Thermodynamic partial derivatives reduction

Together with acid-base reactions, where a proton transfer occurs (pH-dependent dissolution/ precipitation, sorption, complexation) redox reactions play an important role for all interaction processes in aqueous systems. Redox reactions consist of two partial reactions, oxidation and reduction, and can be characterized by oxygen or electron transfer. Many redox reactions in natural aqueous systems can actually not be described by thermodynamic equilibrium equations, since they have slow kinetics. If a redox reaction is considered as a transfer of electrons, the following general reaction can be derived ... 

The first example shows the synthesis of a C-C-bridged bis-macrocycle (Figure 2) [7]. The preparation of 1 is a condensation of a polyamine with a malonic ester derivative, in analogy to the procedure developed by Tabushi et al [8]. The tetraamide 1 is so insoluble that it precipitates and can be obtained practically pure from the reaction mixture. Its reduction to the octaamine takes place if the reaction with is done in diglyme (bis-(2-methoxyethyl)ether), in which 1 is partially soluble. The product 2 is an ideal ditopic ligand,since it has all the typical properties of 1,4,8,11-tetraazacyclotetradecane (cyclam), i. e. the thermodynamic and kinetical stability of its complexes and the C-C linkage between the two macrocyclic subunits does not reduce the coordination tendency of the amine nitrogens. 

The thermodynamic behavior of protactinium oxides is not as well established as for the Th02 system. The free energy of formation of Pa02(s) has been derived from carbothermic reductions. The entropy of formation of the dioxide is comparable to the other actinide dioxides (see table 27 data from Ackermann and Chandrasekharaiah (1974)]. A partial study of the reduction of Pa205 has also provided data for the protactinium oxide system (Kleinschmidt and Ward 1986). 

The same products have been obtained by another route [447], The acyloin condensation of methyl /3-(m-methoxyphenyl)propionate (546) gives in poor yield t e acyloin (543), cyclization of which with polyphosphoric acid leads to a derivative of tetrahydrochrysene (544). Reduction of the central double bond of this compound both with sodium in liquid ammonia and with sodium in butanol takes place nonselectively leading to the dihydro derivatives (540) and (541) in a ratio of 2.1 1 in the first case and 1.25 1 in the second case. The further reduction of the trans isomer (540) by Birches method leads to the most thermodynamically stable trans-anti-trans-isomer (539) [447], the t -enantiomer of which has been obtained by partial synthesis from estradiol [222]. 

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