Industrial Grade 98.5% 99% Phosphorous Acid CAS 13598-36-2

Phosphorous Acid — Product Detail Page

1. Product Overview

Phosphorous acid (H₃PO₃, CAS 13598-36-2) is a white, deliquescent crystalline oxoacid of phosphorus (P(III)) that melts at ≈ 73 °C. As the parent acid of the entire phosphite (P(III)) family, it is the key industrial feedstock for phosphite fertilizers and plant-defense chemistry, for phosphonate scale- and corrosion-inhibitors in water treatment, for organotin PVC stabilizer production, and for a wide range of organophosphorus syntheses. Its dual character — a strong reducing P(III) center plus two acidic protons — makes it one of the most versatile building blocks in phosphorus chemistry.

One acid, four core value propositions:

Phosphite Fertilizer Raw Material (Core Application):

●     direct feedstock for potassium phosphite (KH₂PO₃ / K₂HPO₃) liquid fertilizers and phosphonate plant-defense actives;

Phosphonate Water-Treatment Precursor:

●     raw material for ATMP, HEDP and PBTC scale/corrosion inhibitors;

PVC Stabilizer & Polymer Additive Chemistry:

●     reducing agent in organotin (tin mercaptide) heat-stabilizer synthesis and polymer additive production;

Organophosphorus Synthesis Building Block:

●     phosphonate ester and flame-retardant intermediate chemistry, plus a high-purity laboratory reagent.

2. Product Information (Quick Facts)

3. Chemistry & Structure

Phosphorous acid is the tribasic-looking but actually dibasic oxoacid of phosphorus(III), H₃PO₃ (MW 82.00). Its structure is HP(O)(OH)₂: one hydrogen is bonded directly to phosphorus (P–H) and is not ionizable, while the two –OH protons give pKa₁ ≈ 1.3 and pKa₂ ≈ 6.7 — the same two-step acidity that defines the monopotassium and dipotassium phosphite salts. The P(III) center is a mild reducing agent, and the acid is strongly deliquescent and very soluble in water and ethanol. On heating above ≈ 200 °C it disproportionates to phosphoric acid and toxic, spontaneously flammable phosphine (PH₃) — a critical handling and storage consideration.

4. Key Features & Benefits

●     Dibasic P(III) acid: the clean, controlled source of phosphite (P(III)) chemistry.

●     Key industrial feedstock: one molecule feeds fertilizer, water-treatment and polymer-additive industries.

●     Mild reducing character: dependable P(III) reducing agent for stabilizer and synthesis chemistry.

●     Very soluble: dissolves readily in water and ethanol for fast, uniform neutralization and reaction.

●     Low melting point : convenient liquid-phase handling in warm processing.

●     Deliquescent crystalline solid: easy dosing and storage when kept dry and sealed.

●     High assay grades: ≥ 99% and ≥ 98.5% available with COA.

●     Consistent quality: controlled assay, acidity and impurity profile on every batch.

5. Main Applications

5.1 Phosphite Fertilizer Raw Material (Core Application)

Phosphorous acid is the industrial starting point of the entire phosphite-fertilizer segment:

●     Potassium phosphite fertilizers: neutralized with KOH or K₂CO₃ to make monopotassium (KH₂PO₃) and dipotassium (K₂HPO₃) phosphite — high-analysis PK liquid fertilizers;

●     Foliar and fertigation programs: the P(III) form is systemic and phloem-mobile in crops;

●     Plant-defense actives: phosphonate intermediates supporting oomycete (Phytophthora, downy mildew) defense chemistry;

●     Agrochemical formulations: precise, fully water-soluble P(III) feedstock for specialty agriculture.

5.2 Phosphonate Water-Treatment Precursor

●     Scale inhibitors: raw material for ATMP, HEDP and PBTC phosphonate scale/corrosion inhibitors;

●     Cooling-water and boiler-water programs: phosphonate actives built from phosphorous acid;

●     Oilfield chemistry: scale and corrosion control in production and water-injection systems;

●     Chelation chemistry: phosphonate chelating agents derived from H₃PO₃-based reactions.

5.3 PVC Stabilizer & Polymer Additive Chemistry

●     Organotin stabilizers: reducing agent in the synthesis of tin mercaptide heat stabilizers for PVC;

●     Polymer additives: P(III) intermediate for phosphorus-based antioxidant and processing chemistry;

●     PVC processing stability: enabling chemistry behind efficient heat-stabilizer systems;

●     Plastic and rubber auxiliaries: controlled reduction and esterification steps.

5.4 Organophosphorus Synthesis & Laboratory Reagent

●     Phosphonate esters: building block for organophosphonate derivatives and flame-retardant intermediates;

●     Fine-chemical synthesis: agrochemicals and specialty organics;

●     Analytical reagent: high-purity grade for laboratory use;

●     Research chemistry: reduction and phosphonation steps in R&D.

6. Packaging, Storage

Packaging (customizable):

●     25 kg moisture-barrier drums or bags with PE liner; 500 kg / 1,000 kg big bags; vacuum-sealed small packs on request;

Storage:

●     Store in a cool, dry, well-ventilated area; keep containers tightly closed;

●     Separate from strong bases, oxidizers and combustible materials (corrosive — UN 2834, Class 8);

●     Never heat above ≈ 200 °C without ventilation — decomposition releases toxic phosphine (PH₃).

7. Why Choose Jinan Future Chemical Co., Ltd.?

●     Factory-direct supply: own production and sourcing capability, transparent pricing, no middleman markup;

●     Stable quality: strict internal control, every batch tested (assay, acidity, appearance), COA with every shipment;small trial orders accepted.

●     Export experience: experienced in dangerous-goods (UN 2834 Class 8) documentation and compliant sea/air shipping;

8. FAQ

Q1: What is phosphorous acid used for?

Phosphorous acid is the industrial feedstock for phosphite fertilizers (potassium phosphite for foliar and fertigation programs), for phosphonate scale and corrosion inhibitors (ATMP, HEDP, PBTC) in water treatment, as a reducing agent in organotin PVC heat-stabilizer synthesis, and as an organophosphorus building block for phosphonate esters, flame-retardant intermediates and fine chemicals.

Q2: Why is phosphorous acid the raw material of choice for phosphite fertilizers?

Phosphite (P(III)) fertilizers are made by neutralizing phosphorous acid with potassium hydroxide or carbonate to form monopotassium (KH₂PO₃) and dipotassium (K₂HPO₃) phosphite. The acid's two clean acidic protons (pKa₁ 1.3, pKa₂ 6.7) give a precise, fully water-soluble neutralization, and the resulting phosphite is systemic and phloem-mobile in plants — supporting both PK nutrition and defense activation in specialty agriculture. This makes H₃PO₃ the indispensable building block of the entire phosphite-fertilizer segment.

Q3: What is the difference between phosphorous acid and phosphoric acid?

Phosphorous acid is H₃PO₃ with phosphorus in the +3 oxidation state and one P–H bond (dibasic, pKa₁ 1.3 / pKa₂ 6.7); phosphoric acid is H₃PO₄ with phosphorus in the +5 state and three ionizable protons. The P(III) acid is a mild reducing agent, is less stable to heat (decomposes ≈ 200 °C releasing toxic phosphine) and delivers the phosphite form used in fertilizers and phosphonate chemistry, whereas phosphoric acid is the classical non-reducing phosphate source. They are chemically distinct and not interchangeable.