6PPD

6PPD is an organic chemical that is widely used as an antiozonant and antioxidant in rubber tires.^[1] It is one of several p-phenylenediamine (PPD) additives used to protect various rubber materials.^[2]

6PPD

Names
Preferred IUPAC name N^1-(4-Methylpentan-2-yl)-N^4-phenylbenzene-1,4-diamine
Other names N-(1,3-dimethylbutyl)-N'-phenyl-1,4-benzenediamine N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine 6PPD DMBPPD
Identifiers
CAS Number	793-24-8^Y
3D model (JSmol)	Interactive image
ChEMBL	ChEMBL1558796
ChemSpider	12553
ECHA InfoCard	100.011.222
EC Number	212-344-0
PubChem CID	13101
UNII	HJD0U67PS1^Y
UN number	3077
CompTox Dashboard (EPA)	DTXSID9025114
InChI 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
SMILES CC(C)CC(C)NC1=CC=C(C=C1)NC2=CC=CC=C2
Properties
Chemical formula	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:
Pictograms
Signal word	Danger
Hazard statements	H302, H317, H360, H410
Precautionary statements	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). Infobox references

Manufacturing

6PPD is prepared by reductive amination of methyl isobutyl ketone with 4-aminodiphenylamine.^[3] This produces a racemic mixture.

Environmental impact

6PPD is converted by ozone to a quinone compound 6PPD-quinone (6PPD-Q, CAS:2754428-18-5).

 

Despite 6PPD being used in tires since the mid 1960s, this transformation was first identified in 2020,^[4][5] The 6PPD-quinone is sufficiently water-soluble to enter river systems via surface runoff, where it is toxic to coho salmon, killing them before they spawn in freshwater streams.^[6][7][8]

A 2022 study also identified the toxic impact on species like brook trout and rainbow trout.^[9] The published lethal concentrations are:^[9][10]

• coho salmon: LC₅₀ = 95 ng/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. The Nisqually and nonprofit Long Live the Kings are trying out a mobile stormwater filter at a bridge in the Ohop Valley. The Washington Department of Ecology, Washington State University and the US Tire Manufacturer's Association are working on regulation and education.^[11]

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.^[12]

A synthetic route to the 6PPD-quinone has been posted on ChemRxiv.^[13]

See also

• N-Isopropyl-N'-phenyl-1,4-phenylenediamine a related antiozonant
• N,N'-Di-2-butyl-1,4-phenylenediamine - a phenylenediamine based antioxidant used as a fuel additive

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. Krüger, R H; Boissiére, C; Klein-Hartwig, K; Kretzschmar, H-J (2005). "New phenylenediamine antiozonants for commodities based on natural and synthetic rubber". Food Addit Contam. 22 (10): 968–974. doi:10.1080/02652030500098177. PMID 16227180. S2CID 10548886.
3. Hans-Wilhelm Engels et al., "Rubber, 4. Chemicals and Additives" in Ullmann's Encyclopedia of Industrial Chemistry, 2007, Wiley-VCH, Weinheim. doi:10.1002/14356007.a23_365.pub2
4. 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", Science, 371 (6525): 185–189, doi:10.1126/science.abd6951, PMID 33273063, 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 ...
5. 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.
6. "Pollution from car tires is killing off salmon on US west coast, study finds". The Guardian. 3 December 2020.
7. "Scientists solve mystery of mass coho salmon deaths. The killer? A chemical from car tires". Los Angeles Times. 3 December 2020.
8. Johannessen, Cassandra; Helm, Paul; Lashuk, Brent; Yargeau, Viviane; Metcalfe, Chris D. (February 2022). "The Tire Wear Compounds 6PPD-Quinone and 1,3-Diphenylguanidine in an Urban Watershed". Archives of Environmental Contamination and Toxicology. 82 (2): 171–179. doi:10.1007/s00244-021-00878-4. PMC 8335451. PMID 34347118.
9. Markus Brinkmann, David Montgomery, Summer Selinger, Justin G. P. Miller, Eric Stock (2022-03-02), "Acute Toxicity of the Tire Rubber-Derived Chemical 6PPD-quinone to Four Fishes of Commercial, Cultural, and Ecological Importance", Environmental Science & Technology Letters, vol. 9, no. 4, pp. 333–338, doi:10.1021/acs.estlett.2c00050, S2CID 247336687{{citation}}: CS1 maint: multiple names: authors list (link)
10. 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", Environmental Science & Technology Letters, 9 (2): 140–146, doi:10.1021/acs.estlett.1c00910
11. Lena Beck (17 May 2022). "Your car is killing coho salmon". The Counter.
12. Klauschies, Toni; Isanta-Navarro, Jana (2022-07-10). "The joint effects of salt and 6PPD contamination on a freshwater herbivore" (PDF). Science of the Total Environment. 829: 154675. Bibcode:2022ScTEn.829o4675K. doi:10.1016/j.scitotenv.2022.154675. PMID 35314241. S2CID 247577987 – via Dynatrait.
13. Agua, Alon; Stanton, Ryan; Pirrung, Michael (2021-02-04). "Preparation of 2-((4-Methylpentan-2-Yl)amino)-5-(Phenylamino)cyclohexa-2,5-Diene-1,4-Dione (6PPD-Quinone), an Environmental Hazard for Salmon". ChemRxiv. doi:10.26434/chemrxiv.13698985.v1. S2CID 234062284.