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Inorganic Chemistry
 

Glovebox and Impurity Sensors

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Sensitive substances like organolithium- or organometallic compounds can violently react when exposed to oxygen or water from air. Hence, an inert working environment is required, which can be achieved by using a glovebox.

The glovebox is an important device used in many laboratories, which allows handling and storage of air- and moisture sensitive compounds.

Furthermore, it can be used to measure sensitive substances and carry out reactions.

This video will illustrate how to operate the glovebox, and how to synthesize an indicator to test for oxygen and water within dry solvents.

In general, a glovebox is comprised of a metal box with polycarbonate windows fitted with butyl gloves allowing for manipulation inside the box. Chemicals and supplies are brought into the glovebox via the antechambers, while sensors and a control panel are used for monitoring and regulations.

Furthermore, the functionality of a glovebox can be extended by extra equipment, ranging from vacuum hook ups to freezers for chemical storage.

The glovebox atmosphere is achieved using inert gas such as nitrogen. The box is gas-tight and run at positive pressure, which is controlled by electronically regulating the gas flow into the system.

The inert atmosphere is circulated through a catalyst bed, which is located below the glovebox.

The catalyst is comprised of molecular sieves and copper, which are used to maintain a low level of oxygen and moisture. Copper reacts with oxygen present in the atmosphere, while molecular sieves absorb water. The catalyst has to be regenerated on a regular basis by heating it under a stream of hydrogen and nitrogen gas to assure its activity.

Besides moisture and oxygen, various solvents can contaminate the catalyst. To avoid this, the glovebox chamber is isolated, when working with incompatible chemicals.

Additionally, contamination can be introduced through the antechamber, which must undergo multiple evacuation and purging cycles to remove as much air as possible. The fraction of air remaining can be calculated using this equation.

The content of moisture and oxygen inside the box or any dry solvent can be tested using chemical sensors. Diethylzinc is used to test for contamination inside the box, while sodium benzophenone is used for solvents.

Now that you are familiar with the basics, let's take a look at how to operate the glovebox and test for oxygen and water.

Before you start familiarize yourself with the instrument. For an in detail instruction of glovebox usage watch our video in the laboratory safety collection. Assure that glassware to be brought in has been oven-dried, and empty containers are open.

Check the antechamber log to make sure it is empty. Then, fill the antechamber with inert gas to 1 atm, and close the inlet valve to isolate the chamber.

Once the chamber is purged, open it from the outside, and place the items inside the chamber. Close the chamber, and evacuate it.

Fill in the log including initials, items, and times of each cycle, while the chamber is evacuating. When minimum pressure is reached, leave the antechamber under dynamic vacuum between 5-20 min.

Then, using the inlet valve purge the antechamber again, wait until 1 atm is reached, and evacuate again. Note the time and repeat the cycle. Lastly, refill the chamber with N2 and close off the inert gas supply, when the purging process is finished.

Now you are ready to open the antechamber from inside the glovebox to bring the items in. Close the antechamber door when finished, evacuate it, and fill out the log. 

Check the logbook for the last status of the antechamber and that it is not in use. Repeat the purging process if the antechamber was used to bring out items as the last operation. Then, close the valve connecting the inert gas supply, once antechamber is filled.

Open the door from inside, load the items into the chamber, and close the door. Then open the chamber from outside and remove the items. Evacuate the chamber and fill out the logbook.

Now that you are familiar with the proper usage of a glovebox, let's examine how impurity sensors can be used to test for oxygen and water in the glovebox atmosphere and various solvents.

To test the glovebox atmosphere for oxygen and water levels, first turn off the circulator. Then, open a bottle of diethylzinc solution in hexanes inside the glovebox.

Gently swirl the solution to replace the gas atmosphere with the glovebox atmosphere inside the bottle. Any emerging smoke and white residue indicates oxygen, water, or an ether solvent present in the atmosphere. Then, purge the glovebox for 5 min, turn off the purge, and turn the circulator back on when finished.

In addition to testing the glovebox atmosphere, indicators can be used to test various solvents for oxygen and water impurities. First, turn off the circulator. Then, open the bottle of the desired solvent and transfer 10 mL into a scintillation vial. Add one drop of the ketyl radical solution to test the solvent and observe the color over 1-2 min.

If the solvent is dry, it will hold the purple color of the ketyl-radical indefinitely. If the color changes to blue and then to colorless, then the solvent has impurities. To finish, close all solvent bottles, purge the glovebox and turn the circulator back on.

The glovebox is widely used to handle air- and moisture sensitive materials to carry out reactions, spectroscopic analysis, or to store compounds under air free conditions.

For example, the ketyl radical, which is used to test solvents for water and oxygen, is synthesized using a glovebox. To carry out the synthesis start with turning off the circulator. Weigh out 5 mg of benzophenone into a 20 mL scintillation vial. Then, weigh out 0.5-1 g of sodium and transfer it to the same scintillation vial together with a stir bar. Add 20 mL of dry THF and cap the vial.

Turn the circulator back on, after purging the glovebox for 15 min. Stir the reaction for 48 h or until the color changes from colorless to blue to purple. Once purple is reached, the ketyl radical is ready to use.

Besides chemical indicators, the glovebox can be used for the synthesis of air sensitive compounds, such as 1,2-azaborines. 

In this example N-H-B-ethyl-1,2-azaborine is synthesized starting from N-TBS-B-Cl-1,2-azaborine using a glovebox and a Schlenk line. The isolated compound is then used to prepare a protein-ligand crystal complex with purified lysozyme mutants, and the protein-binding interactions are studied using X-ray diffraction analysis.

You've just watched JoVE's introduction to the glovebox and chemical sensors. You should now understand how to operate a glovebox, how to test for water and oxygen contamination, and how to synthesize air- and moisture sensitive compounds. Thanks for watching!

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