Cupric phosphate (7798-23-4) Physical and Chemical Properties

Chemical Profile

Cupric phosphate

Inorganic copper(II) phosphate (Cu3(PO4)2) — a bluish‑green, insoluble metal phosphate supplied as a solid for use in formulations, catalysts, corrosion‑inhibiting applications and industrial feedstocks.

CAS Number	7798-23-4
Family	Metal phosphates (copper phosphate)
Typical Form	Powder or crystalline solid
Common Grades	EP

Used industrially as a fungicide precursor, catalyst or corrosion‑inhibiting additive and supplied for formulation, coating and feed‑additive processing; typical procurement and QA checks focus on hydration state, particle size and impurity profile. Handle with appropriate dust controls, PPE and environmental release precautions due to its irritant properties and potential aquatic toxicity.

Copper(II) phosphate is an inorganic ionic phosphate salt of copper belonging to the family of metal orthophosphates. Structurally it is a transition‑metal phosphate in which copper exists nominally in the +2 oxidation state coordinated to phosphate oxyanions; the solid exists in multiple hydrated and anhydrous forms (common formulae include variants such as \(\ce{Cu3O8P2}\) and hydrated species like \(\ce{Cu3(PO4)2.3H2O}\)). The lattice is dominated by ionic Cu–O and P–O interactions with significant oxide/oxyphosphate character, producing a crystalline, coloured solid (blue to bluish‑green) typical of many divalent copper salts.

Electronic features derive from partially filled 3d orbitals of \(\ce{Cu^2+}\), giving rise to characteristic blue/green optical absorption and the ability to participate in coordination chemistry (complexation with ammonia and other ligands) and redox‑catalytic behavior. As a phosphate salt, the anion ensemble can hydrolyse and protonate across pH ranges; however, the low aqueous solubility of the solid limits simple acid–base titration behavior in pure water. Cupric phosphate behaves classically as an inorganic, sparingly soluble metal salt: poorly soluble in cold water, more soluble in acidic media and in complexing/basic media (e.g., ammoniacal solutions), and thermally unstable with decomposition products that can include phosphorus oxides.

Common commercial grades reported for this substance include: EP.

Basic Physical Properties

Density

No experimentally established value for this property is available in the current data context.

Melting or Decomposition Point

No single melting point is reported for the anhydrous material in the current data context. Experimental descriptions indicate that cupric phosphate decomposes on heating rather than exhibiting a well‑defined melt; thermal decomposition can produce phosphorus oxides and other decomposition products and is described as hazardous (see Safety and Handling).

Solubility in Water

Reported experimental descriptions are consistent: cupric phosphate is essentially insoluble or only sparingly soluble in water. Typical qualitative statements include: - "Insoluble in cold water, slightly soluble in hot water." - The trihydrate form (\(\ce{Cu3(PO4)2.3H2O}\)) is reported as having limited solubility in water but dissolves in acids and ammoniacal solutions. Additional solvent behavior reported: - Soluble in mineral acids and in ammonium hydroxide (ammoniacal solution) due to protonation of phosphate and complexation of \(\ce{Cu^2+}\). - Slight solubility in acetone in some reports; insoluble in ethanol.

Mechanistic note: dissolution in acid proceeds by protonation of phosphate oxyanions and release of free \(\ce{Cu^2+}\) into solution, whereas dissolution in ammonia occurs via ligand complexation (formation of copper–ammine complexes), which markedly increases apparent solubility.

Solution pH (Qualitative Behavior)

As an undissolved solid dispersed in water, cupric phosphate will not establish a well‑defined solution pH because of its very low solubility. When the solid is dissolved or dispersed under conditions that increase solubility: - In acidic media the solution will be acidic due to the excess acid required to solubilize the phosphate and to protonate phosphate species. - In ammoniacal media the complexation of \(\ce{Cu^2+}\) by ammonia (e.g., formation of \(\ce{[Cu(NH3)4]^2+}\) species) occurs, producing basic to neutral ammine solutions depending on ammonia excess. - In neutral water the aqueous concentration of phosphate and copper ions is low and the pH of the bulk water will be determined by the matrix rather than the solid.

No single numeric solution pH value is available in the current data context.

Chemical Properties

Acid–Base Behavior

Cupric phosphate is an ionic salt of a polyvalent oxyanion (phosphate) and a divalent transition metal cation (\(\ce{Cu^2+}\)). The phosphate component (orthophosphate) can accept and donate protons across the conjugate series \(\ce{H3PO4 <-> H2PO4^- <-> HPO4^2- <-> PO4^3-}\) depending on pH; however, in the solid state the anion is present as coordinated orthophosphate/oxyphosphate units and does not behave as a freely mobile base. Practical acid–base behavior is therefore governed by solubility: acidification increases solubility by converting phosphate to protonated species, while strongly basic, complexing media (e.g., concentrated ammoniacal solutions) solubilize copper by ammine formation. The salt itself does not display Brønsted acidity in the solid state beyond the behavior of any coordinated proton(s) in hydrated forms.

Reactivity and Stability

• Stability: The solid is stable under normal ambient conditions but decomposes upon strong heating; decomposition is hazardous because it can emit phosphorus oxides and related toxic fumes.
• Chemical reactivity: Soluble in mineral acids and concentrated ammoniacal solutions; forms coordination complexes with ligands that complex \(\ce{Cu^2+}\) (e.g., \(\ce{NH3}\)), increasing solubility.
• Catalytic/incompatibility notes: Cupric ions are reported to catalyze decomposition of oxidants such as sodium hypobromite; cupric salts can promote oxidative or redox processes in susceptible reagents. Avoid contact with strong reducing agents or oxidant systems without assessment of reactivity.
• Hydrates: Hydrated forms (e.g., trihydrate) exist and can differ in crystal form and solubility from the anhydrous material.

Molecular and Ionic Parameters

Formula and Molecular Weight

• Molecular formula (computed): \(\ce{Cu3O8P2}\)
• Molecular weight (computed): 380.58

Additional computed parameters (as reported): Exact Mass 380.69382; Monoisotopic Mass 378.69563; Topological Polar Surface Area (TPSA) 173; Hydrogen Bond Donor Count 0; Hydrogen Bond Acceptor Count 8; Rotatable Bond Count 0; Heavy Atom Count 13; Formal Charge 0; Complexity 36.8.

Constituent Ions

• Primary metal cation: \(\ce{Cu^2+}\)
• Primary oxyanion: orthophosphate/oxyphosphate species (nominally \(\ce{PO4^3-}\) in simple stoichiometric terms, with protonation states depending on pH and hydration)
• Hydrated forms: crystalline hydrates such as \(\ce{Cu3(PO4)2.3H2O}\) are reported and alter stoichiometry and molecular weight for that phase.

Structural and chemical behaviour is governed by the interplay of \(\ce{Cu^2+}\) coordination chemistry and the multidentate, polyvalent phosphate oxyanions.

Identifiers and Synonyms

Registry Numbers and Codes

• CAS RN: 7798-23-4
• European Community (EC) number: 232-254-5
• UNII: N8NP6FR80R
• DSSTox Substance ID: DTXSID00872547
• InChIKey: GQDHEYWVLBJKBA-UHFFFAOYSA-H
• Other identifiers reported in the available annotations include historical/deprecated CAS 1913303-43-1.

Synonyms and Common Names

Common names and synonyms reported include (selection as supplied): Copper(II) phosphate; Cupric phosphate; Copper phosphate (3:2); Phosphoric acid copper(2+) salt (2:3); Tricopper diphosphate; Cu3O8P2; Copper (II) phosphate; Tricopper bis(orthophosphate); Cuprum Phosphoricum. The substance is also referenced under descriptive names for hydrated forms (e.g., copper(II) phosphate trihydrate).

Identifiers for structural descriptors (presented as provided): - SMILES: [O-]P(=O)([O-])[O-].[O-]P(=O)([O-])[O-].[Cu+2].[Cu+2].[Cu+2] (inline code)
- InChI: InChI=1S/3Cu.2H3O4P/c;;;21-5(2,3)4/h;;;2(H3,1,2,3,4)/q3*+2;;/p-6 (inline code)
- InChIKey: GQDHEYWVLBJKBA-UHFFFAOYSA-H (inline code)

Industrial and Commercial Applications

Functional Roles and Use Sectors

Reported functional roles include use as a fungicide (agricultural pesticide), catalyst in organic reactions, fertilizer component (source of copper micronutrient), emulsifier, corrosion inhibitor in phosphoric acid processing, metal surface protectant, and as a trace mineral additive in animal feed formulations. These roles reflect its properties as a sparingly soluble copper source that can act as a biocide (copper availability) and as a copper reservoir or catalyst where limited solubility and controlled release are desirable.

Typical Application Examples

• Agriculture: used in formulations for crop protection where copper ions provide fungicidal activity; selection depends on regulatory status and formulation performance.
• Feed additives: employed as a trace copper source in controlled‑release forms for veterinary or agricultural animal nutrition (formulation and dose controlled).
• Chemical manufacturing: used as a heterogeneous catalyst or catalyst precursor in organic synthesis where copper(II) species are required.
• Corrosion control: employed to inhibit corrosion in specific phosphoric acid process streams or metal treatments where copper phosphate films or coatings are desirable.

Manufacturing: common laboratory and industrial preparation methods include precipitation by reaction of copper(II) sulfate (or other soluble copper(II) salts) with soluble phosphate salts (e.g., diammonium hydrogen phosphate) under controlled conditions to yield the desired stoichiometric phase and particle morphology.

If a concise application summary is required beyond these general uses, product‑specific technical literature or formulation data should be consulted.

Safety and Handling Overview

Health and Environmental Hazards

• Hazard statements and effects reported include: causes skin irritation (H315) and serious eye damage (H318); very toxic to aquatic life with long‑lasting effects (H400, H410) in multiple notified classifications.
• Toxicity: copper salts can cause gastrointestinal and systemic effects if ingested in high doses; occupational inhalation of dusts or mists should be controlled. Reported acute oral fatal dose ranges for generic copper salts are noted in historical toxicology summaries (tens of grams), but toxic outcomes are dose‑dependent and matrix dependent.
• Target organs and mechanisms: copper accumulates in liver and can produce hepatotoxic effects when exposure exceeds physiological handling capacity; copper induces oxidative stress mechanisms and can interfere with sulfhydryl‑dependent enzymes.
• Exposure limits (reported for inorganic copper, as Cu): Recommended occupational exposure guidance includes values such as 1 mg/m3 (8‑hr TWA) for copper dusts and mists and related MAK/TLV/PEL values as shown in industrial hygiene compilations. Immediately Dangerous to Life or Health (IDLH) reported as 100 mg/m3 (as Cu) in some occupational references.
• Environmental hazard: cupric phosphate is classified as very toxic to aquatic organisms and should be prevented from entering waterways; disposal and runoff control are critical.

Storage and Handling Considerations

• Handling: minimize dust generation; use local exhaust ventilation for powder handling; implement appropriate respiratory protection, gloves, and eye protection to avoid inhalation and contact. Avoid ingestion and uncontrolled release to the environment.
• Storage: store in a cool, dry, well‑ventilated area in tightly closed containers; segregate from strong reducing agents and incompatible oxidants/organometallic reagents. Protect from conditions that could induce thermal decomposition.
• Fire/thermal decomposition: on heating the material decomposes and can emit toxic phosphorus oxides; fire responders should employ full protective equipment and breathing apparatus.
• Emergency and first aid: in case of exposure, follow standard decontamination procedures—flush eyes/skin with water, remove contaminated clothing, seek medical attention for ingestion or significant inhalation exposure. For detailed emergency treatment and antidotal care consult clinical toxicology resources and product SDS.
• Regulatory and disposal: disposal practices for copper‑containing wastes are subject to environmental regulations; avoid landfill or discharge without evaluation of copper content and local regulatory guidance. For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and local legislation.