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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals
t-butyl hydroperoxide, and di-t-butyl peroxide, are less dangerous than the adventitious peroxides formed in solvents.
Removal of peroxides with alumina:
A 2 x 33 cm column filled with 80 g of 80-mesh basic activated alumina is usually sufficient to remove all peroxides from 100 to 400 mL of solvent, whether water-soluble or water-insoluble. After passage through the column, the solvent should be tested for peroxide content. Peroxides formed by air oxidation are usually decomposed by the alumina, not merely absorbed on it. However, for safety it is best to slurry the wet alumina with a dilute acidic solution of ferrous sulfate before it is discarded.
Removal of peroxides with Molecular Sieves®:
Reflux 100 mL of the solvent with 5 g of 4- to 8-mesh indicating activated 4A Molecular Sieves® for several hours under nitrogen. The sieves are separated from the solvent and require no further treatment because the peroxides are destroyed during their interaction with the sieves.
Removal of peroxides with ferrous sulfate:
A solution of 6 g of FeSO4 · 7H2O, 6 mL of concentrated sulfuric acid, and 11 mL of water is stirred with 1 L of water-insoluble solvent until the solvent no longer gives a positive test for peroxides. Usually only a few minutes are required.
Diacyl peroxides can be destroyed by this reagent as well as by aqueous sodium hydrogen sulfite, sodium hydroxide, or ammonia. However, diacyl peroxides with low solubility in water, such as dibenzoyl peroxide, react very slowly. A better reagent is a solution of sodium iodide or potassium iodide in glacial acetic acid.
Procedure for destruction of diacyl peroxides:
For 0.01 mol of diacyl peroxide, 0.022 mol (10% excess) of sodium or potassium iodide is dissolved in 70 mL of glacial acetic acid, and the peroxide added gradually with stirring at room temperature. The solution is rapidly darkened by the formation of iodine. After a minimum of 30 minutes, the solution is washed down the drain with a large excess of water.
Most dialkyl peroxides (ROOR) do not react readily at room temperature with ferrous sulfate, iodide, ammonia, or the other reagents mentioned above. However, these peroxides can be destroyed by a modification of the iodide procedure.
Procedure for destruction of dialkyl peroxides:
One milliliter of 36% (w/v) hydrochloric acid is added to the above acetic acid/potassium iodide solution as an accelerator, followed by 0.01 mol of the dialkyl peroxide. The solution is heated to 90 to 100 °C on a steam bath over the course of 30 minutes and held at that temperature for 5 hours.
7.D.3.1 Metal Hydrides
Most metal hydrides react violently with water with the evolution of hydrogen, which can form an explosive mixture with air. Some, such as lithium aluminum hydride, potassium hydride, and sodium hydride, are pyrophoric. Most can be decomposed by gradual addition of (in order of decreasing reactivity) methyl alcohol, ethyl alcohol, n-butyl alcohol, or t-butyl alcohol to a stirred, ice-cooled solution or suspension of the hydride in an inert liquid, such as diethyl ether, tetrahydrofuran, or toluene, under nitrogen in a three-necked flask. Although these procedures reduce the hazard and should be a part of any experimental procedure that uses reactive metal hydrides, the products from such deactivation may be hazardous waste that must be treated as such on disposal.
Hydrides commonly used in laboratories are lithium aluminum hydride, potassium hydride, sodium hydride, sodium borohydride, and calcium hydride. The following methods for their disposal demonstrate that the reactivity of metal hydrides varies considerably. Most hydrides can be decomposed safely by one of the four methods, but the properties of a given hydride must be well understood in order to select the most appropriate method. (CAUTION: Most of the methods described below produce hydrogen gas, which can present an explosion hazard. The reaction should be carried out in a hood, behind a shield, and with proper safeguards to avoid exposure of the effluent gas to spark or flame. Any stirring device must be spark-proof.)
Decomposition of lithium aluminum hydride:
Lithium aluminum hydride (LiA1H4) can be purchased as a solid or as a solution in toluene, diethyl ether, tetrahydrofuran, or other ethers. Although drop-