Benzo ( a ) pyrene

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Structural formula
Structural formula of benzo [a] pyrene
General
Surname Benzo [ a ] pyrene
other names
  • B [ a ] p
  • 1,2-benzopyrene
  • Benzo [ def ] chrysen
  • Benzo [ pqr ] tetraphene
Molecular formula C 20 H 12
Brief description

yellowish flakes or needles with an aromatic odor

External identifiers / databases
CAS number 50-32-8
EC number 200-028-5
ECHA InfoCard 100,000,026
PubChem 2336
ChemSpider 2246
Wikidata Q306051
properties
Molar mass 252.32 g · mol -1
Physical state

firmly

density

1.35 g cm −3 (20 ° C)

Melting point

179 ° C

boiling point

495 ° C

solubility
  • practically insoluble in water (3 mg l −1 )
  • soluble in organic solvents
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
08 - Dangerous to health 07 - Warning 09 - Dangerous for the environment

danger

H and P phrases H: 317-340-350-360FD-410
P: 201-280-308 + 313
Authorization procedure under REACH

particularly worrying : carcinogenic, mutagenic, toxic for reproduction ( CMR ), persistent, bioaccumulative and toxic ( PBT ), very persistent and very bioaccumulative ( vPvB )

MAK
  • DFG : not classified, as there is a suspicion of a carcinogenic effect
  • Switzerland: 0.002 mg m −3
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Benzo [ a ] pyrene ( 1,2-benzopyrene ) is a polycyclic aromatic hydrocarbon . The outdated name for this chemical compound is 3,4-benzopyrene ( IUPAC name: Benzo [ pqr ] tetraphen ).

Occurrence and origin

Benzo [ a ] pyrene is found in coal tar . In addition, it arises from the incomplete combustion of organic substances and is therefore widespread. This is how it is found in car and industrial emissions. During smoking of cigarettes , it is formed in considerable quantities at around 300 ° C in the tobacco burning zone .

When roasting coffee beans , benzo [ a ] pyrene is also produced in very small quantities (0.3 to 0.5 µg · kg −1 ).

Benzo [ a ] pyrene can also be detected in grilled products that have been prepared over charcoal or pine cones . Traces of benzo [ a ] pyrene can be found in the soil , in vegetables and cereals .

Extraction and presentation

Benzo [ a ] pyrene can be obtained from coal tar and other tars by extraction . An early synthesis variant described in 1935 starts with a Friedel-Crafts acylation of pyrene with succinic anhydride . The resulting pyrenoylpropionic acid is reduced to pyrenylbutyric acid using zinc and then cyclized in the presence of tin tetrachloride . The intermediate product ketotetrahydrobenzopyrene is then reduced again to tetrahydrobenzopyrene using zinc. Benzo [ a ] pyrene is then formed by dehydration using sulfur or selenium . A more recent three-step synthesis starts from 2-naphthylboronic acid, which is coupled in a Suzuki reaction with 2-bromobenzene-1,3-dicarbaldehyde in the first step . In the second step, the aldehyde functions of the coupling product are reacted with methoxymethylene triphenylphosphine in a Wittig reaction . The cyclization to the target compound is then carried out using methanesulfonic acid .

Synthesis of benzo [a] pyrene

structure

The benzo [ a ] pyrene molecule belongs to the pentacyclic, ie polycyclic aromatic hydrocarbons consisting of five benzene rings . The rings are connected to one another via their edges ( fused ). Like benzene, the molecule has an aromatic character due to its delocalized π-electron system .

properties

Crystalline benzo [a] pyrene under normal and UV light

Benzo [ a ] pyrene is a pale, slightly yellowish crystalline solid that is either in the form of platelets with a density of 1.282 g · cm −3 or as needles (density 1.351 g · cm −3 ). Benzo [ a ] pyrene melts at 179 ° C and boils at 495 ° C. According to August, the vapor pressure function results according to lg (P) = −A / T + B (P in Pa, T in K) with A = 4989 and B = 11.59 in the temperature range from 70 ° C to 180 ° C. It is insoluble or slightly soluble in water and alcohols . In aromatic hydrocarbons , however, it dissolves well; in benzene, for. B. under violet fluorescence .

safety instructions

Benzo [ a ] pyrene has an acceptable concentration of 70 ng / m³ and a tolerance concentration of 700 ng / m³ according to TRGS 910. The K OC value is 4,500,000 l / kg (sediment) and the log K OW value is 6.15 .

carcinogen

Metabolism of benzo [ a ] pyrene to carcinogenic benzo [ a ] pyrene-7,8-dihydroxy-9,10-epoxide

Benzo [ a ] pyrene is one of the longest known and studied carcinogenic ( carcinogenic ) substances. The risk of cigarette smoke causing lung cancer is largely attributed to benzo [ a ] pyrene. Benzo [ a ] pyrene is also considered to be the cause of the so-called chimney sweep cancer, a tumor of the testicular skin that develops primarily due to the irritation of the soot in which benzo [ a ] pyrene is contained.

Benzo [ a ] pyrene itself is not toxic, but is initially converted to benzo [ a ] pyrene-7,8-epoxide in the body by monooxygenases from the cytochrome P450 family (subtypes CYP1A1 and CYP1B1) . After hydrolysis of the epoxide group by an epoxide hydrolase, the 7,8-dihydroxybenzo [ a ] pyrene formed is re-epoxidized in position 9 and thus to the carcinogenic benzo [ a ] pyrene-7,8-dihydroxy-9,10-epoxide implemented. Its epoxide group reacts chemically with DNA (more precisely via N 2 to guanine ) and thus affects the structure of the DNA, which can prevent cell division or promote mutations.

According to Regulation (EC) No. 1272/2008 (CLP Regulation), it is classified as a category 1 B carcinogen.

Water hazard

It is very toxic to organisms living in the water. It is therefore classified as Aquatic Acute 1 and Aquatic Chronic 1 according to the CLP Regulation . According to the German ordinance on systems for handling substances hazardous to water ( AwSV ), it is therefore assigned to the water hazard class (WKG) 3.

ecology

It is considered the prototype of the polycyclic aromatic hydrocarbons. When determining the environmental impact of this group of substances, benzo [ a ] pyrene is usually used as a reference. Benzo [ a ] pyrene is classified as poisonous and dangerous for the environment because of its hazard potential .

proof

Benzo [ a ] pyrene can be detected with the help of fluorescence spectroscopy . It can be isolated from mixtures with other compounds by thin layer chromatography or HPLC .

See also

Individual evidence

  1. a b c d e f g h i Entry on benzo (a) pyrene in the GESTIS substance database of the IFA , accessed on January 23, 2020(JavaScript required) .
  2. ^ Brockhaus ABC chemistry. VEB FA Brockhaus Verlag, Leipzig 1965, p. 172.
  3. Entry on Benzo [def] chrysene Template: Linktext-Check / Escaped in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
  4. Entry in the SVHC list of the European Chemicals Agency , accessed on June 20, 2016.
  5. Swiss Accident Insurance Fund (Suva): Limit values ​​- current MAK and BAT values , accessed on November 9, 2015.
  6. dkfz.de
  7. Umweltanalytik.com
  8. ^ W. Fritz: On the formation of carcinogenic hydrocarbons in the thermal treatment of food. 2. Mitt. Roasting coffee beans and coffee substitutes. In: Food / nutrition. 12, 1968, p. 799, doi: 10.1002 / food.19680120810 .
  9. A. Winterstein, H. Vetter, K. Schön :: To the synthesis of the carcinogenic 3,4-benzpyrene. In: Chem. Ber. 68, 1935, pp. 1079-1085, doi: 10.1002 / cber.19350680617 .
  10. ^ RG Harvey, K. Lim, Q. Dai: A Convenient New Synthesis of Benzo [a] pyrene. In: J. Org. Chem. 69, 2004, pp. 1372-1373.
  11. DA Hinckley, TF Bidleman, WT Foreman, JR Tuschall: Determination of vapor pressures for nonpolar and semipolar organic compounds from gas chromatographic retention data. In: J. Chem. Eng. Data . 35, 1990, pp. 232-237. doi : 10.1021 / je00061a003
  12. Hao Jiang et al.: Metabolism of Benzo [ a ] pyrene in Human Bronchoalveolar H358 Cells Using Liquid Chromatography-Mass Spectrometry. PMC 2423818 (free full text).
  13. G. Eisenbrand, M. Metzler: Toxicology for Chemists. Georg Thieme Verlag, Stuttgart, ISBN 3-13-127001-2 , p. 66.
  14. Albert Gossauer : Structure and reactivity of biomolecules. Verlag Helvetica Chimica Acta, Zurich 2006, ISBN 3-906390-29-2 , p. 218.
  15. Annex VI, Part III, Index No. 601-032-00-3, marking H350; Furthermore, the germ cell mutagenicity is classified as Muta.1B and as reproductive toxic in the category Repr.1B.
  16. Annex VI, Part III, Index No. 601-032-00-3, marking H400 and H410
  17. through H410 and H350 more than 8 evaluation points according to para. 4.2 and 4.4 of Appendix 1 to AwSV