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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals
disposed of in the sanitary sewer should generally be below 1%.
7.D.2.1 Thiols and Sulfides
Small quantities of thiols (mercaptans) and sulfides can be destroyed by oxidation to a sulfonic acid with sodium hypochlorite. If other groups that can be oxidized by hypochlorite are also present, the quantity of this reagent used must be increased accordingly.
Procedure for oxidizing 0.1 mol of a liquid thiol:
Five hundred milliliters (0.4 mol, 25% excess) of commercial hypochlorite laundry bleach (5.25% sodium hypochlorite) is poured into a 5-L three-necked flask located in a fume hood. The flask is equipped with a stirrer, thermometer, and dropping funnel. The thiol (0.1 mol) is added dropwise to the stirred hypochlorite solution, initially at room temperature. A solid thiol can be added gradually through a neck of the flask or can be dissolved in tetrahydrofuran or other appropriate nonoxidizable solvent and the solution added to the hypochlorite. (The use of tetrahydrofuran introduces a flammable liquid that could alter the final disposal method.) Traces of thiol can be rinsed from the reagent bottle and dropping funnel with additional hypochlorite solution. Oxidation, accompanied by a rise in temperature and dissolution of the thiol, usually starts after a small amount of the thiol has been added. If the reaction has not started spontaneously after about 10% of the thiol has been added, addition is stopped and the mixture warmed to about 50 °C to initiate this reaction. Addition is resumed only after it is clear that oxidation is occurring. The temperature is maintained at 45 to 50 °C by adjusting the rate of addition and using an ice bath for cooling if necessary. Addition requires about 15 minutes. If the pH drops below 6 because of generation of the sulfonic acid, it may be necessary to add some sodium hydroxide or additional bleach because hypochlorite is destroyed under acidic conditions. Stirring is continued for 2 hours while the temperature gradually falls to room temperature. The mixture should be a clear solution, perhaps containing traces of oily by-products. The reaction mixture can usually be flushed down the drain with excess water. The unreacted laundry bleach need not be decomposed.
(Because sodium hypochlorite solutions deteriorate on storage, it is advisable to have relatively fresh material available. A 5.25% solution of sodium hypochlorite has 25 g of active chlorine per liter. If determination of the active hypochlorite content is justified, it can be accomplished as follows. Ten milliliters of the sodium hypochlorite solution is diluted to 100.0 mL, and then 10.0 mL of this diluted reagent is added to a solution of 1 g of potassium iodide and 12.5 mL of 2 M acetic acid in 50 mL of distilled water. Using a starch solution as indicator, titrate the solution with 0.1 N sodium thiosulfate. One milliliter of titrant corresponds to 3.5 mg of active chlorine. A 5.25% solution of sodium hypochlorite requires approximately 7 mL of titrant.)
Calcium hypochlorite may be used as an alternative to sodium hypochlorite and requires a smaller volume of liquid. For 0.1 mol of thiol, 42 g (25% excess) of 65% calcium hypochlorite (technical grade) is stirred into 200 mL of water at room temperature. The hypochlorite soon dissolves, and the thiol is then added as in the above procedure.
Laboratory glassware, hands, and clothing contaminated with thiols can be deodorized by a solution of Diaperene®, a tetraalkylammonium salt used to deodorize containers in which soiled diapers have been washed.
Small amounts of sulfides, RSR', can be oxidized to sulfones (RSO2 R') to eliminate their disagreeable odors. The hypochlorite procedure used for thiols can be employed for this purpose, although the resulting sulfones are often water-insoluble and may have to be separated from the reaction mixture by filtration.
Small amounts of the inorganic sulfides, sodium sulfide or potassium sulfide, can be destroyed in aqueous solution by sodium or calcium hypochlorite using the procedure described for oxidizing thiols.
7.D.2.2 Acyl Halides and Anhydrides
Acyl halides, sulfonyl halides, and anhydrides react readily with water, alcohols, and amines. They should never be allowed to come into contact with waste that contains such substances. Most compounds in this class can be hydrolyzed to water-soluble products of low toxicity.
Procedure for hydrolyzing 0.5 mol of RCOX, RSO2X, or (RCO)2O:
A 1-L three-necked flask equipped with a stirrer, dropping funnel, and thermometer is placed on a steam bath in a hood, and 600 mL of 2.5 M aqueous sodium hydroxide (1.5 mol, 50% excess) are poured