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Names | |||
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Preferred IUPAC name Cyclohexa-2,5-diene-1,4-dione [1] | |||
Other names | |||
Identifiers | |||
3D model (JSmol) | |||
3DMet | |||
773967 | |||
ChEBI | |||
ChEMBL | |||
ChemSpider | |||
ECHA InfoCard | 100.003.097 | ||
EC Number |
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2741 | |||
KEGG | |||
PubChem CID | |||
RTECS number |
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UNII | |||
UN number | 2587 | ||
CompTox Dashboard (EPA) | |||
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Properties | |||
C6H4O2 | |||
Molar mass | 108.096 g·mol−1 | ||
Appearance | Yellow solid | ||
Odor | Acrid, chlorine-like [2] | ||
Density | 1.318 g/cm3 at 20 °C | ||
Melting point | 115 °C (239 °F; 388 K) | ||
Boiling point | Sublimes | ||
11 g/L (18 °C) | |||
Solubility | Slightly soluble in petroleum ether; soluble in acetone; 10% in ethanol, benzene, diethyl ether | ||
Vapor pressure | 0.1 mmHg (25 °C) [2] | ||
−38.4·10−6 cm3/mol | |||
Hazards | |||
Occupational safety and health (OHS/OSH): | |||
Main hazards | Toxic | ||
GHS labelling: | |||
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Danger | |||
H301, H315, H319, H331, H335, H400 | |||
P261, P264, P270, P271, P273, P280, P301+P310, P302+P352, P304+P340, P305+P351+P338, P311, P312, P321, P330, P332+P313, P337+P313, P362, P391, P403+P233, P405, P501 | |||
Flash point | 38 to 93 °C; 100 to 200 °F; 311 to 366 K [2] | ||
Lethal dose or concentration (LD, LC): | |||
LD50 (median dose) | 296 mg/kg (mammal, subcutaneous) 93.8 mg/kg (mouse, subcutaneous) 8.5 mg/kg (mouse, IP) 5.6 mg/kg (rat) 130 mg/kg (rat, oral) 25 mg/kg (rat, IV) [3] | ||
NIOSH (US health exposure limits): | |||
PEL (Permissible) | TWA 0.4 mg/m3 (0.1 ppm) [2] | ||
REL (Recommended) | TWA 0.4 mg/m3 (0.1 ppm) [2] | ||
IDLH (Immediate danger) | 100 mg/m3 [2] | ||
Related compounds | |||
Related compounds | 1,2-Benzoquinone | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
1,4-Benzoquinone, commonly known as para-quinone, is a chemical compound with the formula C6H4O2. In a pure state, it forms bright-yellow crystals with a characteristic irritating odor, resembling that of chlorine, bleach, and hot plastic or formaldehyde. This six-membered ring compound is the oxidized derivative of 1,4-hydroquinone. [4] The molecule is multifunctional: it exhibits properties of a ketone, being able to form oximes; an oxidant, forming the dihydroxy derivative; and an alkene, undergoing addition reactions, especially those typical for α,β-unsaturated ketones. 1,4-Benzoquinone is sensitive toward both strong mineral acids and alkali, which cause condensation and decomposition of the compound. [5] [6]
1,4-Benzoquinone is prepared industrially by oxidation of hydroquinone, which can be obtained by several routes. One route involves oxidation of diisopropylbenzene and the Hock rearrangement. The net reaction can be represented as follows:
The reaction proceeds via the bis(hydroperoxide) and the hydroquinone. Acetone is a coproduct. [7]
Another major process involves the direct hydroxylation of phenol by acidic hydrogen peroxide: C6H5OH + H2O2 → C6H4(OH)2 + H2O Both hydroquinone and catechol are produced. Subsequent oxidation of the hydroquinone gives the quinone. [8]
Quinone was originally prepared industrially by oxidation of aniline, for example by manganese dioxide. [9] This method is mainly practiced in PRC where environmental regulations are more relaxed.
Oxidation of hydroquinone is facile. [4] [10] One such method makes use of hydrogen peroxide as the oxidizer and iodine or an iodine salt as a catalyst for the oxidation occurring in a polar solvent; e.g. isopropyl alcohol. [11]
When heated to near its melting point, 1,4-benzoquinone sublimes, even at atmospheric pressure, allowing for an effective purification. Impure samples are often dark-colored due to the presence of quinhydrone, a dark green 1:1 charge-transfer complex of quinone with hydroquinone. [12]
Benzoquinone is a planar molecule with localized, alternating C=C, C=O, and C–C bonds. Reduction gives the semiquinone anion C6H4O2−}, which adopts a more delocalized structure. Further reduction coupled to protonation gives the hydroquinone, wherein the C6 ring is fully delocalized. [13]
Quinone is mainly used as a precursor to hydroquinone, which is used in photography and rubber manufacture as a reducing agent and antioxidant. [8] Benzoquinonium is a skeletal muscle relaxant, ganglion blocking agent that is made from benzoquinone. [14]
It is used as a hydrogen acceptor and oxidant in organic synthesis. [15] 1,4-Benzoquinone serves as a dehydrogenation reagent. It is also used as a dienophile in Diels Alder reactions. [16]
Benzoquinone reacts with acetic anhydride and sulfuric acid to give the triacetate of hydroxyquinol. [17] [18] This reaction is called the Thiele reaction or Thiele–Winter reaction [19] [20] after Johannes Thiele, who first described it in 1898, and after Ernst Winter, who further described its reaction mechanism in 1900. An application is found in this step of the total synthesis of Metachromin A: [21]
Benzoquinone is also used to suppress double-bond migration during olefin metathesis reactions.
An acidic potassium iodide solution reduces a solution of benzoquinone to hydroquinone, which can be reoxidized back to the quinone with a solution of silver nitrate.
Due to its ability to function as an oxidizer, 1,4-benzoquinone can be found in methods using the Wacker-Tsuji oxidation, wherein a palladium salt catalyzes the conversion of an alkene to a ketone. This reaction is typically carried out using pressurized oxygen as the oxidizer, but benzoquinone can sometimes preferred. It is also used as a reagent in some variants on Wacker oxidations.
1,4-Benzoquinone is used in the synthesis of Bromadol and related analogs.
2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) is a stronger oxidant and dehydrogenation agent than 1,4-benzoquinone. [23] Chloranil 1,4-C6Cl4O2 is another potent oxidant and dehydrogenation agent. Monochloro-p-benzoquinone is yet another but milder oxidant. [24]
1,4-Benzoquinone is a toxic metabolite found in human blood and can be used to track exposure to benzene or mixtures containing benzene and benzene compounds, such as petrol. [25] The compound can interfere with cellular respiration, and kidney damage has been found in animals receiving severe exposure. It is excreted in its original form and also as variations of its own metabolite, hydroquinone. [9]
1,4-Benzoquinone is able to stain skin dark brown, cause erythema (redness, rashes on skin) and lead on to localized tissue necrosis. It is particularly irritating to the eyes and respiratory system. Its ability to sublime at commonly encountered temperatures allows for a greater airborne exposure risk than might be expected for a room-temperature solid. IARC has found insufficient evidence to comment on the compound's carcinogenicity, but has noted that it can easily pass into the bloodstream and that it showed activity in depressing bone marrow production in mice and can inhibit protease enzymes involved in cellular apoptosis. [9]
In organic chemistry, a ketone is an organic compound with the structure R−C(=O)−R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group −C(=O)−. The simplest ketone is acetone, with the formula (CH3)2CO. Many ketones are of great importance in biology and in industry. Examples include many sugars (ketoses), many steroids, and the solvent acetone.
In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups bonded directly to an aromatic hydrocarbon group. The simplest is phenol, C
6H
5OH. Phenolic compounds are classified as simple phenols or polyphenols based on the number of phenol units in the molecule.
Mesitylene or 1,3,5-trimethylbenzene is a derivative of benzene with three methyl substituents positioned symmetrically around the ring. The other two isomeric trimethylbenzenes are 1,2,4-trimethylbenzene (pseudocumene) and 1,2,3-trimethylbenzene (hemimellitene). All three compounds have the formula C6H3(CH3)3, which is commonly abbreviated C6H3Me3. Mesitylene is a colorless liquid with sweet aromatic odor. It is a component of coal tar, which is its traditional source. It is a precursor to diverse fine chemicals. The mesityl group (Mes) is a substituent with the formula C6H2Me3 and is found in various other compounds.
The quinones are a class of organic compounds that are formally "derived from aromatic compounds [such as benzene or naphthalene] by conversion of an even number of –CH= groups into –C(=O)– groups with any necessary rearrangement of double bonds", resulting in "a fully conjugated cyclic dione structure". The archetypical member of the class is 1,4-benzoquinone or cyclohexadienedione, often called simply "quinone". Other important examples are 1,2-benzoquinone (ortho-quinone), 1,4-naphthoquinone and 9,10-anthraquinone.
Anthraquinone, also called anthracenedione or dioxoanthracene, is an aromatic organic compound with formula C
14H
8O
2. Several isomers exist but these terms usually refer to 9,10-anthraquinone wherein the keto groups are located on the central ring. It is used as a digester additive to wood pulp for papermaking. Many anthraquinone derivatives are generated by organisms or synthesised industrially for use as dyes, pharmaceuticals, and catalysts. Anthraquinone is a yellow, highly crystalline solid, poorly soluble in water but soluble in hot organic solvents. It is almost completely insoluble in ethanol near room temperature but 2.25 g will dissolve in 100 g of boiling ethanol. It is found in nature as the rare mineral hoelite.
Cyclohexene is a hydrocarbon with the formula (CH2)4C2H2. It is an example of a cycloalkene. At room temperature, cyclohexene is a colorless liquid with a sharp odor. It has few practical applications.
Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula AlCl3. It forms a hexahydrate with the formula [Al(H2O)6]Cl3, containing six water molecules of hydration. Both the anhydrous form and the hexahydrate are colourless crystals, but samples are often contaminated with iron(III) chloride, giving them a yellow colour.
Catechol, also known as pyrocatechol or 1,2-dihydroxybenzene, is an organic compound with the molecular formula C6H4(OH)2. It is the ortho isomer of the three isomeric benzenediols. This colorless compound occurs naturally in trace amounts. It was first discovered by destructive distillation of the plant extract catechin. About 20,000 tonnes of catechol are now synthetically produced annually as a commodity organic chemical, mainly as a precursor to pesticides, flavors, and fragrances. Small amounts of catechol occur in fruits and vegetables.
Cyclohexanone is the organic compound with the formula (CH2)5CO. The molecule consists of six-carbon cyclic molecule with a ketone functional group. This colorless oily liquid has a sweet odor reminiscent of benzaldehyde. Over time, samples of cyclohexanone assume a pale yellow color. Cyclohexanone is slightly soluble in water and miscible with common organic solvents. Millions of tonnes are produced annually, mainly as a precursor to nylon.
Aromatization is a chemical reaction in which an aromatic system is formed from a single nonaromatic precursor. Typically aromatization is achieved by dehydrogenation of existing cyclic compounds, illustrated by the conversion of cyclohexane into benzene. Aromatization includes the formation of heterocyclic systems.
Potassium peroxymonosulfate is widely used as an oxidizing agent, for example, in pools and spas. It is the potassium salt of peroxymonosulfuric acid. Usually potassium peroxymonosulfate is available as the triple salt 2KHSO5·KHSO4·K2SO4, known as Oxone.
Copper chromite often refers to inorganic compounds with the formula Cu2Cr2Ox. They are black solids. Cu2Cr2O4 is a well-defined material. The other copper chromite often is described as Cu2Cr2O5. It is used to catalyze reactions in organic chemistry.
1,2-Benzoquinone, also called ortho-benzoquinone, is an organic compound with formula C6H4O2. It is one of the two isomers of quinone, the other being 1,4-benzoquinone. It is a red volatile solid that is soluble in water and ethyl ether. It is rarely encountered because of its instability, but it is of fundamental interest as the parent compound of many derivatives which are known.
Lead(IV) acetate or lead tetraacetate is an metalorganic compound with chemical formula Pb(C2H3O2)4. It is a colorless solid that is soluble in nonpolar, organic solvents, indicating that it is not a salt. It is degraded by moisture and is typically stored with additional acetic acid. The compound is used in organic synthesis.
The reduction of nitro compounds are chemical reactions of wide interest in organic chemistry. The conversion can be effected by many reagents. The nitro group was one of the first functional groups to be reduced. Alkyl and aryl nitro compounds behave differently. Most useful is the reduction of aryl nitro compounds.
The Glaser coupling is a type of coupling reaction. It is by far one of the oldest coupling reactions and is based on copper compounds like copper(I) chloride or copper(I) bromide and an additional oxidant like air. The base used in the original research paper is ammonia and the solvent is water or an alcohol. The reaction was first reported by Carl Andreas Glaser in 1869. He suggested the following process on his way to diphenylbutadiyne:
4-Nitroaniline, p-nitroaniline or 1-amino-4-nitrobenzene is an organic compound with the formula C6H6N2O2. A yellow solid, it is one of three isomers of nitroaniline. It is an intermediate in the production of dyes, antioxidants, pharmaceuticals, gasoline, gum inhibitors, poultry medicines, and as a corrosion inhibitor.
1-Naphthol, or α-naphthol, is a organic compound with the formula C10H7OH. It is a fluorescent white solid. 1-Naphthol differs from its isomer 2-naphthol by the location of the hydroxyl group on the naphthalene ring. The naphthols are naphthalene homologues of phenol. Both isomers are soluble in simple organic solvents. They are precursors to a variety of useful compounds.
2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (or DDQ) is the chemical reagent with formula C6Cl2(CN)2O2. This oxidant is useful for the dehydrogenation of alcohols, phenols, and steroid ketones. DDQ decomposes in water, but is stable in aqueous mineral acid.
The Jones oxidation is an organic reaction for the oxidation of primary and secondary alcohols to carboxylic acids and ketones, respectively. It is named after its discoverer, Sir Ewart Jones. The reaction was an early method for the oxidation of alcohols. Its use has subsided because milder, more selective reagents have been developed, e.g. Collins reagent.