PBQ

PBQ - Names and Identifiers

Name	1,4-Benzoquinone
Synonyms	PBQ pbq2 Quinone p-Chinon P-quinone Benzoquinone p-Benzochinon p-Benzoquinone 1,4-Benzoquine 1,4-Benzochinon 1,4-Benzoquinone 1,4-Cyclohexadienedione quinone(p-benzoquinone) 1,4-Cyclohexadiene dioxide cyclohexa-3,5-diene-1,2-dione cyclohexa-2,5-diene-1,4-dione
CAS	106-51-4
EINECS	203-405-2
InChI	InChI=1/C6H4O2/c7-5-3-1-2-4-6(5)8/h1-4H
InChIKey	AZQWKYJCGOJGHM-UHFFFAOYSA-N

PBQ - Physico-chemical Properties

Molecular Formula	C6H4O2
Molar Mass	108.09
Density	1.31
Melting Point	113-115°C(lit.)
Boling Point	293°C
Flash Point	38°C
Water Solubility	10 g/L (25 ºC)
Solubility	10g/l
Vapor Presure	0.1 mm Hg ( 25 °C)
Vapor Density	3.73 (vs air)
Appearance	Powder
Color	Yellow to green
Exposure Limit	TLV-TWA 0.4 mg/m3 (0.1 ppm); STEL 1.2mg/m3 (0.3 ppm) (ACGIH); IDLH 75 ppm(NIOSH).
Merck	14,8074
BRN	773967
pKa	7.7
PH	4 (1g/l, H2O, 20℃)
Storage Condition	room temp
Stability	Stable, but light sensitive. Incompatible with strong oxidizing agents. Flammable.
Refractive Index	n20/D 1.453
Physical and Chemical Properties	Yellow crystal. Irritating odor. melting point 116 ℃ relative density 1.318 solubility: soluble in ethanol, ether and alkali, slightly soluble in water.
Use	For the preparation of hydroquinone, used as dyes and pharmaceutical intermediates, rubber antioxidant, polymerization inhibitor, antioxidant, developer, etc

PBQ - Risk and Safety

Risk Codes	R23/25 - Toxic by inhalation and if swallowed. R36/37/38 - Irritating to eyes, respiratory system and skin. R50 - Very Toxic to aquatic organisms R20/21/22 - Harmful by inhalation, in contact with skin and if swallowed. R11 - Highly Flammable
Safety Description	S26 - In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. S28 - After contact with skin, wash immediately with plenty of soap-suds. S45 - In case of accident or if you feel unwell, seek medical advice immediately (show the label whenever possible.) S61 - Avoid release to the environment. Refer to special instructions / safety data sheets. S28A - S23 - Do not breathe vapour. S16 - Keep away from sources of ignition.
UN IDs	UN 2587 6.1/PG 2
WGK Germany	3
RTECS	DK2625000
FLUKA BRAND F CODES	8
TSCA	Yes
HS Code	2914 69 80
Hazard Class	6.1
Packing Group	II
Toxicity	LD50 orally in rats: 130 mg/kg (Woodard)

PBQ - Upstream Downstream Industry

Raw Materials	Aniline Aniline Sulfuric acid Sulfuric acid Manganese Manganese
Downstream Products	2-Chlorohydroquinone etamsylate

PBQ - Nature

Open Data Verified Data

yellow crystals. Has a pungent odor similar to chlorine. No boiling point, sublimation. Its vapor is volatile and partially decomposed. Soluble in hot water, ethanol, ether, alkali. Flammable in case of open flame and high heat. By high thermal sublimation to produce toxic gases. Toxic gases are generated by thermal decomposition. In case of high heat, open flame or contact with oxidant, there is a risk of combustion. By high heat decomposition, emission of irritating smoke.

Last Update：2025-06-10 22:55:16

PBQ - Application

Open Data Verified Data

used as a polymerization inhibitor. For the manufacture of hydroquinone and dye intermediates, rubber antioxidant, acrylonitrile and vinyl acetate polymerization initiator and chlorinating agent.

Last Update：2025-08-19 16:24:40

PBQ - Safety

Open Data Verified Data

rat oral LD50: 130mg/kg. There is a strong stimulation. High-concentration exposure irritates mucous membranes, upper respiratory tract, eyes, and skin. Oral administration may be fatal. Be protected. Store in a cool, ventilated warehouse. Keep away from fire and heat source. The packaging is sealed. Should be stored separately from the oxidant, edible chemicals, avoid mixed storage.

Last Update：2022-01-01 10:06:55

PBQ - Preparation Method

aniline is dissolved in dilute sulfuric acid, oxidized by manganese dioxide, separated and purified by steam direct distillation, and then crystallized, dehydrated and dried to obtain the product.

Last Update：2024-04-10 22:29:15

PBQ - Reference Information

LogP	0.1-0.3 at 23℃ and pH4.8-5.3
(IARC) carcinogen classification	3 (Vol. 15, Sup 7, 71) 1999
NIST chemical information	Information provided by: webbook.nist.gov (external link)
EPA chemical information	Information provided by: ofmpub.epa.gov (external link)
Introduction	p-benzoquinone is a quinone organic matter. Pure p-benzoquinone is a bright yellow crystal with a pungent smell similar to chlorine; impure samples are often dimmed due to the presence of quinone hydroquinone (a 1:1 charge transfer complex formed by p-benzoquinone and hydroquinone). P-benzoquinone contains a non-aromatic six-membered ring, which is the oxidation product of hydroquinone (hydroquinone).
Chemical reaction	The non-aromatic six-membered ring of p-benzoquinone reflects a variety of reactivity: it not only exhibits the properties of ketones (can form oxime), but also exhibits oxidizing properties (the reduction product is hydroquinone), and also exhibits the properties of alkenes (addition reactions can occur, especially typical reactions of α,β-unsaturated ketones. P-benzoquinone is unstable in the presence of strong inorganic acids or strong bases, and reactions such as polycondensation and decomposition occur.
Application	In organic synthesis, p-benzoquinone is used as a hydrogen recipient (dehydrogenation agent) and oxidant. It can also participate in the Diels-Alder reaction as a dienophile. Derivatives of p-benzoquinone interact with acetic anhydride and sulfuric acid to obtain derivatives of 1,2, 4-phloroglucinol triacetate. This reaction was first described by Thiele in 1898, so it is called Thiele reaction.
uses	intermediates for dyes and medicines. Manufacture of hydroquinone and rubber antioxidants, acrylonitrile and vinyl acetate polymerization initiators and oxidants. p-benzoquinone can be used to make hydroquinone, as dye and pharmaceutical intermediate, rubber antioxidant, polymerization inhibitor, antioxidant, developer, etc.; in organic synthesis, it is used to Diels-Alder cycloaddition dienophile to form naphthoquinone and 1, 4-phenanthrene dione. It is used for qualitative determination of toxinine, pyridine, azacene, tyrosine and hydroquinone. For the determination of amino acids in the analysis. 99% and 99.5% high purity grades are used for photometric determination of amines.
production method	aniline is dissolved in dilute sulfuric acid, oxidized by manganese dioxide, separated and purified by steam distillation, crystallized, dehydrated and dried to obtain the finished product. In industrial production, this process is also an intermediate step in the production of hydroquinone. In some occasions, such as reagent production and drug manufacturing, hydroquinone is also oxidized to prepare p-benzoquinone. Raw material consumption quota: aniline 2000kg/t, sulfuric acid (93%)8500kg/t, soft manganese ore powder (manganese 60-65%)9500kg/t.
category	toxic substances
toxicity classification	highly toxic
acute toxicity	oral administration-rat LD50: 130 mg/kg; Oral administration-mouse LDL0: 100 mg/kg
flammability hazard characteristics	open flame is combustible; heated decomposition; combustion releases stimulating smoke
storage and transportation characteristics	warehouse ventilation and low temperature drying; Store separately from oxidants and food additives
fire extinguishing agent	carbon dioxide, foam, sand, mist water.
occupational standard	TWA 0.4 mg/m3; STEL 1.5 mg/m3
auto-ignition temperature	815 °F
toxic substance data	information provided by: pubchem.ncbi.nlm.nih.gov (external link)
immediate life-threatening and health concentration	100 mg/m3