Hydrogen peroxide

Hydrogen peroxide
IUPAC name dihydrogen dioxide
Other names Dioxidane
Identifiers
CAS number	7722-84-1 Y
PubChem	784
ChemSpider	763 Y
UNII	BBX060AN9V Y
EC number	231-765-0
UN number	2015 (>60% soln.) 2014 (20–60% soln.) 2984 (8–20% soln.)
KEGG	D00008 Y
ChEBI	CHEBI:16240 Y
ChEMBL	CHEMBL71595 Y
IUPHAR ligand	2448
RTECS number	MX0900000 (>90% soln.) MX0887000 (>30% soln.)
Jmol-3D images	Image 1
SMILES OO
InChI InChI=1S/H2O2/c1-2/h1-2H Y Key: MHAJPDPJQMAIIY-UHFFFAOYSA-N Y InChI=1/H2O2/c1-2/h1-2H Key: MHAJPDPJQMAIIY-UHFFFAOYAL
Properties
Molecular formula	2(HO)
Molar mass	34.0147 g/mol
Appearance	Very light blue color; colorless in solution
Density	1.110 g/cm3 (20 °C, 30-percent) 1.450 g/cm3 (20 °C, pure)
Melting point	-0.43 °C, 273 K, 31 °F
Boiling point	150.2 °C, 423 K, 302 °F
Solubility in water	Miscible
Solubility	soluble in ether
Acidity (pKa)	11.62 [1]
Refractive index (nD)	1.34
Viscosity	1.245 cP (20 °C)
Dipole moment	2.26 D
Thermochemistry
Std enthalpy of formation ΔfHo298	-4.007 kJ/g
Specific heat capacity, C	1.267 J/g K (gas) 2.619 J/g K (liquid)
Hazards
MSDS	ICSC 0164 (>60% soln.)
EU Index	008-003-00-9
EU classification	Oxidant (O) Corrosive (C) Harmful (Xn)
R-phrases	R5, R8, R20/22, R35
S-phrases	(S1/2), S17, S26, S28, S36/37/39, S45
NFPA 704	0 3 2 OX
Flash point	Non-flammable
LD50	1518 mg/kg
Related compounds
Related compounds	Water Ozone Hydrazine Hydrogen disulfide
Y peroxide (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Hydrogen peroxide (H₂O₂) is the simplest peroxide (a compound with an oxygen-oxygen single bond) and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent. The oxidizing capacity of hydrogen peroxide is so strong that it is considered a highly reactive oxygen species. Hydrogen peroxide is therefore used as a propellant in rocketry.^[2] Hydrogen peroxide is also naturally produced in organisms as a by-product of oxidative metabolism. Nearly all living things (specifically, all obligate and facultative aerobes) possess enzymes known as catalyse peroxidases, which harmlessly and catalytically decompose low concentrations of hydrogen peroxide to water and oxygen.

Structure and properties

H₂O₂ adopts a nonplanar structure of C2 symmetry. Although chiral, the molecule undergoes rapid racemization. The flat shape of the anti conformer would minimize steric repulsions, the 90° torsion angle of the syn conformer would optimize mixing between the filled p-type orbital of the oxygen (one of the lone pairs) and the LUMO of the vicinal O-H bond.^[3] The observed anticlinal "skewed" shape is a compromise between the two conformers.

Although the O−O bond is a single bond, the molecule has a relatively high barrier to rotation, of 29.45 kJ/mol; the rotational barrier is 12.5 kJ/mol for the bulkier molecule ethane. The increased barrier is ascribed to repulsion between nonbonding electrons (lone pairs) on the adjacent oxygen centres. The bond angles are affected by hydrogen bonding, which is relevant to the difference between the structure of gaseous and crystalline forms; indeed a wide range of values is seen in crystals containing H₂O₂.

Comparison with analogues

Analogues of hydrogen peroxide include the chemically identical deuterium peroxide, and hydrogen disulfide.^[4] Hydrogen disulfide has a boiling point of only 70.7 °C despite having a higher molecular weight, indicating that hydrogen bonding increases the boiling point of hydrogen peroxide.

Physical properties of hydrogen peroxide solutions

The properties of aqueous solutions of hydrogen peroxide differ from those of the pure material, reflecting the effects of hydrogen bonding between water and hydrogen peroxide. Hydrogen peroxide and water form a eutectic mixture, exhibiting freezing-point depression. Pure water melts and freezes at approximately 273 K, and pure hydrogen peroxide just 0.4 K below that, but a 50% (by volume) solution melts and freezes at 221 K.^[5]

pH of H₂O₂

Pure hydrogen peroxide has a pH of 6.2; thus it is considered to be a weak acid. The pH can be as low as 4.5 when diluted at approximately 60%.^[6]

History

Hydrogen peroxide was first described in 1818 by Louis Jacques Thénard by reacting barium peroxide with nitric acid.^[7] An improved version of this process used hydrochloric acid, followed by sulfuric acid to precipitate the barium sulfate byproduct. Thénard's process was used from the end of the 19th century until the middle of the 20th century.^[8] Modern production methods are discussed below.

For a long time, pure hydrogen peroxide was believed to be unstable, owing to failed attempts to separate the hydrogen peroxide from the water, which is present during synthesis. This instability was, however, due to traces of impurities (transition metals salts) that catalyze the decomposition of the hydrogen peroxide. One hundred percent pure hydrogen peroxide was first obtained through vacuum distillation by Richard Wolffenstein in 1894.^[9] At the end of 19th century, Petre Melikishvili and his pupil L. Pizarjevski showed that of the many proposed formulas of hydrogen peroxide, the correct one was H−O−O−H.

The use of H₂O₂ sterilization in biological safety cabinets and barrier isolators is a popular alternative to ethylene oxide (EtO) as a safer, more efficient decontamination method. H₂O₂ has long been widely used in the pharmaceutical industry. In aerospace research, H₂O₂ is used to sterilize artificial satellites and space probes.

The U.S. FDA has granted 510(k) clearance to use H₂O₂ in individual medical device manufacturing applications. EtO criteria outlined in ANSI/AAMI/ISO 14937 may be used as a validation guideline. Sanyo was the first manufacturer to use the H₂O₂ process in situ in a cell culture incubator, which is a faster and more efficient cell culture sterilization process.^{[citation needed]}

Manufacture

Formerly, hydrogen peroxide was prepared by the electrolysis of an aqueous solution of sulfuric acid or acidic ammonium bisulfate (NH₄HSO₄), followed by hydrolysis of the peroxodisulfate ((SO₄)₂)²⁻ that is formed. Today, hydrogen peroxide is manufactured almost exclusively by the autoxidation of a 2-alkyl anthrahydroquinone (or 2-alkyl-9,10-dihydroxyanthracene) to the corresponding 2-alkyl anthraquinone in the so called anthraquinone process. Major producers commonly use either the 2-ethyl or the 2-amyl derivative. The cyclic reaction depicted below shows the 2-ethyl derivative, where 2-ethyl-9,10-dihydroxyanthracene (C₁₆H₁₂(OH)₂) is oxidized to the corresponding 2-ethylanthraquinone (C₁₆H₁₂O₂) and hydrogen peroxide. Most commercial processes achieve this 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 group), giving hydrogen peroxide and regenerating the anthraquinone. Hydrogen peroxide is then extracted and the anthraquinone derivative is reduced back to the dihydroxy (anthracene) compound using hydrogen gas in the presence of a metal catalyst. The cycle then repeats itself.^[10][11]

This process is known as the Riedl-Pfleiderer process,^[11] having been first discovered by them in 1936. The overall equation for the process is deceptively simple:^[10]

H₂ + O₂ → H₂O₂

The economics of the process depend heavily on effective recycling of the quinone (which is expensive) and extraction solvents, and of the hydrogenation catalyst.

In 1994, world production of H₂O₂ was around 1.9 million tonnes and grew to 2.2 million in 2006,^[12] 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]}

New developments

A new, so-called "high-productivity/high-yield" process, based on an optimized distribution of isomers of 2-amyl anthraquinone, has been developed by Solvay. In July 2008, this process allowed the construction of a "mega-scale" single-train plant in Zandvliet (Belgium). The plant has an annual production capacity more than twice that of the world's next-largest single-train plant. An even-larger plant is scheduled to come onstream at Map Ta Phut (Thailand) in 2011. It is likely that this will lead to a reduction in the cost of production due to economies of scale.^[13]

A process to produce hydrogen peroxide directly from the elements has been of interest for many years. The problem with the direct synthesis process is that, in terms of thermodynamics, the reaction of hydrogen with oxygen favors production of water. It had been recognized for some time that a finely dispersed catalyst is beneficial in promoting selectivity to hydrogen peroxide, but, while selectivity was improved, it was still not sufficiently high to permit commercial development of the process. However, an apparent breakthrough was made in the early 2000s by researchers at Headwaters Technology. The breakthrough revolves around development of a minute (nanometer-size) phase-controlled noble metal crystal particles on carbon support. This advance led, in a joint venture with Evonik Industries, to the construction of a pilot plant in Germany in late 2005. It is claimed that there are reductions in investment cost because the process is simpler and involves less equipment; however, the process is also more corrosive and unproven. This process results in low concentrations of hydrogen peroxide (about 5–10 wt% versus about 40 wt% through the anthraquione process).^[13]

In 2009, another catalyst development was announced by researchers at Cardiff University.^[14] This development also relates to the direct synthesis, but, in this case, using gold–palladium nanoparticles. Under normal circumstances, the direct synthesis must be carried out in an acid medium to prevent immediate decomposition of the hydrogen peroxide once it is formed. Whereas hydrogen peroxide tends to decompose on its own (which is why, even after production, it is often necessary to add stabilisers to the commercial product when it is to be transported or stored for long periods), the nature of the catalyst can cause this decomposition to accelerate rapidly. It is claimed that the use of this gold-palladium catalyst reduces this decomposition and, as a consequence, little to no acid is required. The process is in a very early stage of development and currently results in very low concentrations of hydrogen peroxide being formed (less than about 1–2 wt%). Nonetheless, it is envisaged by the inventors that the process will lead to an inexpensive, efficient, and environmentally friendly process.^{[13][14][15][16]}

A novel electrochemical process for the production of alkaline hydrogen peroxide has been developed by Dow. The process employs a monopolar cell to achieve an electrolytic reduction of oxygen in a dilute sodium hydroxide solution.^[13]

Availability

Hydrogen peroxide is most commonly available as a solution in water. For consumers, it is usually available from pharmacies at 3 and 6 wt% concentrations. The concentrations are sometimes described in terms of the volume of oxygen gas generated; one milliliter of a 20-volume solution generates twenty milliliters of oxygen gas when completely decomposed. For laboratory use, 30 wt% solutions are most common. Commercial grades from 70% to 98% are also available, but due to the potential of solutions of >68% hydrogen peroxide to be converted entirely to steam and oxygen (with the temperature of the steam increasing as the concentration increases above 68%) these grades are potentially far more hazardous, and require special care in dedicated storage areas. Buyers must typically submit to inspection by the small number of commercial manufacturers.

Reactions

Decomposition

Manganese dioxide decomposing a very dilute solution of hydrogen peroxide

Hydrogen peroxide decomposes (disproportionates) exothermically into water and oxygen gas spontaneously:

2 H₂O₂ → 2 H₂O + O₂

This process is thermodynamically favorable. It has a ΔH^o of −98.2 kJ·mol⁻¹ and a ΔS of 70.5 J·mol⁻¹·K⁻¹. The rate of decomposition is dependent on the temperature (cool environment slows down decomposition, therefore hydrogen peroxide is often stored in refrigerator) and concentration of the peroxide, as well as the pH and the presence of impurities and stabilizers. Hydrogen peroxide is incompatible with many substances that catalyse its decomposition, including most of the transition metals and their compounds. Common catalysts include manganese dioxide, silver, and platinum.^[17] The same reaction is catalysed by the enzyme catalase, found in the liver, whose main function in the body is the removal of toxic byproducts of metabolism and the reduction of oxidative stress. The decomposition occurs more rapidly in alkali, so acid is often added as a stabilizer.

The liberation of oxygen and energy in the decomposition has dangerous side-effects. Spilling high concentrations of hydrogen peroxide on a flammable substance can cause an immediate fire, which is further fueled by the oxygen released by the decomposing hydrogen peroxide. High test peroxide, or HTP (also called high-strength peroxide) 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. A 20-volume concentration of hydrogen peroxide is equivalent to 1.667 mol/dm³ (Molar solution) or about 6%.

Redox reactions

In acidic solutions, H₂O₂ is one of the most powerful oxidizers known—stronger than chlorine, chlorine dioxide, and potassium permanganate. Also, through catalysis, H₂O₂ can be converted into hydroxyl radicals (.OH), which are highly reactive.

Oxidant/Reduced product	Oxidation potential, V
Fluorine/Hydrogen fluoride	3.0
Ozone/Oxygen	2.1
Hydrogen peroxide/Water	1.8
Potassium permanganate/Manganese dioxide	1.7
Chlorine dioxide/HClO	1.5
Chlorine/Chloride	1.4

In aqueous solutions, hydrogen peroxide can oxidize or reduce a variety of inorganic ions. When it acts as a reducing agent, oxygen gas is also produced.

In acidic solutions Fe²⁺ is oxidized to Fe³⁺ (hydrogen peroxide acting as an oxidizing agent),

2 Fe²⁺(aq) + H₂O₂ + 2 H⁺(aq) → 2 Fe³⁺(aq) + 2H₂O(l)

and sulfite (SO2−
3) is oxidized to sulfate (SO2−
4). However, potassium permanganate is reduced to Mn²⁺ by acidic H₂O₂. Under alkaline conditions, however, some of these reactions reverse; for example, Mn²⁺ is oxidized to Mn⁴⁺ (as sodium hypochlorite or potassium permanganate, which is a convenient method for preparing oxygen in the laboratory.

NaOCl + H₂O₂ → O₂ + NaCl + H₂O

2 KMnO₄ + 3 H₂O₂ → 2 MnO₂ + 2 KOH + 2 H₂O + 3 O₂

Hydrogen peroxide is frequently used as an oxidizing agent in organic chemistry. One application is for the oxidation of thioethers to sulfoxides.^{[citation needed]} For example, methyl phenyl sulfide was oxidized to methyl phenyl sulfoxide in 99% yield in methanol in 18 hours (or 20 minutes using a TiCl₃ catalyst):^{[citation needed]}

Ph−S−CH₃ + H₂O₂ → Ph−S(O)−CH₃ + H₂O

Alkaline hydrogen peroxide is used for epoxidation of electron-deficient alkenes such as acrylic acids, and also for oxidation of alkylboranes to alcohols, the second step of hydroboration-oxidation.

Formation of peroxide compounds

Hydrogen peroxide is a weak acid, and it can form hydroperoxide or peroxide 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 carboxylic acids (RCOOH) into peroxy acids (RCOOOH), which are themselves used as oxidizing agents. Hydrogen peroxide reacts with acetone to form acetone peroxide, and it interacts with ozone to form hydrogen trioxide, also known as trioxidane. Reaction with urea produces carbamide peroxide, used for whitening teeth. An acid-base adduct with triphenylphosphine oxide is a useful "carrier" for H₂O₂ in some reactions.

Alkalinity

Hydrogen peroxide can still form adducts with very strong acids. The superacid HF/SbF₅ forms unstable compounds containing the [H₃O₂]⁺ ion.

Uses

Municipal wastewater applications

For over 50 years the standard way to deal with odors entering wastewater treatment plants was to pre-chlorinate the influent sewers. Recently, however, an increasing number of POTWs have revisited this issue and come up with a different answer - hydrogen peroxide (H2O2). Their results show that hydrogen peroxide can replace chlorine with little to no increase in costs, and with notable benefits to downstream operations. This paper looks at four recent studies conducted at large municipalities and identifies the factors that led them to select hydrogen peroxide for liquid-phase headworks odor control. [1]

Cost Effective Control of Hydrogen Sulfide in Municipal Sludge

In many municipal treatment facilities, the processing of wastewater sludge (or biosolids) poses operational and safety challenges due to hydrogen sulfide (H₂S) generation. In addition to being a hazard to operations personnel (H₂S is a poisonous gas), H₂S odors generated during sludge processing can cause community complaints and make plant working conditions unpleasant. Furthermore, damage to equipment and concrete structures caused by H₂S initiated corrosion can be substantial. Typical areas where H₂S problems occur include gravity thickeners, mix tanks, and dewatering presses.

Hydrogen sulfide is generated in sludge via the same mechanism as in collection systems - conversion of sulfates to sulfides by bacteria. This biochemical generation of H₂S is brought about by anaerobic or oxygen limited conditions. There are numerous chemical and non-chemical treatment technologies available which can control H₂S in municipal sludge processing operations. [2]

Industrial applications

ISO tank container for hydrogen peroxide transportation

About 50% of the world's production of hydrogen peroxide in 1994 was used for pulp- and paper-bleaching.^[12] Other bleaching applications are becoming more important as hydrogen peroxide is seen as an environmentally benign alternative to chlorine-based bleaches.^{[citation needed]}

Sulfide Oxidation with Hydrogen Peroxide

Sulfide is found throughout the environment as a result of both natural and industrial processes. Most sulfide found in nature was produced biologically (under anaerobic conditions) and occurs as free hydrogen sulfide (H₂S) - characterized by its rotten egg odor. We are most likely to encounter biogenic H₂S in sour groundwaters, swamps and marshes, natural gas deposits, and sewage collection/treatment systems. Manmade sources of H₂S typically occur as a result of natural materials containing sulfur (e.g., coal, gas and oil) being refined into industrial products. For a variety of reasons - aesthetics (odor control), health (toxicity), ecological (oxygen depletion in receiving waters), and economic (corrosion of equipment and infrastructure) - sulfide laden wastewaters must be handled carefully and remediated before they can be released to the environment. Typical discharge limits for sulfide are < 1 mg/L. Sulfide Oxidation

BOD and COD Removal in Wastewater Using Hydrogen Peroxide

Hydrogen peroxide has been used to reduce the BOD and COD of industrial wastewaters for many years. While the cost of removing BOD/COD through chemical oxidation is typically greater than that through physical or biological means, there are nonetheless specific situations which justify its use. These include:

• Predigestion of wastewaters which contain moderate to high levels of compounds that are toxic, inhibitory, or recalcitrant to biological treatment (e.g., pesticides, plasticizers, resins, coolants, and dyestuffs);
• Pretreatment of high strength / low flow wastewaters – where biotreatment may not be practical – prior to discharge to a Publicly Owned Treatment Works (POTW);
• Enhanced separation of entrained organics by flotation and settling processes; and

Supply of supplemental Dissolved Oxygen (DO) when biological treatment systems experience temporary overloads or equipment failure.

As indicated by these examples, H₂O₂ can be used as a stand-alone treatment or as an enhancement to existing physical or biological treatment processes, depending on the situation. BOD-COD Removal

High Strength Wastewater Pretreatment

Hydrogen peroxide is one of the most versatile, dependable and environmentally compatible oxidizing agents. The relative safety and simplicity of its use as an oxidizing agent has led to the development of a number of applications in refinery wastewater systems.

“Uncatalyzed” Hydrogen Peroxide The strong oxidizing power of H2O2 makes it suitable for the destruction of a variety of pollutants. Optimization of conditions using H2O2 to destroy these pollutants can involve control of pH, temperature and reaction time. No additional additives are required.

“Catalyzed” Hydrogen Peroxide Pollutants that are more difficult to oxidize require H2O2 to be activated with catalysts such as iron. Catalyzed oxidation can also be used to destroy easily oxidized pollutants more rapidly.

Under acid pH conditions, the addition of iron salts to a wastewater solution activates H2O2 to generate free radicals, which can attack a variety of organic compounds. Other metal salts and conditions can apply (e.g. in cyanide destruction, a copper catalyst can be used at a pH of 8.5 - 11.5). High Strength Wastewater Pretreatment

Nitrogen Oxides (NOx) Abatement with Hydrogen Peroxide

Nitrogen oxides are major pollutants in the atmosphere, being a precursor to acid rain, photochemical smog, and ozone accumulation. The oxides are mainly nitric oxide (NO) and nitrogen dioxide (NO₂) both of which are corrosive and hazardous to health. With the use of catalytic converters on automobiles, the initial regulatory focus of controlling of mobile NOx emissions has reached the point where further restriction has become economically impractical. Consequently, the stationary sources of NOx emissions are now being subjected to more stringent standards in many areas of the U.S. Stationary sources include nitric acid manufacturing plants, manufacturers of nitrated materials such as fertilizer and explosives, and industrial manufacturers (metallurgical processors, glass manufacturers, cement kilns, power generators, etc.) where high processing temperatures are used. Because of the environmental concerns posed by air pollution, a great deal of research time and money has been expended to develop methods for controlling NOx emissions. Nitrogen Oxide Abatement (NOx)

Other major industrial applications for hydrogen peroxide include the manufacture of sodium percarbonate and sodium perborate, used as mild bleaches in laundry detergents. It is used in the production of certain organic peroxides, such as dibenzoyl peroxide, used in polymerisations and other chemical processes. Hydrogen peroxide is also used in the production of epoxides, such as propylene oxide. Reaction with carboxylic acids produces a corresponding peroxy acid. Peracetic acid and meta-chloroperoxybenzoic acid (commonly abbreviated mCPBA) are prepared from acetic acid and meta-chlorobenzoic acid, respectively. The latter is commonly reacted with alkenes to give the corresponding epoxide.

In the PCB manufacturing process, hydrogen peroxide mixed with sulfuric acid was used as the microetch chemical for copper surface roughening preparation.

A combination of a powdered precious metal-based catalyst, hydrogen peroxide, methanol and water can produce superheated steam in one to two seconds, releasing only CO₂ and high-temperature steam for a variety of purposes.^[18]

Recently, there has been increased use of vaporized hydrogen peroxide in the validation and bio-decontamination of half-suit and glove-port isolators in pharmaceutical production.

Nuclear pressurized water reactors (PWRs) use hydrogen peroxide during the plant shutdown to force the oxidation and dissolution of activated corrosion products deposited on the fuel. The corrosion products are then removed with the cleanup systems before the reactor is disassembled.

Hydrogen peroxide is also used in the oil and gas exploration industry to oxidize rock matrix in preparation for micro-fossil analysis.

Chemical applications

A method of producing propylene oxide from hydrogen peroxide has been developed. The process is claimed to be environmentally friendly, since the only significant byproduct is water. It is also claimed the process has significantly lower investment and operating costs. Two of these "HPPO" (hydrogen peroxide to propylene oxide) plants came onstream in 2008: One of them located in Belgium is a Solvay, Dow-BASF joint venture, and the other in Korea is a EvonikHeadwaters, SK Chemicals joint venture. A caprolactam application for hydrogen peroxide has been commercialized. Potential routes to phenol and epichlorohydrin utilizing hydrogen peroxide have been postulated.^[13]

Biological function

Hydrogen peroxide is also one of the two chief chemicals in the defense system of the bombardier beetle, reacting with hydroquinone to discourage predators.

A study published in Nature found that hydrogen peroxide plays a role in the immune system. Scientists found that hydrogen peroxide inside of cells increased after tissues are damaged in zebra fish, which is thought to act as a signal to white blood cells to converge on the site and initiate the healing process. When the genes required to produce hydrogen peroxide were disabled, white blood cells did not accumulate at the site of damage. The experiments were conducted on fish; however, because fish are genetically similar to humans, the same process is speculated to occur in humans. The study in Nature suggested asthma sufferers have higher levels of hydrogen peroxide in their lungs than healthy people, which could explain why asthma sufferers have inappropriate levels of white blood cells in their lungs.^[19][20]

Hydrogen peroxide has important roles as a signaling molecule in the regulation of a variety of biological processes.^[21] Hydrogen peroxide also plays an important role in aging^[22] and cancer.^[23]

Domestic uses

Skin immediately after exposure to 30% H₂O₂

• Diluted H₂O₂ (between 3% and 8%) is used to bleach human hair when mixed with ammonium hydroxide, hence the phrase "peroxide blonde".
• It is absorbed by skin upon contact and creates a local skin capillary embolism that appears as a temporary whitening of the skin.
• It is used to whiten bones that are to be put on display.
• 3% H₂O₂ is effective at treating fresh (red) blood-stains in clothing and on other items. It must be applied to clothing before blood stains can be accidentally "set" with heated water. Cold water and soap are then used to remove the peroxide treated blood.
• Some horticulturalists and users of hydroponics advocate the use of weak hydrogen peroxide solution in watering solutions. 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) and a variety of other pests.^[24][25][26]
• 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.^[27][28] Hydrogen peroxide releases oxygen by decomposition when it is exposed to catalysts such as 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 Biochemical Oxygen Demand (BOD).
• Mixed with baking soda and a small amount of hand soap, hydrogen peroxide is effective at removing skunk odor.^[29]
• Hydrogen peroxide is used with phenyl oxalate ester and an appropriate dye in glow sticks as an oxidizing agent. It reacts with the ester to form an unstable CO₂ dimer, which excites the dye to an excited state; the dye emits a photon (light) when it spontaneously relaxes back to the ground state.
• Hydrogen peroxide can be combined with vinegar and table salt to form a substitute for industrial chemicals such as ferric chloride, ammonium persulfate, or hydrochloric acid as a hobbyist's printed circuit board etchant.^[30]
• Hydrogen peroxide can be used to clean tile and grout on floors. Sometimes it is recommended to clean with baking soda together with the hydrogen peroxide. ^[31]

Propellant

For more details on this topic, see High test peroxide.

Rocket Belt hydrogen peroxide propulsion system used in a jet pack

High concentration H₂O₂ is referred to as HTP or High test peroxide. It can be used either as a monopropellant (not mixed with fuel) or as the oxidizer component of a bipropellant rocket. Use as a monopropellant takes advantage of the decomposition of 70–98+% concentration hydrogen peroxide into steam and oxygen. The propellant is pumped into a reaction chamber where a catalyst, usually a silver or platinum screen, triggers decomposition, producing steam at over 600 °C, which is expelled through a nozzle, generating thrust. H₂O₂ monopropellant produces a maximum specific impulse (I_sp) of 161 s (1.6 kN·s/kg), which makes it a low-performance monopropellant. Peroxide generates much less thrust than 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 using an efficient closed cycle. 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, containing oxyquinoline stabilizer, 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. 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.^[32]

While rarely used now as a monopropellant for large engines, small hydrogen peroxide attitude control thrusters are still in use on some satellites.^{[citation needed]} 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.

Therapeutic use

Hydrogen peroxide is generally recognized as safe (GRAS) as an antimicrobial agent, an oxidizing agent and for other purposes by the U.S. FDA.^[33] For example, 35% hydrogen peroxide is used to prevent infection transmission in the hospital environment, and hydrogen peroxide vapor is registered with the US EPA as a sporicidal sterilant.
It is a common misconception that hydrogen peroxide is a disinfectant or antiseptic for treating wounds.^[34][35] While it is an effective cleaning agent, hydrogen peroxide is not an effective agent for reducing bacterial infection of wounds. Further, hydrogen peroxide applied to wounds can impede healing and lead to scarring because it destroys newly formed skin cells.^[36]

• Hydrogen peroxide can be used as a toothpaste, or oral debriding agent, when mixed with correct quantities of baking soda and salt. This use is no more effective than toothpaste alone, however.^[37]
• Hydrogen peroxide and benzoyl peroxide are sometimes used to treat acne.^[38]
• Hydrogen peroxide is used as an emetic in veterinary practice.^[39][40]

Alternative uses

See also: Liquid Oxygen (supplement)

• Following the call by alternative medicine advisors for drinking diluted hydrogen peroxide, and using it in various ways such as in shampoo and as an additive to toothpaste, as a treatment to illness in general and cancer in particular, 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." ^[41]
• Another controversial alternative medical procedure is inhalation of hydrogen peroxide at a concentration of about 1%. Intravenous usage of hydrogen peroxide has been linked to several deaths.^[42][43]

Improvised explosive device / home-made bomb precursor

Hydrogen peroxide was the main ingredient in the 7 July 2005 London bombings that killed 52 London Underground and bus passengers. The bomb-making ingredients are reported to be easier to buy than large numbers of aspirin pills.^[44]

Safety

Regulations vary, but low concentrations, such as 3%, are widely available and legal to buy for medical use. Most over-the-counter peroxide solutions are not suitable for ingestion. Higher concentrations may be considered hazardous and are typically accompanied by a Material Safety Data Sheet (MSDS). In high concentrations, hydrogen peroxide is an aggressive oxidizer and will corrode many materials, including human skin. In the presence of a reducing agent, high concentrations of H₂O₂ will react violently.

High-concentration hydrogen peroxide streams, typically above 40%, should be considered a D001 hazardous waste, due to concentrated hydrogen peroxide's meeting the definition of a DOT oxidizer according to U.S. regulations, if released into the environment. The EPA Reportable Quantity (RQ) for D001 hazardous wastes is 100 pounds (45 kg), or approximately 10 US gallons (38 L), of concentrated hydrogen peroxide.

Hydrogen peroxide should be stored in a cool, dry, well-ventilated area and away from any flammable or combustible substances.^[45] It should be stored in a container composed of non-reactive materials such as stainless steel or glass (other materials including some plastics and aluminium alloys may also be suitable).^[46] Because it breaks down quickly when exposed to light, it should be stored in an opaque container, and pharmaceutical formulations typically come in brown bottles that filter out light.^[47]

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

• Explosive vapors. 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.
• Hazardous reactions. 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, ketones, carboxylic acids (particularly acetic acid), amines and phosphorus.^{[citation needed]}
• Spontaneous ignition. Concentrated hydrogen peroxide, if spilled on clothing (or other flammable materials), will preferentially evaporate water until the concentration reaches sufficient strength, at which point the material may spontaneously ignite.^[48][49]
• Corrosive. Concentrated hydrogen peroxide (>50%) is corrosive, and even domestic-strength solutions can cause irritation to the eyes, mucous membranes and skin.^[50] 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]}
• Bleach agent. Low concentrations of hydrogen peroxide, on the order of 3% or less, will chemically bleach many types of clothing 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.
• Internal ailments. Large oral doses of hydrogen peroxide at a 3% concentration may cause "irritation and blistering to the mouth, (which is known as Black hairy tongue) throat, and abdomen", as well as "abdominal pain, vomiting, and diarrhea".^[51]
• Vapor pressure. Hydrogen peroxide has a significant vapor pressure (1.2 kPa at 50 ^oC[CRC Handbook of Chemistry and Physics, 76th Ed, 1995-1996]) and exposure to the vapor is potentially hazardous. Hydrogen peroxide vapor is a primary irritant, primarily affecting the eyes and respiratory system and the NIOSH Immediately dangerous to life and health limit (IDLH) is only 75 ppm.^[52] Long term exposure to low ppm concentrations is also hazardous and can result in permanent lung damage and Occupational Safety and Health Administration (OSHA) has established a permissible exposure limit of 1.0 ppm calculated as an eight hour time weighted average (29 CFR 1910.1000, Table Z-1) and hydrogen peroxide has also been classified by the American Conference of Governmental Industrial Hygienists (ACGIH) as a "known animal carcinogen, with unknown relevance on humans.[2008 Threshold Limit Values for Chemical Substances and Physical Agents & Biological Exposure Indices, ACGIH] In applications where high concentrations of hydrogen peroxide are used, suitable personal protective equipment should be worn and it is prudent in situations where the vapor is likely to be generated, such as hydrogen peroxide gas or vapor sterilization, to ensure that there is adequate ventilation and the vapor concentration monitored with a continuous gas monitor for hydrogen peroxide. Continuous gas monitors for hydrogen peroxide are available from several suppliers. Further information on the hazards of hydrogen peroxide is available from OSHA^[53] and from the ATSDR.^[54]
• Skin disorders. Vitiligo is an acquired skin disorder with the loss of native skin pigment, which affects about 0.5-1% of the world population. Recent studies have discovered increased H₂O₂ levels in the epidermis and in blood are one of many hallmarks of this disease.^[55]

Historical incidents

• On July 16, 1934, in Kummersdorf, Germany, a rocket engine using hydrogen peroxide exploded, killing three people. As a result of this incident, Wernher von Braun decided not to use hydrogen peroxide as an oxidizer in the rockets he developed afterward.
• Several people received minor injuries after a hydrogen peroxide spill on board Northwest Airlines flight 957 from Orlando to Memphis on October 28, 1998 and subsequent fire on Northwest Airlines flight 7.^[56]
• During the Second World War, doctors in Nazi concentration camps experimented with the use of hydrogen peroxide injections in the killing of human subjects.^[57]
• Hydrogen peroxide was said to be one of the ingredients in the bombs that failed to explode in the July 21, 2005 London bombings.^[58]
• The Russian submarine K-141 Kursk sailed out to sea to perform an exercise of firing dummy torpedoes at the Pyotr Velikiy, a Kirov class battlecruiser. On August 12, 2000 at 11:28 local time (07:28 UTC), there was an explosion while preparing to fire the torpedoes. The only credible report to date is that this was due to the failure and explosion of one of the Kursk's hydrogen peroxide-fueled torpedoes. It is believed that HTP, a form of highly concentrated hydrogen peroxide used as propellant for the torpedo, seeped through rust in the torpedo casing. A similar incident was responsible for the loss of HMS Sidon in 1955
• On August 16, 2010 a spill of about 10 US gallons (38 L) of cleaning fluid spilled on the 53rd floor of 1515 Broadway, in Times Square, New York City. The spill, which a spokesperson for the New York City fire department said was of Hydrogen Peroxide, shut down Broadway between West 42nd and West 48th streets as a number of fire engines responded to the hazmat situation. There were no reported injuries.^[59]

See also

• Elephant toothpaste

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Bibliography

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External links

• Hydrogen Peroxide Distillation for rocket fuel
• Material Safety Data Sheet
• ATSDR Agency for Toxic Substances and Disease Registry FAQ
• Tombes MB, Gallucci B (1993). "The effects of hydrogen peroxide rinses on the normal oral mucosa". Nurs Res 42 (6): 332–7. PMID 8247815. 
• Experimental Rocket Propulsion Society
• International Chemical Safety Card 0164
• NIOSH Pocket Guide to Chemical Hazards
• Oxygenation Therapy:Unproven Treatments for Cancer and AIDS
• Hydrogen Peroxide in the Human Body
• Information on many common uses for hydrogen peroxide, especially household uses.
• Hydrogen peroxide in tooth whiteners summary by GreenFacts of the European Commission SCCP assessment