Aluminium amalgam

Aluminium amalgam is a solution of <a href="/facts/Aluminium/7wmR8jYE">aluminium</a> in mercury. In practice the term refers to particles or pieces of aluminium with a surface coating of the amalgam. A gray solid, it is typically used for <a href="/facts/Organic_reduction/6DdmXG4S">organic reductions</a>. It is written as Al(Hg) in reactions. 
Al(Hg) may be prepared by either grinding aluminium pellets or wire in mercury, or by allowing aluminium wire to react with a solution of <a href="/facts/Mercury(II)_chloride/aUAKsq6a">mercury(II) chloride</a> in water.
This amalgam is used as a chemical <a href="/facts/Reagent/c3GLInCu">reagent</a> to <a href="/facts/Redox/Pyd5RVcj">reduce</a> compounds, such as of <a href="/facts/Imine/yK72z07j">imines</a> to <a href="/facts/Amine/JvfYJfP6">amines</a>. The aluminium is the ultimate electron donor, and the mercury serves to mediate the electron transfer and to remove passivating oxide.
The reaction and the waste from it contains mercury, so special safety precautions and disposal methods are needed. As an <a href="/facts/Environmentally_friendlier/cc9zhfHV">environmentally friendlier</a> alternative, <a href="/facts/Hydride/v2rlBGMg">hydrides</a> or other reducing agents can often be used to accomplish the same synthetic result. An alloy of aluminium and <a href="/facts/Gallium/EucevDs9">gallium</a> was proposed as a method of hydrogen generation, as the gallium renders the aluminium more reactive by preventing it from forming an oxide layer. Mercury has this same effect on aluminium, but also serves additional functions related to electron transfer that make aluminium amalgams useful for some reactions that would not be possible with gallium.

Aluminium amalgam open-in-new

Aluminium amalgam