Copper addition initiated

The most common and useful additives are copper(I) salts (such as CuCl), which produce high yields of 1 1 adducts in many cases.174 Several examples from the extensive work of the Ciba-Geigy group in Basel are compiled in Scheme 54, with an emphasis on subsequent conversions of the highly functionalized products into important heterocycles.175 These procedures are very simple and have been conducted on a multigram scale. Typically, the halogen component and the acceptor are heated without solvent at 110 °C in the presence of 1-10% CuCl. After several hours, the copper salts are removed by filtration and the product is isolated by distillation. It is clear that the copper additive behaves as more than just an initiator, the additions of electrophilic radicals to electron deficient alkenes like those shown in Scheme 54 would not be likely to succeed otherwise. 

It has been known for many years that acidity of paper is one of the variables adversely affecting permanence. However, publications such as the ASTM Specification D-3290-74 imply that paper acidity is the controlling factor in permanence and overrides all other variables such as pulp purity, chemical additives, iron and copper contamination, initial levels of strength, etc. A few practical examples are available to demonstrate the danger of such sweeping allegations ... 

The last step is dominated by the metallic-copper cluster formation. We assume that in the initial process, all the accessible sulfur sites of PMeT are saturated. Then, in the absence of a stabilizing agent in aqueous solution, the monovalent copper ions undergo disproportionation to produce Cu2+ ions and metallic copper. Additional Cu2+ is then drained from the solution, resulting in an increase in the absolute copper content. 

Developments in the 1930s led to zinc chromite for methanol synthesis, with pressures of about 300 atm-required for thermodynamic reasons at about 400°C. Reduction on a single metal centre seems a likely mechanism. The higher initial activity resulting from copper addition was known for many years, but the commercial success achieved by ICI and subsequent developers stems mainly from stabilization of the metal dispersion ... 

Several studies have used palladium catalysis in the arylation of benzoxazoles. A palladium catalyst with a phosphine ligand allows their reaction with aryl mesylates without the requirement for acid or copper additives. In the reaction with arene-sulfonyl chloride, palladium is used in combination with copper. A plausible mechanism involves initial cupration of the benzoxazole followed by copper—palladium exchange and oxidative addition of the sulfonyl chloride to palladium to give (84). This intermediate may lose sulfur dioxide to give an aryl palladium species, which, on reductive elimination, yields 2-arylbenzoxazole. The arylation of benzoxazoles and benzthiazoles with aryl boronic acids is also catalysed by a combination of palladium... 

Proprietary additives have been developed as photodegradation sensitizers. They include ferric compounds, benzophenones, and mixtures of benzophenones and organometallic complexes. One system, based on iron and copper additives, becomes an active light sensitizer after an initial period of antioxidant and light stabilizing behavior. 

Although this mechanism explains most observations, it is an oversimplification because the copper additive behaves as more than a mere initiator the additions of electrophilic radicals to electron-deficient alkenes like those shown in Scheme 25.12 ° would not be likely to succeed otherwise. In this example, carbon tetrachloride adds to acryloyl chloride under ATRA conditions to give 26, which... 

Isothermal polymerizations are carried out in thin films so that heat removal is efficient. In a typical isothermal polymerization, aqueous acrylamide is sparged with nitrogen for 1 h at 25°C and EDTA (C2QH2 N20g) is then added to complex the copper inhibitor. Polymerization can then be initiated as above with the ammonium persulfate—sodium bisulfite redox couple. The batch temperature is allowed to rise slowly to 40°C and is then cooled to maintain the temperature at 40°C. The polymerization is complete after several hours, at which time additional sodium bisulfite is added to reduce residual acrylamide. 

A mixture consisting of 0.69 g (10.5 mmoles) of zinc-copper couple, 12 ml of dry ether, and a small crystal of iodine, is stirred with a magnetic stirrer and 2.34 g (0.7 ml, 8.75 mmoles) of methylene iodide is added. The mixture is warmed with an infrared lamp to initiate the reaction which is allowed to proceed for 30 min in a water bath at 35°. A solution of 0.97 g (2.5 mmoles) of cholest-4-en-3/ -ol in 7 ml of dry ether is added over a period of 20 min, and the mixture is stirred for an additional hr at 40°. The reaction mixture is cooled with an ice bath and diluted with a saturated solution of magnesium chloride. The supernatant is decanted from the precipitate, and the precipitate is washed twice with ether. The combined ether extracts are washed with saturated sodium chloride solution and dried over anhydrous sodium sulfate. The solvent is removed under reduced pressure and the residue is chromatographed immediately on 50 g of alumina (activity III). Elution with benzene gives 0.62 g (62%) of crystalline 4/5,5/5-methylene-5 -cholestan-3/5-ol. Recrystallization from acetone gives material of mp 94-95° Hd -10°. 

The cyanobenzylpiperidine 94 acts as an effective benzoyl anion equivalent for addition to alkynes. As shown, the initial adduct 95 is readily cleaved with copper sulfate to give the ketone product 96 (93LA375). 

Addition of about 0 04% arsenic will inhibit dezincification of a brasses in most circumstances and arsenical a brasses can be considered immune to dezincification for most practical purposes . There are conditions of exposure in which dezincification of these materials has been observed, e.g. when exposed outdoors well away from the sea , or when immersed in pure water at high temperature and pressure, but trouble of this type rarely arises in practice. In other conditions, e.g. in polluted sea-water, corrosion can occur with copper redeposition away from the site of initial attack, but this is not truly dezincification, which, by definition, requires the metallic copper to be produced in situ. The work of Lucey goes far in explaining the mechanism by which arsenic prevents dezincification in a brasses, but not in a-/3 brasses (see also Section 1.6). An interesting observation is that the presence of a small impurity content of magnesium will prevent arsenic in a brass from having its usual inhibiting effect . 

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