Complex cupric tetrammine

The solution of the precipitate cannot be attributed to increase in hydroxide-ion concentration, because sodium hydroxide does not cause it, nor to ammonium ion. because ammonium salts do not cause it. There remains undissociated NH4OH or NH3, which might combine with the cupric ion. It has in fact been found that the new deep blue ion species formed by addition of an excess of ammonium hydroxide is the cupric ammonia complex Cu(N 1 3)4similar to the hydrated cupric ion except that the four water molecules have been replaced by ammonia molecules. This complex is sometimes called the cupric tetrammine complex, the word ammine meaning an attached ammonia molecule. 

Salts of this complex ion can be crystallized from ammonia solution. The best known one is cupric tetrammine sulfate monohydrate, Cu(NH3)4S04-HoO, which has the same deep blue color as the solution. 

Forms cupric hydroxide, Cu(OH)2 with CUSO4 the precipitate, however, dissolves in excess ammonia, forming a tetrammine copper (II) complex ion. 

Catalysis by Cu(NH3)4S04 has been examined by Nikolev (98) who found a maximum rate at pH 8.5 to 9.0. The reaction is strictly first order in peroxide up to 0.25 M peroxide but decreases to zero order at 0.5 M. Addition of ammonium hydroxide at first increases the rate but ultimately depresses it, an effect also noted by Bobtelsky and Kirson (99). Unfortunately the experiments are not very extensive, and it is impossible to separate the effect of ammonia in complexing from the effect of the accompanying pH increase. Information on the relative activities of the complexes with various amounts of coordinated ammonia would be interesting. The only indication from this work is that the depressing effect of high ammonia concentrations supports the authors view that the hexammine probably formed in these conditions is less active than the tetrammine. One other point of interest is that it seems probable that radicals are formed in the reaction, possibly in conjunction with a cupric ammine-cuprous ammine redox system, since organic substances can be oxidized by the cuprammonium-peroxide mixtures. 

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