area. Organic solventswill spoil the plastic, and fancy fingerware,opulent wedding trophies, orpointy fingernails will puncturethe rubber gloves and deflatethe system.The Glove BoxP. Wipf 2 Chem 11402) There is an antichamber (like a submarine or spaceship airlock) which is howthings get in and out without letting in air.The Glove Box3) The gas in the box is constantly circulated over a scrubber (often called the“catalyst”) which removes any air or water that has made its way into theenclosure. Since the catalyst is damaged by many kinds of reactive chemicals(chlorinated solvents, sulfur compounds, etc.), we must be careful what we allowto evaporate into the box atmosphere.A fan inside the box circulates thebox atmosphere through thecanister.The Glove BoxP. Wipf 3 Chem 1140The Glove Box4) The glove box must be able to regulate pressure inside. The device thatregulates the pressure is set to tolerate only a few millibar of positive andnegative pressure and automatically pumps nitrogen out if the pressure gets toohigh or draws fresh nitrogen in from a tank/dewar ifthe pressure gets too low. One can also regulatepressure manually with a foot pedal.The Glove BagP. Wipf 4 Chem 1140The Dry BoxSchlenk TechniquesP. Wipf 5 Chem 1140Schlenk Techniques4) The centerpiece of the defense against atmospheric intrusion is the doublemanifold, or the Schlenk line.Vacuum PumpVacuum TrapManifoldNujol BubblerNitrogen Dewar & RegulatorSchlenk TechniquesP. Wipf 6 Chem 1140BubblersThe Schlenk flask is an ordinary round-bottom flask with a sidearm with astopcock (greased!). You can connect this sidearm to the Schlenk linewith thick rubber tubing and use it to admit nitrogen to the flask or to evacuate it.The tubing needs to be thick so that it won’t collapse under vacuum. Putsomething in the neck of the flask, such as a septa or glass stopper (greased) or anotherpiece of apparatus such as a Schlenk addition funnel or a Schlenk filter .Schlenk TechniquesP. Wipf 7 Chem 1140Schlenk TechniquesConvenient ways to transfer solutions into and from Schlenk flasks is via septa andsyringes or cannula.A cannula is a hollow steelneedle with two sharp ends. It canserve fortransferring liquids when setup as shown. If the pressure in the flaskat the right is greater than that in theother flask, the liquid will be pushed fromthe right to the left flask. Thispressure difference can be achievedby placing one flask under nitrogenand partially evacuating the other.Schlenk TechniquesP. Wipf 8 Chem 1140Schlenk TechniquesTo address the difficult task of no-air filtrations, the Schlenk filter (illustrated below) canbe used. Its effective use requires some practice and “good hands”. The filter is placedon top of the flask with the material to be filtered, and on top of it is placed a flask inwhich to catch the filtrate. The whole assemblage is then inverted, and you try to get asmuch of the solid as possible to run down on to the fritted glass disk. You can help thesolid down with the stir bar,which you can move aroundwith a hand-held magnet onthe outside of the flask.Applying a touch of vacuumto the underside of the fritwhile the top is undernitrogen will move thefiltrate through just like in aordinary suction filtration.Schlenk TechniquesFor instructional videos on Schlenk-line techniques and dry box manipulations, see:http://www.chem.cuhk.edu.hk/lab_technique_6handling.htmP. Wipf 9 Chem 1140The Crown Jewel of SchlenkTechniques - The High Vacuum LineStorageP. Wipf 10 Chem 1140StorageGas HandlingYou must be very careful not to let pressure build up in any piece ofapparatus. Schlenk techniques can tolerate pressures only slightly greater 1atm. If you have a pressure of 2 atm in a flask (twice the external pressure)that’s 15 pounds on every square inch (psi) of your apparatus. So a stopperwith a one square inch opening will have 14.7 pounds pushing it open. This isequivalent to hanging a bowling ball off of it! Be sure!whenever you work withgases!that you know what will happen anytime you open a valve, where thegas is supposed to be going, and where the gas will go if the pressure byaccident gets too high.P. Wipf 11 Chem 1140Gas HandlingFor lecture bottlesSafe Handling of DiazomethaneP. Wipf 12 Chem 1140Solvent Purification and DegassingSolvent Purification and DegassingP. Wipf 13 Chem 1140Solvent Purification and DegassingMethods of Degassing• Freeze-Pump-Thaw This is the most effective methods for solvent degassing. A solvent in a sealed Schlenk orheavy wall sealed tube is frozen by immersion of the flask in liquid N2. When the solvent iscompletely frozen, the flask is opened to the vacuum (high vacuum) and pumped 2-3minutes, with the flask still immersed in liquid N2. The flask is then closed and warmeduntil the solvent has completely melted. This process is repeated (usually three times) andafter the last cycle the flask