Chlorendic Anhydride: Properties, Uses & Safety Guide

Chlorendic anhydride is a chlorinated cyclic dicarboxylic anhydride widely used as a reactive flame retardant and curing agent in polymer and epoxy resin systems.

CAS Number

115-27-5

Molecular Formula

C₉H₂Cl₆O₃

Molecular Weight

370.82 g/mol

Appearance

White to off-white crystalline powder

Chlorine Content

~57% by weight (six chlorine atoms per molecule)

Primary Application

Reactive flame retardant and epoxy resin curing agent

SKU

C129141

Chemical Identity and Physical Properties

Chlorendic anhydride (CAS 115-27-5), also known as 1,4,5,6,7,7-hexachlorobicyclo[2.2.1]-5-heptene-2,3-dicarboxylic anhydride, is a halogenated cyclic anhydride derived from the Diels–Alder reaction of hexachlorocyclopentadiene with maleic anhydride. Its molecular formula is C₉H₂Cl₆O₃ with a molecular weight of approximately 370.82 g/mol.

The compound presents as a white to off-white crystalline solid at room temperature. Its high chlorine content—approximately 57% by mass—is the structural basis for its outstanding flame-retardant performance. The bicyclic norbornene-type skeleton confers rigidity, contributing to an elevated melting point and good thermal stability relative to non-halogenated anhydrides. Researchers should verify precise melting point and solubility values against the certificate of analysis supplied with each lot, as these can vary with purity.

Flame-Retardant Mechanism and Polymer Applications

Chlorendic anhydride functions as a reactive flame retardant, meaning it is chemically incorporated into the polymer backbone rather than simply blended as an additive. This covalent integration prevents migration or leaching during service, providing more durable fire resistance compared with additive-type retardants.

In epoxy resin formulations, chlorendic anhydride acts simultaneously as a curing (hardening) agent and a flame-retardant comonomer. The anhydride groups react with epoxide groups to form ester linkages, building a crosslinked network that is inherently resistant to ignition and flame spread. The flame-retardant effect in the condensed phase is attributed to char formation, while in the gas phase, halogen radicals released during combustion interrupt the radical chain reactions that sustain flames.

Typical research and industrial uses include flame-retardant epoxy laminates for printed circuit boards, corrosion-resistant coatings, unsaturated polyester resins, and specialty alkyd resins. It has also been investigated as a component of flame-retardant polyurethane and polyimide systems.

Handling, Storage, and Safety Considerations

Chlorendic anhydride is classified as a hazardous substance and must be handled with appropriate precautions. As an acid anhydride, it is a lachrymator and skin, eye, and respiratory tract irritant. Exposure to moisture causes slow hydrolysis to chlorendic acid, which may affect reactivity and purity over time.

Personal Protective Equipment (PPE): Wear chemical-splash goggles, a laboratory coat, and chemical-resistant gloves (e.g., nitrile or neoprene). For operations that may generate dust or aerosols, use a NIOSH-approved respirator or conduct work in a fume hood.

Storage: Store in a tightly sealed container in a cool, dry, well-ventilated area away from moisture, bases, and incompatible oxidizers. Refrigerated storage (2–8 °C) is recommended to minimize hydrolysis and maintain purity over extended periods. Consult the Safety Data Sheet (SDS) provided with product C129141 for lot-specific hazard and disposal information.

Disposal: Dispose of waste material in accordance with local, regional, and national environmental regulations. Chlorendic anhydride and its hydrolysis products are persistent organochlorine compounds; licensed hazardous waste disposal is required.

Note: Specific GHS hazard classifications and regulatory listings (e.g., REACH, TSCA) should be verified against the current SDS and applicable regulatory databases before use.

Purity, Specifications, and Quality Assurance

For research applications, the purity of chlorendic anhydride directly influences reproducibility, especially in stoichiometrically controlled curing and polymerization reactions. Aladdin Scientific's product C129141 is offered for laboratory and research use; researchers should consult the product page and certificate of analysis (CoA) for the current lot's purity specification, appearance criteria, and analytical test methods.

Key quality parameters typically evaluated for anhydride reagents include:

• Assay (purity): Commonly determined by titration or HPLC.
• Melting point: A sensitive indicator of purity for crystalline anhydrides.
• Water content: Measured by Karl Fischer titration; low moisture is critical to prevent premature hydrolysis.
• Appearance: White to off-white crystalline powder free from visible contamination.

Lot-to-lot consistency is especially important for researchers developing reproducible polymer formulations. Contact Aladdin Scientific's technical support team for bulk quantities, custom specifications, or additional analytical data.

Frequently asked questions

What is chlorendic anhydride used for in polymer research?

Chlorendic anhydride is primarily used as a reactive flame retardant and curing agent for epoxy resins, unsaturated polyesters, and specialty polymer systems. Because it bonds covalently into the polymer network, it provides durable, non-leaching flame retardancy that persists over the material's service life.

How should chlorendic anhydride be stored to maintain its purity?

Chlorendic anhydride should be stored in a tightly sealed container in a cool, dry environment away from moisture and bases. Refrigerated storage at 2–8 °C is recommended for extended shelf life. Exposure to atmospheric moisture will cause hydrolysis to chlorendic acid, reducing the anhydride content and affecting reactivity in formulations.

Is chlorendic anhydride the same as chlorendic acid?

No. Chlorendic anhydride (CAS 115-27-5) is the cyclic anhydride form, while chlorendic acid (CAS 115-28-6) is its ring-opened dicarboxylic acid form produced by hydrolysis. The anhydride is the reactive species used in curing and polymerization reactions; the acid form has lower reactivity toward epoxides and other electrophilic partners under typical processing conditions.

What personal protective equipment is required when handling chlorendic anhydride?

Handlers should wear chemical-splash goggles, a laboratory coat, and chemical-resistant gloves such as nitrile or neoprene. Operations that may generate dust require a NIOSH-approved respirator or must be conducted in a fume hood. Always consult the Safety Data Sheet (SDS) for product C129141 before use.

References

1. March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 4th ed.; Wiley-Interscience: New York, 1992. (General anhydride chemistry and Diels–Alder synthesis background.)
2. Levchik, S. V.; Weil, E. D. Flame retardancy of thermoplastic polyesters—a review of the recent literature. Polymer International 2005, 54, 11–35.
3. Aladdin Scientific. Product page and Safety Data Sheet for Chlorendic anhydride, SKU C129141. Retrieved from https://www.aladdinscientific.com.

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.