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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals
into the flask. A few milliliters of the acid derivative are added drop wise with stirring. If the derivative is a solid, it can be added in small portions through a neck of the flask. If reaction occurs, as indicated by a rise in temperature and dissolution of the acid derivative, addition is continued at such a rate that the temperature does not rise above 45 °C. If the reaction is sluggish, as may be the case with less soluble compounds such as p-toluenesulfonyl chloride, the mixture is heated before adding any more acid derivative. When the initial added material has dissolved, the remainder is added drop wise. As soon as a clear solution is obtained, the mixture is cooled to room temperature, neutralized to about pH 7 with dilute hydrochloric or sulfuric acid, and washed down the drain with excess water.
Many aldehydes are respiratory irritants, and some, such as formaldehyde and acrolein, are quite toxic. There is sometimes merit in oxidation of aldehydes to the corresponding carboxylic acids, which are usually less toxic and less volatile.
Procedure for permanganate oxidation of 0.1 mol of aldehyde:
A mixture of 100 mL of water and 0.1 mol of aldehyde is stirred in a 1-L round-bottomed flask equipped with a thermometer, dropping funnel, stirrer, steam bath, and, if the aldehyde boils below 100 °C, a condenser. Approximately 30 mL of a solution of 12.6 g (0.08 mol, 20% excess) of potassium permanganate in 250 mL of water is added over a period of 10 minutes. If the temperature rises above 45 °C, the solution should be cooled. If this addition is not accompanied by a rise in temperature and loss of the purple permanganate color, the mixture is heated by the steam bath until a temperature is reached at which the color is discharged. The rest of the permanganate solution is added slowly at within 10 °C of this temperature. The temperature is then raised to 70 to 80 °C, and stirring continued for 1 hour or until the purple color has disappeared, whichever occurs first. The mixture is cooled to room temperature and acidified with 6 N sulfuric acid. (CAUTION: Do not add concentrated sulfuric acid to permanganate solution because explosive manganese oxide (Mn2O7) may precipitate.) Enough solid sodium hydrogen sulfite (at least 8.3 g, 0.08 mol) is added with stirring at 20 to 40 °C to reduce all the manganese, as indicated by loss of purple color and dissolution of the solid manganese dioxide. The mixture is washed down the drain with a large volume of water.
If the aldehyde contains a carbon-carbon double bond, as in the case of the highly toxic acrolein, 4 mol (20% excess) of permanganate per mol of aldehyde is required to oxidize the alkene bond and the aldehyde group.
Formaldehyde is oxidized conveniently to formic acid and carbon dioxide by sodium hypochlorite. Thus 10 mL of formalin (37% formaldehyde) in 100 mL of water is stirred into 250 mL of hypochlorite laundry bleach (5.25% NaOC1) at room temperature and allowed to stand for 20 minutes before being flushed down the drain. This procedure is not recommended for other aliphatic aldehydes because it leads to chloro acids, which are more toxic and less biodegradable than corresponding unchlorinated acids.
Acidified potassium permanganate efficiently degrades aromatic amines. Diazotization followed by hypophosphorus acid protonation is a method for deamination of aromatic amines, but the procedure is more complex than oxidation.
Procedure for permanganate oxidation of 0.01 mol of aromatic amine:
A solution of 0.01 mol of aromatic amine in 3 L of 1.7 N sulfuric acid is prepared in a 5-L flask; 1 L of 0.2 M potassium permanganate is added, and the solution allowed to stand at room temperature for 8 hours. Excess permanganate is reduced by slow addition of solid sodium hydrogen sulfite until the purple color disappears. The mixture is then flushed down the drain.
7.D.2.5 Organic Peroxides and Hydroperoxides
(CAUTION: Peroxides are particularly dangerous. These procedures should be carried out only by knowledgeable laboratory workers.) Peroxides can be removed from a solvent by passing it through a column of basic activated alumina, by treating it with indicating Molecular Sieves®, or by reduction with ferrous sulfate. Although these procedures remove hydroperoxides, which are the principal hazardous contaminants of peroxide-forming solvents, they do not remove dialkyl peroxides, which may also be present in low concentrations. Commonly used peroxide reagents, such as acetyl peroxide, benzoyl peroxide,