Antimicrobial agents: hydrogen peroxide


Hydrogen peroxide (H2O2) is an excellent oxidizing agent capable of destroying most forms of microorganisms

As one of the most environmentally friendly substances produced by the chemical industry, hydrogen peroxide is both a powerful germicidal agent and a gentle bleaching agent. In the environment, only hydrogen monoxide (otherwise called water, or H2O) remains from it. The problem with hydrogen peroxide is that it is extremely unstable. If a number of measures are not taken, this substance quickly decomposes into water and oxygen. This decomposition is catalyzed by trace amounts of metals, dust and enzymes. And the enzyme catalase directly specializes in the decomposition of hydrogen peroxide, in a second it deals with 50 thousand molecules of this substance. You can observe the rate at which decomposition occurs if you dip a piece of raw meat in hydrogen peroxide. (The same can be done with a raw potato slice, but the reaction will be slower.)

Plants and animals need catalase because hydrogen peroxide is a product of their own metabolism — our body produces about 30 grams of hydrogen peroxide per day — but this substance can be dangerous as it is a potential source of free radicals. Other organisms can synthesize H2O2 at a relatively faster rate because they use peroxide to generate light through what is called chemiluminescence. Some fish use the light they produce to attract their victims in the pitch darkness of the ocean depths.

In everyday life, we use hydrogen peroxide for disinfection and for bleaching. For almost a century, this substance has served us as an antiseptic and hair bleaching agent. It can also be used to remove certain types of stains from clothes, tablecloths, furniture and carpets. At the same time, peroxide acts more gently than Mountain bleach and does not discolor fabric dye. These cleaners contain about 8% H2O2.

Hydrogen peroxide can also be sold as a dry powder in the form of sodium percarbonate. Sodium percarbonate can be added to a washing machine to improve wash performance or mixed with water to clean soiled surfaces.

Hydrogen peroxide works best on coffee, tea, red wine, and fruit juice stains. Hydrogen peroxide can also be used as a disinfecting agent, and its solution is good at removing bacteria living on the surface of wooden verandas or outdoor wooden furniture. H2O2 can fight bacteria in swimming pools and hot water pipes, while maintaining a peroxide concentration of about 100 parts per million in the water — much more than the concentration of hypochlorite used for the same purpose. Hydrogen peroxide can be used as an antiseptic to clean cuts and abrasions, as an ingredient in mouthwashes, to treat athlete’s foot and ear infections.

A new method of room sterilization uses hydrogen peroxide vapor. This method is preferred over other gas sterilization methods that use formaldehyde, ethylene oxide, which are toxic and harmful to hands, although entering the room soon after peroxide sterilization can also be dangerous due to the high content of residual H2O2. Special equipment converts H2O2 (30% solution) into a gaseous form with a concentration of about 1-2 mg per liter of air at 25 ° C and blows it into the bodies of the apparatus and into rooms that must be in a sterile state, as well as into the packaging of pharmaceutical products. Peroxide sterilization appeared in 1991, it is now implemented in more than five hundred institutions around the world.

History of hydrogen peroxide

Hydrogen peroxide has a long history, having been discovered in 1818 by the French chemist Louis Tenard, who obtained it as a result of the reaction of barium peroxide (Ba02) with sulfuric acid. (He obtained barium peroxide by simply heating barium oxide (BaO) in air.) Later, for several years, the scientist studied a new substance, he even managed to isolate it in an almost pure form. This was a great achievement, given the instability of the peroxide, which, as it turned out later, is a consequence of the contamination of the solution with small amounts of metal ions, such as iron and manganese, which catalyze the decomposition of the substance. The industrial production of peroxide according to the Tenard method began in 1873 in Berlin, the product was to be used almost immediately after receipt.

Even at the beginning of the twentieth century, when the electrochemical technology for the production of H2O2, based on the electrolysis of sulfuric acid or potassium sulfate, began to be used, the shelf life of peroxide remained quite short, only a few weeks. But, despite this, industrial hydrogen peroxide in 30% concentration, used for bleaching fabrics, and hydrogen peroxide in 3% and 6% concentrations, sold for household needs, were actively produced. The most significant increase in hydrogen peroxide production occurred during the heyday of the Third Reich in the 1930s and 1940s.

Nazi scientists and engineers used H2O2 to create the first liquid-propellant rocket engine, which was tested in 1936. And at the end of World War II, the Komet jet fighter even managed to serve Nazi Germany. The aircraft was powered by the energy released by the reaction of hydrogen peroxide with hydrazine and methanol. The maximum speed of the fighter reached 965 km / h. Hydrogen peroxide was also an indispensable component of the first V-2 ballistic missile, which was first used in September 1944. These rockets were fired at London and then at Antwerp.

Hydrogen peroxide was also needed to launch the most destructive German weapon — the V-1, also known as the «flying bomb» or «projectile aircraft», which, in fact, is the prototype of modern cruise missiles. These types of weapons were created specifically to destroy London, they really caused great material damage to England. Although the V-1 navigation system was rather primitive, and their flight time was set by the number of turns of a small crank, they had tremendous destructive power. About five thousand rockets were launched towards London 2419 ill-fated Vs reached the city between June 1944 and May 1945, the explosions of some of these shells led to major human casualties. V-1s were launched from an inclined platform using a piston catapult, which pushed them into the air due to the flow of oxygen and water vapor formed by the reaction of 100 kilograms of hydrogen peroxide with potassium permanganate.

To carry out the launch, a high concentration of peroxide (80% H2O2) was needed, for its production German chemists developed a method based on the reactions of anthraquinone with hydrogen gas (H2) and the resulting product with oxygen gas (O2), the final equation of the process was as follows: H2 + O2 = H2O2. After that, the anthraquinone was regenerated, and the process could be repeated again and again. The method turned out to be so effective that it is still used today. Humans were not the first to use hydrogen peroxide for military purposes. Bombardier beetles perfectly mastered this method of launching projectiles a few million years ago. This insect, whose Latin name is Stenaptinus insignis, lives in tropical countries such as Kenya and Malaysia, its body length is about two centimeters. When frightened, it immediately shoots a hot spray containing quinol, an irritant substance, which flies out of nozzles located at the back of the beetle’s body and directed towards the enemy. The energy needed to shoot and heat the liquid is generated by the decomposition reaction of hydrogen peroxide in the presence of the catalase enzyme. Quinol and hydrogen peroxide accumulate in one internal cavity of the beetle, and catalase in the other, these cavities are separated by a flap, which the beetle opens in case of danger. The insect can fire up to thirty volleys before it runs out of ammo. Having escaped from a predator, the beetle will be able to replenish its hydrogen peroxide reserves in a day.

After the Second World War, the production of hydrogen peroxide increased again, although this substance was no longer used for military purposes. Then, in addition to bleaching linen, cotton and paper, hydrogen peroxide became necessary for the production of sodium perborate, a bleaching agent widely used for washing clothes. Now this substance has been replaced by sodium percarbonate, which is a simple mixture of sodium carbonate and hydrogen peroxide in a ratio of 1:1.5.

Obtaining hydrogen peroxide

To date, hydrogen peroxide is obtained on the basis of a reaction with anthraquinone. The concentration of the resulting solution varies from 20 to 40%. If necessary, the concentration can be increased to 50-70% using a vacuum distiller. The vacuum distiller is under reduced pressure, causing water to evaporate below 100°C while hydrogen peroxide, which normally boils at 155°C, remains in solution. The final product is stored and transported in tanks made of stainless steel or aluminum. By adding a stabilizer to a hydrogen peroxide solution, we are able to significantly extend its shelf life, it is possible to ensure that less than 0.1% of the substance undergoes decomposition in a month. Such protection is provided by substances such as sodium stannate and various phosphates, which bind all metals in solution and prevent them from catalyzing the decomposition of peroxide.

More than a million tons of hydrogen peroxide are produced annually worldwide. About 30% of this amount goes to paper bleaching and about 20% to textile bleaching, solid peroxides are obtained from about the same amount of the substance. The remaining 30% is used in a variety of ways: as a chemical reagent; as a disinfectant for purification and deodorization of polluted water; to obtain metals from ores, for example, during the extraction and purification of uranium; for the creation of washing and detergents. (A relatively small proportion of the peroxide is sold in traditional liquid form.) Hydrogen peroxide is also used in the production of chlorophenol.

Use of hydrogen peroxide

In addition to bleaching and disinfecting, hydrogen peroxide has another remarkable property. In emergency situations, it can significantly increase the productivity of livestock farms. This is achieved by converting inedible materials such as sawdust and straw into complete ruminant feed. The fact is that when sawdust and straw are treated with an alkaline solution (pH between 11 and 12) of 1% hydrogen peroxide, inedible lignin is split off from the cellulose contained in them, as a result of which cellulose becomes a suitable food for livestock. In nature, this technology is also used, for example, tree parasitic fungi secrete their own alkaline hydrogen peroxide solution.

Although in theory hydrogen peroxide is a strong oxidizing agent, activation is necessary for it to exhibit oxidative activity. In industry, sulfuric acid is used as an activator; (H2SO4), which in a solution of hydrogen peroxide turns into sulfuric acid (H2SO5), also known as Caro’s acid or acetic acid (CH3CO2H), which turns into peroxyacetic acid (CH3CO3H), and already these intermediate substances act as oxidizing agents. Alternatively, hydrogen peroxide can be activated with alkali, some catalysts, and also with UV rays. It is generally accepted that all the above agents lead to the decomposition of H2O2 into more active fragments, such as HO+ and HO2- ions or free radicals HO- (dot means an unpaired electron).

The chemical industry loves hydrogen peroxide because its only end products are oxygen and water. Environmentalists consider it an ideal chemical reagent — absolutely not contrary to nature and with a wide range of applications. True, sometimes the supporters of this substance go too far, attributing to it the possibilities that it lacks. At the same time, they do not provide any scientific evidence for their statements.

It is believed that if you take a bath for half an hour, adding a glass of hydrogen peroxide to the water, this will have a rejuvenating and detoxifying effect on the body. There is also an opinion that rubbing the face with a 3% hydrogen peroxide solution will help get rid of acne, spraying this solution all over the body will tone the skin, and douching the colon with it will help normalize digestive function. Proponents of peroxide also claim that watering plants with a solution prepared from one part of a 3% peroxide solution and forty parts of water has a beneficial effect on them, and seeds soaked in such a plant sprout faster. It is believed that chickens fed with water containing a few drops of hydrogen peroxide produce tastier eggs. It is also said that cows mixed with peroxide in their water produce more milk. Of course, all of these statements should be treated critically, but it is also unlikely that any of these folk methods can cause serious harm.

Peroxide lovers have come up with an even more ridiculous way to use it. They claim that peroxide dissolved in spring water (the main thing is naturalness), when taken orally, allows you to get rid of any disease, from multiple sclerosis to AIDS, not to mention cancer, arthritis and bronchial asthma. The Zeon Church, which has several thousand adherents in Canada and Hong Kong, suggests that its adherents take a daily dose of such a cure for all diseases. (when ingested, the peroxide tastes sweetish, but after a few minutes, a bitter aftertaste appears from it). Those who choose to experience the questionable medicinal properties of hydrogen peroxide should be aware of the possible side effects. «Cleansing» the body with peroxide can cause nausea, headache, fatigue, indigestion, diarrhea — all these reactions are associated by supporters of alternative therapy with a painful process of removing toxins from the body.

Source: based on the book by John Emsley «On the benefits and harms of the products we love to buy»

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