6PPD

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6PPD
Names
Preferred IUPAC name
N1-(4-Methylpentan-2-yl)-N4-phenylbenzene-1,4-diamine
Other names
N-(1,3-dimethylbutyl)-N'-phenyl-1,4-benzenediamine
  • N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine
  • 6PPD
  • HPPD
  • DMBPPD
Identifiers
3D model (
JSmol
)
ChEMBL
ChemSpider
ECHA InfoCard
 100.011.222 Edit this at Wikidata
EC Number
  • 212-344-0
UNII
UN number 3077
  • InChI=1S/C18H24N2/c1-14(2)13-15(3)19-17-9-11-18(12-10-17)20-16-7-5-4-6-8-16/h4-12,14-15,19-20H,13H2,1-3H3
    Key: ZZMVLMVFYMGSMY-UHFFFAOYSA-N
  • CC(C)CC(C)NC1=CC=C(C=C1)NC2=CC=CC=C2
Properties
C18H24N2
Molar mass 268.404 g·mol−1
Appearance brown or violet solid powder
Density 1.07
Melting point 45 °C (113 °F; 318 K)
Boiling point 260 °C (500 °F; 533 K)
log P 3.972
Hazards
GHS labelling:
GHS07: Exclamation markGHS08: Health hazardGHS09: Environmental hazard
Danger
H302, H317, H360, H410
P201, P202, P261, P264, P270, P272, P273, P280, P281, P301+P312, P302+P352, P308+P313, P321, P330, P333+P313, P363, P391, P405, P501
Flash point 204 °C (399 °F; 477 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

6PPD is an

p-phenylenediamine.[2]

Manufacturing

6PPD is prepared by

racemic
mixture.

Application

6PPD is a common rubber antiozonant, with major application in vehicle tires. It is mobile within the rubber and slowly migrates to the surface via

aminoxyl radicals[5][6] and was first thought to degrade only to the quinone diimine, but has since been understood to continue to oxidize to quinones, amongst other products.[7] Despite 6PPD being used in tires since the mid 1960s, its transformation to quinones was first recognized in 2020.[8][9]
The oxidized products are not effective antiozonants, meaning that 6PPD is a sacrificial agent.

The tendency of 6PPD to bloom towards the surface is protective because the surface film of antiozonant is replenished from reserves held within the rubber. However, this same property facilitates the transfer of 6PPD and its oxidation products into the environment as tire-wear debris. The 6PPD-quinone (6PPD-Q, CAS RN: 2754428-18-5) is of particular and increasing concern, due to its toxicity to fish.

Environmental impact

6PPD and 6PPD-quinone enter the environment through tire-wear and are sufficiently water-soluble to enter river systems via urban runoff. From here they become widely distributed (at decreasing levels) from urban rivers through to estuaries, coasts and finally deep-sea areas.[10]

6PPD-quinone is of environmental concern because it is toxic to

freshwater streams.[11][12][13]

A 2022 study also identified the toxic impact on species like brook trout and rainbow trout.[14] The published lethal concentrations are:[14][15]

  • coho salmon: LC50 = 0.095 μg/L
  • brook trout: LC50 = 0.59 μg/L
  • rainbow trout: LC50 = 1.0 μg/L

It is not known why the ozone-oxidised 6PPD is toxic to coho salmon, but has been suggested that the large differences in lethal dose between species may relate to their ability to rid themselves of 6PPD-Q via

Washington Department of Ecology, Washington State University and the US Tire Manufacturer's Association are working on regulation and education.[17]

6PPD itself is deadly to rotifers, especially in combination with sodium chloride, though not at the level generally found in the runoff from road salt.[18] A small-scale biomonitoring study in South China has shown shown both 6PPD and 6PPDQ to be present in human urine; concentrations were low but the health implications are unknown.[19] A synthetic route to the 6PPD-quinone has been posted on ChemRxiv.[20]

See also

References

  1. ^ U.S. Tire Manufacturers Association (July 15, 2021). "Statement of Sarah E. Amick Vice President EHS&S and Senior Counsel U.S. Tire Manufacturers Association". Committee on Natural Resources Subcommittee on Oversight and Investigations United States House of Representatives.
  2. S2CID 10548886
    .
  3. doi:10.1002/14356007.a23_365.pub2
  4. doi:10.5254/1.3538136
    .
  5. doi:10.1016/j.polymdegradstab.2014.11.011
    .
  6. doi:10.1016/j.polymdegradstab.2017.11.020
    .
  7. S2CID 246336931
    .
  8. ^ Tian, Zhenyu; Zhao, Haoqi; Peter, Katherine T.; Gonzalez, Melissa; Wetzel, Jill; Wu, Christopher; Hu, Ximin; Prat, Jasmine; Mudrock, Emma; Hettinger, Rachel; Cortina, Allan E.; Biswas, Rajshree Ghosh; Kock, Flávio Vinicius Crizóstomo; Soong, Ronald; Jenne, Amy; Du, Bowen; Hou, Fan; He, Huan; Lundeen, Rachel; Gilbreath, Alicia; Sutton, Rebecca; Scholz, Nathaniel L.; Davis, Jay W.; Dodd, Michael C.; Simpson, Andre; McIntyre, Jenifer K. (3 December 2020), "A ubiquitous tire rubber–derived chemical induces acute mortality in coho salmon",
    S2CID 227281491
    , ... existing TWP [tire wear particle] loading, leaching, and toxicity assessments are clearly incomplete. ... Accordingly, the human health effects of such exposures merit evaluation. ... It is unlikely that coho salmon are uniquely sensitive ... ( in print 8 Jan 2021)
  9. ^ Also an erratum to this paper published in Science vol. 375, No. 6582, 18 Feb 2022
    doi:10.1126/science.abo5785
    reporting the updated toxicity estimates, as referenced below.
  10. S2CID 256458111
    .
  11. ^ "Pollution from car tires is killing off salmon on US west coast, study finds". The Guardian. 3 December 2020.
  12. ^ "Scientists solve mystery of mass coho salmon deaths. The killer? A chemical from car tires". Los Angeles Times. 3 December 2020.
  13. PMID 34347118
    .
  14. ^
    S2CID 247336687
  15. ^ Tian, Zhenyu; Gonzalez, Melissa; Rideout, Craig; Zhao, Hoaqi Nina; Hu, Ximin; Wetzel, Jill; Mudrock, Emma; James, C. Andrew; McIntyre, Jenifer K; Kolodziej, Edward P (11 January 2022), "6PPD-Quinone: Revised Toxicity Assessment and Quantification with a Commercial Standard",
    S2CID 245893533
  16. S2CID 265658590
    .
  17. ^ Lena Beck (17 May 2022). "Your car is killing coho salmon". The Counter.
  18. S2CID 247577987
    – via Dynatrait.
  19. S2CID 253828438
    .
  20. S2CID 234062284
    .
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