# 6PPD

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Organic chemical used in rubber tires

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 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

Chemical compound

**6PPD** is an [organic chemical](/source/Organic_chemical) widely used as [stabilising](/source/Stabilizer_(chemistry)) [additive](/source/Plastic#Additives) (or antidegradant) in rubbers, such as [natural rubber](/source/Natural_rubber), [styrene-butadiene](/source/Styrene-butadiene) and [butyl rubber](/source/Butyl_rubber); all of which are common in vehicle tires.[1] Although it is an effective [antioxidant](/source/Antioxidant), it is primarily used because of its excellent [antiozonant](/source/Antiozonant) performance. It is one of several antiozonants based around [*p*-phenylenediamine](/source/P-phenylenediamine).[2]

It has been used in rubber since the late 1970s,[3] but has been the subject of increasing scrutiny since 2021, when it was determined that its oxidation product (6PPD-Q) causes [pre-spawn mortality in coho salmon](/source/Pre-spawn_mortality_in_coho_salmon).[4][5]

## Manufacturing

6PPD is prepared by [reductive amination](/source/Reductive_amination) of [methyl isobutyl ketone](/source/Methyl_isobutyl_ketone) (which has six carbon atoms, hence the '6' in the name) with [phenyl phenylenediamine](/source/4-aminodiphenylamine) (PPD).[6] This produces a [racemic](/source/Racemic) mixture.

## Application

6PPD is a common rubber antiozonant found in vehicle tires. It is mobile within the rubber and slowly migrates to the surface via [blooming](/source/Bloom_(phase)). On the surface it forms a "scavenger-protective film" that reacts with the ozone more quickly than the ozone can react with the rubber.[7] This process forms [aminoxyl radicals](/source/Aminoxyl_radical)[8][9] and was first thought to degrade only to the quinone diimine, but has since been understood to continue to oxidize to [quinones](/source/Quinone), amongst other products.[10] Despite 6PPD being used in tires since the mid 1970s, its transformation to quinones was first recognized in 2020.[11][12] 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 particles and are sufficiently water-soluble to enter river systems via [urban runoff](/source/Urban_runoff). From here they become widely distributed (at decreasing levels) from urban rivers through estuaries, coasts and finally deep-sea areas.[13]

6PPD-quinone is of environmental concern because it is toxic to [coho salmon](/source/Coho_salmon), killing them before they [spawn](/source/Spawn_(biology)) in [freshwater streams](/source/Freshwater_ecosystems).[14][15][16]

A 2022 study also identified the toxic impact on species like [brook trout](/source/Brook_trout) and [rainbow trout](/source/Rainbow_trout).[17] The published [lethal concentrations](/source/Median_lethal_dose) are:[17][18]

- 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 [glucuronidation](/source/Glucuronidation).[19] The [Nisqually](/source/Nisqually_people) and nonprofit Long Live the Kings installed a mobile stormwater filter at a bridge in the [Ohop Valley](/source/Ohop_Valley) in 2022. The [Washington Department of Ecology](/source/Washington_Department_of_Ecology), [Washington State University](/source/Washington_State_University) and the US Tire Manufacturer's Association are working on regulation and education.[20]

6PPD itself is deadly to [rotifers](/source/Rotifer), especially in combination with [sodium chloride](/source/Sodium_chloride), though not at the level generally found in the [runoff](/source/Surface_runoff) from road salt.[21] A small-scale [biomonitoring](/source/Biomonitoring) study in South China has shown both 6PPD and 6PPDQ to be present in human urine; concentrations were low but the health implications are unknown.[22] A synthetic route to the 6PPD-quinone has been posted on [ChemRxiv](/source/ChemRxiv).[23]

## See also

- [*N*-Isopropyl-*N'*-phenyl-1,4-phenylenediamine](/source/N-Isopropyl-N'-phenyl-1%2C4-phenylenediamine) (IPPD), a related antiozonant

- [*N*,*N'*-Di-2-butyl-1,4-phenylenediamine](/source/N%2CN'-Di-2-butyl-1%2C4-phenylenediamine), a phenylenediamine-based antioxidant used as a fuel additive

## References

1. **[^](#cite_ref-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"](https://naturalresources.house.gov/download/2021_07_15_written_testimony_sarah-amickpdf). Committee on Natural Resources Subcommittee on Oversight and Investigations United States House of Representatives.

1. **[^](#cite_ref-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](/source/Doi_(identifier)):[10.1080/02652030500098177](https://doi.org/10.1080%2F02652030500098177). [PMID](/source/PMID_(identifier)) [16227180](https://pubmed.ncbi.nlm.nih.gov/16227180). [S2CID](/source/S2CID_(identifier)) [10548886](https://api.semanticscholar.org/CorpusID:10548886).

1. **[^](#cite_ref-3)** Ashworth, B. T.; Hill, P. (1979). ["Chapter 7: Protective Agents"](https://books.google.com/books?id=Sa8Kq50AkvgC&dq=6PPD&pg=PA227). *Developments in Rubber Technology, Volume 1*. London: Applied Science Publishers. pp. 227–239. [ISBN](/source/ISBN_(identifier)) [0853348626](https://en.wikipedia.org/wiki/Special:BookSources/0853348626).

1. **[^](#cite_ref-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.; Kolodziej, Edward P. (8 January 2021). "A ubiquitous tire rubber–derived chemical induces acute mortality in coho salmon". *Science*. **371** (6525): 185–189. [Bibcode](/source/Bibcode_(identifier)):[2021Sci...371..185T](https://ui.adsabs.harvard.edu/abs/2021Sci...371..185T). [doi](/source/Doi_(identifier)):[10.1126/science.abd6951](https://doi.org/10.1126%2Fscience.abd6951). [PMID](/source/PMID_(identifier)) [33273063](https://pubmed.ncbi.nlm.nih.gov/33273063).

1. **[^](#cite_ref-5)** Chadwick, Julie (12 July 2024). ["How researchers uncovered the coho killing tire toxin 6PPD-Q"](https://thediscourse.ca/nanaimo/6ppd-q-coho-killer). *The Discourse*. Retrieved 26 July 2024.

1. **[^](#cite_ref-6)** Hans-Wilhelm Engels et al., "Rubber, 4. Chemicals and Additives" in *Ullmann's Encyclopedia of Industrial Chemistry*, 2007, Wiley-VCH, Weinheim. [doi](/source/Doi_(identifier)):[10.1002/14356007.a23_365.pub2](https://doi.org/10.1002%2F14356007.a23_365.pub2)

1. **[^](#cite_ref-7)** Lattimer, R. P.; Hooser, E. R.; Layer, R. W.; Rhee, C. K. (1 May 1983). "Mechanisms of Ozonation of N-(1,3-Dimethylbutyl)-N′-Phenyl-p-Phenylenediamine". *Rubber Chemistry and Technology*. **56** (2): 431–439. [doi](/source/Doi_(identifier)):[10.5254/1.3538136](https://doi.org/10.5254%2F1.3538136).

1. **[^](#cite_ref-8)** Cataldo, Franco; Faucette, Brad; Huang, Semone; Ebenezer, Warren (January 2015). "On the early reaction stages of ozone with N,N′-substituted p-phenylenediamines (6PPD, 77PD) and N,N′,N"-substituted-1,3,5-triazine "Durazone®": An electron spin resonance (ESR) and electronic absorption spectroscopy study". *Polymer Degradation and Stability*. **111**: 223–231. [doi](/source/Doi_(identifier)):[10.1016/j.polymdegradstab.2014.11.011](https://doi.org/10.1016%2Fj.polymdegradstab.2014.11.011).

1. **[^](#cite_ref-reaction_9-0)** Cataldo, Franco (January 2018). "Early stages of p-phenylenediamine antiozonants reaction with ozone: Radical cation and nitroxyl radical formation". *Polymer Degradation and Stability*. **147**: 132–141. [doi](/source/Doi_(identifier)):[10.1016/j.polymdegradstab.2017.11.020](https://doi.org/10.1016%2Fj.polymdegradstab.2017.11.020).

1. **[^](#cite_ref-10)** Seiwert, Bettina; Nihemaiti, Maolida; Troussier, Mareva; Weyrauch, Steffen; Reemtsma, Thorsten (April 2022). ["Abiotic oxidative transformation of 6-PPD and 6-PPD quinone from tires and occurrence of their products in snow from urban roads and in municipal wastewater"](https://doi.org/10.1016%2Fj.watres.2022.118122). *Water Research*. **212** 118122. [Bibcode](/source/Bibcode_(identifier)):[2022WatRe.21218122S](https://ui.adsabs.harvard.edu/abs/2022WatRe.21218122S). [doi](/source/Doi_(identifier)):[10.1016/j.watres.2022.118122](https://doi.org/10.1016%2Fj.watres.2022.118122). [PMID](/source/PMID_(identifier)) [35101694](https://pubmed.ncbi.nlm.nih.gov/35101694). [S2CID](/source/S2CID_(identifier)) [246336931](https://api.semanticscholar.org/CorpusID:246336931).

1. **[^](#cite_ref-11)** 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](/source/Science_(journal))*, **371** (6525): 185–189, [Bibcode](/source/Bibcode_(identifier)):[2021Sci...371..185T](https://ui.adsabs.harvard.edu/abs/2021Sci...371..185T), [doi](/source/Doi_(identifier)):[10.1126/science.abd6951](https://doi.org/10.1126%2Fscience.abd6951), [PMID](/source/PMID_(identifier)) [33273063](https://pubmed.ncbi.nlm.nih.gov/33273063), [S2CID](/source/S2CID_(identifier)) [227281491](https://api.semanticscholar.org/CorpusID: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)

1. **[^](#cite_ref-12)** Also an erratum to this paper published in Science vol. 375, No. 6582, 18 Feb 2022 [doi](/source/Doi_(identifier)):[10.1126/science.abo5785](https://doi.org/10.1126%2Fscience.abo5785) reporting the updated toxicity estimates, as referenced below.

1. **[^](#cite_ref-13)** Zeng, Lixi; Li, Yi; Sun, Yuxin; Liu, Liang-Ying; Shen, Mingjie; Du, Bibai (31 January 2023). "Widespread Occurrence and Transport of p -Phenylenediamines and Their Quinones in Sediments across Urban Rivers, Estuaries, Coasts, and Deep-Sea Regions". *Environmental Science & Technology*. **57** (6): 2393–2403. [Bibcode](/source/Bibcode_(identifier)):[2023EnST...57.2393Z](https://ui.adsabs.harvard.edu/abs/2023EnST...57.2393Z). [doi](/source/Doi_(identifier)):[10.1021/acs.est.2c07652](https://doi.org/10.1021%2Facs.est.2c07652). [PMID](/source/PMID_(identifier)) [36720114](https://pubmed.ncbi.nlm.nih.gov/36720114). [S2CID](/source/S2CID_(identifier)) [256458111](https://api.semanticscholar.org/CorpusID:256458111).

1. **[^](#cite_ref-14)** ["Pollution from car tires is killing off salmon on US west coast, study finds"](https://www.theguardian.com/environment/2020/dec/03/coho-salmon-pollution-car-tires-die-off). *[The Guardian](/source/The_Guardian)*. 3 December 2020.

1. **[^](#cite_ref-15)** ["Scientists solve mystery of mass coho salmon deaths. The killer? A chemical from car tires"](https://www.latimes.com/california/story/2020-12-03/coho-salmon-tire-chemical). *[Los Angeles Times](/source/Los_Angeles_Times)*. 3 December 2020.

1. **[^](#cite_ref-16)** 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"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8335451). *Archives of Environmental Contamination and Toxicology*. **82** (2): 171–179. [Bibcode](/source/Bibcode_(identifier)):[2022ArECT..82..171J](https://ui.adsabs.harvard.edu/abs/2022ArECT..82..171J). [doi](/source/Doi_(identifier)):[10.1007/s00244-021-00878-4](https://doi.org/10.1007%2Fs00244-021-00878-4). [PMC](/source/PMC_(identifier)) [8335451](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8335451). [PMID](/source/PMID_(identifier)) [34347118](https://pubmed.ncbi.nlm.nih.gov/34347118).

1. ^ [***a***](#cite_ref-Brinkmann_17-0) [***b***](#cite_ref-Brinkmann_17-1) 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](/source/Environmental_Science_%26_Technology_Letters)*, vol. 9, no. 4, pp. 333–338, [Bibcode](/source/Bibcode_(identifier)):[2022EnSTL...9..333B](https://ui.adsabs.harvard.edu/abs/2022EnSTL...9..333B), [doi](/source/Doi_(identifier)):[10.1021/acs.estlett.2c00050](https://doi.org/10.1021%2Facs.estlett.2c00050), [S2CID](/source/S2CID_(identifier)) [247336687](https://api.semanticscholar.org/CorpusID:247336687)

1. **[^](#cite_ref-18)** 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](/source/Environmental_Science_%26_Technology_Letters)*, **9** (2): 140–146, [Bibcode](/source/Bibcode_(identifier)):[2022EnSTL...9..140T](https://ui.adsabs.harvard.edu/abs/2022EnSTL...9..140T), [doi](/source/Doi_(identifier)):[10.1021/acs.estlett.1c00910](https://doi.org/10.1021%2Facs.estlett.1c00910), [S2CID](/source/S2CID_(identifier)) [245893533](https://api.semanticscholar.org/CorpusID:245893533)

1. **[^](#cite_ref-19)** Montgomery, David; Ji, Xiaowen; Cantin, Jenna; Philibert, Danielle; Foster, Garrett; Selinger, Summer; Jain, Niteesh; Miller, Justin; McIntyre, Jenifer; de Jourdan, Benjamin; Wiseman, Steve; Hecker, Markus; Brinkmann, Markus (19 December 2023). "Interspecies Differences in 6PPD-Quinone Toxicity Across Seven Fish Species: Metabolite Identification and Semiquantification". *Environmental Science & Technology*. **57** (50): 21071–21079. [Bibcode](/source/Bibcode_(identifier)):[2023EnST...5721071M](https://ui.adsabs.harvard.edu/abs/2023EnST...5721071M). [doi](/source/Doi_(identifier)):[10.1021/acs.est.3c06891](https://doi.org/10.1021%2Facs.est.3c06891). [PMID](/source/PMID_(identifier)) [38048442](https://pubmed.ncbi.nlm.nih.gov/38048442). [S2CID](/source/S2CID_(identifier)) [265658590](https://api.semanticscholar.org/CorpusID:265658590).

1. **[^](#cite_ref-20)** Lena Beck (17 May 2022). ["Your car is killing coho salmon"](https://thecounter.org/coho-salmon-pacific-northwest-car-tire-toxins-nisqually-tribe-research/). *The Counter*.

1. **[^](#cite_ref-21)** Klauschies, Toni; Isanta-Navarro, Jana (2022-07-10). ["The joint effects of salt and 6PPD contamination on a freshwater herbivore"](https://www.dynatrait.de/fileadmin/projects/dynatrait/PDF/2022_Klauschies_and_Isanta-Navarro_STOTEN.pdf) (PDF). *Science of the Total Environment*. **829** 154675. [Bibcode](/source/Bibcode_(identifier)):[2022ScTEn.82954675K](https://ui.adsabs.harvard.edu/abs/2022ScTEn.82954675K). [doi](/source/Doi_(identifier)):[10.1016/j.scitotenv.2022.154675](https://doi.org/10.1016%2Fj.scitotenv.2022.154675). [PMID](/source/PMID_(identifier)) [35314241](https://pubmed.ncbi.nlm.nih.gov/35314241). [S2CID](/source/S2CID_(identifier)) [247577987](https://api.semanticscholar.org/CorpusID:247577987) – via Dynatrait.

1. **[^](#cite_ref-22)** Du, Bibai; Liang, Bowen; Li, Yi; Shen, Mingjie; Liu, Liang-Ying; Zeng, Lixi (13 December 2022). "First Report on the Occurrence of N -(1,3-Dimethylbutyl)- N ′-phenyl- p -phenylenediamine (6PPD) and 6PPD-Quinone as Pervasive Pollutants in Human Urine from South China". *Environmental Science & Technology Letters*. **9** (12): 1056–1062. [Bibcode](/source/Bibcode_(identifier)):[2022EnSTL...9.1056D](https://ui.adsabs.harvard.edu/abs/2022EnSTL...9.1056D). [doi](/source/Doi_(identifier)):[10.1021/acs.estlett.2c00821](https://doi.org/10.1021%2Facs.estlett.2c00821). [S2CID](/source/S2CID_(identifier)) [253828438](https://api.semanticscholar.org/CorpusID:253828438).

1. **[^](#cite_ref-23)** 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"](https://chemrxiv.org/engage/api-gateway/chemrxiv/assets/orp/resource/item/60c754ab842e658615db41c8/original/preparation-of-2-4-methylpentan-2-yl-amino-5-phenylamino-cyclohexa-2-5-diene-1-4-dione-6ppd-quinone-an-environmental-hazard-for-salmon.pdf) (PDF). *[ChemRxiv](/source/ChemRxiv)*. [doi](/source/Doi_(identifier)):[10.26434/chemrxiv.13698985.v1](https://doi.org/10.26434%2Fchemrxiv.13698985.v1). [S2CID](/source/S2CID_(identifier)) [234062284](https://api.semanticscholar.org/CorpusID:234062284).

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Adapted from the Wikipedia article [6PPD](https://en.wikipedia.org/wiki/6PPD) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/6PPD?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.