Copper , as oxidant

II. Ascorbic acid and copper as oxidation catalysts. J. Lipid Res. 10, 561-567. 

Haase, G., Dunkley, W.L. 1969b. Ascorbic acid and copper in linoleate oxidation. II. Ascorbic acid and copper as oxidation catalysts. J. Lipid Res. 10, 561-567. 

Wet methods of extraction are applied to low-grade ores containing not less than 0-25 to 1 per cent, of copper, or to products containing copper associated with gold and silver. For ores containing copper as oxide or carbonate, the solvents employed are sulphuric acid, hydrochloric acid, and ferrous chloride. 

Copper can also be used as a catalyst, like nickel, alone, on carriers, or as a mixed catalyst with metals of the first to the eighth Group of the Periodic Table. The temperature needed for reduction of the catalyst, usually containing the copper as oxide, hydroxide, or basic carbonate, is 150-300°. Preparation of a copper-kieselguhr catalyst is similar to that of a nickel-kieselguhr catalyst.175... 

The C-H/C-H coupling of protected indoles with unactivated arenes takes place using air and copper as oxidants (eq 153). A mixture of C-2 and C-3 arylation is obtained, and the ratio is dependent on the protecting group employed. Benzofuran and its derivatives participate in a similar oxidative coupling under similar reaction conditions.Later, it was demonstrated that switching from acetic acid to 1,4-dioxane as the solvent, selective C-2 arylation could be obtained when Cu(OAc)2 was the oxidant in contrast, use of AgOAc as the oxidant favored arylation at the C-3 position. 

Copper(l) sulphate, CU2SO4, is obtained as a white powder by heating together dimethyl sulphate and copper(I) oxide ... 

The formation of a red precipitate of copper(I) oxide by reduction of Cu(II) is taken as a positive test for an aldehyde Carbohydrates that give positive tests with Benedict s reagent are termed reducing sugars... 

Oxidation with Benedict s reagent (Section 25 19) Sugars that con tain a free hemiacetal function are called reducing sugars They react with copper(ll) sulfate in a sodium citrate/sodium carbonate buffer (Benedict s reagent) to form a red precipitate of copper(l) oxide Used as a qualitative test for reducing sugars... 

However, compounds known to be double oxides in the solid state are named as such for example, Cr2Cu04 (actually Cr203 CuO) is chromium(III) copper(II) oxide (and not copper chromite). 

The equilibrium is more favorable to acetone at higher temperatures. At 325°C 97% conversion is theoretically possible. The kinetics of the reaction has been studied (23). A large number of catalysts have been investigated, including copper, silver, platinum, and palladium metals, as well as sulfides of transition metals of groups 4, 5, and 6 of the periodic table. These catalysts are made with inert supports and are used at 400—600°C (24). Lower temperature reactions (315—482°C) have been successhiUy conducted using 2inc oxide-zirconium oxide combinations (25), and combinations of copper-chromium oxide and of copper and silicon dioxide (26). 

Copper. Some 15 copper compounds (qv) have been used as micronutrient fertilizers. These include copper sulfates, oxides, chlorides, and cupric ammonium phosphate [15928-74-2] and several copper complexes and chelates. Recommended rates of Cu appHcation range from a low of 0.2 to as much as 14 kg/hm. Both soil and foHar appHcations are used. 

This reaction is first conducted on a chromium-promoted iron oxide catalyst in the high temperature shift (HTS) reactor at about 370°C at the inlet. This catalyst is usually in the form of 6 x 6-mm or 9.5 x 9.5-mm tablets, SV about 4000 h . Converted gases are cooled outside of the HTS by producing steam or heating boiler feed water and are sent to the low temperature shift (LTS) converter at about 200—215°C to complete the water gas shift reaction. The LTS catalyst is a copper—zinc oxide catalyst supported on alumina. CO content of the effluent gas is usually 0.1—0.25% on a dry gas basis and has a 14°C approach to equihbrium, ie, an equihbrium temperature 14°C higher than actual, and SV about 4000 h . Operating at as low a temperature as possible is advantageous because of the more favorable equihbrium constants. The product gas from this section contains about 77% H2, 18% CO2, 0.30% CO, and 4.7% CH. ... 

Aromatic rings in lignin may be converted to cyclohexanol derivatives by catalytic hydrogenation at high temperatures (250°C) and pressures (20—35 MPa (200—350 atm)) using copper—chromium oxide as the catalyst (11). Similar reduction of aromatic to saturated rings has been achieved using sodium in hquid ammonia as reductants (12). 

Low molecular weight poly(l,3-phenylene oxide) [25190-64-1] has been prepared from the sodium salt of y -chlorophenol with copper as a catalyst... 

Production and Economic Aspects. Thallium is obtained commercially as a by-product in the roasting of zinc, copper, and lead ores. The thallium is collected in the flue dust in the form of oxide or sulfate with other by-product metals, eg, cadmium, indium, germanium, selenium, and tellurium. The thallium content of the flue dust is low and further enrichment steps are required. If the thallium compounds present are soluble, ie, as oxides or sulfates, direct leaching with water or dilute acid separates them from the other insoluble metals. Otherwise, the thallium compound is solubilized with oxidizing roasts, by sulfatization, or by treatment with alkaU. The thallium precipitates from these solutions as thaUium(I) chloride [7791 -12-0]. Electrolysis of the thaUium(I) sulfate [7446-18-6] solution affords thallium metal in high purity (5,6). The sulfate solution must be acidified with sulfuric acid to avoid cathodic separation of zinc and anodic deposition of thaUium(III) oxide [1314-32-5]. The metal deposited on the cathode is removed, kneaded into lumps, and dried. It is then compressed into blocks, melted under hydrogen, and cast into sticks. 

The catalytic activity of copper as an oxidant can be inhibited by the use of a metal deactivator such as N,1S7-disahcyhdene-l,2-diaminopropane (31) at a concentration of 5—10 ppm. 

High pressure processes P > 150 atm) are catalyzed by copper chromite catalysts. The most widely used process, however, is the low pressure methanol process that is conducted at 503—523 K, 5—10 MPa (50—100 atm), space velocities of 20, 000-60,000 h , and H2-to-CO ratios of 3. The reaction is catalyzed by a copper—zinc oxide catalyst using promoters such as alumina (31,32). This catalyst is more easily poisoned than the older copper chromite catalysts and requites the use of sulfiir-free synthesis gas. 

The U.S. Department of Energy has funded a research program to develop the Hquid-phase methanol process (LPMEOH) (33). This process utilizes a catalyst such as copper—zinc oxide suspended in a hydrocarbon oil. The Hquid phase is used as a heat-transfer medium and allows the reaction to be conducted at higher conversions than conventional reactor designs. In addition, the use of the LPMEOH process allows the use of a coal-derived, CO-rich synthesis gas. Typical reactor conditions for this process are 3.5—6.3 MPa (35—60 atm) and 473—563 K (see Methanol). 

The fixed-bed catalyst is a siUca-based extmdate containing precipitated iron oxide promoted with potassium and copper. The catalyst is activated by hydrogen reduction of most of the iron cataly2ed by small amounts of copper. As the catalyst is used, additional reduction occurs and Hagg carbide [12127 5-6] Fe C2, is formed. 

Copper(I) oxide [1317-39-1] is 2lp-ty e semiconductor, Cu2 0, in which proper vacancies act as acceptors to create electron holes that conduct within a narrow band in the Cu i7-orbitals. Nickel monoxide [1313-99-17, NiO, forms a deficient semiconductor in which vacancies occur in cation sites similar to those for cuprous oxide. For each cation vacancy two electron holes must be formed, the latter assumed to be associated with regular cations ([Ni " h = Semiconduction results from the transfer of positive charges from cation to cation through the lattice. Conduction of this type is similar... 

Hydrometallurigcal Processes. In hydrometaHurgical processes, metal values and by-products are recovered from aqueous solution by chemical or electrolytic processes. Values are solubilized by treating waste, ore, or concentrates. Leaching of copper ores in place by rain or natural streams and the subsequent recovery of copper from mnoff mine water as impure cement copper have been practiced since Roman times. Most hydrometaHurgical treatments have been appHed to ores or overburden in which the copper was present as oxide, mixed oxide—sulfide, or native copper. PyrometaHurgical and hydrometaHurgical processes are compared in Reference 34. 

HydrometaHurgical processes for copper can be categorized as (/) acid extraction of copper from oxide ore (2) oxidation and solution of sulfides in waste rock from mining, concentrator tailings, or in situ ore bodies (J) dissolution of copper in concentrates to avoid conventional smelting and (4) extraction of copper from deep-sea manganese nodules. 

Coppet(II) oxide [1317-38-0] CuO, is found in nature as the black triclinic tenorite [1317-92-6] or the cubic or tetrahedral paramelaconite [71276-37 ]. Commercially available copper(II) oxide is generally black and dense although a brown material of low bulk density can be prepared by decomposition of the carbonate or hydroxide at around 300°C, or by the hydrolysis of hot copper salt solutions with sodium hydroxide. The black product of commerce is most often prepared by evaporation of Cu(NH2)4C02 solutions (35) or by precipitation of copper(II) oxide from hot ammonia solutions by addition of sodium hydroxide. An extremely fine (10—20 nm) copper(II) oxide has been prepared for use as a precursor in superconductors (36). 

Copper(II) sulfate monohydrate [10257-54-2] CuS04-H2 0, which is almost white in color, is hygroscopic and packaging must contain moisture barriers. This product is produced by dehydration of the pentahydrate at 120—150°C. Trituration of stoichiometric quantities of copper(II) oxide and sulfuric acid can be used to prepare a material of limited purity. The advantages of the monohydrate as opposed to the pentahydrate are lowered freight cost and quickness of solubilization. However, these advantages are offset by the dustiness of the product and probably less than one percent of copper sulfate is used in the monohydrate form. 

An example of the use of copper as a catalyst is Acid Blue 25 [6408-78-2] (Cl 62055) in which l-amino-2-sulfonic-4-bromoanthraquinone is condensed with aniline using copper salts (Ullmann reaction) (314). Another example is oxidation to the tria2ole of Direct YeUow 106 [12222-60-5] (Cl 40300) (315,316). 

The use of peroxyacids, including PMSA, makes it possible to improve photometric method of nickel determination - to increase selectivity, accuracy and reproducibility of measurements. Peroxyacids as oxidants ai e used for nickel determination in aluminium and copper alloys, natural waters, stomatological products. 

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