Copper 8-hydroxyquinoline is the copper salt of a chelating ligand, and that structure explains almost everything about it: why it is far gentler on plant tissue than inorganic copper, why it stays in a coating instead of leaching out, and why its chloride limit is written to two decimal places. This guide covers the chemistry, both application routes, the regulatory questions a buyer has to answer before ordering, and how to read the specification. The parameter table is on the copper 8-hydroxyquinoline product page.
Identity and properties
| Property | Value | Practical significance |
|---|---|---|
| Chemical name | Bis(8-hydroxyquinolinato)copper(II); copper oxinate; copper quinolinolate | Two ligand molecules per copper ion |
| CAS | 10380-28-6 | – |
| Formula / molecular weight | C18H12CuN2O2 / about 352 | Copper is roughly 18% of the molecule by mass – the number behind the dose calculations |
| Appearance | Yellow-green crystalline powder | Visually distinct from the blue of inorganic copper salts, which makes it a useful identity check on receipt |
| Water solubility | Essentially insoluble | Applied as a dispersion, not a solution |
| Organic solubility | Sparingly soluble in organic solvents | Compatible with solvent-borne coating systems to a degree |
| Stability | Stable in normal storage; decomposes in strong acid | Do not formulate with strongly acidic components – the ligand is released |
| Copper availability | Slow, because the copper is chelated | The core of its behaviour compared with inorganic copper |
The chelate is the point
In an inorganic copper spray the copper is present largely as free or loosely bound ions. That is effective and it is also why inorganic copper burns young tissue: the same availability that kills the fungus also stresses the plant. Chelation changes the delivery profile.
| Aspect | Inorganic copper (hydroxide, oxychloride, Bordeaux) | Copper 8-hydroxyquinoline |
|---|---|---|
| Copper form at application | Largely free ionic copper | Chelated, released gradually |
| Phytotoxicity | Significant; leaf burn, fruit marking, particularly in cool wet weather | Substantially lower |
| Use rate | Higher, and constrained by annual copper caps | Lower per unit of copper, which matters where copper loading is limited |
| Rain fastness | Depends on the formulation; inorganic copper can wash off | Good, because the active is insoluble and retained |
| Cost per kilogram | Lower | Higher – the reason inorganic copper still dominates by volume |
| Where it is chosen | Mature tissue, high disease pressure, cost-sensitive programmes | Sensitive crops, young tissue, programmes near their copper limit |
How it acts
| Mechanism | What it means in practice |
|---|---|
| Copper ion interferes with microbial enzyme systems and protein function | Broad-spectrum, non-selective activity against fungi and bacteria |
| The ligand increases uptake into microbial cells relative to free copper | Activity at lower total copper than an inorganic salt would need |
| Action is protective rather than curative | Application timing before infection is what matters – it is a protectant, not a rescue treatment |
| Insoluble deposit resists Rain | Residual protection on the leaf surface |
| Slow release limits plant damage | Lower phytotoxicity, but also a slower knockdown than a soluble copper salt |
Agricultural use
| Point | Detail |
|---|---|
| Formulation types | Wettable powder and suspension concentrate are the common forms; the powder is insoluble by design |
| Target spectrum | Fungal and bacterial disease on fruit, vegetables and field crops – the specific crops and rates are set by the registration, not by the raw material |
| Application | Protectant sprays timed to infection periods; coverage and reapplication interval drive performance |
| Compatibility | Generally compatible in tank mixes, but check against alkaline and strongly acidic partners – acid releases the ligand |
| Resistance management | Copper is multi-site and not prone to single-point resistance, which is part of its continued value in programmes |
Industrial preservation
| Application | Why the chelate helps | Formulation constraint |
|---|---|---|
| Paints and renders | Insoluble and non-leaching, so protection persists through weathering | Must be compatible with the binder and with co-biocides; colour contribution must be acceptable |
| Flexible PVC and polymers | Thermally stable in processing and effective at low loadings | Processing temperature ceiling; dispersion quality |
| Textiles and leather | Fixes to the substrate rather than washing out | Application bath compatibility and effluent treatment |
| Timber | Fixes in the wood, resisting leaching | Penetration and fixation chemistry |
| Antifouling coatings | Controlled copper release at the surface | Registration and discharge rules differ sharply between markets |
Reading the specification
| Parameter | Limit | What it is controlling |
|---|---|---|
| Content | 98% min | Chelated copper content – the basis for dosing and for the label claim |
| Chloride (Cl) | 0.01% max | The tightest limit on the sheet, and for good reason. Chloride is the classic cause of leaf burn with copper sprays, and in coatings it drives corrosion of the substrate. A 0.01% figure means the manufacturer has washed the product properly |
| Sulphate (SO4) | 0.1% max | Residual from the copper salt used to make the chelate; affects formulation stability and contributes to phytotoxicity |
| Loss on drying | 0.5% max | Moisture affects dispersibility in wettable powders and the assay basis |
| Appearance | Yellow-green crystal powder | Brown or dull cast indicates free copper or degraded ligand |
The chloride limit is the parameter that separates a properly made agricultural grade from a cheaper one. If a supplier cannot report chloride at 0.01%, the material is unlikely to be suitable for foliar use on sensitive crops.
Regulatory position
| Framework | What applies | What the buyer must confirm |
|---|---|---|
| Pesticide registration | Agricultural use requires registration in the destination market; the label defines crops, rates, intervals and protective equipment | That the product is registered for your crop and market. Availability of the raw material does not create a lawful use |
| Biocidal products | Industrial preservation uses are regulated as biocidal products in many markets | The product type and whether an authorisation exists for that use |
| Copper loading caps | Several markets limit total copper applied per hectare per year | Whether chelated copper counts towards the cap in your market, and how the rate is calculated |
| Organic certification | Copper compounds are restricted, not freely permitted, in organic systems | Whether this specific compound is listed by your certifier – check, do not assume |
| Transport | Classified as a hazardous substance for transport in many jurisdictions | The classification and packaging your market applies |
We supply the technical material, not the registration. We make no efficacy claims and give no agronomic advice. What may be claimed on a label, and how the product may be applied, is defined by the registration held by the marketing authorisation holder in each market. Declare the destination and end use at enquiry so the documentation can be matched to it.
Buying notes
| Item | What to fix in writing |
|---|---|
| Content and chloride | 98% min and 0.01% max – these two define the grade |
| Sulphate and moisture | 0.1% and 0.5% maximum, with the methods |
| Particle size | For wettable powder use, the distribution affects suspension stability – specify it if you mill or blend |
| Grade statement | Technical or agricultural grade, and the registration status in the destination |
| Packaging | 25 kg drum or sack with PE liner; confirm liner integrity on arrival |
| Documentation | Batch COA, SDS, and any registration support documents available for the market |
Frequently asked questions
Is copper 8-hydroxyquinoline the same as copper oxychloride or Bordeaux mixture?
No. Those are inorganic copper products where the copper is largely free at application. This is a chelate, which releases copper slowly – lower phytotoxicity, lower use rate, higher cost per kilogram.
Why is the chloride limit so tight at 0.01%?
Because chloride causes leaf burn on sensitive crops and corrosion in coatings. A low chloride figure is direct evidence of proper washing after the copper salt is reacted with the ligand.
Can it be used in organic production?
Copper compounds are restricted rather than freely allowed in organic systems, and whether a specific chelate is listed depends on the certifier and the market. Confirm with your certification body before planning a programme.
Is it curative or protective?
Protective. It forms an insoluble deposit that interferes with fungal and bacterial development on the plant surface, so timing ahead of infection is what determines performance.
Why does it cost more than inorganic copper?
Because the ligand and the chelation step cost more than a simple copper salt, and the product delivers activity at a lower copper loading. The comparison that matters is cost per hectare per season, not cost per kilogram.