Aqueous cuprous-cupric solutions

Since the oxidation of aqueous cuprous-cupric solutions is well-known... 

A bottle of cuprous chloride solution prepared by standing cupric chloride in strong hydrochloric acid over excess copper burst on standing. In the presence of some complexing agents, copper can react with aqueous media to form hydrogen. Slow pressurisation by this means explains the above explosion (Editor s comments). The metal is also known to dissolve in cyanides and some amine solutions. 

An interesting process for the production of acetaldehyde was based on the work of F. C. Phillips, who showed that ethylene could be oxidized to acetaldehyde by an aqueous palladium chloride solution. The palladium chloride was reduced to metallic palladium. During the late 1950 s, Wacker Chemie introduced a new process for the manufacture of acetaldehyde by direct oxidation of ethylene with air. The palladium metal was converted back to (PdCU) by an acidic solution of cupric chloride, which was, itself, reduced to cuprous chloride. The cupric chloride was regenerated by reaction with air in hydrochloric acid solution. The reaction sequence is shown in the following equations ... 

Metallic Derivatives, (a) Cuprous Acetylide. CujCg. Prepare an ammoniacal solution of cuprous chloride by first adding dilute ammonia to 2-3 ml. of dilute copper sulphate solution until the initial precipitate just redissolves and a clear deep-blue solution is obtained now add an aqueous solution of hydroxylamine hydrochloride drop by drop with shaking until the solution becomes first green and then completely colourless, the cupric salt being thus reduced to the cuprous derivative. 

The palladium chloride process for oxidizing olefins to aldehydes in aqueous solution (Wacker process) apparendy involves an intermediate anionic complex such as dichloro(ethylene)hydroxopalladate(II) or else a neutral aqua complex PdCl2 (CH2=CH2)(H2 0). The coordinated PdCl2 is reduced to Pd during the olefin oxidation and is reoxidized by the cupric—cuprous chloride couple, which in turn is reoxidized by oxygen, and the net reaction for any olefin (RCH=CH2) is then... 

K has the value of about 1 x 10 at 298 K, and in solutions of copper ions in equilibrium with metallic copper, cupric ions therefore greatly predominate (except in very dilute solutions) over cuprous ions. Cupric ions are therefore normally stable and become unstable only when the cuprous ion concentration is very low. A very low concentration of cuprous ions may be produced, in the presence of a suitable anion, by the formation of either an insoluble cuprous salt or a very stable complex cuprous ion. Cuprous salts can therefore exist in contact with water only if they are very sparingly soluble (e.g. cuprous chloride) or are combined in a complex, e.g. [Cu(CN)2) , Cu(NH3)2l. Cuprous sulphate can be prepared in non-aqueous conditions, but because it is not sparingly soluble in water it is immediately decomposed by water to copper and cupric sulphate. 

The +1 state of copper is found only in complex compounds or slightly soluble compounds. The reason for this is that in aqueous solution cuprous ion is unstable with respect to disproportionation to copper metal and cupric ion. This comes about because cuprous going to cupric is a stronger reducing agent than copper going to cuprous. The following exercise in the use of E° puts this on a more quantitative basis ... 

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. 

In addition to water, a variety of organic liquids, including amines, carboxylic acids, and hydrocarbons, have been used as solvents in the study of the homogeneous reactions of hydrogen with metal salts. In general, there is more uncertainty about the nature of the species present in such systems than in aqueous solution and, correspondingly, it is usually more difficult to elucidate the reaction mechanisms in detail. The most extensive solvent effect studies have been made on cupric, cuprous, and silver salts. A number of the more important results are considered below. 

The high reactivity of the cuprous species, relative to that of the cupric species, is in marked contrast to the properties of the corresponding ions in aqueous solution. 

The deactivation of cupric (and cuprous) heptanoate by further com-plexing with heptanoate contrasts with the effect of acetate complexing in aqueous solution. The reasons for this, as well as for the previous observation, are not clear. 

No activation of hydrogen by the cupric species can be detected. It is not possible, however, to rule out activities of the order of those exhibited by cupric salts in aqueous or heptanoic acid solution, since these would probably be masked by the very high activity of the cuprous species in this system. 

The stabilities of the triammino-cuprous halides are almost identical, and the dissociation pressures of the ammino-cupric halides lie very near together.6 The stabilities of hexammino-copper halides is also almost identical the compounds are very readily decomposed by water, and hence do not seem to be formed in aqueous solution. Ammino-derivatives of cupric carbonate, cupric acetate, cupric oxide, and cuprous cyanide and thiocyanate are known. These have the general characteristics of the ammines already described. 

As in the case of ferric chloride, cupric chloride is only incompletely reduced by sulphur dioxide in concentrated hydrochloric acid solution, but in aqueous solution this forms an excellent method for the preparation of cuprous chloride ... 

Recently Halpern and Dakers 16) studied the reduction of cupric acetate in aqueous solution. They found, as did Ipatieff and Werchowsky 12), that the reaction takes place at relatively moderate temperatures and hydrogen pressures with the formation of cuprous oxide under certain conditions. Halpern and Dakers found that the reduction of cupric ion does not require an added catalyst and that the activation of hydrogen proceeds homogeneously in solution. 

Chloroprene (boiling point 59.4°C, density 0.9583) is, chemically, a chlorovinyl ester of hydrochloric acid and can be manufactured by polymerizing acetylene to vinyl acetylene using a weak solution containing ammonium chloride (NH4C1), cuprous chloride (Cu2Cl2), and potassium chloride (KC1) as catalyst. The off-gas from the reactor has its water condensed out and is then fractionated. Aqueous hydrochloric acid at 35 to 45 °C is then reacted with the vinyl acetylene in the presence of cupric chloride to give chloroprene (2-chloro-l,3-butadiene). 

Accurate self-consistent thermochemical data for the copper chlorides up to 200°C are required, in order to improve solubility calculations and electrochemical modelling capabilities for Aspen Plus and OLI software. Experimental work has been initiated at the University of Guelph, Canada and UOIT to determine a comprehensive thermochemical database, for solubility limits of OMIT, and aqueous cupric chloride versus chloride concentration and temperature using UV-VIS spectroscopy (Suppiah, 2008). The chloride ion is obtained by adding LiCl OMIT. The conditions of tests are primarily 25-200°C, up to 20 bars. Specialised equipment for this task is needed to reach elevated temperatures and pressures, because cupric chloride is chemically aggressive, and because changes in the solution concentrations must be made precisely. A titanium test cell has been custom made, including a UV-VIS spectrometer with sapphire windows, HPLC pumps and an automated injection system. The data acquired will be combined with past literature data for the cuprous chloride system to develop a self-consistent database for the copper (I) and copper (II) chloride-water systems. 

In water, the cuprous ion, Cu+, may not exist in appreciable quantities, for it disproportionates (dismutates) into the cupric ion, Cu2+, and copper metal. Certain very slightly dissociated complexes of univalent copper (for example, Cu(CN)J3 and CuClJ") are stable in aqueous solutions and relatively insoluble cuprous compounds (for example, CuCl, and CU2O) may survive in the presence of water if strong oxidizing agents are not also present. The iodide, Cul, and sulfide, Cu2S, are particularly stable. Aside from the instability of the hydrated Cu+ ion, the chemistry of univalent copper is quite similar to that of univalent silver. 

Identification Add a few drops of a 1 20 aqueous solution to 5 mL of hot alkaline cupric tartrate TS. A copious red precipitate of cuprous oxide forms. 

HydroCopper A process for leaching copper from sulfide ores, using dilute aqueous cupric chloride. The copper is precipitated from the leach solution by sodium hydroxide, and the precipitated cuprous oxide is reduced to the metal by hydrogen. An intergrated chlor-alkali cell provides the sodium hydroxide and hydrogen. Planned for demonstration in Finland in 2003. 

Besides these two main classes of copper compounds, there appear to be other types of copper derivatives, among them oxides of the formulae Cu40, CusO, Cu203, and Cu02. The cuprous ion, Cu, corresponds with the cuprous compounds, which are colourless in aqueous solution. The cupric ion, Cu, corresponds with the cupric compounds, which have a blue, green, violet, yellow, or brown colour in solution. 

Sulphur dioxide precipitates the chloride from an aqueous solution of cupric sulphate and sodium chloride. After being washed with dilute sulphurous acid, and then glacial acetic acid, the salt can be dried by the aid of heat.4 The reduction of a solution of cupric chloride, with formation of cuprous chloride, can also be-effected by means of phosphorous acid.5... 

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