Stoltz Lab

[Allen H.]

taken from: http://pubs.acs.org/hotartcl/chas/98/julaug/quench.html

Chemical Health & Safety
July/August 1998
Chemical Health & Safety 1998, 5(4), 28-31.
Copyright © 1998 by the American Chemical Society.

Standard Operating Procedure:
Quenching the bottom of a solvent-drying still
Designated area
The operation should be conducted only in a clean, properly operating fume hood. Do not perform this process alone! Make sure an informed, prepared person is in the area.

Personal protective equipment
Eye protection
Safety glasses or goggles
Face shield if desired
Protective clothing
Apron or lab coat
Gloves: nitrile, butyl, PVC

Training
Only instructors and teaching assistants who have participated in the University of California's Laboratory Safety Training may use this procedure.

Ventilation
Use a fume hood, preferably with sliding sash windows. Perform all operations in the hood, standing behind the sliding windows, and reach around to perform the manipulations required.

Process and product
When a distillation flask becomes discolored and filled with a brown semisolid, it is time to start over with new solvent and drying material (usually sodium or lithium metal or a metal hydride). One must first "quench" the old flask. This procedure should be performed as soon as possible to avoid the possible formatio n of peroxides in the solvents. Also, it is a good policy to quench the strong b ases in a timely fashion to avoid injuries.

Remove the flask to a clean, clear fume hood.

Acquire a labeled container in which to place the unused portion of the solvent to be dried. If this is to be discarded, then it must first be properly labeled as hazardous waste. Obtain a container of sufficient size to hold both ice water and the flask.

Decant the bulk of the remaining solvent into the appropriate labeled container. Place the flask into the ice-water bucket, and secure it with a clamp and ring stand if necessary to prevent it from falling over. Aim the mouth of the flask a way from any people or equipment. If you feel uncomfortable, or are quenching a large volume of alkali metal or metal hydride, obtain and use a blast shield.

Now, use a pipette to add a small aliquot of sec-butanol. If gaseous bubb les appear, wait until they stop, then add another small aliquot of sec-b utanol. Continue this cautious stepwise addition until the generation of gaseous bubbles becomes very slow.

After the sec-butanol has been added, try adding an alcohol with more fre ely available protons, such as n-butanol. Continue the same cautious step wise approach until the gas-bubble generation slows considerably. Remember to st ir or swirl the flask occasionally, always keeping the mouth of the flask pointe d away from anyone.

Once you have used n-butanol, try the same stepwise, cautious addition wi th these solvents in sequence: isopropyl alcohol, ethanol, methanol, and water. Be very careful with the addition of water. Even after methanol has been added, the drying agent can still react violently with water, especially if there hasn' t been sufficient mechanical stirring of the solution.

Once the reaction with water is complete, use a suitable acid solution (such as 3 M HCl) to neutralize the basic solution you have created. Add the acid in aliq uots with the goal of obtaining a pH of 7. Don't be obsessive about obtaining th is exact value; the range of 5-9 is okay.

Pour this solution into a properly labeled waste container, and see that it is d isposed of in a safe, legal manner. In order to properly label the waste contain er with the percentages, you must keep track of the approximate amounts of the v arious solvents you used in this quenching process.

Spill and accident procedures
If you spill the unquenched flask, move quickly away. The drying agent ma y spontaneously ignite in the air, and the flammable solvent may cause a flash f ire. Inform everyone in the immediate area and have them move to a safe location .

If the spill is large, call the hazardous materials response spill team and info rm them of the condition. There are two likely occurrences: (1) the flammable so lvent will evaporate and the alkali metal or metal hydride will oxidize with the moisture in the air; or (2) the alkali metal or metal hydride will react vigoro usly with a proton source (such as water) and will generate hydrogen gas, which may spontaneously ignite with the heat of the reaction. If this occurs, exit and call the fire department; the entire area may be quickly engulfed in flames.

If the spill is small and doesn't contain any alkali metal or metal hydride, tre at it as a flammable materials spill and "dike" it with absorbent spill cleanup material (polypropylene, silicates). Cover the spill with the absorbent, and onc e the spill is absorbed, sweep it into a bag that is properly labeled with the c ontents for hazardous waste disposal.

If the spill evaporates completely and leaves the slowly oxidizing alkali metal or metal hydride behind, gather these carefully into a beaker and quench with th e same previously described procedure.

Waste disposal
Dispose of the properly labeled hazardous waste in a safe, legal manner. Nonhaza rdous waste may be placed in a container to go to a sanitary landfill or, if app ropriate, washed into the sewer system.

Hazardous chemicals involved in the procedure
Flammable solvents
GLYME (1,2-dimethoxyethane)
THF (tetrahydrofuran)
Et2O (ether, diethyl ether, or ethyl ether)
Dioxane (1,4-dioxane or p-dioxane)
Pentane
Benzene
Caustic solids
Sodium
Lithium
Corrosive liquids
Hydrochloric acid

Special handling requirements and storage
Label the hazardous materials with their full name (e.g., tetrahydrofuran, not T HF). Store the flammables in the approved flammables storage cabinet. Use second ary containment carriers whenever transporting hazardous material outside of the laboratory. Use due care and caution when moving hazardous materials around any where.

Approval required
Before conducting this operation, Chemistry 123 students must have approv al from the principal investigator.

Decontamination
All contaminated personal protective equipment and glassware used should be wash ed with soap (or detergent) and water.

Original document available on the Internet at http://chem-courses.ucsd.edu/CoursePages/Uglabs/Course.Specific.Info/123/

Chemistry 123
University of California-San Diego
September 11, 1995
Russell Vernon Clark, Ph.D.
Environment, Health & Safety Specialist
Department of Chemistry and Biochemistry, 0303
University of California-San Diego
9500 Gilman Drive
La Jolla, CA 92093-0303

rvernonclark@ucsd.edu