Complex cupric ammonia

If copper is present in the boiler FW (normally as the cupric ammonia complex ion), boiler surfaces are directly attacked by electrolytic reduction. In strongly alkaline conditions the ferrous ion is present as ferrous hydroxide [Fe(OH)2] ... 

Cupric ammonia complex ion corrosion Resulting plated copper acts as cathode to surrounding anodic boiler steel, inducing corrosion. 

An ion which contains several atoms, such as the sulfate ion, SO4 is called a complex ion. Familiar examples of complex ions other than those of the oxygen acids are the deep blue cupric ammonia complex ion, Cu(NH3)4++, which is formed by adding ammonium hydroxide... 

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 NH OH or NHg, 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is the cupric ammonia complex Cu(NH3)4+, similar to the hydrated cupric ion except thar the four water molecules have been replaced by ammonia molecules. This complex is sometimes called the cupric tetrammlne complex the word ammine meaning an attached ammonia molecule. 

The reason that the precipitate of cupric hydroxide dissolves in an excess of ammonium hydroxide can be given in the following way. A precipitate of cupric hydroxide is formed because the concentration of cupric ion and the concentration of hydroxide ion are greater than the alues corresponding to the solubility product of cupric hydroxide. If there were some way for copper to be present in the solution without exceeding the solubility product of cupric hydroxide then precipitation would not occur. In the presence of ammonia, copper exists in the solution not as the cupric ion (that is, the hydrated cupric ion), but principally as the cupric ammonia complex Cu(NHg)4++. This complex is far more stable than the hydrated cupric ion. The reaction of formation of the cupric ammonia complex is... 

An inorganic molecule that contains several atoms, including one or more metal atoms, is called an inorganic complex or coordination compound. An example is nickel tetracarbonyl, Ni(CO)4. An inorganic complex with an electric charge is called a complex ion. Familiar examples of complex ions are the ferrocyanide ion, Fe(CN)e - the ferricyanide ion, Fe(CN)e the hydrated aluminum ion, A1(H20)6, and the deep blue cupric ammonia complex ion, Cu(NH3)4 +, which is formed by adding ammonium hydroxide to a solution of cupric salt. Complex ions are important in the methods of separation used in qualitative and quantitative chemical analysis and in various industrial processes. 

We see from the equation for the reaction that the addition of ammonia to the solution causes the equilibrium to shift to the right, more of the cupric ion being converted into cupric ammonia complex as more and more ammonia is added to the solution. When sufficient ammonia is present a large amount of copper may exist in the solution as cupric ammonia complex, at the same time that the cupric ion concentration is less than that required to cause precipitation of cupric hydroxide. When ammonia is added to a solution in contact with the precipitate of cupric hydroxide, the cupric ion in the solution is converted to cupric ammonia... 

Although this reaction may cause slight problems, the primary issue concerning ammonia is ammoniacal corrosion of CR system metals where oxygen is present and the pH is over 8.3. Under these circumstances, copper and its alloys and other nonferrous metals are attacked, and severe damage results due to the formation of a stable cupric ammonium complex ion. 

Copper forms practically aU its stable compounds in -i-l and +2 valence states. The metal oxidizes readily to -i-l state in the presence of various com-plexing or precipitating reactants. However, in aqueous solutions +2 state is more stable than -i-l. Only in the presence of ammonia, cyanide ion, chloride ion, or some other complexing group in aqueous solution, is the +1 valence state (cuprous form) more stable then the +2 (cupric form). Water-soluble copper compounds are, therefore, mostly cupric unless complexing ions or molecules are present in the system. The conversion of cuprous to cupric state and metalhc copper in aqueous media (ionic reaction, 2Cu+ — Cu° -i- Cu2+) has a Kvalue of 1.2x106 at 25°C. 

To explain this phenomenon we might postulate the formation of a complex ion, remembering the solubility of cupric hydroxide and nickel hydroxide in ammonium hydroxide with formation of ammonia complexes. This is indeed the explanation the complex ion which is formed is the rincate ion, Zn(OH)4, by the reaction... 

Nikolev also measured the relative catalytic properties of a series of complexes of cupric ion with aliphatic amines. These are less effective than the ammonia complexes and among themselves show a variation of about a hundred-fold in their efficiencies. However no account was taken of the relative stability of the complexes under the experimental conditions, and since also oxidation of the organic amine compounds probably occurs it is doubtful whether the results give a true picture of the relative reactivities of the compounds. 

All coppei -nickel catalysts were prepared from the magnetically pure copper which was itself completely inactive in the hydrogenation of benzene under the conditions described below. Cupric hydroxide was precipitated from a nitrate solution by dilute ammonium hydroxide solution so that the supernatant liquid was faintly colored by the copper-ammonia complex. The precipitate was filtered and washed. Nickel nitrate in water solution was now added in the proportion desired, and the mixture was stirred to a paste of even consistency. It was dried at 95°, ignited at 180° for 36 hours, and finally at 400° for 20 hours. The oxide mixture was reduced in purified hydrogen at 150° for 20 hours. Most finished catalysts contained 1.0 per cent of nickel. 

In addition, the synthetic cupric tetraammine complex of cellulose (CACC) can be used to depress gangue mineral in the flotation of nickel ore. The proportion of cellulose to copper to ammonia is 1 0.4 2.5. 

Aqueous ammonia also acts as a base precipitating metallic hydroxides from solutions of their salts, and in forming complex ions in the presence of excess ammonia. For example, using copper sulfate solution, cupric hydroxide, which is at first precipitated, redissolves in excess ammonia because of the formation of the complex tetramminecopper(TT) ion. 

As feed systems usually contain copper alloys, the use of amines for their protection may seem somewhat strange as copper is prone to attack in ammonia/carbon dioxide/oxygen environments, with the formation of complex cupric or cuprous compounds. The requisite degree of protection can be achieved, however, by maintaining the concentrations strictly within the acceptable target range. 

Complexing, using a complexing agent such as thiourea or ammonia, for example, to remove mixtures of cuprous oxide, cupric oxide, and plated copper metal. 

An alternate procedure used in a few specialty applications is the cuprammonium process. This involves stabilization of cellulose in an ammonia solution of cupric oxide. Solubilization occurs by complex formation of cupric ion with ammonia and the hydroxyl groups of cellulose. Regeneration of cellulose, after formation of the desired products, is accomplished by treatment with acid. The main application of the cuprammonium process is for the synthesis of films and hollow fibers for use in artificial kidney dialysis machines. The cuprammonium process yields products with superior permeability and biocompatibility properties compared to the xanthation process. Less than 1% of all regenerated cellulose is produced by the cuprammonium process. 

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

The valency of the complex radicle is the same as that of the central metallic atom when the complex contains only ammonia, substituted ammonia, water, or other neutral group. For example, cobalt in eobaltie. salts is trivalent, and the cobalt complex with ammonia, Co(NI13)8 ", is likewise trivalent copper in cupric sulphate is divalent, and the copper complex, [Cu(NH3)4] , is also divalent. In the same wn.y [Co(NH3)5.H30] " and [Co(NII3)4.(II20)2] " are trivalent, as also [Co(NH3)2.en2]" and [Co.en3] ", where en represents cthyleucdiamine, CH NH2... 

Ammino-cupric Bromides.—Cupric bromide, like euprie chloride, absorbs ammonia gas, forming complex ammino-compounds. The following ammines of cupric bromide have been described Hexammino-cupric bromide, [Cu(NH3)6]Br2 pentammino-cupric bromide, [Cu(NH3)5]Br2 diammino-cupric bromide, [Cu(NTI3)2]Br2 and decammino-tricupric bromide, [Cu3(NH3)10]Br8. 

---