Oxidative using copper salts

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). 

Because all currently known mechanisms of oxidative acetylenic homocouplings are very specific to single reaction conditions, e.g. pH or oxidation state of the used copper salt, this section summarizes the most reasonable mechanistic ideas proposed for the commonly utilized coupling procedures. 

Oxidations employing copper salts are among the newer methods introduced and have proven to be quite usefiil. For example, CuBr2/DBU/HMTA was used to convert oxazolines to 2-aIkyl(aryl)-4-oxazolecarboxyIic acid esters or amides (Scheme Banish and co-workers" proposed that the mechanism of... 

One of the best known oxidative transformations of alkenes is the conversion of terminal alkenes to methyl ketones, known as the Wacker oxidation. While this reaction is used industrially on extremely large scale, its application in laboratory settings (known as the Tsuji-Wacker oxidation) has been problematic. This is due to selectivity problems with several substrate classes as well as the need for co-oxidants, typically copper salts. The use of copper has prevented the use of ligands on Pd to modulate catalysis, which could... 

Using copper salts to promote the decarboxylative cross-coupling between the propiolic acids and secondary phosphine oxides would be a reasonable approach to this chemistry [482]... 

Lithium is used in metallurgical operations for degassing and impurity removal (see Metallurgy). In copper (qv) refining, lithium metal reacts with hydrogen to form lithium hydride which subsequendy reacts, along with further lithium metal, with cuprous oxide to form copper and lithium hydroxide and lithium oxide. The lithium salts are then removed from the surface of the molten copper. 

The action of redox metal promoters with MEKP appears to be highly specific. Cobalt salts appear to be a unique component of commercial redox systems, although vanadium appears to provide similar activity with MEKP. Cobalt activity can be supplemented by potassium and 2inc naphthenates in systems requiring low cured resin color lithium and lead naphthenates also act in a similar role. Quaternary ammonium salts (14) and tertiary amines accelerate the reaction rate of redox catalyst systems. The tertiary amines form beneficial complexes with the cobalt promoters, faciUtating the transition to the lower oxidation state. Copper naphthenate exerts a unique influence over cure rate in redox systems and is used widely to delay cure and reduce exotherm development during the cross-linking reaction. 

Tendering Effects. CeUulosic materials dyed with sulfur black have been known to suffer degradation by acid tendering when stored under moist warm conditions. This effect may result from the Hberation of small quantities of sulfuric acid which occurs when some of the polysulfide links of the sulfur dye are mptured. A buffer, such as sodium acetate, or a dilute alkaH in the final rinse, especially after oxidation in acidic conditions, may prevent this occurrence. Copper salts should never be used with sulfur black dyes because they cataly2e sulfuric acid generation. Few instances of tendering with sulfur dyes other than black occur and the problem is largely confined to cotton. 

Salts of neodecanoic acid have been used in the preparation of supported catalysts, such as silver neodecanoate for the preparation of ethylene oxide catalysts (119), and the nickel soap in the preparation of a hydrogenation catalyst (120). Metal neodecanoates, such as magnesium, lead, calcium, and zinc, are used to improve the adherence of plasticized poly(vinyl butyral) sheet to safety glass in car windshields (121). Platinum complexes using neodecanoic acid have been studied for antitumor activity (122). Neodecanoic acid and its esters are used in cosmetics as emoUients, emulsifiers, and solubilizers (77,123,124). Zinc or copper salts of neoacids are used as preservatives for wood (125). 

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). 

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. 

The Glaser reaction is an oxidative coupling of terminal alkynes 1 to yield a symmetrical Z -acetylene 2 the coupling step is catalyzed by a copper salt. Closely related is the Eglinton reaction, which differs from the Glaser reaction mainly by the use of stoichiometric amounts of copper salt as oxidizing agent. 

Small amounts of amine salt are also generated as a side product.8-10 Other oxidative chlorinating approaches have been used with dialkyl phosphites as well, including methods using copper(II) chloride,11 sulfuryl chloride,12 and elemental chlorine.13 All of these provide the target dialkyl phosphorochloridate in high yield. 

The allylic acyloxylation of alkenes, the Kharasch-Sosnovsky reaction, Eq. 81, would be an effective route to nonracemic allylic alcohol derivatives, if efficient, enantioselective catalysts were available. The reaction is mediated by a variety of copper salts, and as such, has been the target of considerable research in an attempt to render the process enantioselective. The original reaction conditions described by Kharasch require high temperatures when CuBr is used as the catalyst (93). However, the use of CuOTf (PhH)0 5 allows the reaction to proceed at temperatures as low as -20°C. Unfortunately, long reaction times are endemic in these processes and the use of excess alkene (2-100 equiv) is conventional. Most yields reported in this field are based on the oxidant. 

Although a variety of oxidants other than copper salts have been used ferricyanide is the only other one of note. Ferricyanide ions (yellow solution) are reduced to ferrocyanide ions (colourless solution) by reducing carbohydrates when heated in an alkaline solution. The concentration of the carbohydrate can be related to the decrease in absorbance at 420 nm. 

The metal-catalysed autoxidation of alkenes to produce ketones (Wacker reaction) is promoted by the presence of quaternary ammonium salts [14]. For example, using copper(II) chloride and palladium(II) chloride in benzene in the presence of cetyltrimethylammonium bromide, 1-decene is converted into 2-decanone (73%), 1,7-octadiene into 2,7-octadione (77%) and vinylcyclohexane into cyclo-hexylethanone (22%). Benzyltriethylammonium chloride and tetra-n-butylammo-nium hydrogen sulphate are ineffective catalysts. It has been suggested that the process is not micellar, although the catalysts have the characteristics of those which produce micelles. The Wacker reaction is also catalysed by rhodium and ruthenium salts in the presence of a quaternary ammonium salt. Generally, however, the yields are lower than those obtained using the palladium catalyst and, frequently, several oxidation products are obtained from each reaction [15]. 

---