Introduction
Di(4-methylbenzoyl) peroxide (CAS 895-85-2), also known as di-p-toluoyl peroxide or PMBP, is a diacyl peroxide featuring p-methyl-substituted benzoyl groups. The methyl substituents on the aromatic rings modify the electronic properties of the peroxide and the reactivity of the resulting radicals, providing distinct characteristics compared to the parent benzoyl peroxide (BPO).
Key Facts
- CAS Number: 895-85-2
- Molecular Formula: C16H14O4
- Molecular Weight: 270.28 g/mol
- Appearance: White to off-white powder or crystals
- Active Oxygen: ~5.9% (theoretical)
- 10-Hour Half-Life Temperature: ~70-72 deg C
- Melting Point: ~94-98 deg C (decomposes)
Physical Properties
| Property | Value |
|---|---|
| Appearance | White to off-white powder |
| Molecular Weight | 270.28 g/mol |
| Active Oxygen | 5.9% |
| Solubility in Water | Insoluble |
| Solubility in Organics | Soluble in benzene, chloroform, acetone |
| 10-Hour Half-Life | ~70-72 deg C |
Applications
1. Polymerization Initiator
PMBP serves as a medium-temperature initiator for the polymerization of styrene, methyl methacrylate, and other vinyl monomers. Its 10-hour half-life of ~70-72 deg C is similar to BPO (~73 deg C), making it a direct alternative in many applications with potentially different decomposition product profiles.
2. Unsaturated Polyester Curing
In combination with amine accelerators, PMBP can initiate room-temperature curing of unsaturated polyester resins, similar to BPO-based redox systems.
3. Specialty Applications
The p-methyl substituent provides slightly different electronic characteristics that may be advantageous in specific polymerization or chemical synthesis applications where the reactivity or selectivity of the toluoyloxy radical differs from the benzoyloxy radical.
Safety
Like BPO, PMBP is classified as Organic Peroxide Type D and is typically supplied in phlegmatized form (water-wet or plasticizer paste) to ensure safe handling. The dry material is sensitive to impact and friction.
Frequently Asked Questions
Q: How does PMBP differ from benzoyl peroxide?
A: The p-methyl substituent on each aromatic ring is the key difference. This substitution: (1) slightly modifies the electron density of the carbonyl group, potentially affecting the O-O bond dissociation energy; (2) changes the decomposition product profile — 4-methylbenzoic acid (p-toluic acid) is produced instead of benzoic acid; (3) may influence the reactivity of the toluoyloxy radical in hydrogen abstraction and addition reactions; (4) increases the molecular weight (270 vs. 242 g/mol) and decreases active oxygen content (5.9% vs. 6.6%).
Key Takeaways
- Di(4-methylbenzoyl) peroxide (CAS 895-85-2) is a p-methyl-substituted diacyl peroxide.
- Its thermal stability and reactivity are similar to BPO, with some differentiation in decomposition products.
- Applications include styrene/acrylate polymerization and unsaturated polyester curing.
- Phlegmatized formulations are required for safe handling, as with other diacyl peroxides.
- Shandong Do Sender Chemicals supplies PMBP as part of its diacyl peroxide portfolio.