Cadmium Suboxide

There is good evidence for the existence of Cd₄O as an amorphous green powder, and of Cd₂O both as an amorphous green powder and as small yellow crystals.

March and obtained a green product, which he regarded as Cd₂O, by heating cadmium oxalate to the melting-point of lead. Since dilute acetic acid dissolved part of it and left a residue of metallic cadmium, subsequent workers regarded his product as a mixture of cadmium and its normal oxide, CdO.

According to Tanatar, amorphous green Cd₄O is formed when cadmium oxalate is carefully heated in an atmosphere of dry carbon dioxide, which is converted into a yellowish-brown mixture of cadmium and cadmic oxide by heating to the melting-point of the metal. Denham says that if the metallic cadmium, which is always formed during the reaction, is distilled off in vacuo, green amorphous Cd₄O is obtained, but it never amounts to more than 4 per cent, by weight of the original oxalate.

Tanatar and Levin obtained dark green Cd₃O₂ and Cd₂O by heating cadmium oxalate and cadmic oxide in appropriate proportions. Either oxide, when heated in the absence of air, was converted into a mixture of metal and normal oxide. Denham, using this method and finally distilling off metallic cadmium under reduced pressure, obtained some homogeneous green Cd₂O.

Hydrogen reduces heated cadmium oxide either to metal or to metal containing unchanged oxide.

When cadmium oxide is reduced by carbon monoxide in the heat, there is a distinct lessening of the velocity of reduction at a point corresponding to the formation of Cd₂O, but the lower oxide could not be isolated from this reaction.

When the compounds Cd₄Cl₇, Cd₄Br₇, or Cd₁₂I₂₃ are treated with water, the normal halogen compounds and cadmous hydroxide, CdOH, are produced. Minute yellow translucent crystals of Cd₂O are obtained by heating this cadmous hydroxide in a current of dry nitrogen. When strongly heated it gives a green mixture of cadmium and cadmic oxide, and it acts as a strong reducing agent towards acids. Denham could not convert more than 5 per cent, of the original chloride into suboxide.