Commercially anhydrous chromium(III) chloride may be prepared by chlorination of chromium metal directly, or indirectly by chlorination of chromium(III) oxide in the presence of carbon at 800 °C, with carbon monoxide as a side-product:
Cr2O3 + 3 C + 3 Cl2 → 2 CrCl3 + 3 CO
It may also be prepared by treating the hexahydrate with thionyl chloride.
In laboratory it's usually prepared by dissolving the elemental chromium or chromium(III) oxide in hydrochloric acid.
However, it is also a chloro complex which is quite inert to substitution, so in fact it is ordinarily quite unreactive. Slow reaction rates are common with chromium(III) complexes in general. The low reactivity of the d3 Cr3+ ion can be explained using crystal field theory. One way of opening CrCl3 up to substitution in solution is to reduce even a trace amount to CrCl2, for example using zinc in hydrochloric acid. This chromium(II) compound undergoes substitution easily, and it can exchange electrons with CrCl3 via a chloride bridge, allowing all of the CrCl3 to react quickly.
Read More: Chromium chloride price
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