Copper catalysts reactions

Generally, reactions with anilines are slower than those with aliphatic amines, in part because anilines are less nucleophilic7. Condensation of aromatic amines with unactivated aryl halides usually requires the presence of copper catalysts. Reactions of diarylamines, such as diphenylamine and carbazole, are even slower. 

Another type of multicomponent [2 + 2+1] cycloaddition is achieved with diazo carbonyl compounds in the presence of rhodium or copper catalysts. Reaction with additional carbonyl groups within the substrate gives carbonyl ylides. These, as formal 1,3-dipoles, can undergo [3 + 2] cycloaddition with alkenes or alkynes to form heterocyclic ring systems,7 83... 

However, hydrogen chloride gas, obtained as a by-product in chlorination reactions, is commercially converted to chlorine by passing the hydrogen chloride mixed with air over a copper catalyst at a temperature of 600-670K when the following reaction occurs ... 

Arylation or alkenylation of soft carbon nucleophiles such as malonate is carried out by using a copper catalyst, but it is not a smooth reaction. The reaction of malononitrile, cyanoacetate, and phenylsulfonylacetonitrile with aryl iodide is possible by using a Pd catalyst to give the coupling products. 

Silver Catalyst Process. In early formaldehyde plants methanol was oxidized over a copper catalyst, but this has been almost completely replaced with silver (75). The silver-catalyzed reactions occur at essentially atmospheric pressure and 600 to 650°C (76) and can be represented by two simultaneous reactions ... 

Reactions. The most important commercial reaction of cyclohexane is its oxidation (ia Hquid phase) with air ia the presence of soluble cobalt catalyst or boric acid to produce cyclohexanol and cyclohexanone (see Hydrocarbon oxidation Cyclohexanoland cyclohexanone). Cyclohexanol is dehydrogenated with 2iac or copper catalysts to cyclohexanone which is used to manufacture caprolactam (qv). 

Biacetyl is produced by the dehydrogenation of 2,3-butanediol with a copper catalyst (290,291). Prior to the availabiUty of 2,3-butanediol, biacetyl was prepared by the nitrosation of methyl ethyl ketone and the hydrolysis of the resultant oxime. Other commercial routes include passing vinylacetylene into a solution of mercuric sulfate in sulfuric acid and decomposing the insoluble product with dilute hydrochloric acid (292), by the reaction of acetal with formaldehyde (293), by the acid-cataly2ed condensation of 1-hydroxyacetone with formaldehyde (294), and by fermentation of lactic acid bacterium (295—297). Acetoin [513-86-0] (3-hydroxy-2-butanone) is also coproduced in lactic acid fermentation. 

Significant quantities of the diphenoquinone are also produced if the ortho substituents are methoxy groups (36). Phenols with less than two ortho substituents produce branched and colored products from the reactions that occur at the open ortho sites. It is possible to minimize such side reactions in the case of o-cresol oxidation by using a bulky ligand on the copper catalyst to block the open ortho position (38). 

The Guerbet reaction can be used to obtain higher alcohols 2-propyl-1-heptanol [10042-59-8] from 1-pentanol condensation and 6-methyl-4-nonanol from 2-pentanol (80—83). Condensations with alkah phenolates as the base, instead of copper catalyst, produce lower amounts of carboxyhc acids and requke lower reaction temperatures (82,83). The crossed Guerbet reaction of 1-pentanol with methanol in the presence of sodium methoxide catalyst afforded 2-heptanol in selectivities of about 75% (84). 

Dkect synthesis is the preparative method that ultimately accounts for most of the commercial siUcon hydride production. This is the synthesis of halosilanes by the dkect reaction of a halogen or haUde with siUcon metal, siUcon dioxide, siUcon carbide, or metal sihcide without an intervening chemical step or reagent. Trichlorosilane is produced by the reaction of hydrogen chloride and siUcon, ferrosiUcon, or calcium sihcide with or without a copper catalyst (82,83). Standard purity is produced in a static bed at 400—900°C. 

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). 

In this case the ylide was not isolated but allowed to react with ben2ophenone to give, after hydrolysis with hydrochloric acid, 1,1-diphenylethylene, diphenylacetaldehyde, and triphenylarsine (160). An excellent method for preparing arsonium ylides involves the reaction between a stable dia2o compound and triphenylarsine in the presence of a copper catalyst such as bis(acetylacetonato)copper(II) (161). Rather than a dia2o compound, an iodonium yhde can be used again a copper catalyst is necessary for an optimum yield of product. An example of the use of a dia2o compound is shown in the formulation of triphenyl arsonium 2,3,4-triphenylcyclopentadienyLide [29629-32-17, C H As ... 

Although copper catalysts were known to be highly active for this reaction for many years, it was not until the late 1960s that gas purification processes for synthesis gas were introduced that would allow the commercial use of these catalysts, which require very low sulfur, chlorine, and phosphoms feed impurity levels to maintain catalyst activity. 

Many anthraquinone reactive and acid dyes are derived from bromamine acid. The bromine atom is replaced with appropriate amines in the presence of copper catalyst in water or water—alcohol mixtures in the presence of acid binding agents such as alkaU metal carbonate, bicarbonate, hydroxide, or acetate (Ullmaim condensation reaction). 

Yields depend on the reactivity of the amines and the choice of reaction conditions, including the choice of copper catalyst. Generally, the reactivity increases with increasing amine basicity. Thus, i7n7-toluidine (pTf = 5.1) reacts four times faster than aniline (pif = 4.7) (27). StericaHy hindered amines such as 3,5-di-amino-2,4,6-trimethylbenzenesulfonic acid react very slowly. 

The main by-products of the Ullmaim condensation are l-aniinoanthraquinone-2-sulfonic acid and l-amino-4-hydroxyanthraquinone-2-sulfonic acid. The choice of copper catalyst affects the selectivity of these by-products. Generally, metal copper powder or copper(I) salt catalyst has a greater reactivity than copper(Il) salts. However, they are likely to yield the reduced product (l-aniinoanthraquinone-2-sulfonic acid). The reaction mechanism has not been estabUshed. It is very difficult to clarify which oxidation state of copper functions as catalyst, since this reaction involves fast redox equiUbria where anthraquinone derivatives and copper compounds are concerned. Some evidence indicates that the catalyst is probably a copper(I) compound (28,29). 

Cl Reactive Blue 19 (9) is prepared by the reaction of bromamine acid (8) with y -aminophenyl-P-hydroxyethylsulfone [5246-57-1] (76) ia water ia the presence of an acid-hinding agent such as sodium bicarbonate and a copper catalyst (Ullmann condensation reaction) and subsequent esterification to form the sulfuric ester. 

There are two ways to produce acetaldehyde from ethanol oxidation and dehydrogenation. Oxidation of ethanol to acetaldehyde is carried out ia the vapor phase over a silver or copper catalyst (305). Conversion is slightly over 80% per pass at reaction temperatures of 450—500°C with air as an oxidant. Chloroplatinic acid selectively cataly2es the Uquid-phase oxidation of ethanol to acetaldehyde giving yields exceeding 95%. The reaction takes place ia the absence of free oxygen at 80°C and at atmospheric pressure (306). The kinetics of the vapor and Uquid-phase oxidation of ethanol have been described ia the Uterature (307,308). 

The reaction kinetics for the dehydrogenation of ethanol are also weU documented (309—312). The vapor-phase dehydrogenation of ethanol ia the presence of a chromium-activated copper catalyst at 280—340°C produces acetaldehyde ia a yield of 89% and a conversion of 75% per pass (313). Other catalysts used iaclude neodymium oxide and samarium hydroxide (314). 

Cyclization of the diazo compound (108) with a copper catalyst affords the clavulanic acid derivatives (110) and (111), possibly via rearrangement of the sulfur ylide (109) (80H(14)1999). Similar reactions have been reported in the recent literature (80H(14)1967, 81H(16)1305, 80TL31). 

This reaction is carried out in tall fluidized beds of high L/dt ratio. Pressures up to 200 kPa are used at temperatures around 300°C. The copper catalyst is deposited onto the surface of the silicon metal particles. The product is a vapor-phase material and the particulate silicon is gradually consumed. As the particle diameter decreases the minimum fluidization velocity decreases also. While the linear velocity decreases, the mass velocity of the fluid increases with conversion. Therefore, the leftover small particles with the copper catalyst and some debris leave the reactor at the top exit. 

The direct process is less flexible than the Grignard process and is restricted primarily to the production of the, nevertheless all-important, methyl- and phenyl-chlorosilanes. The main reason for this is that higher alkyl halides than methyl chloride decompose at the reaction temperature and give poor yields of the desired products and also the fact that the copper catalyst is only really effective with methyl chloride. 

Maximum conversion occurs by equilibration at the lowest possible temperature so the reaction is carried out sequentially on two beds of catalyst (a) iron oxide (400°C) which reduces the CO concentration from 11% to 3% (b) a copper catalyst (200°) which reduces the CO content to 0.3%. Removal of CO2 ( 18%) is effected in a scrubber containing either a concentrated alkaline solution of K2CO3 or an amine such as ethanolamine ... 

In addition to the Raney nickel catalysts, Raney catalysts derived from iron, cobalt, and copper have been examined for their action on pyridine. At the boiling point of pyridine, degassed Raney iron gave only a very small yield of 2,2 -bipyridine but the activity of iron in this reaction is doubtful as the catalyst was subsequently found to contain 1.44% of nickel. Traces of 2,2 -bipyridine (detected spectroscopically) were formed from pyridine and a degassed, Raney cobalt catalyst but several Raney copper catalysts failed to produce detectable quantities of 2,2 -bipyridine following heating with pyridine. 

Among the many chiral Lewis acid catalysts described so far, not many practical catalysts meet these criteria. For a,/ -unsaturated aldehydes, Corey s tryptophan-derived borane catalyst 4, and Yamamoto s CBA and BLA catalysts 3, 7, and 8 are excellent. Narasaka s chiral titanium catalyst 31 and Evans s chiral copper catalyst 24 are outstanding chiral Lewis acid catalysts of the reaction of 3-alkenoyl-l,2-oxazolidin-2-one as dienophile. These chiral Lewis acid catalysts have wide scope and generality compared with the others, as shown in their application to natural product syntheses. They are, however, still not perfect catalysts. We need to continue the endeavor to seek better catalysts which are more reactive, more selective, and have wider applicability. 

Compared to tlie intensive and successfrd development of copper catalysts for asymmetric 1,4-addition reactions, discussed in Cbapt. 7, catalytic asymmetric al-lylic substitution reactions have been tlie subjects of only a few studies. Diflictilties arise because, in tlie asymmetric y substitution of unsymniettical allylic electto-pb des, tlie catalyst bas to be capable of controlling botli tegioselectivity and enan-tioselectivity. 

Hie coppetfl) arenetliiolate complexes 19 [ 30], brsl developed and studied by van Rolen s group, can be used as catalysts for a number of copper-niedialed reactions SLidi as 1,4-addilion reactions lo etiones [31] and 1,6-addition reactions lo enynes [32]. 

The two reactions described above can be applied for the synthesis of symmetrical -acetylenes only. Unsymmetrical bis-acetylenes can be prepared by using the Cadiot-Chodkiew icz reaction For that method a terminal alkyne 1 is reacted with a bromoalkyne 8 in the presence of a copper catalyst, to yield an unsymmetrical coupling product 9 ... 

The oxidation process uses air as the oxidant over a silver or copper catalyst. The conditions are similar to those used for the dehydrogenation reaction. 

Recently, other authors when studying the activation of hydrogen by nickel and nickel-copper catalysts in the hydrogen-deuterium exchange reaction concentrated for example only on the role of nickel in these alloys (56) or on a correlation between the true nickel concentration in the surface layer of an alloy, as stated by the Auger electron spectroscopy, and the catalytic activity (57). 

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