Copper(I) Chloride
Properties
| State | Solid (white powder when pure) |
| Color | White (pure); gray-green (oxidized surface) |
| Solubility | Slightly soluble in water (0.047 g/L at 25°C); soluble in HCl, NH3 solutions |
| Melting Point | 423°C |
| Boiling Point | 1490°C |
About Copper(I) Chloride
Copper(I) chloride is interesting because Cu(I) shouldn't really exist in water — the Cu⁺ ion disproportionates to Cu²⁺ + Cu⁰ as soon as you put it in solution, with an equilibrium constant around 10⁶ in favor of products. CuCl gets around this by being only sparingly soluble (0.047 g/L at 25°C) and by forming the linear CuCl₂⁻ complex when chloride is in excess, which is why CuCl dissolves readily in concentrated HCl but barely at all in pure water. Pure CuCl is white with a zinc-blende structure, but you almost never see it pure — it picks up O₂ from air within minutes, and the surface Cu²⁺ species turn the powder gray-green. The Sandmeyer reaction (ArN₂⁺ + CuCl → ArCl + N₂ + Cu) is the classical use: it's how chlorine gets onto an aromatic ring when direct electrophilic chlorination won't give the right regiochemistry, and it goes through a single-electron-transfer mechanism with Cu(I)/Cu(II) shuttling. CuCl also shows up as the chloride source in the Wacker process, paired with PdCl₂, where it reoxidizes Pd(0) back to Pd(II) so the catalytic cycle for ethylene → acetaldehyde keeps turning. The Cu(I)–CO complex is strong enough that CuCl in concentrated HCl will selectively absorb CO from gas mixtures — old gas analysis kits exploited this.
Where you'll encounter it
If you've ever run a Sandmeyer in an undergrad lab, the off-white powder you weighed out was CuCl, and the bottle probably had a green tinge from oxidation. In practice you almost always make it fresh by reducing CuCl₂ with sodium sulfite or copper metal in HCl, because old bottles are mostly Cu(II) on the outside. In industry, CuCl shows up in Wacker process plants making acetaldehyde from ethylene, and in ammoniacal CuCl solutions used historically to absorb CO from synthesis gas streams.
Common Uses
- Sandmeyer reaction catalyst converting aryl diazonium salts to aryl chlorides via single-electron transfer
- Co-catalyst with PdCl₂ in the Wacker process for ethylene oxidation to acetaldehyde
- Selective absorbent for CO in gas analysis via the linear Cu(I)–CO complex
- Source of Cu(I) for click-chemistry style copper-mediated couplings under inert atmosphere
- Lewis-acid catalyst for atom-transfer radical polymerization (ATRP) initiator systems
- Chloride source in the Deacon process oxidation of HCl back to Cl₂
- Reagent for converting aryl Grignards to aryl-aryl coupled biphenyls
- Dehydration catalyst in selected isomerization reactions of allyl alcohols
Safety Information
Toxic if swallowed (LD50 oral rat ~140 mg/kg). GHS: H302 (harmful if swallowed), H400/H410 (very toxic to aquatic life with long-lasting effects). Copper dust exposure limits are reckoned as Cu, not as the salt. Not regulated as a strong carcinogen but copper salts at gram-scale exposure cause serious GI distress and hemolysis. The bigger handling issue is air-oxidation: store under N₂ or argon, and discard greenish material. Dissolves with HCl evolution if it contacts strong acid in the trash, so neutralize before disposal.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.