罗伯特 M Rioux, 阿杰萨特, 刘志峰陈, 宾夕法尼亚州立大学, 大学公园, PA
使用对氧化或湿气敏感的试剂需要使用无技术。Schlenk 线是一种常规使用的玻璃器具, 用于在化学实验室中进行空气和水分的自由操作 1 。Schlenk 线是广泛使用的许多化学家, 因为它允许他们进行空气或水敏感的反应, 即使没有费用和限制的手套箱。Schlenk 线可配置为惰性气体气氛, 如氮气和氩气, 或将玻璃器皿暴露在真空中。另一种实现空气和水分自由环境的方法涉及使用手套。Schlenk 线和手套箱的主要区别在于, 清洗和重新灌装直接适用于反应容器, 而清洗和重新灌装则适用于气闸, 而不是手套。此外, 在手套, 传统的实验室设备可以建立一个大的惰性空间, 但手套必须用于处理实验和手套本身也是昂贵的。
The Schlenk line is an extremely useful system, allowing the manipulation of air- and/or water-sensitive reagents without the expense and restriction of a glove box. It is most safely utilized inside a working fume hood. Care should be taken to prevent pressure build-up in the schlenk line by ensuring proper ventilation through a gas bubbler.
A Schlenk line is a piece of laboratory equipment that allows for the safe handling of air- and water-sensitive chemicals.
A Schlenk line requires a vacuum, inert gas, and cryogenic temperatures. It must be operated with care to prevent equipment failure and thus release of hazardous chemicals. This video discusses the potential hazards associated with the Schlenk line, and precautions necessary for its safe use. For more information about the operation and applications of the Schlenk line, please watch JoVE’s video on “Schlenk Lines Transfer of Solvent.”
We begin by briefly examining the components of a Schlenk line. A Schlenk line consists of a pair of glass tubes together called a “dual manifold.” One tube connects to a vacuum pump, and the other to a source of inert gas. A Schlenk flask, or other apparatus, connects to the dual manifold via a two-way valve that permits access to either the vacuum line or the inert gas line, but never both simultaneously.
Let’s examine the vacuum line in greater detail. The vacuum line is sealed at one end. The other end connects to a cold trap, which is in turn connected to the vacuum pump. A Schlenk flask exposed to this line will be evacuated, and the gases sent to the cold trap, a glass container submerged in liquid nitrogen. It freezes volatile organics, protecting the pump from damage, and the user from exposure. Potential dangers of the vacuum line include glass imploding under vacuum, and the safety hazards associated with liquid nitrogen.
Next, we turn to the inert gas line. The inert gas, usually nitrogen or argon, is regulated by a valve and often passes through a desiccant before entering the Schlenk line. A Schlenk flask exposed to this line will be filled with the inert gas. The excess gas then leaves the system via a mineral oil bubbler, to prevent air from entering the inert gas line. Potential hazards of this line include glass exploding due to over pressurization, and the exposure of the inert gas line to the vacuum.
It is important to perform regular safety checks while setting up the apparatus.
The Schlenk line is mounted inside a fume hood and operated with the sash lowered, to protect the user from inadvertent exposure. A blast shield may be used additionally, when handling very sensitive reagents. Wear safety goggles or a face shield, a flame-proof lab coat, and cryogenic gloves when working with liquid nitrogen.
Check the tubing for tears or other defects before connecting the dual manifold to the vacuum pump and the inert gas line. Ensure there is sufficient oil in the oil bubbler.
The Schlenk line contains check valves to prevent backflow of air into the system, and pressure relief valves on the dual manifold and the cold trap. The connectors use glass clamps sealed with U-clamps and airtight O-rings. Ensure these valves and connectors are not damaged. Apply vacuum grease to the glassware at the interface between surfaces.
Dry the Schlenk flask and other glassware by oven- or flame-drying. Check the glassware and the dual manifold for cracks. Cracked glass can implode under vacuum, exposing the reagents to the atmosphere and injuring the user. Seal the Schlenk flask carefully with a rubber septum or a ground glass adapter before connecting it to the line.
Now that we’ve seen the preliminary precautions, let’s turn to safety concerns while operating the Schlenk line.
One potential hazard is the formation of liquid oxygen in the cold trap. Liquid oxygen is extremely explosive. To prevent its formation, start the vacuum pump and evacuate the vacuum line before submerging the cold trap in the liquid nitrogen Dewar. Never allow the cold trap to contact liquid nitrogen unless the vacuum pump is running, and never open the vacuum line to air while the Dewar is in place.
Liquid oxygen can also form if air inadvertently enters the cold trap during the experiment. Check the cold trap for a light blue liquid. If detected, quench the reaction and call for assistance, but keep the apparatus under vacuum and liquid nitrogen. It is only safe to stop the vacuum and remove the Dewar once the liquid oxygen vaporizes into the pump.
When working with the inert gas line, regularly check the inert gas supply and the flow rate using the inert gas bubbler. The flow rate should be about one bubble per second when the Schlenk flask is open to the line, and slightly greater otherwise. Bubbling should be visible at the oil bubbler at all times. If no bubbles are seen, close the inert gas source to prevent the line from over-pressurizing.
If the inert gas contacts the vacuum, it will depressurize, causing the check valve to close or mineral oil to backflow into the inert line, followed by air. If this occurs, switch off the pump and close all valves.
When purging the Schlenk line or a Schlenk flask, turn the valve very slowly. This prevents glassware from cracking due to rapid pressure changes. Before the reagents are added, expose the Schlenk flask to the inert line slowly, to prevent depressurization of the inert line.
Before withdrawing an air- or water-sensitive reagent, purge syringe and needle and the septum-sealed reagent bottle in the inert gas line. Withdraw the reagent from the bottle, making sure to overdraw and then plunge to the correct volume. Slowly add the reagent to the Schlenk flask and place the needle tip in a beaker of quenching agent if necessary.
After the reaction is complete and quenched, remove the liquid nitrogen Dewar. Then switch off the pump.
You’ve just watched JoVE’s introduction to safe Schlenk line operation. You should now be familiar with its design, its operating procedure, and safety precautions. Thanks for watching!
