Hydrogen peroxide

Hydrogen peroxide (H₂O₂) is a very pale blue liquid which appears colorless in a dilute solution, slightly more viscous than water. It is a weak reactive oxygen species.

History

Hydrogen peroxide was first isolated in 1818 by barium sulfate byproduct. Thénard's process was used from the end of the 19th century until the middle of the 20th century.^[1] Modern production methods are discussed below.

Uses

Industrial applications

About 50% of the world's production of hydrogen peroxide in 1994 was used for pulp- and paper-bleaching. Other bleaching applications are becoming more important as hydrogen peroxide is seen as an environmentally benign alternative to chlorine-based bleaches.

Other major industrial applications for hydrogen peroxide include the manufacture of epoxide. In PCB manufacturing process, hydrogen peroxide mixed with sulfuric acid was used as the microetch chemical for copper surface roughening preparation.

New industrial and home applications may be developed with the discovery of a catalytic reaction using powdered precious metal-based catalyst, hydrogen peroxide and methyl alcohol ^[2]. A small plastic bottle incorporating these can produce superheated steam in one to two seconds releasing only CO₂ and high temperature steam for a variety of purposes.

Domestic uses

• Diluted H₂O₂ (around 15%) is used to bleach human hair, hence the phrase "peroxide blonde". It is absorbed by skin upon contact and creates a local skin capillary embolism which appears as a temporary whitening of the skin. It is used to whiten bones that are to be put on display. The strength of a solution may be described as a percentage or volume, where 1% hydrogen peroxide releases 3.3 volumes of oxygen during decomposition.Thus, a 3% solution is equivalent to 10 volume and a 6% solution to 20 volume, etc.
• 3% H₂O₂ is used medically for cleaning wounds, removing dead tissue, and as an oral debriding agent. Most over-the-counter peroxide solutions are not suitable for ingestion.
• The Food and Drug Administration (FDA) has classified hydrogen peroxide as a Low Regulatory Priority (LRP) drug for use in controlling fungus on fish and fish eggs. (See ectoparasite.)
• Some gardeners and users of hydroponics advocate the use of hydrogen peroxide in watering solutions. They claim that its spontaneous decomposition releases oxygen that enhances a plant's root development and helps to treat root rot (cellular root death due to lack of oxygen).
• Laboratory tests conducted by fish culturists in recent years have demonstrated that common household hydrogen peroxide can be used safely to provide oxygen for small fish.^[3][4] Hydrogen peroxide releases oxygen by decomposition when it is exposed to manganese dioxide.
• Hydrogen peroxide is a strong oxidizer effective in controlling sulfide and organic related odors in wastewater collection and treatment systems. It is typically applied to a wastewater system where there is a retention time of 30 minutes to 5 hours before hydrogen sulfide is released. Hydrogen peroxide oxidizes the hydrogen sulfide and promotes bio-oxidation of organic odors. Hydrogen peroxide decomposes to oxygen and water, adding dissolved oxygen to the system thereby negating some Biological Oxygen Demand (BOD).
• Commercial peroxide, as bought at the drugstore in a 2.5%-3% solution, can be used to remove bloodstains from fabrics, although it will bleach or discolor many fabrics. If a little peroxide is poured onto the stain it will bubble up in the area of the blood, due to a reaction with catalase.[1] After a few minutes the excess liquid can be wiped up with a cloth or paper towel and the stain will be gone.
• Hydrogen peroxide is used with spontaneously relaxes back to the ground state.
• Hydrogen peroxide is used as a disinfectant in CIBA Vision's Clear Care no rub contact lens cleaning solution, due to its ability to break down the proteins that build up on the lense from the eye's immune response, resulting in increased comfort for those with sensitive eyes.

Storage

Regulations vary, but low concentrations, such as 2.5% are widely available and legal to buy for medical use. Small quantities of many different concentrations and grades can be legally stored and used with few regulations.^{[citation needed]}

Hydrogen peroxide should be stored in a container made from a material that it doesn't react with and doesn't catalyze its decomposition. Numerous materials and processes are available, some stainless steels, many plastics, glasses and some aluminium alloys are compatible.^[5]

Peroxide is a strong oxidant and should be stored away from fuel sources and sources of catalytic contamination (see decomposition section). Apart from obvious fire risks, peroxide vapour can react with hydrocarbons and alcohols to form contact explosives. Because oxygen is formed during the natural decomposition of the peroxide, the resulting increase in pressure can cause a container (e.g. made of glass) to shatter. Peroxide should be kept cool, as peroxide vapour can detonate above 70 °C. Deaths have occurred from storage in inadequately labeled containers due to its apparent similarity to water.

Use as propellant

H₂O₂ can be used either as a hydrazine, but is not toxic. The Bell Rocket Belt used hydrogen peroxide monopropellant.

As a bipropellant H₂O₂ is decomposed to burn a fuel as an oxidizer. Specific impulses as high as 350 s (3.5 kN·s/kg) can be achieved, depending on the fuel. Peroxide used as an oxidizer gives a somewhat lower I_sp than liquid oxygen, but is dense, storable, noncryogenic and can be more easily used to drive gas turbines to give high pressures. It can also be used for regenerative cooling of rocket engines. Peroxide was used very successfully as an oxidizer in World-War-II German rockets (e.g. T-Stoff for the Me-163), and for the low-cost British Black Knight and Black Arrow launchers.

In the 1940s and 1950s the Walter turbine used hydrogen peroxide for use in submarines while submerged; it was found to be too noisy and require too much maintenance compared to diesel-electric power systems. Some torpedoes used hydrogen peroxide as oxidizer or propellant, but this was dangerous and has been discontinued by most navies. Hydrogen peroxide leaks were blamed for the sinkings of HMS Sidon and the Russian submarine Kursk. It was discovered, for example, by the Japanese Navy in torpedo trials, that the concentration of H₂O₂ in right-angle bends in HTP pipework can often lead to explosions in submarines and torpedoes. Hydrogen peroxide is still used on Soyuz for driving gas turbines to power turbopumps, however. SAAB Underwater Systems is manufacturing the Torpedo 2000. This torpedo, used by the Swedish navy, is powered by a piston engine propelled by HTP as an oxidizer and kerosene as a fuel in a bipropellant system^[6].

While rarely used now as a monopropellant for large engines, small hydrogen peroxide attitude control thrusters are still in use on some satellites. They are easy to throttle, and safer to fuel and handle before launch than hydrazine thrusters. However, hydrazine is more often used in spacecraft because of its higher specific impulse and lower rate of decomposition.

Recently H₂O₂/cryogenic storage or hardware, and greatly reduces the cost of the booster. The potential of this and other alternative systems is discussed in some detail at Dunn Engineering.

Therapeutic use

Hydrogen peroxide is generally recognized as safe (GRAS) as an Food and Drug Administration.^[7]

Hydrogen peroxide has been used as an antiseptic and anti-bacterial agent for many years due to its oxidizing effect. While its use has decreased in recent years with the popularity of better-smelling and more readily-available over the counter products, it is still used by many hospitals, doctors and dentists in sterilizing, cleaning and treating everything from floors to root canal procedures.

• Hydrogen peroxide can be used as a toothpaste when mixed with correct quantities of baking soda and salt.^[8]
• Hydrogen peroxide and benzoyl peroxide are sometimes used to treat acne.^[9]
• Hydrogen peroxide is used as an emetic in veterinary practice.^[10]

"Alternative" uses

• Some people have tried using peroxide as a treatment for cancer. The American Cancer Society states that "there is no scientific evidence that hydrogen peroxide is a safe, effective or useful cancer treatment", and advises cancer patients to "remain in the care of qualified doctors who use proven methods of treatment and approved clinical trials of promising new treatments." ^[11]
• Another controversial alternative medical procedure is inhalation of hydrogen peroxide at a concentration of about 1%. Internal use of hydrogen peroxide has a history of causing fatal blood disorders, and its recent use as a therapeutic treatment has been linked to several deaths.^[12][13]

Physical properties

While the hydrogen bonding, which is relevant to the structural difference between gaseous and crystalline forms; indeed a wide range of values is seen in crystals containing molecular H₂O₂.

Chemical properties

H₂O₂ is one of the most powerful oxidizers known -- stronger than potassium permanganate. Also, through catalysis, H₂O₂ can be converted into hydroxyl radicals (.OH) with reactivity second only to fluorine.

Hydrogen peroxide can decompose spontaneously into water and oxygen. It usually acts as an reducing agent, releasing oxygen as a by-product.

It also readily forms both inorganic and organic peroxides.

Decomposition

Hydrogen peroxide always decomposes (disproportionates) spontaneously:

2 H₂O₂ → 2 H₂O + O₂

This process is very favorable; it has a acid is often added as a stabilizer.

The liberation of oxygen and energy in the decomposition has dangerous side effects. Spilling high concentration peroxide on a flammable substance can cause an immediate fire, which is further fueled by the oxygen released by the decomposing hydrogen peroxide. High-strength peroxide (also called high-test peroxide, or HTP) must be stored in a suitable,^{[citation needed]} vented container to prevent the buildup of oxygen gas, which would otherwise lead to the eventual rupture of the container.

In the presence of certain catalysts, such as Fe²⁺ or Ti³⁺, the decomposition may take a different path, with free radicals such as HO· (hydroxyl) and HOO· being formed. A combination of H₂O₂ and Fe²⁺ is known as Fenton's reagent.

A common concentration for hydrogen peroxide is "20 volume", which means that when 1 volume of hydrogen peroxide is decomposed, it produces 20 volumes of oxygen. This is equivalent to about 6% or 1.7M.

Hydrogen peroxide available at drug stores is three percent solution. In such small concentrations, it is less stable, and decomposes faster. It is usually stabilized with acetanilide, a substance that has toxic side effects in significant amounts.

Redox reactions

In aqueous solution, hydrogen peroxide can oxidize or reduce a variety of inorganic ions. When it acts as a reducing agent, acid solution Fe²⁺ is oxidized to Fe³⁺,

2 Fe³⁺(aq) + 2H₂O(l)

and sulfite (SO₃²⁻) is oxidized to MnO₂).

Another example of hydrogen peroxide acting as a reducing agent is the reaction with oxygen in the laboratory.

NaOCl + H₂O₂ → O₂ + NaCl + H₂O

Hydrogen peroxide is frequently used as an TiCl₃ catalyst):

Ph-S-CH₃ + H₂O₂ → Ph-S(O)-CH₃ + H₂O

Alkaline hydrogen peroxide is used for epoxidation of electron-deficient alkenes such as hydroboration-oxidation.

Formation of peroxide compounds

Hydrogen peroxide is a weak acid, and it can form salts or derivatives of many metals.

For example, on addition to an aqueous solution of chromic acid (CrO₃) or acidic solutions of dichromate salts, it will form an unstable blue peroxide CrO(O₂)₂. In aqueous solution it rapidly decomposes to form oxygen gas and chromium salts.

It can also produce peroxoanions by reaction with anions; for example, reaction with borax leads to sodium perborate, a bleach used in laundry detergents:

Na₂B₄O₇ + 4 H₂O₂ + 2 NaOH → 2 Na₂B₂O₄(OH)₄ + H₂O

H₂O₂ converts triphenylphosphine oxide is a useful "carrier" for H₂O₂ in some reactions.

Hydrogen peroxide reacts with trioxidane.

Alkalinity

Hydrogen peroxide is a much weaker HF/SbF₅ forms unstable compounds containing the [H₃O₂]⁺ ion.

Manufacture

Hydrogen peroxide is manufactured today almost exclusively by the catalyst. The overall equation for the process is deceptively simple:

H₂ + O₂ → H₂O₂

However the economics of the process depend on effective recycling of the quinone and extraction solvents, and of the catalyst.

Formerly inorganic processes were used, employing the hydrolysis of the peroxydisulfate ((SO₄)₂)²⁻ which is formed.

In 1994, world production of H₂O₂ was around 1.9 million tonnes^{[citation needed]}, most of which was at a concentration of 70% or less^{[citation needed]}. In that year bulk 30% H₂O₂ sold for around US $0.54 per kg, equivalent to US $1.50 per kg (US $0.68 per lb) on a "100% basis^{[citation needed]}".

Concentration

Hydrogen peroxide works best as a propellant in extremely high concentrations-- roughly over 70%. Although any concentration of peroxide will generate some hot gas (oxygen plus some steam), at concentrations above approximately 67%, the heat of decomposing hydrogen peroxide becomes large enough to completely vaporize all the liquid at standard temperature. This represents a safety and utilization turning point, since decomposition of any concentration above this amount is capable of transforming the liquid entirely to heated gas (the higher the concentration, the hotter the resulting gas). This very hot steam/oxygen mixture can then be used to generate maximal thrust, power, or work, but it also makes explosive decomposition of the material far more hazardous.

Normal propellant grade concentrations therefore vary from 70 to 98%, with common grades of 70, 85, 90, and 98%. Many of these grades and variations are described in detail in the United States propellant specification number MIL-P-16005 Revision F, which is currently available. The available suppliers of high concentration propellant grade hydrogen peroxide are generally one of the large commercial companies which make other grades of hydrogen peroxide; including Solvay Interox, FMC, Degussa and Peroxide Propulsion. Other companies which have made propellant grade hydrogen peroxide in the recent past include Air Liquide and DuPont. DuPont recently sold its hydrogen peroxide manufacturing business to Degussa.

Propellant grade hydrogen peroxide is available to qualified buyers. Typically this chemical is only sold to commercial companies or government institutions which have the ability to properly handle and utilize the material. Non-professionals have purchased 70% or lower concentration hydrogen peroxide (the remaining 30% is water with traces of impurities and stabilizing materials, such as tin salts, phosphates, nitrates, and other chemical additives), and increased its concentration themselves. Many amateurs try distillation, but this is extremely dangerous with hydrogen peroxide; peroxide vapor can ignite or detonate depending on specific combinations of temperature and pressure. In general any boiling mass of high concentration hydrogen peroxide at ambient pressure will produce vapor phase hydrogen peroxide which can detonate. This hazard is mitigated, but not entirely eliminated with vacuum distillation. Other approaches for concentrating hydrogen peroxide are sparging and fractional crystallization.

High concentration hydrogen peroxide is readily available in 70, 90, and 98% concentrations in sizes of 1 gallon, 30 gallon, and bulk tanker truck volumes. Propellant grade hydrogen peroxide is being used on current military systems and is in numerous defense and aerospace research and development programs. Many privately funded rocket companies are using hydrogen peroxide, notably Blue Origin, and some amateur groups have expressed interest in manufacturing their own peroxide, for their use and for sale in small quantities to others.

Hazards

Hydrogen peroxide, either in pure or diluted form, can pose several risks:

• Above roughly 70% concentrations, hydrogen peroxide can give off vapor that can detonate above 70 °C (158 °F) at normal atmospheric pressure.^{[citation needed]} This can then cause a boiling liquid expanding vapor explosion (BLEVE) of the remaining liquid. Distillation of hydrogen peroxide at normal pressures is thus highly dangerous.

• Hydrogen peroxide vapors can form sensitive contact explosives with hydrocarbons such as greases. Hazardous reactions ranging from ignition to explosion have been reported with alcohols, phosphorus.^{[citation needed]} The saying is 'peroxides kill chemists'.^{[citation needed]}

• Hydrogen peroxide, if spilled on clothing (or other flammable materials), will preferentially evaporate water until the concentration reaches sufficient strength, then clothing will spontaneously ignite. ^{[15][citation needed]} ;

• Concentrated hydrogen peroxide (>50%) is corrosive, and even domestic-strength solutions can cause irritation to the eyes, mucous membranes and skin.^[16] Swallowing hydrogen peroxide solutions is particularly dangerous, as decomposition in the stomach releases large quantities of gas (10 times the volume of a 3% solution) leading to internal bleeding. Inhaling over 10% can cause severe pulmonary irritation.^{[citation needed]}

• Low concentrations of hydrogen peroxide, on the order of 3% or less, will chemically bleach many types of clothing it comes into contact with to a pinkish hue. Caution should be exercised when using common products that may contain hydrogen peroxide, such as facial cleaner or contact lens solution, which easily splatter upon other surfaces.

Hydrogen peroxide is naturally produced as a byproduct of oxygen metabolism, and virtually all organisms possess enzymes known as peroxidases, which apparently harmlessly catalytically decomposes low concentrations of hydrogen peroxide to water and oxygen (see Decomposition above).

In one incident, several people were injured after a hydrogen peroxide spill on board Northwest Airlines Flight 957 because they mistook it for water.^[17]

During the Second World War some extermination camps experimentally killed people with hydrogen peroxide injections.^[18]

Hydrogen peroxide was also part of the ingredients in the July 21, 2005 London Underground bombs, which failed to explode.^[19]

An MSDS will contain more information on the risks of working with this chemical.

References