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13598-36-2
futurechem
13598-36-2
Phosphorous acid, also known as phosphite (chemical formula H3PO3), is a trivalent oxyacid of phosphorus. It is a white crystalline acid with strong reducing properties and pH bond reactivity. It is the main raw material for PVC plastic stabilisers, organophosphonic acid water treatment agents and agricultural phosphite formulations. Phosphorous acid is used in many industrial and scientific research fields such as plastic pipes, drinking water treatment, crop disease prevention, electroless nickel plating, flame retardants and scientific reagents.
Typical identification data: Molecular formula H3PO3 (actually a binary HP(O)(OH)2 with the 3rd hydrogen directly bonded to phosphorus) Molecular weight 82.00 CAS number 13598-36-2 EC number 237-066-7
Phosphorous acid is a white crystalline solid. It is hygroscopic. Its density is 1.651 g/cm3. Its melting point is 73.6℃. Its boiling point is about 200℃ (decomposes). It is extremely soluble in water (310 g/100 mL) and ethanol. Its aqueous solution is acidic.
Chemically, phosphorous acid is a diprotic moderately strong acid (pKa 1.3, 6.7). Phosphorus is in a +3 oxidation state, thus it is both a strong reducing agent (easily oxidized to +5 phosphoric acid/phosphate) and capable of disproportionation (disproportionating to phosphoric acid and phosphine PH3 upon heating to approximately 200℃). The pH bond in the molecule is reactive, participating in free radical addition (preparation of phosphite esters/phosphonic acids), and reactions with aldehydes, ketones, and amines (preparation of organophosphonic acids). It can also participate in coordination chemistry as a ligand in the P(OH)3 tautomer form. Storage must be airtight and moisture-proof, away from oxidants, and care must be taken to prevent the generation of phosphine gas when heated.
From the perspective of its mechanism of action, phosphorous acid plays an irreplaceable role due to its "+3 valence reducing property + pH bond activity + phosphonic acid chelating ability". The mechanism of action in different applications is as follows:
Phosphorus in phosphorous acid is in a +3 valence intermediate oxidation state, which is easily oxidized to +5 valence phosphoric acid/phosphate and releases electrons. It is the basis of reducing agent in processes such as electroless nickel plating, metal reduction, precious metal recovery, and antioxidant. Its reduction potential is also used to remove impurity metal ions.
The pH bond in the phosphorous acid molecule can undergo free radical addition and electrophilic addition: it reacts with formaldehyde and amines to produce organophosphonic acids such as aminotrimethylenephosphonic acid (ATMP), and reacts with olefins/alcohols to produce phosphite esters. The pH bond is the reaction center for the synthesis of organophosphorus compounds (water treatment agents, stabilizers, flame retardants).
Organophosphonic acids derived from phosphorous acid have multiple phosphonic acid functionalities and show strong chelating/complexing ability with metal ions such as Ca2+, Mg2+, and Fe3+. They are based on the chemical principle of scale inhibition and corrosion inhibition in water treatment, which can prevent the growth of scale crystal and disperse scale particles.
Lead phosphite (basic lead phosphite) and phosphite ester stabilizers: the former absorbs HCl released from PVC degradation and blocks ultraviolet light, while the latter chelates metal chloride catalysts such as ZnCl2 and prevents "zinc burning". The two work together to extend the thermal stability time of PVC and are an irreplaceable stabilization system for PVC processing.
When phosphorous acid (in the form of potassium phosphite) is applied to crops, phosphorus is absorbed by the plants in a +3 valence form, which can induce the plants to produce systemically acquired resistance (SAR) and directly inhibit the growth and development of oomycetes such as downy mildew and Phytophthora, thus achieving the dual function of "nutrition + disease resistance".
In summary, phosphorous acid is the "cornerstone of organophosphorus chemistry." Due to its reducing properties and pH bond activity, it is used in a wide range of fields, from PVC stabilization to scale inhibition in water treatment, from crop disease prevention to chemical nickel plating, from flame retardant additives to scientific research synthesis, spanning plastics, water treatment, agriculture, surface treatment, fine chemicals, and scientific research.
Phosphorous acid has applications in plastics, water treatment, agriculture, surface treatment, plastic additives, fine chemicals, scientific research, and other fields.
1.PVC heat stabiliser raw materials (core application in plastic industry)
Use areas: Processing of plastics and PVC products.
Matching products: Dibasic Lead Phosphite (heat stabiliser for PVC pipes/wires/cables/artificial leather), phosphite chelating auxiliary stabiliser (anti-"zinc burning"), and composite calcium-zinc stabiliser components.
Why it works for this: PVC decomposes at high temperature and produces HCl gas which accelerates degradation. Dibasic Lead Phosphite absorbs HCl and blocks ultraviolet light. Phosphite chelates can chelate with metal chloride catalysts such as ZnCl2. The synergistic effect of both greatly prolongs the heat stability time of PVC; it is an indispensable stabilising system for PVC pipes, cables, artificial leather and other products.
Application Fields: Water treatment and circulating water systems.
Related Products: Aminotrimethylene Phosphonic Acid (ATMP), Hydroxyethylidene Diphosphonic Acid (HEDP), Polyphosphonic Acid Scale and Corrosion Inhibitors, Boiler/Cooling Water Scale Inhibitors.
Why it works for this application: The P-H bond of phosphorous acid reacts with formaldehyde, amines and ketones to form organic phosphonic acids containing a number of phosphonic acid groups. These strongly chelate metal ions such as Ca2+, Mg2+, Fe3+ and thus prevent scale crystal growth, disperse scale particles and inhibit corrosion. It is one of the main components of scale and corrosion inhibitors used in waterworks, power plants and factory cooling water systems.
Areas of application: Surface Treatment & Electroplating Industry.
Related products: Electroless nickel plating bath reducing agent: Sodium hypophosphite (NaH2PO2) synthesis raw material; Electroless plating bath replenishing reducing agent.
Why it works for this purpose: Electroless nickel plating uses hypophosphite as a reducing agent to reduce Ni2+ and plate it on substrates. Phosphite (trivalent phosphorus) can be electrochemically reduced to hypophosphite. Phosphite in the plating bath is also part of the reduction/complexation balance, and thus is an important source of phosphorus for both the electroless nickel plating process and hypophosphite production.
Industries: Additives and flame retardants for plastics.
The corresponding products are phosphite flame retardants (e.g. triphenyl phosphite), auxiliary antioxidants (e.g. organic phosphite, Irgafos 168) and polymer processing stabilisers.
How it works for this purpose: Phosphite esterifies with phenols/alcohols to form organic phosphite. The phosphorus element promotes the formation of char, and inhibits gas-phase combustion (flame retardancy) during combustion. It can also decompose peroxides in the process and protect the primary antioxidant (auxiliary antioxidant). It is an important subsidiary raw material for flame retardancy and anti-aging of plastic and rubber products.
Application Fields: Fine Chemicals.
Corresponding Products: Organophosphorus compounds, phosphonate esters, other fine chemicals.
Why it is effective for this purpose: The P-H bond of phosphorous acid can participate in addition, esterification and phosphorylation reactions, forming the framework of fine chemicals. It is one of the most common phosphorus sources for preparation of fine chemicals containing organophosphorus compounds.
Applications: fine chemicals, hydrometallurgy, recovery of precious metals.
Related products: Reducing agents for metal ions, Reducing agents for recovery of precious metals (gold, silver, platinum group metals), Reducing systems for hydrometallurgical gold extraction from electronic wastes.
Why it works for this purpose: Phosphorous acid and trivalent phosphorus have reducing properties that can reduce the ions of precious metals to elemental metals for precipitation. It is used for hydrometallurgical recovery of precious metals such as gold, silver and platinum from electronic waste and spent catalysts. The reduction process is mild, controllable and the recovery rates are high.
Application Areas: Science research, test and education.
Related products: Phosphorous acid analytical grade / high purity reagent, phosphorus standard solution, reducing reagent for synthesis of organic compounds, P(OH)3 tautomer ligand research, synthesis of complexes.
Benefits of this application: Phosphorous acid is soluble, can be purified to high purity and its reactivity is well-defined. It is a commonly used analytical chemical reagent for determination of phosphorus, research on organophosphorus synthesis and research on coordination chemistry, and also a basic chemical raw material in universities and research institutes.
Application Areas: Chemical industry of phosphorus.
Related Products: Phosphite series (intermediate for plasticisers, stabilisers and flame retardants), phosphine/hypophosphite derivative systems, speciality phosphorus chemicals.
Reason for suitability for this application: Phosphite is an important raw material of trivalent phosphorus chemical system. It can obtain various phosphorus chemical products such as phosphites, hypophosphites and phosphates through esterification, disproportionation, oxidation and other reactions, and is an important intermediate in the phosphorus chemical industry chain.
In summary, phosphorous acid (H3PO3, CAS 13598-36-2) is the "cornerstone of organophosphorus chemistry." With its "+3 valence reducing properties, pH bond reactivity, and phosphonic acid chelating ability," it has mature applications in nine major sectors, including PVC heat stabilizers (basic lead phosphite/phosphite esters), organophosphoric acid water treatment agents (ATMP/HEDP), agricultural fungicides and phosphite fertilizers, chemical nickel plating reduction systems, plastic flame retardants and auxiliary antioxidants, fine chemicals, chemical reducing agents and precious metal recovery, analytical reagents and scientific research applications, and the synthesis of phosphorus-based chemicals. From plastic pipes, drinking water, and crop disease prevention to hardware plating, household flame retardants, and precious metal recovery, phosphorous acid has deeply penetrated daily life and industrial systems through downstream products.
