Difference between revisions of "Peroxide forming chemicals"

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Peroxide forming chemicals are a group of chemical compounds capable of forming very sensitive peroxides if exposed to atmospheric oxygen. While most are organic, potassium metal is known to form the unstable potassium peroxide (K₂O₂) in contact with air.

Chemicals that form peroxides when treated with hydrogen peroxide or some other form of peroxide are not included in this group, as these compounds require an already existing peroxide and do not form such peroxides in contact with atmospheric oxygen. Like wise, chemicals that form peroxides at high temperatures (like barium oxide) or other extreme/unique conditions are also not included here.

General

Chemical compounds, such as ethers, secondary alcohols or certain unsaturated hydrocarbons will produce unstable peroxides upon contact with air, process accelerated by light or heat, over the course of months or years. The autoxidation of said compounds produces both normal peroxides, as well as hydroperoxides.^[1][2] There are 2 main categories of peroxide forming chemicals, as well as two additional more.^[3][4]

Ethers like dimethyl ether, methyl tert-butyl ether and tertiary ethers do not form explosive peroxides in contact with air, due to the either lack of α-hydrogens (in the case of t-butyl-groups) or the lack of hyperconjugation contributing alkyl groups (in the case of methyl groups).

Categories

Group A

Compounds that form explosive levels of peroxides without concentration, and can explode without warning at high enough concentrations.

Group B

Compounds that form explosive levels of peroxides during concentration, and tend to explode when dry. Safe when wet.

Group C

Compounds which are hazardous due to peroxide initiation of autopolymerization.

Group D

Chemicals that may form peroxides but cannot be classified in the previous categories

Properties

Organic peroxides are liquid or solid compounds, often very sensitive to mechanical stress such as friction and shock, as well as heat. They are non-volatile, and explode if heated to high temperature.^[5][6]

Most commonly solvents contain mainly hydroperoxide species, but their decomposition products can also be present. Diisopropyl ether for example may contain dimeric or trimeric acetone peroxide.^[7]

Peroxide detection

There are numerous methods reported for peroxide detection. Almost all organic peroxides can be detected by using a solution of potassium iodide in water or acetic acid. If any peroxides are present in the liquid, the iodide solution will turn yellow at low levels of peroxides, and brown to purple-ish at high concentrations.^[6] Starch may be added to further increase sensitivity.^[8] This test does not work for acetone peroxide, for which titanium sulfate in 50% sulfuric acid is used: a yellow to orange color indicates the presence of peroxides.^[6]

Vanadate(V) and sulfuric acid reagent can also be used for non-cyclic ethers. An orange- to redbrown color indicates the presence of peroxides.^[8] Another method involves the use of hemin chloride and luminol in sodium carbonate solution. Peroxide containing solvents show blue chemiluminescence.^[8]

For ease of convenience, a method for the iodide test is given below:^[8]

Potassium iodide-starch reagent according to Ph. Eur.: 0.75 g KI are dissolved in 100 mL water, heated to boiling and a suspension of 0.5 g soluble starch in 35 mL water is added. Boiling is continued for two minutes, then left to cool. Keeps in a closed bottle for about four weeks and if going turbid should be discarded.

Sensitivity test: The reagent should pass the following test. 5 mL of the reagent should turn blue when 0.17 mL acetic acid and 0.1 mL 0.0005 N iodine solution in water (50 µL 0.1 N iodine solution diluted to 10 mL) are added.

Peroxide test: 8 mL potassium iodide-starch reagent are placed in a 12 mL flask/test tube and filled up to the top with the ether that should be tested. If the sample contains basic impurities like alkali hydroxides, the addition of a small amount of acetic acid is advised to prevent a false negative. The sample is capped, shaken and left to stand in the dark for 30 minutes. If no color develops, the test is negative (compare with pure reagent solution). Sensitivity threshold: About 10 ng H₂O₂.

Handling

Safety

Compounds prone to forming dangerous peroxides should not be distilled to dryness, as the explosive peroxides will explode when dry. A good tip would be to add some high boiling solvent, like glycerol.

Storage

Compounds known to form peroxides should be kept in sealed bottles. BHT should be added as anti-oxidant, though a sheet of fresh metal, like copper can also be used. Sodium hydroxide can be added to precipitate any peroxides formed.

Disposal

Hydroperoxides are generally quite reactive and can be destroyed with a multitude of reagents. For the removal from solvents there have been reported the following methods (if compatible with the solvent):^[6]

• Bisulfite^[9]
• Copper-zinc-alloy^[10]
• Permanganates^[11]
• Lead(IV) oxide^[12]
• Iron(II) sulfate^[13]
• Chromatography over activated aluminium oxide^[14]
• Sodium metal
• Sodium hydroxide or potassium hydroxide^[15]

For ease of convenience, two of the tested methods for the removal of peroxides from diethyl ether are presented below:^[15]

With iron(II):^[15] A cold saturated solution of ammonium iron(II) sulfate in 2 mol/L (~17%) sulfuric acid is prepared and filtered. 7 mL of this solution and 25 mL of peroxide containing diethyl ether are occasionally shaken during a few hours and then left standing over night. No visual changes took place. After 12 h the ether tested negative for peroxides.

With sodium hydroxide:^[15] About 5 g of granulated sodium hydroxide and 25 mL of peroxide containing ether was occasionally shaken during a few hours. In the beginning vigorous shaking is advised to prevent the granules caking together. After 12 h a fine brown-yellow flocculent precipitate was observed. The ether tested negative for peroxides.

DO NOT ATTEMPT TO OPEN VERY OLD BOTTLES THAT HAVE PEROXIDES ON THE CAP!

See also

• Ether

References

1. ↑ http://www.ilpi.com/msds/ref/peroxide.html
2. ↑ http://www.sigmaaldrich.com/chemistry/solvents/learning-center/peroxide-formation.html
3. ↑ http://ccc.chem.pitt.edu/wipf/Web/16340.pdf
4. ↑ http://www.baylor.edu/ehs/doc.php/203991.pdf
5. ↑ http://ccc.chem.pitt.edu/wipf/Web/16340.pdf
6. ↑ ^{6.0 6.1 6.2 6.3} R. Criegee in Houben-Weyl, Methoden der organischen Chemie, Sauerstoffverbindungen III, Band VIII, "Herstellung und Umwandlung von Peroxyden", Georg-Thieme, Stuttgart 1952, p. 73-74.
7. ↑ A. Rieche, K. Koch, Ber. dtsch. Chem. Ges. A/B, 75, 1016-1028 (1942). https://doi.org/10.1002/cber.19420750815
8. ↑ ^{8.0 8.1 8.2 8.3} Test auf Peroxide in Diethylether, https://illumina-chemie.de/viewtopic.php?f=22&t=4541
9. ↑ Gattermann-Wieland, Die Praxis des organischen Chemikers, 33rd edition 1948, p. 87
10. ↑ H. Fierz-David, Chimia 1, 246 (1948)
11. ↑ A. Harmse, Pharm. Weekb. 78, 1085 (1941)
12. ↑ F. R. Fisher, R. A. Baxter, Mines Mag. (1940), 447
13. ↑ L. Brandt, Ch. Z. 51, 981 (1927)
14. ↑ W. Dasler, C. D. Bauer, Ind. Eng. Chem. Anal. Ed. 18, 1, 52–54 (1946), https://doi.org/10.1021/i560149a017
15. ↑ ^{15.0 15.1 15.2 15.3} Entfernung von Peroxiden aus Diethylether, https://illumina-chemie.de/viewtopic.php?f=33&t=5794

Relevant Sciencemadness threads

• Peroxide Safety
• Explosive Peroxide Testing and Prevention
• testing for organic peroxides
• Diethyl ether peroxide