He hydrogen peroxide Or hydrogen peroxide, dioxogen or dioxidane is a chemical compound represented by the formula H2O2. In its pure form, it shows no color, besides being in the liquid state, but is slightly more viscous than water, due to the amount of"hydrogen bonds"that can be formed.
To this peroxide in addition, it is recognized as one of the simpler peroxides, understanding peroxide those compounds that have a simple oxygen-oxygen bond.
Its uses are varied, ranging from its power as an oxidizer, bleaching agent and disinfectant, and even at high concentrations, has been used as a spacecraft fuel, taking special interest in the chemistry of propellants and explosives.
Hydrogen peroxide, is an unstable, and decomposes slowly in the presence of bases or catalysts. Because of this instability, the peroxide is usually stored with some type of stabilizer, which is in the presence of slightly acidic solutions.
Hydrogen peroxide can be found in biological systems that are part of the human body, and the enzymes that act by decomposing it are known as"peroxidases".
The discovery of hydrogen peroxide is assigned to the French scientist Louis Jacques Thenard , When he reacted the barium peroxide with nitric acid.
An improved version of this process used hydrochloric acid, and addition of sulfuric acid so that barium sulfate could precipitate out. This process was used from the late nineteenth century until the mid-twentieth century to produce peroxide.
It was always thought that the peroxide was unstable because of all the failed attempts to isolate it from the water. But the instability was mainly due to traces of impurities in the salts of the transition metals, which catalyzed their decomposition.
Pure hydrogen peroxide was synthesized for the first time in 1894, almost 80 years after its discovery, thanks to the scientist Richard Wolffenstein who produced it through vacuum distillation.
Its molecular structure was difficult to determine, but the Italian physicist, Giacomo Carrara, was the one who determined its molecular mass by cryoscopic descent, thanks to which its structure can be confirmed. Until that time, at least, a dozen hypothetical structures had been proposed.
Previously, hydrogen peroxide was industrially prepared by hydrolysis of ammonium peroxydisulfate, which was obtained by electrolysis of a solution of ammonium bisulfate (NH4HSO4) in sulfuric acid .
Today, hydrogen peroxide is almost exclusively manufactured by the anthraquinone process, which was formalized in 1936 and patented in 1939. It begins with the reduction of an anthraquinone (such as 2-ethylanthraquinone or the 2-amyl derivative) to the Corresponding anthrahydroquinone, typically by hydrogenation over a palladium catalyst.
The anthrahydroquinone then undergoes autoxidation to regenerate the starting anthraquinone, with hydrogen peroxide as a by-product. Most commercial processes obtain oxidation by bubbling compressed air through a solution of the derivatized anthracene, whereby the oxygen present in the air reacts with the labile hydrogen atoms (of the hydroxy groups), giving hydrogen peroxide and regenerating The anthraquinone.
The hydrogen peroxide is then extracted, and the anthraquinone derivative is reduced again to the dihydroxy compound (anthracene) using hydrogen gas in the presence of a metal catalyst. Then the cycle is repeated.
The economy of the process depends to a large extent on the effective recycling of the quinone (which is expensive), the extraction solvents, and the hydrogenation catalyst.
Properties of hydrogen peroxide
Hydrogen peroxide is shown as a clear blue liquid in dilute solutions, and colorless at room temperature, with a slight bitter taste. It is slightly more viscous than water due to the hydrogen bonds it can form.
It is considered a weak acid (PubChem, 2013). It is also a strong oxidizing agent, which is responsible for most of its applications that in addition to the proper oxidizer, are bleaching - for the paper industry - and also as a disinfectant. At low temperatures it behaves like a crystalline solid.
When it is found to form carbamide peroxide (CH6N2O3) (PubChem, 2011) it has a well-known use as a dental bleach, whether administered in a professional way, or, in a particular way.
There is much literature on the importance of hydrogen peroxide in living cells, since it plays an important role in the defense of the organism to harmful hosts, in addition to oxidative biosynthetic reactions.
In addition, there is more evidence (PubChem, 2013) that even at low levels of hydrogen peroxide in the body, it plays a fundamental role especially in higher organisms. Thus, it is considered as an important agent of cell signaling, capable of modulating both contractive and growth-promoting pathways.
Due to the accumulation of hydrogen peroxide in the skin of patients suffering from the depigmenting disorder"vitiligo"(López-Lázaro, 2007), the human epidermis does not have the normal ability to perform its functions, in this way it is suggested, that The accumulation of peroxide can play an important role in the development of cancer.
Even experimental data (López-Lázaro, 2007) show that cancer cells produce large amounts of peroxide, which are associated with DNA alternations, cell proliferation, and so on.
Small amounts of hydrogen peroxide can be produced spontaneously in the air. Hydrogen peroxide is unstable, and decomposes rapidly into oxygen and water, releasing heat into the reaction.
Although not flammable, as already mentioned it is a potent oxidizing agent (ATSDR, 2003), which can cause spontaneous combustion when put in contact with organic materials.
In hydrogen peroxide, oxygen (Rayner-Canham, 2000) has an"abnormal"oxidation state, since pairs of atoms with the same electronegativity are bound, so it is presumed that the pair of bonding electrons Divides between them. In this case, each oxygen atom has an oxidation number of 6 minus 7, or -1, while the hydrogen atoms have + 1.
The potent oxidizing power of hydrogen peroxide to water is explained by its oxidation potential (Rayner-Canham, 2000), so that it can oxidize the ferrous ion (II), to ferric ion (III), as shown in The following reaction:
Hydrogen peroxide also has the property of dismantling, ie, both reducing and oxidizing (Rayner-Canham, 2000), as shown by the following reactions together with their potentials:
Adding the two equations gives the following global equation:
Although"dismutation"is favored thermodynamically speaking, it is kinetically NOT favored. But (Rayner-Canham, 2000), the kinetics of this reaction can be favored with the use of catalysts such as iodide ion or other transition metal ions.
For example, the enzyme"catalase"that is present in our body, is able to catalyze this reaction, so that it destroys the harmful peroxide that may exist in our cells.
All oxides in the alkali group react vigorously with water to give the corresponding metal hydroxide solution but sodium dioxide generates hydrogen peroxide and the dioxides produce hydrogen peroxide and oxygen as shown in The following reactions (Rayner-Canham, 2000):
Other relevant data collected from hydrogen peroxide are:
- Molecular mass: 34,017 g / mol
- Density: 1.11 g / cm3 at 20 ºC, in 30% (w / w) solutions, and 1,450 g / cm3 at 20 ºC in pure solutions.
- Melting and boiling points are -0.43 ° C and 150.2 ° C respectively.
- It is miscible with water.
- Soluble in ethers, alcohols and insoluble in organic solvents.
- The value of its acidity is pKa = 11.75.
The hydrogen peroxide molecule is a non-planar molecule. Although the oxygen-oxygen bond is simple, the molecule has a relatively high, rotation barrier (Wikipedia Free Encyclopedia, 2012), if we compare it with, for example, that of ethane that is also formed by a single bond.
This barrier is due to the repulsion between the ionic pairs of the adjacent oxygen and it turns out that the peroxide is capable of showing"atropisomers"which are stereoisomers arising due to the impeded rotation around a single bond, where the energy differences due To the steric deformation or other contributors, create a rotation barrier that is high enough to allow isolation of the individual conformers.
The structures of the gaseous and crystalline forms of hydrogen peroxide differ significantly, and these differences are attributed to the hydrogen bond which is absent in the gaseous form.
It is common to find hydrogen peroxide in low concentrations (from 3 to 9%), in many homes for medical applications (hydrogen peroxide), as well as for bleaching clothes or hair.
At high concentrations it is used industrially, also for the bleaching of textiles and paper, as well as fuel for spacecraft, the manufacture of sponge rubber, and organic compounds.
It is advisable to handle hydrogen peroxide solutions, even those diluted, With gloves and eye protection, because it attacks the skin.
Hydrogen peroxide is an important industrial chemical compound (Rayner-Canham, 2000); Producing around the order of 106 tons worldwide each year. Hydrogen peroxide is also used as an industrial reagent, for example in the synthesis of sodium peroxoborate.
Hydrogen peroxide has an important application in the restoration of ancient paints (Rayner-Canham, 2000), since one of the most commonly used white pigments was lead white, corresponding to a mixed basic carbonate, whose formula is Pb3 ( OH) 2 (CO 3) 2.
Traces of hydrogen sulphide cause this white compound to become lead sulfide (Il), which is black, which stains the paint. The application of hydrogen peroxide oxidizes lead sulfide (II) to white lead sulfate (II), thereby restoring the correct color of the paint, following the following reaction:
Another interesting application (Rayner-Canham, 2000) is its application to alter the shape of the hair permanently attacking the disulfide bridges that this naturally has by means of hydrogen peroxide in slightly basic solutions, discovered by the Rockefeller Institute in the year 1930.
Propellants and explosives have many properties in common (Rayner-Canham, 2000). Both function by means of a rapid exothermic reaction that Produces a large volume of gas. The expulsion of this gas is what drives the rocket forward, but in the case of the explosive is mainly the shock wave that generates the production of the gas which causes the damage.
The reaction that was used in the first rocket-powered aeonave used a mixture of hydrogen peroxide with hydrazine, in which both reacted giving molecular gaseous nitrogen and water, as illustrated in the following reaction:
By summing the reaction energies of each of the reactants and products, an energy of 707 Kj / mol of heat is released, for each mole of hydrazine consumed, which means a very exothermic reaction.
This means that it fulfills the necessary expectations to be used as fuel in propellants, since very large volumes of gas are produced, through very small volumes of the two reactive liquids. Due to the reactivity and corrosion of these two liquids, they have now been replaced by safer mixtures on bases to the same criteria that were chosen to be used as fuels.
In the medical aspect, hydrogen peroxide is used as a topical solution in wound cleaning, suppurating ulcers, and local infections. It has been used frequently in the treatment of inflammatory processes in the external auditory canal, or also to gargle in pharyngitis treatments.
It is also used in the field of dentistry to clean the root canals of teeth or other cavities of the dental pulp, in processes such as endodontics, ultimately in minor dental processes.
Its use in cleaning wounds, or ulcers, etc. Is because it is an agent capable of destroying microorganisms, but not the spores of bacteria, this does not mean that it kills all microorganisms, but it does reduce the level of these, so that infections do not go to major problems. So it would belong to the level of disinfectants and low level antiseptics.
Hydrogen peroxide reacts with certain di-esters, such as the phenyl oxalate ester, and produces chemiluminescence, this is a rather secondary type application, which is found in light bars, known by their English name as"glow stick" .
In addition to all its uses, there are historical incidents with the use of hydrogen peroxide, since it is a chemical compound that at high concentrations and given their reactivity, can lead to explosions, which makes protective equipment necessary During handling, as well as taking into account suitable storage conditions.
- ATSDR. (2003). Toxic Substances - Hydrogen Peroxide. Retrieved January 17, 2017, from atsdr.cdc.gov.
- Famous Scientists - Louis Jacques Thenard discovers hydrogen peroxide. (2015). Retrieved January 17, 2017, from humantouchofchemistry.com.
- López-Lázaro, M. (2007). Dual role of hydrogen peroxide in cancer: possible relevance to cancer chemoprevention and therapy. Cancer Letters, 252 (1), 1-8.
- PubChem. (2011). Urea hydrogen peroxide.
- PubChem. (2013). Hydrogen Peroxide. Retrieved January 15, 2017.
- Rayner-Canham, G. (2000). Descriptive inorganic chemistry (2a). Pearson Education.
- Wikipedia The Free Encyclopedia. (2012). Peroxide hydrogen. Retrieved from wikipedia.org.