Cuprous ions

Because the solution is capable of absorbing one mole of carbon monoxide per mole of cuprous ion, it is desirable to maximize the copper content of the solution. The ammonia not only complexes with the cuprous ion to permit absorption but also increases the copper solubiUty and thereby permits an even greater carbon monoxide absorption capacity. The ammonia concentration is set by a balance between ammonia vapor pressure and solution acidity. Weak organic acids, eg, formic, acetic, and carbonic acid, are used because they are relatively noncorrosive and inexpensive. A typical formic acid... 

The preferred ratio of cuprous to cupric ion ranges from 5 1 to 10 1, depending on system conditions. Too high a concentration of cuprous ion causes the system to disproportionate and form metallic copper (eq. 26) ... 

Copper (I) (cuprous) ion serves as a catalyst for both the photochemical darkening and thermal fading reactions (1). Therefore, a smaU amount of cuprous ion is normally added to the glass batch. 

The darkening reaction involves the formation of silver metal within the silver haUde particles containing traces of cuprous haUde. With the formation of metallic silver, cuprous ions are oxidized to cupric ions (1,4). The thermal or photochemical (optical bleaching) reversion to the colorless or bleached state corresponds to the reoxidation of silver to silver ion and the reduction of cupric ion to reform cuprous ion. 

CUPROUS ION-CATALYZED OXIDATIVE CLEAVAGE OF AROMATIC o-DIAMINES BV OXYGEN [(Z,Z)-2,4-HEXADIENEDINITRILE]... 

Concern for the conservation of energy and materials maintains high interest in catalytic and electrochemistry. Oxygen in the presence of metal catalysts is used in CUPROUS ION-CATALYZED OXIDATIVE CLEAVAGE OF AROMATIC o-DIAMINES BY OXYGEN (E,Z)-2,4-HEXADIENEDINITRILE and OXIDATION WITH BIS(SALI-CYLIDENE)ETHYLENEDIIMINOCOBALT(II) (SALCOMINE) 2,6-DI-important industrial method, is accomplished in a convenient lab-scale process in ALDEHYDES FROM OLEFINS CYCLOHEXANE-CARBOXALDEHYDE. An effective and useful electrochemical synthesis is illustrated in the procedure 3,3,6,6-TETRAMETHOXY-1,4-CYCLOHEX ADIENE. ... 

House investigated the role of cuprous ions in the conjugate addition of organometallic reagents. He found that the catalytic effect can be explained by the intervention of a methyl copper derivative, which reacts rapidly with the carbon-carbon double bonds of the conjugated system. 

Several substituted pyridines have been examined using the degassed Raney nickel, and the results are summarized in Table I. As all the biaryls obtained formed colored chelates with either ferrous or cuprous ions, they must be derivatives of 2,2 -bipyridine. Structural ambiguities cannot arise with 2,2 -bipyridines derived from 2- and 4-substituted pyridines but 3-substituted pyridines could conceivably give three isomeric 2,2 -bipyridines (e.g., 3, 4, 5). In fact, however, each 3-substituted pyridine so far examined has given only one 2,2 -bipyridine. 

The allylic position of olefins is subject to attack by free radicals with the consequent formation of stable allylic free radicals. This fact is utilized in many substitution reactions at the allylic position (cf. Chapter 6, Section III). The procedure given here employs f-butyl perbenzoate, which reacts with cuprous ion to liberate /-butoxy radical, the chain reaction initiator. The outcome of the reaction, which has general applicability, is the introduction of a benzoyloxy group in the allylic position. 

Copper is the first member of Group IB of the periodic table, having atomic number 29 and electronic configuration 2.8.18.1. Loss of the outermost electron gives the cuprous ion Cu, and a second electron may be lost in the formation of the cupric ion Cu. ... 

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. 

Little work has been carried out on the mechanism of inhibition of the corrosion. of copper in neutral solutions by anions. Inhibition occurs in solutions containing chromate , benzoate or nitrite ions. Chloride ions and sulphide ions act aggressively. There is evidence that chloride ions can be taken up into the cuprous oxide film on copper to replace oxide ions and create cuprous ion vacancies which permit easier diffusion of cuprous ions through the film, thus increasing the corrosion rate. 

These figures furnish a handy summary of solubility behavior. We see from Figure 10-5A that few chlorides have low solubilities. The few that do contain cations of metals clustered toward the right side of the periodic table (silver ion, Ag+, cuprous ion, Cu+, mercurous ion, HgJ2, and lead ion, Pb+2) but they do not fall in a single column. This irregularity is not un-... 

Expression (25) indicates that cuprous chloride dissolves, according to reaction (25), until the molar concentrations of cuprous ion and chloride ion rise enough to make their product equal to 3.2 X 10-7. 

Now is the time to dust off the algebra and put it to work. Suppose we designate the solubility of cuprous chloride in water by a symbol, s. This symbol s equals the number of moles of solid cuprous chloride that dissolve in one liter of water. Remembering equation (23), we see that s moles of solid cuprous chloride will produce s moles of cuprous ion, Cu+, and s moles of chloride ion, Cl-. Hence these concentrations must be equal, as shown below. 

The reaction between ferric ion, Fe+3, and cuprous ion, Cu+, to produce ferrous ion, Fe+2, and cupric ion, Cu+2, is plainly an oxidation-reduction reaction ... 

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 ... 

From the first of the two reactions shown, it can be seen that in the acid cleaning solution the cupric ion (Cu2+) is formed from cupric oxide. The thiourea component then reduces the cupric ion to the cuprous ion (Cu+) and, in a series of reactions, complexes it, essentially preventing the cupric ion from ultimately plating out as copper. 

Apart from generating the cupric ion, the acidic oxidation reaction (loss of electrons) produces cuprous ion as an intermediate from any cuprous oxide that may be present in the deposit. It is therefore neces-... 

Localized deposits containing copper and copper oxides demand a high local concentration of thiourea, and if an inadequate excess of thiourea is present to complex the cuprous ion, precipitation of the insoluble, white copper-thiourea monochloride salt may occur. 

Kochi (1956a, 1956b) and Dickerman et al. (1958, 1959) studied the kinetics of the Meerwein reaction of arenediazonium salts with acrylonitrile, styrene, and other alkenes, based on initial studies on the Sandmeyer reaction. The reactions were found to be first-order in diazonium ion and in cuprous ion. The relative rates of the addition to four alkenes (acrylonitrile, styrene, methyl acrylate, and methyl methacrylate) vary by a factor of only 1.55 (Dickerman et al., 1959). This result indicates that the aryl radical has a low selectivity. The kinetic data are consistent with the mechanism of Schemes 10-52 to 10-56, 10-58 and 10-59. This mechanism was strongly corroborated by Galli s work on the Sandmeyer reaction more than twenty years later (1981-89). 

As discussed in Section 10.3, the system consisting of a diazonium ion and cuprous ions can be used for hydroxy-de-diazoniation at room temperature in the presence of large concentrations of hydrated cupric ions (Cohen et al., 1977 see Schemes 10-7 to 10-9). With (Z)-stilbene-2-diazonium tetrafluoroborate under these conditions, however, the major product of ring closure of the initially formed radical was phenanthrene (64%). When the cupric nitrate was supplemented by silver nitrate the yield increased to 86% phenanthrene. Apparently, the radical undergoes such rapid ring closure that no electron transfer to the cupric ion takes place. 

Despite its synthetic importance, the mechanism of the copper-quinoline method has been studied very little, but it has been shown that the actual catalyst is cuprous ion. In fact, the reaction proceeds much faster if the acid is heated in quinoline with cuprous oxide instead of copper, provided that atmospheric oxygen is rigorously excluded. A mechanism has been suggested in which it is the cuprous salt of the acid that actually undergoes the decarboxylation. It has been shown that cuprous salts of aromatic acids are easily decarboxylated by heating in quinoline and that arylcopper compounds are intermediates that can be isolated in some cases. Metallic silver has been used in place of copper, with higher yields. ... 

The first step involves a reduction of the diazonium ion by the cuprous ion, which results in the formation of an aryl radical. In the second step, the aryl radical abstracts halogen from cupric chloride, reducing it. The CuX compound is regenerated and is thus a true catalyst. 

Nitro compounds can be formed in good yields by treatment of diazonium salts with sodium nitrite in the presence of cuprous ion. The reaction occurs only in neutral or alkaline solution. This is not usually called the Sandmeyer reaction, although, like 14-25, it was discovered by Sandmeyer. The BFJ ion is often used as the negative ion to avoid competition from the chloride ion. The mechanism is probably like that... 

Another procedure which has adequate sensitivity for determining the glucose in 1 microliter of serum of filtrate, is the method which uses copper reduction, and subsequently determination of the cuprous ion with a suitable reagent (15) However, one must be careful that one has obtained complete precipitation, for, if uric acid or any other impurities remain, false high values will be obtained. This would result in disaster for the hypoglycemic infant. To uncover this condition is often one of the major reasons for doing this test. 

The kinetics in aqueous solution are more complex than those for the aldehydes . Initial rates indicate the reaction order in Cu(II) to be one-half and an approximately first-order dependence on chloride ion was noted cuprous ion retards reaction. The mechanism proposed includes dimerisation of CuClj which is not a feature of other reactions of this oxidant. 

At high cuprous ion concentrations the reaction becomes zero-order in reduc-and is determined by the rate of passage of O2 from the gaseous to... 

The cupric ions formed react further with metallic copper to form cuprous ions ... 

In the manufacture of printed circuit boards, the unwanted copper is etched away by acid solutions of cupric chloride (Equation 1.1). As the copper dissolves, the effectiveness of the solution tails and it must be regenerated. The traditional way of doing this is to oxidize the cuprous ion produced with acidified hydrogen peroxide. During the process the volume of solution increases steadily and the copper in the surplus liquor is precipitated as copper oxide and usually landfilled. 

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