7PPD vs 6PPD: An Overview
6PPD and 7PPD are the two best-known members of the substituted p-phenylenediamine (PPD) family of rubber antiozonants. They look similar, do the same job, and are often discussed together — but they are different substances with different CAS numbers, different alkyl groups, different ketone feedstocks and, increasingly, different regulatory profiles. Choosing between them is a common compounding and procurement decision.
This article compares 6PPD and 7PPD on identity, properties, performance, supply and regulatory status. For the full background on 7PPD, see our main article on antioxidant 7PPD (CAS 3081-01-4).
At a Glance
| Property | 7PPD | 6PPD |
|---|---|---|
| CAS number | 3081-01-4 | 793-24-8 |
| Chemical name | N-(1,4-Dimethylpentyl)-N’-phenyl-p-phenylenediamine | N-(1,3-Dimethylbutyl)-N’-phenyl-p-phenylenediamine |
| Alkyl group | 1,4-Dimethylpentyl (C7) | 1,3-Dimethylbutyl (C6) |
| Molecular formula | C19H26N2 | C18H24N2 |
| Molecular weight | 282.42 g/mol | 268.40 g/mol |
| Ketone feedstock | Methyl isoamyl ketone (MIAK) | Methyl isobutyl ketone (MIBK) |
| Typical form | Dark viscous liquid | Dark viscous liquid |
| Function | Rubber antiozonant / antioxidant | Rubber antiozonant / antioxidant |
What They Have in Common
Both are substituted p-phenylenediamines: a p-phenylenediamine core with a phenyl group on one nitrogen and a branched alkyl group on the other. That shared core is what makes both effective:
- Both act as sacrificial antiozonants, reacting with ozone at the rubber surface to form a protective film.
- Both also act as antioxidants, scavenging the radicals that drive thermal-oxidative ageing.
- Both are dark, lipophilic liquids that bloom to the surface and migrate through the rubber.
- Both are skin sensitisers and are hazardous to the aquatic environment.
What Sets Them Apart
The difference is the alkyl group, and a one-carbon change in a branched chain affects physical properties, compatibility, volatility and performance:
- Alkyl chain length. 7PPD carries a longer C7 chain, which tends to increase molecular weight and lipophilicity and can influence how the additive migrates and blooms.
- Ketone feedstock. 7PPD uses methyl isoamyl ketone (MIAK), 6PPD uses methyl isobutyl ketone (MIBK). This matters for cost and supply, since the ketone is a major raw-material input.
- Performance profile. Both are highly effective antiozonants; the optimum choice depends on the rubber compound, the service conditions and the balance the compounder wants between antiozonant action, wax synergy, bloom and cost.
- Regulatory attention. 6PPD has attracted intense environmental and regulatory scrutiny, notably because of a quinone transformation product associated with aquatic toxicity. 7PPD is a related homologue with its own profile; it should not be assumed to be either identical to or automatically safer than 6PPD. Always work from the specific substance’s data.
Choosing Between 6PPD and 7PPD
| Consideration | What to weigh |
|---|---|
| Performance target | The ozone-resistance and ageing protection required by the compound and service conditions |
| Wax synergy | How the antiozonant interacts with the wax barrier system in the compound |
| Cost and availability | The relative cost and availability of MIAK and MIBK feedstock streams |
| Regulatory status | The current legal and customer requirements in the target market for each substance |
| Colour and staining | Both are dark; neither suits non-staining compounds |
| Supply chain | Producer portfolios often include both, sometimes as homologues or blends |
Are They Interchangeable?
They are functionally similar but not identical, and they should never be treated as interchangeable without a specification check:
- Different CAS numbers and identities. Always confirm which substance is being supplied.
- Re-formulation may be needed. Because physical properties differ, a switch may require adjustment of the dose and of the wax balance.
- Documentation differs. Regulatory and customer-approval status is substance-specific; check it before substituting.
Frequently Asked Questions
Are 6PPD and 7PPD the same?
No. They are different substances in the same PPD family: 7PPD is CAS 3081-01-4 with a 1,4-dimethylpentyl group, 6PPD is CAS 793-24-8 with a 1,3-dimethylbutyl group.
Which is the more widely used tire antiozonant?
6PPD is the most widely used, and it has drawn the most regulatory and environmental attention. 7PPD is a closely related homologue used where its properties or supply profile suit the compound.
Can I substitute 7PPD for 6PPD directly?
Not without checking the specification and re-validating the compound. They are similar but not identical, so dose and wax balance may need adjustment, and regulatory approval is substance-specific.
Which ketone is used to make each?
7PPD uses methyl isoamyl ketone (MIAK); 6PPD uses methyl isobutyl ketone (MIBK).
Do both need the same safety controls?
Both are skin sensitisers and hazardous to aquatic life, but each has its own hazard classification; follow the specific SDS for the substance you handle.