Copper oxidation reactions

We should note that any reduction reaction is necessarily also an oxidation We showed the copper oxide reaction above to emphasise that the CuO was reduced by the hydrogen, but by the same token the hydrogen is oxidised by the CuO. Each donor is always matched by an acceptor. It takes two to tango. 

Using the electron transfer definition, many more reactions can be identified as redox (reduction-oxidation) reactions. An example is the displacement of a metal from its salt by a more reactive metal. Consider the reaction between zinc and a solution of copper(If) sulphate, which can be represented by the equation... 

Metals. Transition-metal ions, such as iron, copper, manganese, and cobalt, when present even in small amounts, cataly2e mbber oxidative reactions by affecting the breakdown of peroxides in such a way as to accelerate further attack by oxygen (36). Natural mbber vulcani2ates are especially affected. Therefore, these metals and their salts, such as oleates and stearates, soluble in mbber should be avoided. 

Nucleophilic Reactions. Useful nucleophilic substitutions of halothiophenes are readily achieved in copper-mediated reactions. Of particular note is the ready conversion of 3-bromoderivatives to the corresponding 3-chloroderivatives with copper(I)chloride in hot /V, /V- dim ethyl form am i de (26). High yields of alkoxythiophenes are obtained from bromo- and iodothiophenes on reaction with sodium alkoxide in the appropriate alcohol, and catalyzed by copper(II) oxide, a trace of potassium iodide, and in more recent years a phase-transfer catalyst (27). 

The oxidation reaction between butadiene and oxygen and water in the presence of CO2 or SO2 produces 1,4-butenediol. The catalysts consist of iron acetylacetonate and LiOH (99). The same reaction was also observed at 90°C with Group (VIII) transition metals such as Pd in the presence of I2 or iodides (100). The butenediol can then be hydrogenated to butanediol [110-63-4]. In the presence of copper compounds and at pH 2, hydrogenation leads to furan (101). 

Sihcon carbide is comparatively stable. The only violent reaction occurs when SiC is heated with a mixture of potassium dichromate and lead chromate. Chemical reactions do, however, take place between sihcon carbide and a variety of compounds at relatively high temperatures. Sodium sihcate attacks SiC above 1300°C, and SiC reacts with calcium and magnesium oxides above 1000°C and with copper oxide at 800°C to form the metal sihcide. Sihcon carbide decomposes in fused alkahes such as potassium chromate or sodium chromate and in fused borax or cryohte, and reacts with carbon dioxide, hydrogen, ak, and steam. Sihcon carbide, resistant to chlorine below 700°C, reacts to form carbon and sihcon tetrachloride at high temperature. SiC dissociates in molten kon and the sihcon reacts with oxides present in the melt, a reaction of use in the metallurgy of kon and steel (qv). The dense, self-bonded type of SiC has good resistance to aluminum up to about 800°C, to bismuth and zinc at 600°C, and to tin up to 400°C a new sihcon nitride-bonded type exhibits improved resistance to cryohte. 

Oxidation. Carbon monoxide can be oxidized without a catalyst or at a controlled rate with a catalyst (eq. 4) (26). Carbon monoxide oxidation proceeds explosively if the gases are mixed stoichiometticaHy and then ignited. Surface burning will continue at temperatures above 1173 K, but the reaction is slow below 923 K without a catalyst. HopcaUte, a mixture of manganese and copper oxides, catalyzes carbon monoxide oxidation at room temperature it was used in gas masks during World War I to destroy low levels of carbon monoxide. Catalysts prepared from platinum and palladium are particularly effective for carbon monoxide oxidation at 323 K and at space velocities of 50 to 10, 000 h . Such catalysts are used in catalytic converters on automobiles (27) (see Exhaust CONTHOL, automotive). 

Other special additions are used to deoxidize copper. Such alloys may be preferred in appHcations where embrittlement by hydrogen through reaction with internally dispersed copper oxide particles is a concern, such as in CllO. The most common deoxidized copper is C122, in which phosphoms reacts with copper oxide to form phosphoms pentoxide that can be slagged from the copper while molten. 

The production of copper from sulphide minerals is accomplished with a preliminary partial roast of die sulphides before reaction widr air in the liquid state, known as mattes, to form copper metal (conversion). The principal sources of copper are minerals such as chalcopyrite, CuFeSa and bornite CuaFeSa, and hence the conversion process must accomplish the preferential oxidation of non, in the form of FeO, before the copper metal appears. As mentioned before, tire FeO-SiOa liquid system is practically Raoultian, and so it is relatively easy to calculate the amount of iron oxidation which can be canned out to form this liquid slag as a function of the FeO/SiOa ratio before copper oxidation occurs. The liquid slag has a maximum mole fraction of FeO at the matte blowing temperatures of about 0.3, at solid silica saturation. 

This synthesis is only one example of a wide range of reactions which involve aryl (or alkyl) radical addition to electron-deficient double bonds resulting in reduction.The corresponding oxidative reaction using aryl radicals is the well known Meerwein reaction, which uses copper(II) salts. 

To exploit the energy produced in this reaction, the half reactions are separated. The oxidation reaction is carried out at a zinc electrode (Zn Zir + 2 electrons) and the reduction reaction is carried out at a copper electrode (Cu"" + 2 electrons Cu metal). Electrons flow through a metal wire from the oxidizing electrode (anode) to the reducing electrode (cathode), creating electric current that can be harnessed, for example, to light a tungsten bulb. 

A salt bridge serves as an ionconducting connection between the two half-cells. When the external circuit is closed, the oxidation reaction starts with the dissolution of the zinc electrode and the formation of zinc ions in half-cell I. In half-cell II copper ions are reduced and metallic copper is deposited. The sulfate ions remain unchanged in the aqueous solution. The overall cell reaction consists of an electron transfer between zinc and copper ions ... 

There are few studies in the literature on the kinetics and mechanism of oxidation over base metal oxides. Blumenthal and Nobe studied the oxidation of CO over copper oxide on alumina between 122 and 164°C. They reported that the kinetics is first order with respect to CO concentration, and the activation energy is 20 kcal/mole (77). Gravelle and Teichner studied CO oxidation on nickel oxide, and found that the kinetics is also first order with respect to CO concentration (78). They suggested that the mechanism of reaction is by the Eley-Rideal mechanism... 

Copper oxide, oxidation of CO over, 86 Coupled heterogeneous catalytic reactions, kinetics of, 1-49, see also Kinetics coupling through catalytic surface, 9-13 experimental studies, 22-49 apparatus and procedure, 25, 26 catalysts, 26-28... 

NOTE Cupric copper (Cu2+) is a catalyst for the hydrazine-oxygen reaction, as well as a catalyst for sulfite, DEHA, erythorbic acid, and hydroquinone. Cuprous copper (Cu+) acts as a complexing agent in the desirable formation of protective, pasivated copper oxide films. 

Table 14.2 lists the principal copper-oxide complexes now under development and their properties. The CVD reactions used to deposit these materials are described in Ch. 11. 

In addition to a-additions to isocyanides, copper oxide-cyclohexyl isocyanide mixtures are catalysts for other reactions including olefin dimerization and oligomerization 121, 125, 126). They also catalyze pyrroline and oxazoline formation from isocyanides with a protonic a-hydrogen (e.g., PhCH2NC or EtOCOCHjNC) and olefins or ketones 130), and the formation of cyclopropanes from olefins and substituted chloromethanes 131). The same catalyst systems also catalyze Michael addition reactions 119a). 

It was found that the value of F, is markedly increased by ions which are effective catalysts of oxidation reactions of peroxydisulphate. These are silver(I) copper(n), and iron(III). Cobalt(II) and nickel(II) ions, although they are good catalysts for the decomposition of hydrogen peroxide, exert their effect merely as inert electrolytes in the induced reaction. Therefore it can be concluded that, in this process, activation of the rather less reactive 8203 is more important than that of hydrogen peroxide . ... 

In the present study, we report the synthesis, characterisation and catalytic properties (in selective oxidation reactions) of copper acetate, copper tetradecachlorophthalocyanine and copper tetranitrophthalocyanine encapsulated in molecular sieves Na-X, Na-Y, MCM-22 and VPI-5. Both molecular oxygen and aqueous HjOj have been used as the oxidants. The... 

The CuO + H2S reaction caused an accident, which was blamed on either reaction (9) or (10) catalysed by copper oxide. The comparison of the IR risk degrees makes it probable that the second interpretation is the most plausible. 

---