Copper hydride, decomposition

Fig. 11. X-ray diffraction pattern of a Ni99Cul alloy partially transformed into its (3-hydride (0 NiCuH) before (a) and after (b) hydride decomposition. Arrows point to the diffraction peaks representing the rich in copper alloy phsae desegregated from the initial alloy after a multiple hydrogen absorption-desorption treatment. After Palczew-ska and Majchrzak (48).

According to H. Rose, the blue soln. of cupric hydroxide in cold hypophosphorous acid may remain unaltered for a long time and if very dil., it may even be heated without decomposition. If the soln. be evaporated in vacuo at a low temp., the copper is completely reduced as soon as the liquid is highly concentrated. C. A. Wurtz found that the soln. obtained by double decomposition of barium hypophosphite and copper sulphate at about 60° precipitates copper hydride— vide supra. Once blue crystals of copper hypophosphite, Cu(H2P02)2, were obtained they decomposed abruptly at 65°. According to R. Engel, this salt... 

The method used by Coates and Robinson" involved the copper-catalysed decomposition of trans,trans-farnesyl diazoacetate (4) to the cyclopropyl-lactone (5) having the stereochemistry shown. This was transformed into the cis-aldehyde-ester (6) by standard methods. Base epimerization gave the more stable transcompound (7). A Wittig reaction between the trans-aldehyde-ester (7) and the phosphorane (8), followed by lithium aluminium hydride reduction, yielded presqualene alcohol (1) as the major product accompanied by the minor isomer (9). 

Reaction with enoi ethers. Wenkert and co-workers have examined the copper-catalyzed decomposition of this -diazo compound in the presence of an enol ether of an aldehyde (1) and a ketone (5). In the first case, the expected cyclopropane ester (2) was obtained. This was reduced by lithium aluminum hydride to the diol, which cyclized to the hemiaceta (3) on exposure to acid. Collins oxidation of 3 gave the spiro- 3-methylene-y-lactone 4. 

The mechanism of reaction of a variety of triphenylphosphinealkyl-gold(i) complexes, and of triphenylphosphinetrimethylgold(iii), with mercury(n) chloride in a variety of solvents is St2. But when the alkyl group is cyano(ethoxycarbonyl)pentyl then the mechanism is dissociative. Decomposition of triphenylphosphine-n-butylcopper must involve initial formation of butene and a transient copper hydride rather than of n-butyl radicals, since no octane can be detected in the ultimate products. ... 

Bur] Burtovyy, R., Utzig, E., Tkacz, M., Study of the Thermal Decomposition of the Copper Hydride , Thermochim. Acta, 363, 157-163 (2000) (Crys. Structure, Thermodyn., Experimental, 16)... 

It has also been shown that reduction of the ethylenic bond in enones may occur via copper hydride derivatives formed by thermal decomposition of the lithium organocuprate. This can pose a problem since such decomposition occurs above 243 K in the temperature region where many cuprates are only beginning to react at appreciable rates with the substrate. However, addition of excess n-butyl-lithium appears to eliminate this complication. 

The formation of a copper hydride as an intermediate in the reaction was deduced from the presence of hydrogen among the products of thermal decomposition of the Cu(I) yl, and from the formation of additional hydrogen on acidification of the solution that remained after complete decomposition. 

Baranowski [680] concluded that the decomposition of nickel hydride was rate-limited by a volume diffusion process the first-order equation [eqn. (15)] was obeyed and E = 56 kJ mole-1. Later, Pielaszek [681], using volumetric and X-ray diffraction measurements, concluded from observations of the effect of copper deposited at dislocations that transportation was not restricted to imperfect zones of the crystal but also occurred by diffusion from non-defective regions. The role of nickel hydride in catalytic processes has been reviewed [663]. 

Catalysts suitable specifically for reduction of carbon-oxygen bonds are based on oxides of copper, zinc and chromium Adkins catalysts). The so-called copper chromite (which is not necessarily a stoichiometric compound) is prepared by thermal decomposition of ammonium chromate and copper nitrate [50]. Its activity and stability is improved if barium nitrate is added before the thermal decomposition [57]. Similarly prepared zinc chromite is suitable for reductions of unsaturated acids and esters to unsaturated alcohols [52]. These catalysts are used specifically for reduction of carbonyl- and carboxyl-containing compounds to alcohols. Aldehydes and ketones are reduced at 150-200° and 100-150 atm, whereas esters and acids require temperatures up to 300° and pressures up to 350 atm. Because such conditions require special equipment and because all reductions achievable with copper chromite catalysts can be accomplished by hydrides and complex hydrides the use of Adkins catalyst in the laboratory is very limited. 

Carbenoid transformations involving competition between intramolecular cyclopropa-nation and /8-hydride elimination have been investigated149. The chemoselectivity of these catalytic transformations can be effectively controlled by the choice of catalyst. Rhodium(II) trifluoroacetate catalysed decomposition of diazoketone 111 proceeds cleanly to give only enone 112. However, rhodium(II) acetate or bis-(iV-t-butylsalicyladiminato) copper(II) cu(TBs)2 provides exclusively cyclopropanation product 113 (equation 102)149. 

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