CuCl react with acetylenes to form the explosive copper(I) acetylide, Cu2C2. Alkene complexes o can be prepared by reduction of CuCl2 by sulfur dioxide in the presence of the alkene in alcohol solution. Complexes with dienes such as 1,5-cyclooctadiene are particularly stable: In absence of other ligands, its aqueous solutions are unstable with respect to disproportionation: 2 CuCl → Cu + CuCl2 In part for this reason samples in air assume a green coloration. Uses The main use of copper(I) chloride is as a precursor to the fungicide copper oxychloride. For this purpose aqueous copper(I) chloride is generated by comproportionation and then air-oxidized: Cu + CuCl2 → 2 CuCl 4 CuCl + O2 + 2 H2O → Cu3Cl2(OH)4 + CuCl2 Copper(I) chloride catalyzes a variety of organic reactions, as discussed above. Its affinity for carbon monoxide in the presence of aluminium chloride is exploited in the COPureSM process. In organic synthesis CuCl is used with carbon monoxide, aluminium chloride, and hydrogen chloride in the Gatterman-Koch reaction to form benzaldehydes. In the Sandmeyer reaction. Treatment of an arenediazonium salt with CuCl leads to an aryl chloride, for example: The reaction has wide scope and usually gives good yields. Early investigators observed that copper(I) halides catalyse 1,4-addition of Grignard reagents to alpha,beta-unsaturated ketones led to the development of organocuprate reagents that are widely used today in organic synthesis: This finding led to the development of organocopper chemistry. For example, CuCl reacts with methyllithium (CH3Li) to form "Gilman reagents" such as (CH3)2CuLi, which find extensive use in organic synthesis. Grignard reagents form similar organocopper compounds. Although other copper(I) compounds such as copper(I) iodide are now more often used for these types of reactions, copper(I) chloride is still recommended in some cases: Here, Bu indicates an n-butyl group. Without CuCl, the Grignard reagent alone gives a mixture of 1,2- and 1,4-addition products (i.e., the butyl adds at the C closer to the C=O). Copper(I) chloride is also an intermediate formed from copper(II) chloride in the Wacker process. In polymer chemistry CuCl is used as a catalyst in Atom Transfer Radical Polymerization (ATRP). Niche uses Copper(I) chloride is also used in pyrotechnics as a blue/green coloring agent. In a flame test, copper chlorides, like all copper compounds, emit green-blue. Natural occurrence Natural form of CuCl is the rare mineral nantokite. References External links National Pollutant Inventory – Copper and compounds fact sheet The COPureSM Process