Hydrogen peroxide, H 2 O 2 , is a very simple yet versatile compound. The oxygen single bond makes hydrogen peroxide one of the simplest molecules and indeed is the simplest peroxide. However, its simplicity is also the key to its versatility. This paper will show how the many applications of hydrogen peroxide are easily traceable to its molecular simplicity. In the US economy, hydrogen peroxide has important applications in several industries. It is used as bleach in the paper and textile industries. In agriculture, farmers use the compound to keep the water of hydroponic gardens free of harmful germs like bacteria that would otherwise reduce their yield. Like in many households, I keep a bottle of 3% hydrogen peroxide in the medicine cabinet at home for when I accidentally cut myself. I have also used the same preparation to remove stains from my clothing and from the carpet many times in the past. To be honest, I thought I was already an expert on the household uses of hydrogen peroxide. I then found out that this same preparation is useful as mouthwash and is an ingredient of whitening toothpaste and I realized that there is more to hydrogen peroxide than I already knew. As I kept reading, what impressed me most was learning how our cells produce, store, make use of, and break down hydrogen peroxide. I was pleasantly surprised to learn that I was using the same disinfectant as my cells were using, albeit at a different scale. Pure hydrogen peroxide is a pale blue to a colorless clear liquid. Its density is 1.11 g/cm 3 and its viscosity is 1.245 cP. It is denser and more viscous than water and is thus often described as syrupy. It has a sharp odor similar to vinegar and like vinegar is also weakly acidic. At room temperature, however, it has a bitter taste like other things with alkaline properties. It is highly soluble in water but also in ether and alcohol. A molecule of hydrogen peroxide has two atoms of hydrogen and two atoms of oxygen bonded covalently. It has a molar mass of 34.01 g/mol. It is a polar molecule because the two oxygen atoms in the middle are much more electronegative than the two hydrogen atoms at either end. This polarity explains why hydrogen peroxide is highly miscible in a polar solvent like water. In turn, this is why most of the available preparations are solutions in water. Hydrogen peroxide may be formed by a combination reaction between molecules of hydrogen and oxygen. This reaction may be expressed in the following simple equation: H 2 + O 2 → H 2 O 2 (1)
However, such a reaction favors the production of water instead of hydrogen peroxide. The production of hydrogen peroxide is done via the anthroquinone process, a reduction-oxidation (redox) reaction that uses palladium as a catalyst (Jones & Clark, 1999). In the first step of the reaction, hydrogen is added to a diketone. This reduces the diketone into a diol. In an oxidation reaction, an oxygen molecule is then added to the diol to generate the original diketone and a molecule of hydrogen peroxide. The process can be summarized as follows: H 2 + R-(CO) 2 → R-C(OH) 2 (1a) , R-C(OH) 2 + O 2 → R-(CO) 2 + H 2 O 2 (1b) , H 2 + O 2 → H 2 O 2 (1)
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In the body, one way that hydrogen peroxide is produced is from superoxide (O 2 1- ) using the catalyst the enzyme superoxide dismutase (SOD) (Lehninger, Nelson & Cox, 2013). Again, this is a redox reaction. The enzyme-catalyst SOD has a metal component, like copper, at its active site. Copper, as cupric, is reduced and superoxide is oxidized. In the presence of hydrogen ions in solution, the reduced copper-SOD may react with another superoxide and thus hydrogen peroxide is produced. This time, the copper is oxidized and the superoxide is reduced. These are summarized in the following equations: Cu 2+ -SOD + O 2 1- → Cu 1+ -SOD + O 2 (1c) , Cu 1+ -SOD + O 2 1- + 2H + → Cu 2+ -SOD + H 2 O 2 (1d)
In the body, dissolved hydrogen peroxide reacts with both iron (II), ferrous, and iron (III), ferric to create hydroxyl, HO . , and hydroperoxyl, HOO . , radicals respectively. These reactions may be written as follows: Fe 2+ + H 2 O 2 → Fe 3+ + HO . + OH - (2a) , Fe 3+ + H 2 O 2 → Fe 2+ + HOO . + H + (2b)
The free radicals generated in this reaction destroy infectious organisms such as bacteria by disrupting their cell walls and DNA structure. This is why hydrogen peroxide is an important substance in the immune system ( Kumar, Abbas, Aster, & Perkins, 2018 ).
In vitro, a similar reaction called the Fenton reaction is used to clean the water supply. Diluted hydrogen peroxide is mixed into the water. In the presence of aqueous iron, free radicals are generated as in the aforementioned reaction and these kill the bacterial contaminants. This process has been used to keep the bacterial levels in swimming pools and hydroponic setups relatively low.
The production of free radical species from hydrogen peroxide is also the underlying chemical process in the use of this substance as a bleaching agent in making paper and textiles (). The substances that give paper and fabric their color are mainly organic substances such as alizarin, also known as the dye Turkey Red. Alizarin has many hydroxyl groups to which a free radical may react, as in the following equation: R-OH + HOO. → R-C=O + H 2 + O 2 (3)
This redox reaction produces hydrogen and oxygen gases (Spiro & Griffith, 1999). The decomposition reaction of two molecules of hydrogen peroxide produces two molecules of water, one molecule of oxygen, and a lot of energy as heat. This exothermic reaction may be written as follows: 2H 2 O 2 ( l ) ⇾ H 2 O ( l ) + O 2 ( g ) △ f H = -98.2 k J/mol (4)
The products, liquid water and gaseous oxygen, are so much more stable than the reactant, liquid hydrogen peroxide, that this decomposition reaction is highly favored and occurs spontaneously. The addition of energy to this reaction process would greatly enhance the speed of this reaction. Therefore to prevent its rapid breakdown, hydrogen peroxide is kept in opaque bottles during its transport and storage to prevent heat and light from coming into contact with the hydrogen peroxide molecules. Another way to prevent rapid breakdown is to keep the solution highly diluted. Most products deemed safe for household use range from 3% to 6% in concentration.
On the other hand, there are instances when a rapid breakdown process is desirable. Take for instance the use of hydrogen peroxide as a propellant. High-test peroxide or HTP is up to 98% hydrogen peroxide, therefore highly concentrated. The breakdown process of HTP is nearly identical: 2H 2 O 2 ( l ) ⇾ H 2 O ( g ) + O 2 ( g ) (4a)
HTP breaks down rapidly because the hydrogen molecules are so highly concentrated they cannot but bump into each other. These collisions make a lot of heat in a very short amount of time. The amount of heat is enough to boil the water to vapor and this mixes readily with oxygen gas. The production of this water vapor-gas mixture provides plenty of thrust, making HTP a very good propellant for rockets and torpedoes. The Lunar Landing Research Vehicle by NASA, for example, used HTP in its thrusters (Ventura & Garboden, 1999).
In the same manner that hydrogen peroxide and its derivatives can harm bacterial cells, they can also endanger humans. Concentrated solutions can oxidize tissues of the eyes, skin, and mucosal surfaces leading to burns. Due to decomposition leading to the production of gases, air embolism is a theoretically possible but probably rare event. Moreover, repeated use in the treatment of wounds are theorized to prevent healing due to damage to fibroblasts, cells that repair wounds. Thus, in industrial and laboratory settings, the judicious use of goggles and other safety equipment are a must to prevent accidental burns and alternative wound care agents for chronic wounds should probably be considered (2015). In September 2014, global hydrogen peroxide consumption was said to be driven mainly by the paper industry, where its main use is as an oxidant-bleach. While this might change as the world increasingly shifts towards less use of paper, the increase in population as well as hydrogen peroxide’s reputation as an environment-friendly reactant could still buoy the demand. This sector was expected to have an annual growth rate of 3.8%.
Conclusion
Hydrogen peroxide is a simple compound of four atoms of only two different elements. However, due to the arrangement of these atoms, the compound has many properties that make it versatile such as its polarity and and its ability to act as both an oxidizing and reducing agent. A chemist, even an amateur one, capitalize on its versatility by manipulating factors such as its concentration and pH. Indeed, its chemistry is useful for a wide array of applications not all of which are apparent. Our immune system hoards hydrogen peroxide for possible use against invading bacteria. At home, we use it in many products for personal care and as household cleansers. Some of the food we eat might have been grown using technology that uses hydrogen peroxide extensively. In the past, some of our nation’s greatest achievements in exploring space has literally been propelled by hydrogen peroxide.
References
Hydrogen peroxide. (2014, September). Retrieved June 24, 2018, from https://ihsmarkit.com/products/hydrogen-peroxide-chemical-economics-handbook.html
Hydrogen peroxide health & safety tips. (2015, June 17). Retrieved June 24, 2018, from https://www.msdsonline.com/2015/06/17/hydrogen-peroxide-health-safety-tips/
Jones, C.W., Clark J.H. (1999). Applications of hydrogen peroxide and derivatives. RSC Clean Technology Monographs. doi:10.1039/9781847550132
Kumar, V., Abbas, A.K., Aster J.C., & Perkins, J.A. (2018). Robbins basic pathology . Philadephia, PA: Elsevier.
Lehninger, A.L, Nelson, D.L, & Cox, M.M. (2013). Principles of biochemistry. New York: W.H. Freeman.
Spiro, M., & Griffith, W. P. (1997). The mechanism of hydrogen peroxide bleaching. Textile Chemist and Colorist, 29 (11), 12-13. Retrieved June 20, 2018
Ventura, M. & Garboden, G. (1999). A brief history of concentrated hydrogen peroxide uses. 35th Joint Propulsion Conference and Exhibit. doi: 10.2514/6.1999-2739.
