High purity, low color.
Purity ≥99.5% with molten color ≤20 APHA, suited to light-colored plasticizers and resins.
Phthalic Anhydride (PA)
Phthalic Anhydride (PA) Supplier — Plasticizer and Resin Raw Material
Phthalic anhydride (PA, CAS 85-44-9) is one of the most widely used organic intermediates. It is the starting material for phthalate plasticizers such as DBP, DIBP and DOP, and a core acid component of unsaturated polyester and alkyd resins. SUNCHEM supplies PA with purity ≥99.5% and a COA for every batch.
CAS 85-44-9 · C₈H₄O₃ · 1,3-Isobenzofurandione
- Lot COA with every shipment
- Samples for your trials
- Technical support for your trial
Product overview & key benefits
Phthalic anhydride is the cyclic anhydride of phthalic acid. The anhydride ring opens readily with alcohols, which is why PA is the standard route to phthalate esters and to the polyester backbone of many resins.
Most PA goes into plasticizers for PVC, such as dibutyl phthalate (DBP), diisobutyl phthalate (DIBP) and dioctyl phthalate (DOP). The second large outlet is resins: in unsaturated polyester resin (UPR) PA is the saturated acid used alongside maleic anhydride, and in alkyd resins for paints and coatings it supplies the aromatic acid component.
PA is also an intermediate for dyes and pigments, the laxative phenolphthalein, saccharin sodium, and agrochemicals including the insecticide phosmet, the fungicide folpet and the herbicide bentazone. A high-purity grade is used as an analytical reagent.
For resin and plasticizer makers, purity, color (molten, heat-stability and sulfuric-acid color) and free phthalic acid are the numbers that decide product color and reactivity.
Batch COA on every shipment.
Purity, three color tests, crystallization point and free acid are reported for each lot.
Resin raw materials from one supplier.
Phthalic anhydride and maleic anhydride can be quoted together for UPR and alkyd production.
Technical specifications
| Parameter | Specification | Typical batch result |
|---|---|---|
| Product name | Phthalic Anhydride (PA) | — |
| CAS No. | 85-44-9 | — |
| EC No. | 201-607-5 | — |
| Molecular formula | C₈H₄O₃ | — |
| Molecular weight | 148.12 | — |
| Appearance | White flake or crystalline powder | White flake or crystalline powder |
| Purity, % | ≥ 99.5 | 99.96 |
| Molten color, APHA | ≤ 20 | 20 |
| Heat-stability color, APHA | ≤ 50 | 40 |
| Sulfuric-acid color, APHA | ≤ 40 | 10 |
| Crystallization point, °C | ≥ 130.5 | 131.2 |
| Free acid (as phthalic acid), % | ≤ 0.20 | 0.06 |
Typical batch result is from one production lot (batch 20260709) and is shown for reference only. Each shipment is supplied with the COA of the batch you receive.
Applications by Industry
Where phthalic anhydride is used, and what to confirm before you switch supply.
Phthalate plasticizers for PVC
The largest use. PA is esterified with alcohols to make DBP, DIBP, DOP and other phthalate plasticizers for flexible PVC.
Check before trial
- Target ester and alcohol
- Color limits for the finished plasticizer
- Monthly volume and delivery form
Unsaturated polyester resins
Used with maleic anhydride and glycols in ortho-phthalic UPR for FRP, gelcoats, artificial stone and putties. PA is the saturated acid that balances stiffness and cost.
Check before trial
- Resin type and color target
- Purity and free-acid limits
- PA / MA ratio in your recipe
Alkyd resins, paints & coatings
Supplies the aromatic acid component of alkyd resins for paints, enamels and other coatings.
Check before trial
- Resin or paint type
- Color and heat-stability color
- Bag size that suits your charging
Dyes, pharma & agrochemical intermediates
An intermediate for dyes and pigments, phenolphthalein, saccharin sodium, and agrochemicals such as phosmet, folpet and bentazone. A high-purity grade is used as an analytical reagent.
Check before trial
- Synthesis route and impurity limits
- Documents your QA team needs
- Annual volume
Selection & comparison
Choosing the right PA supply
| Your requirement | What usually works |
|---|---|
| General plasticizer and resin production | Industrial PA, purity ≥ 99.5% |
| Light-colored plasticizers, gelcoats and clear resins | Specify molten, heat-stability and sulfuric-acid color limits |
| Ortho-phthalic UPR | PA together with maleic anhydride — both can be quoted on one order |
| Replacing an existing supplier | Send your current TDS or COA; we quote against the parameters you approve |
Phthalic anhydride vs maleic anhydride
Swipe or scroll horizontally to see all columns →
| Phthalic Anhydride (PA) | Maleic Anhydride (MA) | |
|---|---|---|
| CAS No. | 85-44-9 | 108-31-6 |
| Structure | Aromatic anhydride, no C=C double bond | Unsaturated anhydride with a C=C double bond |
| Role in UPR | Saturated acid — stiffness, cost balance | Unsaturated acid — sites for styrene crosslinking |
| Other main uses | Phthalate plasticizers, alkyd resins, dyes | Alkyds, maleic rosin, SMA copolymers, malathion |
In ortho-phthalic UPR the two are used together; the PA / MA ratio sets the balance between cost and cured hardness. Confirm your recipe by trial.
Packaging & storage
Packaging
Packaging is confirmed in the quotation. Tell us your bag size and pallet requirements with your inquiry.
Storage
Keep bags closed in a cool, dry, ventilated store away from heat. Moisture slowly converts PA to phthalic acid. The dust can sensitize skin and airways and damage eyes — follow the SDS.
Transport & terms
Regulated for transport as a corrosive (UN 2214, Class 8, PG III). We quote FOB and CIF; for large volumes, lead time is confirmed in the quotation.
From first email to approved supply
Name the end product.
Plasticizer, UPR, alkyd or an intermediate: tell us which one, because color and free-acid limits differ.
Compare the numbers that matter.
Purity, molten color, heat-stability color, sulfuric-acid color, crystallization point and free acid. Ask for the same parameters on our COA that appear on your incoming-inspection sheet.
Keep the TDS and COA separate.
The specification sets the limits. A COA reports results for one batch only. Ask for the COA of the batch you will receive.
Trial, then lock the spec.
Run a sample in your own process and keep the approved lot COA as the reference for contract limits.
Tell us your requirement. We match the grade.
Tell us the product you make, the quantity and the destination port. Add your current specification and we will quote against it.
| Information | Example |
|---|---|
| Application | Plasticizer (DBP, DOP), UPR, alkyd, dye or intermediate |
| Required specification | Purity, color limits, free acid |
| Form & packaging | Flakes; bag size and pallet requirements |
| Quantity | Trial order / monthly / annual volume |
| Destination | Country and port |
| Documents needed | COA, SDS, TDS, other documents your quality team needs |
Related products
Tetrabromophthalic Anhydride
Brominated derivative of phthalic anhydride for flame-retardant resins.
View product →Phthalic Acid (Electronic Grade)
High-purity phthalic acid for electronic applications.
View product →Phthalic Anhydride (PA) FAQ
What is phthalic anhydride used for?
Mainly for phthalate plasticizers such as DBP, DIBP and DOP used in PVC. It is also a core raw material for unsaturated polyester and alkyd resins, paints and coatings, and an intermediate for dyes and pigments, phenolphthalein, saccharin sodium and agrochemicals such as phosmet, folpet and bentazone.
What is the CAS number of phthalic anhydride?
The CAS number is 85-44-9. The molecular formula is C₈H₄O₃ and the molecular weight is 148.12.
What purity do you supply?
Purity ≥ 99.5%, with molten color ≤ 20 APHA and free acid ≤ 0.20%. A recent batch tested 99.96% purity. Every shipment comes with the COA of that batch.
How should phthalic anhydride be stored?
In closed bags in a cool, dry, ventilated store. Moisture slowly converts it to phthalic acid, and the dust can sensitize skin and airways, so follow the SDS for handling.
Is phthalic anhydride dangerous goods?
Yes. It is regulated as a corrosive for transport under UN 2214, Class 8, PG III.
Can I get a sample before ordering?
Yes. Free samples are available for buyers evaluating the product for production use. Shipping cost is agreed case by case, and each sample comes with a COA.
