Aluminium can form an amalgam in solution with mercury. Aluminium amalgam may be prepared by either grinding aluminium pellets or wire in mercury, or by allowing aluminium wire to react with a solution of mercury(II) chloride in water.This amalgam is used as a chemical reagent to reduce compounds, such as the reduction of imines to amines.
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The aluminium is the ultimate electron donor, and the mercury serves to mediate the electron transfer.The reaction itself and the waste from it contain mercury, so special safety precautions and disposal methods are needed.
As an environmentally friendlier alternative, hydrides or other reducing agents can often be used to accomplish the same synthetic result. Another environmentally friendly alternative is an alloy of aluminium and gallium which similarly renders the aluminium more reactive by preventing it from forming an oxide layer.
Aluminum is normally protected by a thick oxide layer, but the formation of the amalgam disrupts it. It allows fresh aluminum to react with air to form white aluminum oxide. As the oxide grows, it forms as these cool white fibers.