Direct formation, ternary compound from

The aldehyde or ketone can now desorb, leading to the initial copper(I) hydrazide complex 13 which re-enters the catalytic cycle. The replacement of DEAD-H2 12 by DEAD 19 can be easily understood when considering this catalytic cycle. Indeed, several entries to the main catalytic cycle are possible, either via the hydrazino copper species 13 or via the direct formation of the ternary loaded complex 18 from the azo-derivative 19, Phen CuCl 3 and the alcohol 1. The key-role played by the hydrazine or azo compounds can also be readily appreciated when considering the proposed mechanistic rationale. The hydrazide, not only helps in reducing the copper(II) salt to the copper(I) state but, by virtue of its easy passage into the azo derivative, it also acts as a hydrogen acceptor, allowing the efficient oxidation of the alcohol into the carbonyl compound. 

Less direct support for a ternary mechanism comes from measurements by Ingold and his collaborators (118,119) on the base-catalyzed interconversion of azomethines in alcoholic solution. It was possible to measure both the rate of racemization of one isomer and its rate of conversion to the other isomer. These two rates were found to be equal. If the mechanism involved the formation of a free anion, the rate of racemization should be greater than that of conversion, since the known position of equilibrium shows that an appreciable fraction of the anions would revert to the original compound instead of going on to form the isomer. The experimental findings thus suggest that no kinetically free anion is formed, and support a ternary mechanism for this reaction. 

It is difficult to prepare many of the compounds of the A° —systems by synthesis from the elemental components and alloys, because of the comparatively hi melting points of many binary materials (CdS, CdSe, ZnS, and others) or the incongruent ternary-phase melting. Therefore, to prepare new semiconducting compounds, it is sometimes advisable to use doubledecomposition reactions [16,17]. The thermal effect of these reactions, which is necessarily dependent on the direction of the exchange reaction, is calculated from the heats of formation or the energies of the crystal lattices. Various experimental results demonstrate the success of this approach [16]. An example is the preparation of lead metaselenoarsenite ... 

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