Hydroquinone

from Wikipedia, the free encyclopedia
Structural formula
Hydroquinone structural formula
General
Surname Hydroquinone
other names
  • 1,4-dihydroxybenzene
  • Benzene-1,4-diol
  • Benzene-1,4-diol
  • Quinol
  • HYDROQUINONE ( INCI )
Molecular formula C 6 H 6 O 2
Brief description

colorless and odorless, crystalline solid

External identifiers / databases
CAS number 123-31-9
EC number 204-617-8
ECHA InfoCard 100.004.199
PubChem 785
ChemSpider 764
DrugBank DB09526
Wikidata Q419164
properties
Molar mass 110.11 g mol −1
Physical state

firmly

density
  • 1.364 g cm −3 (α form)
  • 1.258 g cm −3 (β-form)
  • 1.380 g cm −3 (γ form)
Melting point

170 ° C (α-form)

boiling point

286 ° C

Vapor pressure

15 m Pa (20 ° C)

pK s value
  • pK s 1 : 9.91
  • pK s 2 : 11.65
solubility

soluble in water: 72 g l −1 (20 ° C)

safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
05 - Corrosive 08 - Dangerous to health 07 - Warning 09 - Dangerous for the environment

danger

H and P phrases H: 351-341-302-318-317-400
P: 273-280-305 + 351 + 338-302 + 352-313
MAK
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Hydroquinone ( 1,4-dihydroxybenzene ) is a phenol and next to pyrocatechol (1,2-dihydroxybenzene) and resorcinol (1,3-dihydroxybenzene) the third possible dihydroxybenzene. Here the two hydroxyl groups are in the para position .

discovery

In 1844, Friedrich Wöhler obtained a product mixture from dry distillation (> 280 ° C) of quinic acid which, in addition to benzene , benzoic acid and salicylic acid, contained a new colorless compound as the main component. After dissolving the distillate in water, filtering off the insoluble components and distilling off the more volatile components, benzoic acid first crystallized from the remaining solution and finally hydroquinone from its mother liquor, which he obtained in pure form by repeated recrystallization in the form of colorless, six-sided prisms.

Occurrence

Hydroquinone occurs as a 10% solution together with 28% hydrogen peroxide in the defense glands of bombardier beetles . In the event of a defense, catalase is added to the mixture and the attacker is sprayed as a 100 ° C hot, corrosive repellent. Bearberry leaves as well as pears contain the glycoside arbutin , which is hydroquinone-β-D-glucoside, a compound of hydroquinone with glucose .

presentation

Hydroquinone can be synthesized from phenol by the Elbs oxidation .

Production of hydroquinone with the Elbs oxidation.

properties

Hydroquinone is a colorless solid that can occur in four polymorphic crystal forms. The α, β and γ forms exist under normal pressure . The α and β forms crystallize in a hexagonal crystal lattice, the γ form in a monoclinic lattice. At room temperature, the α-form is the thermodynamically stable form. The β and γ forms are metastable and can spontaneously transform into the α form. The commercial product corresponds to the α-form. The β form can be obtained from small molecule clathrates such as methanol . The γ-form can be obtained via sublimation or rapid evaporation. At higher pressures above 40 MPa, the δ-form can be detected as the fourth crystal form. The melting point of the δ-form is 78.5 MPa at 191 ° C. The triple point between α, δ and liquid phase is 176 ° C and 15.7 MPa.

Hydroquinone is a stronger reducing agent than catechol because the o-benzoquinone produced from catechol is more energetic and therefore a stronger oxidizing agent. The cause of the latter is the electrostatic repulsion of the neighboring carbonyl groups.

It can be converted into benzoquinone ( quinone ) by oxidation :

Quinone

During this reaction, the deep-colored, poorly water-soluble charge-transfer complex quinhydrone is formed as an intermediate product (not shown).

Reactions

The simple bromination of hydroquinone with potassium bromide and bromine in carbon tetrachloride leads to the bromohydroquinone .

Simple bromination of hydroquinone

2,5-Dibromohydroquinone , whose melting point is 186 ° C, provides complete bromination for analytical detection . Also known is the tetrabromohydroquinone , which is, however, shown for benzoquinone.

Methylation with dimethyl sulfate gives 1,4-dimethoxybenzene , the melting point of which is 56 ° C.

Methylation of hydroquinone

A direct nitration of the hydroquinone is not possible because it decomposes in the process. The hydroxyl groups must therefore be protected with acetyl groups by reaction with acetic anhydride and sulfuric acid as a catalyst , then nitration takes place at positions 2 and 6. The saponification of the dinitrodiacetylhydroquinone finally leads to 2,6-dinitrohydroquinone (melting point 135-136 ° C).

Production of 2,6-dinitrohydroquinone


use

In photo laboratory technology, hydroquinone is used as a reducing agent for developing films and images. Because of the dangers to the environment and health, efforts are being made to replace the substance for these applications with less risky substances if possible. It is also used as an inhibitor for radical reactions to prevent the formation of ether peroxides.

Cosmetic use in skin creams, for example for skin lightening , is prohibited in EU countries.

toxicology

There are no studies of the direct toxicity of hydroquinone in humans. However, several studies in animals have shown that hydroquinone is toxic to the kidney. In addition, hydroquinone is immunotoxic and probably also plays an important role in the immunotoxicity of benzene .

If hydroquinone is applied dermally, allergic and systematic allergic reactions can occur.

Carcinogenicity

Two cohort studies are available on humans, one by Danish lithographers and one by industrial workers, in which the relationship between exposure to hydroquinone and the occurrence of cancer in general and also specific tumors was investigated. A connection could not be established in either of the two studies, even if the incidence of melanoma was increased among the lithographers .

In rat experiments, repeated administration of hydroquinone showed an increased incidence of certain tumors in the liver and kidneys.

It is therefore assumed that hydroquinone, like other dihydroxybenzenes (e.g. catechol), is carcinogenic and genatoxic.

Possible mechanisms of action

In experiments on liver cells , hydroquinone led to a depletion of antioxidants in the cell, specifically glutathione . It could also be shown in cell culture that hydroquinone forms DNA adducts and increases the formation of 8-OHdG, a standard marker for DNA damage. It is believed that this DNA damage is related to the formation of ROS.

metabolism

In humans, hydroquinone is mainly metabolized to form sulphate and glucoronide conjugates. In addition to reactive intermediates such as semiquinones and ROS , 1,4-benzoquinone is also produced within the framework of these metabolic pathways . This metabolism is catalyzed by a number of oxidases . The metabolism of hydroquinone is thus similar to that of catechol .

Hazard assessment

Hydroquinone was included by the EU in 2012 in accordance with Regulation (EC) No. 1907/2006 (REACH) in the context of substance evaluation in the Community's ongoing action plan ( CoRAP ). The effects of the substance on human health and the environment are re-evaluated and, if necessary, follow-up measures are initiated. Hydroquinone uptake was driven by concerns about its classification as a CMR substance, consumer use , high (aggregated) tonnage, high risk characterization ratio (RCR) and widespread use. The re-evaluation took place from 2012 and was carried out by Italy . A final report was then published.

Individual evidence

  1. ↑ entry to HYDROQUINONE in CosIng database of the European Commission, accessed on May 14, 2020th
  2. ↑ a b c d e f g h i Entry for CAS no. 123-31-9 in the GESTIS substance database of the IFA , accessed on December 6, 2015(JavaScript required) .
  3. ^ A b S. C. Wallwork, HM Powell: The crystal structure of the α form of quinol. In: J. Chem. Soc. Perkin Trans. Vol. 2, 1980, pp. 641-646, doi: 10.1039 / P29800000641 .
  4. ^ A b c S. V. Lindemann, VE Shklover, Yu. T. Struchkov: The β-modification of hydroquinone, C6H6O2. In: Cryst. Struct. Commun. Volume 10, 1981, pp. 1173-1179.
  5. ^ A b c K. Maartmann-Moe: The crystal structure of γ-hydroquinone. In: Acta Cryst. Volume 21, 1966, pp. 979-982, doi: 10.1107 / S0365110X66004286 .
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  8. ↑ Swiss Accident Insurance Fund (Suva): Limit values ​​- current MAK and BAT values (search for 123-31-9 or hydroquinone ), accessed on November 2, 2015.
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  17. ^ DE Palin, HM Powell: Hydrogen Bond Linking of Quinol Molecules. In: Nature . Volume 156, 1948, p. 334. doi: 10.1038 / 156334a0 .
  18. ^ DE Palin, HM Powell: The structure of molecular compounds. Part III. Crystal structure of addition complexes of quinol with certain volatile compounds. In: J. Chem. Soc. 1947, pp. 208-221. doi: 10.1039 / JR9470000208 .
  19. ^ DE Palin, HM Powell: The structure of molecular compounds. Part VI. The β-type clathrate compounds of quinol. In: J. Chem. Soc. 1948, pp. 815-821. doi: 10.1039 / JR9480000815 .
  20. ^ Association of authors: Organikum . 19th edition. Johann Ambrosius Barth, Leipzig / Berlin / Heidelberg 1993, ISBN 3-335-00343-8 , p. 331.
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  22. ^ Association of authors: Organikum . 19th edition. Johann Ambrosius Barth, Leipzig / Berlin / Heidelberg 1993, ISBN 3-335-00343-8 , p. 653.
  23. ↑ a b Gustav Walther: methyl ether of 2,6-dinitrohydroquinone and some derivatives. Dissertation. University of Basel, 1904.
  24. ↑ H. Bock, S. Nick, C. Näther, JW Bats: Disodium and Dipotassium Nitranilate: The cyanine distortion of the carbon six-membered rings. In: Journal of Nature Research B . 49, 1994, pp. 1021-1030 ( PDF , free full text).
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  27. ↑ Masa-Aki Shibata, Masao Hirose, Hikaru Tanaka, Emiko Asakawa, Tomoyuki Shirai: Induction of Renal Cell Tumors in Rats and Mice, and Enhancement of Hepatocellular Tumor Development in Mice after Long-Term Hydroquinone Treatment . In: Japanese Journal of Cancer Research . tape 82 , no. 11 , 1991, ISSN  1349-7006 , pp. 1211–1219 , doi : 10.1111 / j.1349-7006.1991.tb01783.x , PMID 1752780 , PMC 5918322 (free full text).
  28. ^ A b International Agency for Research on Cancer .: Re-evaluation of some organic chemicals, hydrazine and hydrogen peroxide. World Health Organization, International Agency for Research on Cancer, Lyon, France 1999, ISBN 978-92-832-1271-3 .
  29. ↑ A. Barbaud, P. Modiano, M. Cocciale, S. Reichert, J.-L. Dirt: The topical application of resorcinol can provoke a systemic allergic reaction . In: British Journal of Dermatology . tape 135 , no. 6 , 1996, ISSN  1365-2133 , pp. 1014-1015 , doi : 10.1046 / j.1365-2133.1996.d01-1121.x .
  30. ^ JW Pifer, FT Hearne, FA Swanson, JL O'Donoghue: Mortality study of employees engaged in the manufacture and use of hydroquinone . In: International Archives of Occupational and Environmental Health . tape 67 , no. 4 , 1995, ISSN  0340-0131 , p. 267-280 , doi : 10.1007 / BF00409409 , PMID 7591188 .
  31. ↑ Vol Carlton, H Shah: Re: “Malignant melanoma among lithographers” by H Nielsen, L Henriksen, JH Olsen. Scand J Work Environ Health 1996; 22: 108--11 . In: Scandinavian Journal of Work, Environment & Health . tape 23 , no. 4 , August 1997, ISSN  0355-3140 , p. 308 , doi : 10.5271 / sjweh.224 .
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  33. ↑ Junzo Suzuki, Yuichiro Inoue, Shizuo Suzuki: Changes in the urinary excretion level of 8-hydroxyguanine by exposure to reactive oxygen-generating substances . In: Free Radical Biology and Medicine . tape 18 , no. 3 , March 1, 1995, ISSN  0891-5849 , p. 431-436 , doi : 10.1016 / 0891-5849 (94) 00152-A ( sciencedirect.com [accessed June 30, 2020]).
  34. ↑ G. Lévay, WJ Bodell: Role of hydrogen peroxide in the formation of DNA adducts in HL-60 cells treated with benzene metabolites . In: Biochemical and Biophysical Research Communications . tape 222 , no. 1 , May 6, 1996, ISSN  0006-291X , p. 44-49 , doi : 10.1006 / bbrc.1996.0695 , PMID 8630072 .
  35. ^ G. Levay, K. Pongracz, WJ Bodell: Detection of DNA adducts in HL-60 cells treated with hydroquinone and p-benzoquinone by 32P postlabeling . In: Carcinogenesis . tape 12 , no. 7 July 1991, ISSN  0143-3334 , pp. 1181-1186 , doi : 10.1093 / carcin / 7.12.1181 , PMID 2070482 .
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  40. ↑ Community rolling action plan ( CoRAP ) of the European Chemicals Agency (ECHA): Hydroquinone , accessed on March 26, 2019.