Hydrogen peroxide

Hydrogen peroxide

Ball stick model of the hydrogen peroxide molecule
Names
IUPAC name Hydrogen peroxide
Other names Dioxidane Oxidanyl Perhydroxic acid 0-hydroxyol Dihydrogen dioxide Oxygenated water Peroxaan
Identifiers
CAS Number	7722-84-1 Y
3D model ( JSmol )	Interactive image
ChEBI	CHEBI:16240 Y
ChEMBL	ChEMBL71595 Y
ChemSpider	763 Y
ECHA InfoCard	100.028.878
EC Number	231-765-0
IUPHAR/BPS	2448
KEGG	D00008 Y
PubChem CID	784
RTECS number	MX0900000 (>90% soln.) MX0887000 (>30% soln.)
UNII	BBX060AN9V Y
UN number	2015 (>60% soln.) 2014 (20–60% soln.) 2984 (8–20% soln.)
CompTox Dashboard (EPA)	DTXSID2020715
InChI InChI=1S/H2O2/c1-2/h1-2H Y Key: MHAJPDPJQMAIIY-UHFFFAOYSA-N Y InChI=1/H2O2/c1-2/h1-2H Key: MHAJPDPJQMAIIY-UHFFFAOYAL
SMILES OO
Properties
Chemical formula	H2O2
Molar mass	34.0147 g/mol
Appearance	Very light blue liquid
Odor	slightly sharp
Density	1.11 g/cm3 (20 °C, 30% (w/w) solution)[1] 1.450 g/cm3 (20 °C, pure)
Melting point	−0.43 °C (31.23 °F; 272.72 K)
Boiling point	150.2 °C (302.4 °F; 423.3 K) (decomposes)
Solubility in water	Miscible
Solubility	soluble in ether, alcohol insoluble in petroleum ether
log P	-0.43[2]
Vapor pressure	5 mmHg (30 °C)[3]
Acidity (pKa)	11.75
Magnetic susceptibility (χ)	−17.7·10−6 cm3/mol
Refractive index (nD)	1.4061
Viscosity	1.245 cP (20 °C)
Dipole moment	2.26 D
Thermochemistry
Heat capacity (C)	1.267 J/(g·K) (gas) 2.619 J/(g·K) (liquid)
Std enthalpy of formation (ΔfH⦵298)	−187.80 kJ/mol
Pharmacology
ATC code	A01AB02 (WHO) D08AX01 (WHO), D11AX25 (WHO), S02AA06 (WHO)
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H271, H302, H314, H332, H335, H412
Precautionary statements	P280, P305+P351+P338, P310
NFPA 704 (fire diamond)	3 0 3 OX
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	1518 mg/kg[citation needed] 2000 mg/kg (oral, mouse)[4]
LC50 (median concentration)	1418 ppm (rat, 4 hr)[4]
LCLo (lowest published)	227 ppm (mouse)[4]
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 1 ppm (1.4 mg/m3)[3]
REL (Recommended)	TWA 1 ppm (1.4 mg/m3)[3]
IDLH (Immediate danger)	75 ppm[3]
Safety data sheet (SDS)	ICSC 0164 (>60% soln.)
Related compounds
Related compounds	Water Ozone Hydrazine Hydrogen disulfide Dioxygen difluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Hydrogen peroxide is a

Hydrogen peroxide is a

peroxidases

.

Properties

The boiling point of H₂O₂ has been extrapolated as being 150.2 °C (302.4 °F), approximately 50 °C (90 °F) higher than water. In practice, hydrogen peroxide will undergo potentially explosive thermal decomposition if heated to this temperature. It may be safely distilled at lower temperatures under reduced pressure.^[7]

Structure

Hydrogen peroxide (H₂O₂) is a nonplanar molecule with (twisted) C₂

is 1040 cm⁻¹ (12.4 kJ/mol).

The approximately 100°

The molecular structures of gaseous and

Aqueous solutions

In

Phase diagram

of H₂O₂ and water: Area above blue line is liquid. Dotted lines separate solid–liquid phases from solid–solid phases.

Density of aqueous solution of H₂O₂

H2O2 ( w/w )	Density (g/cm3)	Temp. (°C)
3%	1.0095	15
27%	1.10	20
35%	1.13	20
50%	1.20	20
70%	1.29	20
75%	1.33	20
96%	1.42	20
98%	1.43	20
100%	1.45	20

Comparison with analogues

Hydrogen peroxide has several structural analogues with H_mX−XH_n bonding arrangements (water also shown for comparison). It has the highest (theoretical) boiling point of this series (X = O, S, N, P). Its melting point is also fairly high, being comparable to that of hydrazine and water, with only hydroxylamine crystallising significantly more readily, indicative of particularly strong hydrogen bonding. Diphosphane and hydrogen disulfide exhibit only weak hydrogen bonding and have little chemical similarity to hydrogen peroxide. Structurally, the analogues all adopt similar skewed structures, due to repulsion between adjacent lone pairs.

Properties of H₂O₂ and its analogues
Values marked * are extrapolated

Name	Formula	Molar mass (g/mol)	Melting point (°C)	Boiling point (°C)
Water	HOH	18.02	0.00	99.98
Hydrogen peroxide	HOOH	34.01	−0.43	150.2*
Hydrogen disulfide	HSSH	66.15	−89.6	70.7
Hydrazine	H2NNH2	32.05	2	114
Hydroxylamine	NH2OH	33.03	33	58*
Diphosphane	H2PPH2	65.98	−99	63.5*

Discovery

Alexander von Humboldt is sometimes said to have been the first to report the first synthetic peroxide, barium peroxide, in 1799 as a by-product of his attempts to decompose air, although this is disputed due to von Humboldt's ambiguous wording.^[15] Nineteen years later Louis Jacques Thénard recognized that this compound could be used for the preparation of a previously unknown compound, which he described as eau oxygénée ("oxygenated water") – subsequently known as hydrogen peroxide.^[16][17][18] Today, the term "oxygenated water" may appear on retail packaging referring to mixtures containing either water and hydrogen peroxide or water and dissolved oxygen. This could cause personal injury if the difference is not properly understood by the user.^[19]

An improved version of Thénard's process used hydrochloric acid, followed by addition of sulfuric acid to precipitate the barium sulfate byproduct. This process was used from the end of the 19th century until the middle of the 20th century.^[20]

The bleaching effect of peroxides and their salts on

Early attempts failed to produce neat hydrogen peroxide. Anhydrous hydrogen peroxide was first obtained by vacuum distillation.^[22]

Determination of the molecular structure of hydrogen peroxide proved to be very difficult. In 1892, the Italian physical chemist Giacomo Carrara (1864–1925) determined its molecular mass by freezing-point depression, which confirmed that its molecular formula is H₂O₂.^[23] H₂O=O seemed to be just as possible as the modern structure, and as late as in the middle of the 20th century at least half a dozen hypothetical isomeric variants of two main options seemed to be consistent with the available evidence.^[24] In 1934, the English mathematical physicist William Penney and the Scottish physicist Gordon Sutherland proposed a molecular structure for hydrogen peroxide that was very similar to the presently accepted one.^[25][26]

Previously, hydrogen peroxide was prepared industrially by hydrolysis of ammonium persulfate:

${\displaystyle {\ce {[NH4]2S2O8 + 2 H2O -> 2 [NH4]HSO4 + H2O2}}}$

which was itself obtained by the electrolysis of a solution of ammonium bisulfate ([NH₄]HSO₄) in sulfuric acid:^[27]

${\displaystyle {\ce {2 [NH4]HSO4 -> [NH4]2S2O8 + H2}}}$

Production

Today, hydrogen peroxide is manufactured almost exclusively by the anthraquinone process, which was originally developed by BASF 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 on a palladium catalyst. In the presence of oxygen, the anthrahydroquinone then undergoes autoxidation: the labile hydrogen atoms of the hydroxy groups transfer to the oxygen molecule, to give hydrogen peroxide and regenerating the anthraquinone. Most commercial processes achieve oxidation by bubbling compressed air through a solution of the anthrahydroquinone, with the hydrogen peroxide then extracted from the solution and the anthraquinone recycled back for successive cycles of hydrogenation and oxidation.^[28][29]

The net reaction for the anthraquinone-catalyzed process is :^[28]

H₂ + O₂ → H₂O₂

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

Other sources

Small, but detectable, amounts of hydrogen peroxide can be formed by several methods. Small amounts are formed by electrolysis of dilute acid around the

A commercially viable process to produce hydrogen peroxide directly from the environment has been of interest for many years. Efficient direct synthesis is difficult to achieve, as the reaction of hydrogen with oxygen thermodynamically favours production of water. Systems for direct synthesis have been developed, most of which employ finely dispersed metal catalysts similar to those used for hydrogenation of organic substrates.[31]^[32] One economic obstacle has been that direct processes give a dilute solution uneconomic for transportation. None of these has yet reached a point where it can be used for industrial-scale synthesis.

Availability

Hydrogen peroxide is most commonly available as a solution in water. For consumers, it is usually available from pharmacies at 3 and 6

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 more than 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 allow inspection by commercial manufacturers.

In 1994, world production of H₂O₂ was around 1.9 million tonnes and grew to 2.2 million in 2006,

Natural occurrence

Hydrogen peroxide occurs in surface water, in groundwater, and in the

Reactions

Decomposition

Hydrogen peroxide decomposes to form water and oxygen with a

of 70.5 J/(mol·K):

${\displaystyle {\ce {2 H2O2 -> 2 H2O + O2}}}$

The rate of decomposition increases with rise in temperature, concentration, and

. The decomposition of hydrogen peroxide liberates oxygen and heat; this can be dangerous, as spilling high-concentration hydrogen peroxide on a flammable substance can cause an immediate fire.

Redox reactions

The redox properties of hydrogen peroxide depend on pH as acidic conditions exacerbate the power of oxidizing agents and basic conditions exacerbate the power of reducing agents. As hydrogen peroxide exhibits ambivalent redox properties, being simultaneously an oxidizer or a reductant, its redox behavior immediately depends on pH.

In acidic solutions, H₂O₂ is a powerful

.

H₂O₂ is a source of hydroxyl radicals (^•OH), which are highly reactive.

Oxidizing reagent	Reduced product	Oxidation potential (V)
F2	HF	3.0
O3	O2	2.1
H2O2	H2O	1.8
KMnO4	MnO2	1.7
ClO2	HClO	1.5
Cl2	Cl−	1.4

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

${\displaystyle {\ce {2 Fe^2+_{(aq)}{}+ H2O2 + 2 H+_{(aq)}-> 2 Fe^3+_{(aq)}{}+ 2 H2O_{(l)}}}}$

and sulfite (SO2−3) is oxidized to sulfate (SO2−4). However, potassium permanganate is reduced to Mn²⁺ by acidic H₂O₂.

${\displaystyle {\ce {2 MnO4- + 5 H2O2 + 6 H+ -> 2 Mn^2+ + 8 H2O + 5 O2}}}$^[37]

Under

).

In basic solutions, hydrogen peroxide is a strong reductant and can reduce a variety of inorganic ions. When H₂O₂ acts as a reducing agent, oxygen gas is also produced. For example, hydrogen peroxide will reduce sodium hypochlorite and potassium permanganate, which is a convenient method for preparing oxygen in the laboratory:

${\displaystyle {\ce {NaOCl + H2O2 -> O2 + NaCl + H2O}}}$

${\displaystyle {\ce {2 KMnO4 + 3 H2O2 -> 2 MnO2 + 2 KOH + 2 H2O + 3 O2}}}$

Organic reactions

Hydrogen peroxide is frequently used as an

${\displaystyle {\ce {Ph-S-CH3 + H2O2 -> Ph-S(O)-CH3 + H2O}}}$

Alkaline hydrogen peroxide is used for

process.

Precursor to other peroxide compounds

Hydrogen peroxide is a weak acid, forming hydroperoxide or peroxide salts with many metals.

It also converts metal oxides into the corresponding peroxides. For example, upon treatment with hydrogen peroxide, chromic acid (CrO₃ and H₂SO₄) forms a blue peroxide CrO(O₂)₂.

This kind of reaction is used industrially to produce peroxoanions. For example, reaction with borax leads to sodium perborate, a bleach used in laundry detergents:

${\displaystyle {\ce {Na2B4O7 + 4 H2O2 + 2 NaOH -> 2 Na2B2O4(OH)4 + H2O}}}$

H₂O₂ converts carboxylic acids (RCO₂H) into peroxy acids (RC(O)O₂H), which are themselves used as oxidizing agents. Hydrogen peroxide reacts with acetone to form acetone peroxide and with ozone to form trioxidane. Hydrogen peroxide forms stable adducts with urea (Hydrogen peroxide - urea), sodium carbonate (sodium percarbonate) and other compounds.^[41] An acid-base adduct with triphenylphosphine oxide is a useful "carrier" for H₂O₂ in some reactions.

Hydrogen peroxide is both an oxidizing agent and reducing agent. The oxidation of hydrogen peroxide by sodium hypochlorite yields singlet oxygen. The net reaction of a ferric ion with hydrogen peroxide is a ferrous ion and oxygen. This proceeds via single electron oxidation and hydroxyl radicals. This is used in some organic chemistry oxidations, e.g. in the Fenton's reagent. Only catalytic quantities of iron ion is needed since peroxide also oxidizes ferrous to ferric ion. The net reaction of hydrogen peroxide and permanganate or manganese dioxide is manganous ion; however, until the peroxide is spent some manganese ions are reoxidized to make the reaction catalytic. This forms the basis for common monopropellant rockets.

Biological function

Hydrogen peroxide is formed in humans and other animals as a short-lived product in biochemical processes and is toxic to cells. The toxicity is due to oxidation of proteins, membrane lipids and DNA by the peroxide ions.^[42] The class of biological enzymes called superoxide dismutase (SOD) is developed in nearly all living cells as an important antioxidant agent. They promote the disproportionation of superoxide into oxygen and hydrogen peroxide, which is then rapidly decomposed by the enzyme catalase to oxygen and water.^[43]

${\displaystyle {\ce {2 O2- + 2 H+ -> O2 + H2O2}}}$

${\displaystyle {\ce {2 H2O2 -> O2 + 2 H2O}}}$

${\displaystyle {\ce {R-CH2-CH2-CO-SCoA + O2 ->[{\ce {FAD}}] R-CH=CH-CO-SCoA + H2O2}}}$

Catalase, another peroxisomal enzyme, uses this H₂O₂ to oxidize other substrates, including phenols, formic acid, formaldehyde, and alcohol, by means of a peroxidation reaction:

${\displaystyle {\ce {H2O2 + R'H2 -> R' + 2 H2O}}}$

thus eliminating the poisonous hydrogen peroxide in the process.

This reaction is important in liver and kidney cells, where the peroxisomes neutralize various toxic substances that enter the blood. Some of the ethanol humans drink is oxidized to acetaldehyde in this way.^[47] In addition, when excess H₂O₂ accumulates in the cell, catalase converts it to H₂O through this reaction:

${\displaystyle {\ce {H2O2 ->[{\ce {CAT}}] {1/2O2}+ H2O}}}$

Another origin of hydrogen peroxide is the degradation of adenosine monophosphate which yields hypoxanthine. Hypoxanthine is then oxidatively catabolized first to xanthine and then to uric acid, and the reaction is catalyzed by the enzyme xanthine oxidase:^[48]

The degradation of guanosine monophosphate yields xanthine as an intermediate product which is then converted in the same way to uric acid with the formation of hydrogen peroxide.^[48]

Eggs of sea urchin, shortly after fertilization by a sperm, produce hydrogen peroxide. It is then quickly dissociated to HO• radicals. The radicals serve as initiator of radical polymerization, which surrounds the eggs with a protective layer of polymer.^[49]

The

Hydrogen peroxide is a

Hydrogen peroxide has roles as a signalling molecule in the regulation of a wide variety of biological processes.

]

The amount of hydrogen peroxide in biological systems can be assayed using a fluorometric assay.^[60]

Uses

Bleaching

About 60% of the world's production of hydrogen peroxide is used for

, which facilitate cleaning at lower temperatures. It has also been used as a flour bleaching agent and a tooth whitening agent.

Production of organic compounds

It is used in the production of various

.

Sewage treatment

Hydrogen peroxide is used in certain waste-water treatment processes to remove organic impurities. In

Disinfectant

Hydrogen peroxide may be used for the sterilization of various surfaces,

Hydrogen peroxide is seen as an environmentally safe alternative to

Propellant

High-concentration H₂O₂ is referred to as "high-test peroxide" (HTP). It can be used either as a

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, non-cryogenic and can be more easily used to drive gas turbines to give high pressures using an efficient closed cycle. It may also be used for regenerative cooling of rocket engines. Peroxide was used very successfully as an oxidizer in World War II German rocket motors (e.g.

suborbital rockets.

In the 1940s and 1950s, the Hellmuth Walter KG–conceived 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. Operator error in the use of hydrogen-peroxide torpedoes was named as possible causes for the sinking of HMS Sidon and the Russian submarine Kursk.^[77] 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.^[78][79]

Household use

Hydrogen peroxide has various domestic uses, primarily as a cleaning and disinfecting agent.

Hair bleaching

Diluted H₂O₂ (between 1.9% and 12%) mixed with

Hydrogen peroxide is also used for tooth whitening. It may be found in most whitening toothpastes. Hydrogen peroxide has shown positive results involving teeth lightness and chroma shade parameters.^[81] It works by oxidizing colored pigments onto the enamel where the shade of the tooth may become lighter.^{[further explanation needed]} Hydrogen peroxide may be mixed with baking soda and salt to make a homemade toothpaste.^[82]

Removal of blood stains

Hydrogen peroxide reacts with blood as a bleaching agent, and so if a blood stain is fresh, or not too old, liberal application of hydrogen peroxide, if necessary in more than single application, will bleach the stain fully out. After about two minutes of the application, the blood should be firmly blotted out.^[83][84]

Acne treatment

Hydrogen peroxide may be used to treat

is a more common treatment.

Niche uses

cyalume

, as found in a glow stick