Copper II complex salts, inner

Pale yellow inner complex copper sahcylaldoxime (II) is precipitated. The test for hydroxylamine based on this behavior, like (1), consists therefore in the formation of an inner complex salt from its components. A stock mixture of salicylaldehyde and copper acetate cannot be used as a reagent, because, depending upon the concentration, a green copper salt of salicylaldehyde separates after short or long standing. The reagents must be added separately to the solution in the prescribed order, and concentrations. 

Rubeanic acid (I) reacts in ammoniacal solution in its aci-form (II) with copper, cobalt and nickel salts giving insoluble colored compounds (see page 329). In solutions containing strong mineral acid, rubeanic acid reacts only with certain elements of the platinum group. With palladium and platinum salts, red crystalline precipitates are obtained they are inner complex salts (III) of a semi-aci-form of rubeanic acid. Ruthenium salts give a soluble blue compound, whose structure is not known. 

Salicylaldoxime (I) gives a yellow-greenish precipitate of the inner complex copper salicylaldoxime (II) with acetic acid solutions of copper salts. 

In view of its constitution, Alizarin Blue (I) might be expected to display the characteristics of alizarin (page 96) and 8-hydroxyquinoline (page 335). This is not the case, as shown by the facts that it is neither soluble in alkali as is alizarin nor in dilute acids as is oxine. Probably Alizarin Blue is a chelate compound as represented in (la). Solutions can be prepared in dioxane, pyridine, acetic anhydride, concentrated sulfuric acid. These solutions react with strongly acid solutions of copper salts to produce a com-flower-blue crystalline precipitate, whose constitution as an inner complex compound is shown in (II). 

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