Copper displacement reactions

Rates of debromination of bromonitro-thiophenes and -selenophenes with sodium thio-phenoxide and sodium selenophenoxide have been studied. Selenophene compounds were about four times more reactive than the corresponding thiophene derivatives. The rate ratio was not significantly different whether attack was occurring at the a- or /3-position. As in benzenoid chemistry, numerous nucleophilic displacement reactions are found to be copper catalyzed. Illustrative of these reactions is the displacement of bromide from 3-bromothiophene-2-carboxylic acid and 3-bromothiophene-4-carboxylic acid by active methylene compounds (e.g. AcCH2C02Et) in the presence of copper and sodium ethoxide (Scheme 77) (75JCS(P1)1390). 

The extrapolation of physical attributes of substances to the submicroscopic level of representation was evident when students explained the changes in the displacement reaction between zinc powder and aqueous copper(II) sulphate. The decrease in intensity of the blue colour of the solution was attributed by 31% of students to the removal of blue individual Cu + ions from aqueous solution. The suggestion that individual Cu + ions (the submicroscopic level) are blue may be indicative of the extrapolation of the blue colour of the aqueous copper(II) sulphate (the macroscopic level) to the colour of individual Cu + ions (the submicroscopic level). Thirty-one percent of students also suggested that reddish-brown, insoluble individual atoms of copper were produced in this chemical reaction, again suggesting extrapolation of the bulk properties of copper, i.e., being reddish-brown and insolnble in water (the macroscopic level), to individual copper atoms having these properties (the snbmicroscopic level). 

When a strip of zinc metal is added to a solution of copper(II) sulfate, the blue color slowly fades, and the zinc metal is replaced by copper metal (Figure 4-13). As copper ions in the solution are reduced to copper metal, zinc atoms are oxidized to Zn cations. This is an example of a metal displacement reaction, in which a metal ion in solution (Cu ) is displaced by another metal (Zn) by means of a redox reaction. Figure 4-13 also shows molecular views of this displacement reaction. 

Many other metal displacement reactions can be visualized, but not all of them occur. Some metals are oxidized readily, but others are highly resistant to oxidation. Likewise, some metal cations are highly susceptible to reduction, but others resist reduction. Zinc displaces copper ions from aqueous solutions, but copper will not replace zinc ions, because Cu is easier to reduce than Zn . Zinc will not displace ions, because... 

The electrons that are being lost by the zinc metal are the same electrons that are being gained by the copper(II) ion. The zinc metal is being oxidized and the copper(II) ion is being reduced. Further discussions on why reactions such as these occur can be found in the section on single-displacement reactions later in this chapter. 

Copper(n) sulfate, CUSO4, reacts with sodium hydroxide, NaOH, in a double displacement reaction. A precipitate of copper(n) hydroxide, Cu(OH)2, and aqueous sodium sulfate, Na2S04, is produced. 

In your previous chemistry course, you compared the reactivities of metals. You may recall that, when a piece of zinc is placed in an aqueous solution of copper(II) sulfate, the zinc displaces the copper in a single displacement reaction. This reaction is shown in Figure 10.1. As the zinc dissolves, the zinc strip gets smaller. A dark red-brown layer of solid copper forms on the zinc strip, and some copper is deposited on the bottom of the beaker. The blue colour of the solution fades, as blue copper(ll) ions are replaced by colourless zinc ions. 

You have seen that the single displacement reaction of zinc with copper(II) sulfate is a redox reaction, represented by the following chemical equation and net ionic equation. 

Compound 26, likewise, undergoes a series of displacement reactions (Scheme 34). Whereas reaction with copper(I) cyanide replaces only one chlorine atom to yield 136, all are displaced by reactions with ammonia and isopropylamine, diethyl(trimethylsilyl)amine, water, and thiols to give, respectively, 137-140. Some additional transformations are also shown. 

The use of lithium aluminum hydride gives slightly lower yields and probably involves a displacement reaction by hydride ion. The zinc-copper couple technique probably involves formation of an organozinc intermediate. Sodium, magnesium, and aluminum metal may be used to replace the zinc-copper couple [59a, b]. These organometal intermediates react with aldehydes and... 

The scope of the copper promoted nucleophilic displacement reactions on heterocyclic systems is not limited to nitrogen, oxygen and phosphorous nucleophiles. Buchwald and co-workers demonstrated that the same catalyst system that is efficient in carbon-phosphorous bond formation is also the... 

The lithium-copper oxide cell is voltage compatible (OCV = 1.5 V), i.e. it may be used as a direct replacement for conventional Leclanche or alkaline zinc cells. CuO has a particularly high volumetric capacity (4.2 Ah/cm3) so that cells are characterized by high specific energy -300 Wh/kg (700 Wh/dm3). The discharge curve shows a single step which may be attributed to the simple displacement reaction ... 

Many metals, such as zinc, iron, lead, copper, and aluminum are found chemically bonded to oxygen in nature. Sometimes, chemists can use single displacement reactions to get the pure metal. 

In a displacement reaction, a more reactive metal will displace a less reactive metal from a solution of its salt. Zinc is above copper in the reactivity series. 

This experiment allows you to carry out the sequential conversion of copper metal to copper(II) nitrate to copper(II) hydroxide to copper(II) oxide to copper(II) sulfate and back to copper metal. This conversion is carried out using synthesis, decomposition, single displacement, and double displacement reactions. 

Q O Copper can be recovered from scrap metal by adding sulfuric acid. Soluble copper sulfate is formed. The copper sulfate then reacts with metallic iron in a single displacement reaction. To simulate this reaction, a student places 1.942 g of iron wool in a beaker that contains 136.3 mL of 0.0750 mol/L aqueous copper(II) sulfate. What mass of copper is formed ... 

An alternative mechanism for conjugate addition to a,j8-unsaturated ketones is a free-radical chain process in which copper(I) would serve as the metallic center in a radical displacement reaction. However, the Li(RjCu) ------------------------ R- (93)... 

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