6PPD

Last updated
6PPD
6PPD skeletal.svg
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 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 212-344-0
PubChem CID
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
Appearancebrown 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:
GHS-pictogram-exclam.svg GHS-pictogram-silhouette.svg GHS-pictogram-pollu.svg
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 organic chemical widely used as stabilising additive (or antidegradant) in rubbers, such as NR, SBR and BR; all of which are common in vehicle tires. [1] Although it is an effective antioxidant it is primarily used because of its excellent antiozonant performance. It is one of several antiozonants based around p-phenylenediamine. [2]

Contents

It has been used in rubber since the late 1970s, [3] however it has been the subject of increasing scrutiny since 2020, when it was determined that it's oxidation product (6PPD-Q) causes pre-spawn mortality in coho salmon. [4] [5]

Manufacturing

6PPD is prepared by reductive amination of methyl isobutyl ketone (which has six carbon atoms, hence the '6' in the name) with phenyl phenylenediamine (PPD). [6] This produces a 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 blooming. Here it forms a "scavenger-protective film", reacting with the ozone more quickly than the ozone can react with the rubber. [7] This process forms aminoxyl radicals [8] [9] 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. [10] Despite 6PPD being used in tires since the mid 1960s, 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.

6PPD ozone-oxidation overview.svg

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. [13]

6PPD-quinone is of environmental concern because it is toxic to coho salmon, killing them before they spawn in freshwater streams. [14] [15] [16]

A 2022 study also identified the toxic impact on species like brook trout and rainbow trout. [17] The published lethal concentrations are: [17] [18]

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. [19] The Nisqually and nonprofit Long Live the Kings installed a mobile stormwater filter at a bridge in the Ohop Valley in 2022. The Washington Department of Ecology, Washington State University and the US Tire Manufacturer's Association are working on regulation and education. [20]

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. [21] 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. [22] A synthetic route to the 6PPD-quinone has been posted on ChemRxiv. [23]

See also

Related Research Articles

<i>p</i>-Phenylenediamine Chemical compound

p-Phenylenediamine (PPD) is an organic compound with the formula C6H4(NH2)2. This derivative of aniline is a white solid, but samples can darken due to air oxidation. It is mainly used as a component of engineering polymers and composites like kevlar. It is also an ingredient in hair dyes and is occasionally used as a substitute for henna.

Polybrominated diphenyl ethers or PBDEs, are a class of organobromine compounds that are used as flame retardants. Like other brominated flame retardants, PBDEs have been used in a wide array of products, including building materials, electronics, furnishings, motor vehicles, airplanes, plastics, polyurethane foams, and textiles. They are structurally akin to polychlorinated diphenyl ethers (PCDEs), polychlorinated biphenyls (PCBs) and other polyhalogenated compounds, consisting of two halogenated aromatic rings. PBDEs are classified according to the average number of bromine atoms in the molecule. The life-saving benefits of fire retardants led to their popularization. Standards for mass transit vehicles continues to increase as of 2021.

<span class="mw-page-title-main">Organophosphate</span> Organic compounds with the structure O=P(OR)3

In organic chemistry, organophosphates are a class of organophosphorus compounds with the general structure O=P(OR)3, a central phosphate molecule with alkyl or aromatic substituents. They can be considered as esters of phosphoric acid. Organophosphates are best known for their use as pesticides.

<span class="mw-page-title-main">Persistent organic pollutant</span> Organic compounds that are resistant to environmental degradation

Persistent organic pollutants (POPs) are organic compounds that are resistant to degradation through chemical, biological, and photolytic processes. They are toxic and adversely affect human health and the environment around the world. Because they can be transported by wind and water, most POPs generated in one country can and do affect people and wildlife far from where they are used and released.

In organic chemistry, ozonolysis is an organic reaction where the unsaturated bonds are cleaved with ozone. Multiple carbon–carbon bond are replaced by carbonyl groups, such as aldehydes, ketones, and carboxylic acids. The reaction is predominantly applied to alkenes, but alkynes and azo compounds are also susceptible to cleavage. The outcome of the reaction depends on the type of multiple bond being oxidized and the work-up conditions.

<span class="mw-page-title-main">Peroxyacyl nitrates</span> Pollutant chemicals of the form R–C(O)OONO2

In organic chemistry, peroxyacyl nitrates are powerful respiratory and eye irritants present in photochemical smog. They are nitrates produced in the thermal equilibrium between organic peroxy radicals by the gas-phase oxidation of a variety of volatile organic compounds (VOCs), or by aldehydes and other oxygenated VOCs oxidizing in the presence of NO2.

<span class="mw-page-title-main">Methyl isobutyl ketone</span> Chemical compound

Methyl isobutyl ketone (MIBK, 4-methylpentan-2-one) is an organic compound with the condensed chemical formula (CH3)2CHCH2C(O)CH3. This ketone is a colourless liquid that is used as a solvent for gums, resins, paints, varnishes, lacquers, and nitrocellulose.

Autoxidation refers to oxidations brought about by reactions with oxygen at normal temperatures, without the intervention of flame or electric spark. The term is usually used to describe the gradual degradation of organic compounds in air at ambient temperatures. Many common phenomena can be attributed to autoxidation, such as food going rancid, the 'drying' of varnishes and paints, and the perishing of rubber. It is also an important concept in both industrial chemistry and biology. Autoxidation is therefore a fairly broad term and can encompass examples of photooxygenation and catalytic oxidation.

Chlorinated paraffins (CPs) are complex mixtures of polychlorinated n-alkanes. The chlorination degree of CPs can vary between 30 and 70 wt%. CPs are subdivided according to their carbon chain length into short-chain CPs, medium-chain CPs and long-chain CPs. Depending on chain length and chlorine content, CPs are colorless or yellowish liquids or solids.

Polymer stabilizers are chemical additives which may be added to polymeric materials, such as plastics and rubbers, to inhibit or retard their degradation. Common polymer degradation processes include oxidation, UV-damage, thermal degradation, ozonolysis, combinations thereof such as photo-oxidation, as well as reactions with catalyst residues, dyes, or impurities. All of these degrade the polymer at a chemical level, via chain scission, uncontrolled recombination and cross-linking, which adversely affects many key properties such as strength, malleability, appearance and colour.

<span class="mw-page-title-main">Antiozonant</span> Class of chemical compounds

An antiozonant, also known as anti-ozonant, is an organic compound that prevents or retards damage caused by ozone. The most important antiozonants are those which prevent degradation of elastomers like rubber. A number of research projects study the application of another type of antiozonants to protect plants as well as salmonids that are affected by the chemicals.

<span class="mw-page-title-main">Ethylene diurea</span> Chemical compound

Ethylene diurea (EDU) is an organic compound with the formula (CH2NHCONH2)2. It is a white solid.

Pre-spawn mortality is a phenomenon where adult coho salmon, Oncorhynchus kisutch, die before spawning when returning to freshwater streams to spawn. It is also known as Urban Runoff Mortality Syndrome in more recent studies. This occurrence has been observed in much of the Puget Sound region of the Pacific Northwest. During fall migration, salmonids pass through urban watersheds which are contaminated with stormwater runoff. As the coho salmon pass through these waters, many will show symptoms of lethargy, loss of equilibrium and disorientation, and die within a few hours of showing these symptoms. These symptoms and behaviors are prevalent after rain events. Mortality often occurs before salmon have the opportunity to spawn, which is determined by cutting open female carcasses and observing for unfertilized eggs. Rates of pre-spawn mortality could impact the local salmon populations. Based on model projections, if rates continue, populations of coho salmon could become extinct within the next few decades.

<span class="mw-page-title-main">Aminoxyl group</span>

Aminoxyl denotes a radical functional group with general structure R2N–O•. It is commonly known as a nitroxyl radical or a nitroxide, however IUPAC discourages the use of these terms, as they erroneously suggest the presence of a nitro group. Aminoxyls are structurally related to hydroxylamines and N-oxoammonium salts, with which they can interconvert via a series of redox steps.

<i>N</i>-Isopropyl-<i>N</i>-phenyl-1,4-phenylenediamine Chemical compound

N-Isopropyl-N′-phenyl-1,4-phenylenediamine (often abbreviated IPPD) is an organic compound commonly used as an antiozonant in rubbers. Like other p-phenylenediamine-based antiozonants it works by virtue of its low ionization energy, which allows it to react with ozone faster than ozone will react with rubber. This reaction converts it to the corresponding aminoxyl radical (R2N–O•), with the ozone being converted to a hydroperoxyl radical (HOO•), these species can then be scavenged by other antioxidant polymer stabilizers.

<span class="mw-page-title-main">Rubber pollution</span> Pollution due to rubber dust particles

Rubber pollution, similar to plastic pollution, occurs in various environments, and originates from a variety of sources, ranging from the food industry processing chain to tire wear. Synthetic and natural rubber dust and fragments now occur in food, airborne as particulates in air pollution, hidden in the earth as soil pollution, and in waterways, lakes and the sea.

<span class="mw-page-title-main">4-Aminodiphenylamine</span> Chemical compound

4-Aminodiphenylamine is a diphenylamine with an additional amine substituent. This dimer of aniline has various industrial uses, including as a hair dye ingredient, but also has raised concerns about toxicity by skin contact. It is also a starting material for the synthesis of 6PPD, an antiozonant for various rubber products. A colorimetric test for the quantitative analysis of nitrite, at levels below 100 nanograms per milliliter, is based on nitrite-catalyzed coupling of 4-aminodiphenylamine with N,N-dimethylaniline.

<span class="mw-page-title-main">Hexamethoxymethylmelamine</span> Chemical compound

Hexa(methoxymethyl)melamine (HMMM) is a hemiaminal ether commonly used as a crosslinking agent in the production of coatings and rubber items. It is produced via the reaction of melamine with formaldehyde and excess methanol, with the later also acting as a solvent for the reaction. It can be considered as a monomeric intermediate in the formation of melamine resin.

<span class="mw-page-title-main">TOP Assay</span> Laboratory analysis method

The TOP Assay is a laboratory method developed in 2012 that oxidatively converts (unknown) precursor compounds of perfluorocarboxylic acids (PFCAs) into the latter. This makes quantification possible. Potassium peroxodisulfate is used. This sum parameter can be used to determine the concentration of precursor compounds present by comparing the sample before and after the application of the TOP Assay.

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. ↑ Ashworth, B. T.; Hill, P. (1979). "Chapter 7: Protective Agents". Developments in Rubber Technology, Volume 1. London: Applied Science Publishers. pp. 227–239. ISBN   0853348626.
  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:2021Sci...371..185T. doi:10.1126/science.abd6951. PMID   33273063.
  5. ↑ Chadwick, Julie (12 July 2024). "How researchers uncovered the coho killing tire toxin 6PPD-Q". The Discourse. Retrieved 26 July 2024.
  6. ↑ 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
  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:10.5254/1.3538136.
  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:10.1016/j.polymdegradstab.2014.11.011.
  9. ↑ 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:10.1016/j.polymdegradstab.2017.11.020.
  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". Water Research. 212: 118122. Bibcode:2022WatRe.21218122S. doi: 10.1016/j.watres.2022.118122 . PMID   35101694. S2CID   246336931.
  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 , 371 (6525): 185–189, Bibcode:2021Sci...371..185T, 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 ... ( in print 8 Jan 2021)
  12. ↑ 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.
  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:2023EnST...57.2393Z. doi:10.1021/acs.est.2c07652. PMID   36720114. S2CID   256458111.
  14. ↑ "Pollution from car tires is killing off salmon on US west coast, study finds". The Guardian . 3 December 2020.
  15. ↑ "Scientists solve mystery of mass coho salmon deaths. The killer? A chemical from car tires". Los Angeles Times . 3 December 2020.
  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". Archives of Environmental Contamination and Toxicology. 82 (2): 171–179. Bibcode:2022ArECT..82..171J. doi:10.1007/s00244-021-00878-4. PMC   8335451 . PMID   34347118.
  17. 1 2 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, Bibcode:2022EnSTL...9..333B, doi:10.1021/acs.estlett.2c00050, S2CID   247336687
  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 , 9 (2): 140–146, Bibcode:2022EnSTL...9..140T, doi:10.1021/acs.estlett.1c00910, S2CID   245893533
  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:2023EnST...5721071M. doi:10.1021/acs.est.3c06891. PMID   38048442. S2CID   265658590.
  20. ↑ Lena Beck (17 May 2022). "Your car is killing coho salmon". The Counter.
  21. ↑ 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.82954675K. doi:10.1016/j.scitotenv.2022.154675. PMID   35314241. S2CID   247577987 – via Dynatrait.
  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:2022EnSTL...9.1056D. doi:10.1021/acs.estlett.2c00821. S2CID   253828438.
  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" (PDF). ChemRxiv . doi:10.26434/chemrxiv.13698985.v1. S2CID   234062284.
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