Introduction to Antioxidant 7PPD
Antioxidant 7PPD (CAS 3081-01-4) is a substituted p-phenylenediamine (PPD) used mainly as an antiozonant and antioxidant in rubber. It is the higher alkyl homologue of the better-known 6PPD: both belong to the same family of PPD antiozonants that protect tyres and rubber goods from attack by ozone, oxygen, heat and fatigue. 7PPD is also used as a polymerisation inhibitor and in some lubricant and industrial formulations.
For buyers and compounders, the important facts about 7PPD are its correct chemical identity, the way it protects rubber, the ketone-based production route, the specification it must meet and the way it compares with 6PPD. This article covers all of these, with a deliberate focus on accurate chemistry and on the health, safety and environmental considerations that apply to PPD antiozonants.
PolyBlueChem can supply antioxidant 7PPD (CAS 3081-01-4) as a bulk rubber-chemical raw material; see the 7PPD product page for the current specification.
Chemical Identity and Structure
7PPD is a p-phenylenediamine in which one nitrogen carries a phenyl group and the other carries a 1,4-dimethylpentyl (a branched C7) group. The two amine nitrogens are the functional heart of the molecule: they are what allow it to intercept ozone and free radicals. It is important not to confuse 7PPD with 6PPD, whose alkyl group is a shorter 1,3-dimethylbutyl (C6) chain.
| Property | Value |
|---|---|
| Common name | Antioxidant 7PPD (7-PPD) |
| Chemical name | N-(1,4-Dimethylpentyl)-N’-phenyl-p-phenylenediamine |
| Other names | N-Phenyl-N’-(1,4-dimethylpentyl)-p-phenylenediamine |
| CAS number | 3081-01-4 |
| EC (EINECS) number | 221-374-3 |
| Molecular formula | C19H26N2 |
| Molecular weight | 282.42 g/mol |
| Class | Substituted p-phenylenediamine (PPD) antiozonant / antioxidant |
Do not confuse 7PPD with 6PPD. 6PPD is N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine (CAS 793-24-8) and uses methyl isobutyl ketone (MIBK) as the alkyl source; 7PPD uses a one-carbon-longer branched chain. They are closely related products with similar function but different physical properties. The comparison is covered in the related reading below.
Physical and Chemical Properties
7PPD is a high-boiling, water-insoluble, lipophilic amine. Commercial material is typically a dark, viscous liquid rather than a crystalline solid, which reflects both its molecular structure and the grade in which it is supplied.
| Property | Typical value / behaviour |
|---|---|
| Appearance | Dark brown viscous liquid (commercial grade) |
| Boiling point | High (reported around 415 °C, estimated); decomposes before distilling |
| Density / specific gravity | Approx. 0.95 (neat); commercial grade 0.99–1.01 at 60/15 °C |
| Water solubility | Very low (on the order of 0.7 mg/L) |
| Solubility in organics | Soluble in common organic solvents (acetone, aromatic and chlorinated solvents, alcohols) |
| Log P (octanol/water) | Approx. 5.2 (strongly lipophilic) |
| Reactive groups | Two amine nitrogens (the sites of antiozonant and antioxidant action) |
The strongly lipophilic character and low water solubility are exactly what a rubber antiozonant needs: the additive must be compatible with the rubber hydrocarbon, yet able to migrate to the surface where ozone attack occurs.
How PPD Antiozonants Protect Rubber
Rubber fails outdoors through two linked processes. Ozone cracking is caused by atmospheric ozone attacking the strained rubber surface, cutting it into cracks that grow and eventually cause failure. Oxidation is driven by oxygen, heat and metal ions and causes the rubber to harden, crack and lose elasticity. PPD antiozonants such as 7PPD fight both, in two ways:
- Antiozonant (sacrificial) action. The amine reacts preferentially with ozone at the rubber surface, forming a protective, ozonated surface film that shields the bulk material. Because 7PPD can migrate to the surface, it continually renews this protection, which is why PPDs are far more effective antiozonants than simple antioxidants.
- Antioxidant (radical-scavenging) action. The amine moieties also trap the peroxy and alkyl radicals that propagate oxidative degradation, so the same molecule slows thermal-oxidative ageing.
This dual action is why PPDs dominate in dynamic, ozone-exposed applications — principally tyre sidewalls and treads and other rubber goods exposed to outdoor service. The trade-offs are that PPDs are coloured, can stain and bloom to the surface, and are known skin sensitisers; these points are covered in the safety section.
Industrial Production: Reductive Alkylation
7PPD is produced by the catalytic reductive alkylation of 4-aminodiphenylamine (ADPA) with a branched ketone. The alkyl group in 7PPD is a 1,4-dimethylpentyl group, so the ketone used is the corresponding C7 ketone, 5-methyl-2-hexanone (methyl isoamyl ketone, MIAK). Hydrogen is required, and the reaction runs over a hydrogenation catalyst.
It is worth stating clearly what the old, incorrect account got wrong: 7PPD is not made by alkylating p-phenylenediamine with isobutene. Isobutene would introduce a tert-butyl group, giving a different (tert-butylated) product, not the 1,4-dimethylpentyl chain found in 7PPD. The correct industrial logic is a reductive-alkylation (amine + ketone → secondary amine) using the matching ketone.
| Stage | Purpose | Notes |
|---|---|---|
| 1. ADPA feedstock | Supply the phenylamino-aniline backbone | 4-Aminodiphenylamine (ADPA); sourced or made from aniline/nitrobenzene chemistry |
| 2. Reductive alkylation | Attach the 1,4-dimethylpentyl group | ADPA + 5-methyl-2-hexanone (MIAK) + hydrogen over a hydrogenation catalyst |
| 3. Water separation | Remove the water formed in the reaction | Reaction water is separated to drive the equilibrium |
| 4. Catalyst removal and purification | Obtain a clean product | Filtration of catalyst; distillation/refining to specification |
| 5. Quality control | Confirm the active content and specification | Assay (HPLC), specific gravity, ash, heating loss |
The same reductive-alkylation logic produces the whole PPD family: 6PPD from MIBK, and other homologues (including 77PD, the “88”-type products and mixtures) from other ketones or ketone blends. Producers choose the ketone to tune the balance of compatibility, volatility, cost and performance.
Specifications and Quality Control
The commercial grade is controlled by active-ingredient content, specific gravity, volatile loss and ash. A representative specification is shown below; the PolyBlueChem grade is typical of the liquid 7PPD supplied to the rubber industry.
| Parameter | Typical specification |
|---|---|
| Appearance | Dark brown viscous liquid |
| Active ingredient (HPLC) | ≥ 96% |
| RT | ≤ 2.0 |
| Specific gravity (60/15 °C) | 0.992–1.010 |
| Heating weight loss (70 ± 1 °C) | ≤ 0.3% |
| Ash | ≤ 0.1% |
| Residue (85 °C, 100 mesh) | No granular impurities |
Quality control focuses on the active content (a low assay means more inert material in the compound) and on the volatile and ash figures, which reflect the cleanliness of the product. Because 7PPD is a liquid supplied in drums or tankers, sampling and handling practice matters as much as the laboratory methods.
Grades and Forms
- Standard liquid grade: the dark viscous liquid most commonly used in tyre and rubber compounding.
- Blends and mixtures: PPD antiozonants are frequently supplied as blends of homologues, tuned for cost and performance; the buyer should confirm the exact composition and the active content.
- Solution / pre-dispersed forms: for easier dosing into continuous mixing systems.
- Technical / industrial grade: for rubber and polymerisation-inhibitor uses.
Applications: Tyres and Rubber Goods
The dominant use of 7PPD is in rubber, above all in tyres, where it protects the parts most exposed to ozone and dynamic stress.
| Application | Role of 7PPD |
|---|---|
| Tyre sidewalls and treads | Antiozonant and antioxidant; prevents cracking and ageing of the most exposed rubber |
| Other tyres and inner components | Protection of rubber against oxidative ageing |
| Hoses, belts and conveyor belting | Durability in outdoor and dynamic service |
| Seals, gaskets and mouldings | Ageing resistance in automotive and industrial parts |
| General rubber goods | Long-term protection where ozone and weathering are a concern |
Because PPDs bloom to the surface to work, they are dosed into the compound rather than applied as a coating, and they are usually used at a few parts per hundred of rubber. The exact level depends on the rubber type, the filler system and the severity of the service.
Other Uses
- Polymerisation inhibitor: substituted p-phenylenediamines are used to inhibit unwanted free-radical or oxidative polymerisation during monomer storage and processing.
- Lubricants and greases: as an oxidation inhibitor in some formulations, where a high-temperature amine antioxidant is useful.
- Industrial rubber and elastomer compounds: in any application where ozone and oxygen ageing must be controlled.
7PPD, 6PPD and the PPD Antiozonant Family
PPD antiozonants are a family defined by the substituent on one nitrogen. The table compares the two best-known members.
| Property | 7PPD | 6PPD |
|---|---|---|
| CAS number | 3081-01-4 | 793-24-8 |
| Alkyl group | 1,4-Dimethylpentyl (C7) | 1,3-Dimethylbutyl (C6) |
| Molecular formula | C19H26N2 | C18H24N2 |
| Ketone feedstock | 5-Methyl-2-hexanone (MIAK) | Methyl isobutyl ketone (MIBK) |
| Form | Dark viscous liquid | Dark viscous liquid |
| Function | Antiozonant / antioxidant in rubber | Antiozonant / antioxidant in rubber |
6PPD is the most widely used tyre antiozonant, and a great deal of environmental and regulatory attention has focused on it and on its quinone transformation product. 7PPD is a related homologue; buyers should differentiate them on CAS number, alkyl group and the specific performance and regulatory profile required. A fuller comparison, including how to choose between them, is given in the related reading below.
Formulation and Dosage Guidance
- Dosage. PPD antiozonants are typically used at a few parts per hundred of rubber (phr); the level is set by the rubber compounder to meet a target ozone resistance and service life.
- Compounding. 7PPD is added during mixing as a liquid; dosing accuracy and good dispersion matter because the additive must be distributed throughout the compound to bloom uniformly.
- Interactions. In tyre compounds, PPD antiozonants are used together with waxes, which provide a physical barrier at the surface, and with other antioxidants; the balance between chemical and physical protection is a standard compounding decision.
- Colour and staining. Because PPDs are dark and can stain and bloom, they are not suitable for light-coloured or non-staining compounds; substitution of another protective system is required there.
- Storage. Keep drums sealed, cool and out of direct sunlight; avoid contamination and minimise exposure to air over long periods.
Safety, Health and Environment
PPD antiozonants require careful handling. 7PPD is classified as hazardous under GHS, and users should always work from the current safety data sheet (SDS) and their own risk assessment. The key points are:
- Skin sensitisation. PPDs are well-known skin sensitisers; repeated skin contact can cause allergic dermatitis. Avoid skin contact and use appropriate gloves and protective clothing.
- Reproductive/health hazards. The material carries hazard classifications relating to health (including reproductive toxicity concern) and to the aquatic environment; handle it as an industrial chemical with the controls specified in the SDS.
- Aquatic toxicity. 7PPD and related PPDs are toxic to aquatic life, and their transformation products are the subject of ongoing environmental research. Prevent release to drains and watercourses, and manage waste and wastewater properly.
- Environment. Emissions from tyre and rubber wear mean PPD antiozonants have become an area of environmental interest; buyers and users should follow current regulatory guidance rather than rely on older characterisations.
A note on accuracy: older descriptions of 7PPD sometimes label it a “persistent organic pollutant (POP)”. That label is not accurate for 7PPD. It is a substituted PPD antiozonant with its own hazard profile, and it should be described using its actual classifications and current regulatory status, not as a POP.
Regulatory Status
As an industrial rubber chemical, 7PPD is subject to the general chemical regulatory framework of each market. In the European Union the substance is registered under REACH; in the United States it appears on the TSCA inventory. Because the PPD antiozonant family is under active environmental scrutiny, buyers should verify the current regulatory status in their target markets and confirm the documentation the supplier can provide:
- Safety data sheet (SDS) in the required format and language.
- Certificate of analysis (COA) per batch.
- REACH registration, TSCA and any applicable market-specific statements.
Market and Supply Overview
- Demand driver. PPD antiozonants are driven by tyre and rubber production, which is why their demand tracks the automotive and industrial rubber cycle.
- Production base. Made by a limited number of specialised producers; 7PPD is one grade within a broader PPD antiozonant portfolio, often supplied as a homologue blend.
- Price drivers. The cost of ADPA and the ketone feedstock (MIAK), hydrogen and catalyst costs, and plant utilisation.
- Quality differentiators. Active-ingredient content, colour, volatile and ash content, and documentation.
- Packaging. Typically in steel drums or intermediate bulk containers (IBCs) for a liquid product.
Procurement and Sourcing Guide
- Confirm the identity. Check the CAS number (3081-01-4) and the alkyl group, and do not accept 6PPD material supplied as 7PPD or vice versa without a clear specification.
- Active content. Confirm the active-ingredient content; blends and mixtures should be specified by composition.
- Physical form. Confirm the form (liquid, solution, blend) and its compatibility with your dosing system.
- Documentation. Require an SDS and per-batch COA, plus REACH/TSCA statements as needed.
- Handling and packaging. Confirm drum/IBC packaging, and plan for the skin-sensitisation and aquatic-toxicity controls.
PolyBlueChem can supply antioxidant 7PPD (CAS 3081-01-4) as a bulk raw material. To request current specifications, a COA or a quotation, contact the PolyBlueChem team.
How Tyre Protection Systems Work Together
7PPD is rarely used alone. In a tyre or rubber compound it is combined with waxes and with other antioxidants, and the overall ozone and ageing resistance comes from the way these systems interact.
| Protective system | How it works | Typical role |
|---|---|---|
| PPD antiozonant (e.g. 7PPD) | Reacts with ozone at the surface; scavenges radicals | Chemical antiozonant and antioxidant; the main defence |
| Paraffin / microcrystalline wax | Blooms to form a physical barrier film | Physical barrier; protects at low strain and in static service |
| Phenolic or amine antioxidants | Trap radicals during thermal-oxidative ageing | Complementary ageing protection |
| Metal deactivators | Complex metal ions that catalyse oxidation | Protection where copper or other metals are present |
The classic combination is a PPD antiozonant plus a wax. The wax provides a physical barrier that is effective in static service and at low strain, while the PPD provides chemical protection that continues to work under dynamic strain, where a wax film would be disrupted. Because the two mechanisms are complementary, compounders tune the ratio to the service conditions: more wax for static, low-strain applications, more PPD for dynamic, high-strain duty such as tyre sidewalls. Getting this balance right is one of the central skills of tyre-compound design, and it is the reason a single “best dose” for 7PPD does not exist.
Polymerisation Inhibitor and Industrial Uses
Beyond rubber, substituted p-phenylenediamines find use where unwanted free-radical or oxidative reactions must be suppressed during storage or processing:
- Polymerisation inhibition. PPD-type inhibitors are used to prevent premature or runaway polymerisation of reactive monomers during storage, transport and distillation, protecting against gel formation and equipment fouling.
- Lubricant and grease antioxidant. As a high-temperature amine antioxidant, PPD chemistry is used in some lubricant formulations to slow oxidative breakdown at elevated temperatures.
- Industrial elastomers. Any elastomer compound exposed to ozone, oxygen and dynamic stress can benefit from a PPD antiozonant, subject to the colour and staining limitations.
In all of these uses, the same molecular feature — the two amine nitrogens — provides the function, whether the target is ozone, peroxy radicals or a polymerising monomer.
Handling, Packaging and Storage
- Packaging. Supplied as a liquid in steel drums or IBCs; confirm the packaging and the transfer method suited to your plant.
- Storage. Keep containers sealed, cool and out of direct sunlight. Prolonged air and heat exposure can darken and oxidise the product, so use stock in rotation.
- Dosing. Liquid antiozonants are usually dosed by weight or volume into the mixer; accuracy and dispersion affect performance, so calibrate the dosing system.
- Hygiene. Because PPDs are skin sensitisers, use closed-transfer systems where possible and provide appropriate PPE and washing facilities.
- Spill and waste. Prevent release to drains and watercourses; absorb spills with inert material and dispose of as hazardous waste in line with the SDS.
Frequently Asked Questions
What is antioxidant 7PPD and what is its CAS number?
7PPD is N-(1,4-dimethylpentyl)-N’-phenyl-p-phenylenediamine, a substituted p-phenylenediamine used mainly as a rubber antiozonant and antioxidant; its CAS number is 3081-01-4. See the 7PPD product page for specifications.
Is 7PPD the same as 6PPD?
No. They are different substances. 7PPD (CAS 3081-01-4) has a 1,4-dimethylpentyl group; 6PPD (CAS 793-24-8) has a shorter 1,3-dimethylbutyl group. They are closely related homologues in the same PPD family. See the comparison in the related reading.
What is the molecular formula and weight of 7PPD?
C19H26N2 and 282.42 g/mol.
How is 7PPD made?
By catalytic reductive alkylation of 4-aminodiphenylamine (ADPA) with 5-methyl-2-hexanone (methyl isoamyl ketone) in the presence of hydrogen. It is not made by alkylating p-phenylenediamine with isobutene.
What is 7PPD used for?
Mainly as an antiozonant and antioxidant in rubber, especially tyres; also as a polymerisation inhibitor and in some lubricant and industrial formulations.
How does 7PPD protect rubber?
It acts as a sacrificial antiozonant at the rubber surface and as a radical-scavenging antioxidant, protecting against both ozone cracking and oxidative ageing.
Is 7PPD a persistent organic pollutant?
No. Describing 7PPD as a POP is not accurate. It is a substituted PPD antiozonant with its own GHS hazard profile, including skin sensitisation and aquatic toxicity, and should be handled according to its SDS.
How should 7PPD be stored and handled?
Store in sealed drums or IBCs, cool and out of direct sunlight. Handle as a hazardous industrial chemical: avoid skin contact, use appropriate PPE, and prevent release to watercourses.
What dosage of 7PPD is typical in rubber?
PPD antiozonants are generally used at a few parts per hundred of rubber (phr); the exact level is set by the compounder to meet the target ozone resistance and is balanced against waxes and other antioxidants.
Can 7PPD be used in light-coloured rubber?
Generally no. PPDs are dark and can stain and bloom to the surface, so they are unsuitable for light-coloured or non-staining compounds, which need a different protective system.
What is the difference between an antiozonant and an antioxidant?
An antioxidant slows oxidative degradation by trapping radicals; an antiozonant specifically protects against ozone attack, largely by reacting at the rubber surface. PPDs such as 7PPD do both.
Does 7PPD bloom to the surface of rubber?
Yes. Like other PPD antiozonants, it migrates to the rubber surface, which is how it renews its protection against ozone; this is also why it can stain and bloom.
References and Disclaimer
References. Substance identification data for N-(1,4-dimethylpentyl)-N’-phenyl-p-phenylenediamine (CAS 3081-01-4); published chemistry of p-phenylenediamine antiozonants and of rubber antiozonant/antioxidant mechanisms; manufacturer technical data for the liquid 7PPD grade. Specifications quoted are representative and should be confirmed against the current certificate of analysis.
Disclaimer. This article is provided for general technical and commercial information only and does not constitute a specification or a warranty of fitness for any particular use. Users are responsible for confirming regulatory status, safe handling and suitability of the material for their own application.