Reduction process developing agents

In many studies of asymmetric reductions no attempts were made to rationalize either the extent or the sense of the observed asymmetric induction, that is, the absolute configuration of the predominant enantiomer. It is believed that it is premature in certain cases to attempt to construct a model of the transition state of the key reaction step, given the present state of knowledge about the mechanism of these reduction processes. The complexity of many of the reducing systems developed is shown by the fact that the enantiomeric excess or even the sense of asymmetric induction may depend not only on the nature of the reducing agent and substrate, but also on temperature, solvent, concentration, stoichiometry of the reaction, and in some cases the age of the reagent. 

The nucleus or development center in physical development can be described as a dual electrode on which the reduction of silver ion to silver and the oxidation of developing agent take place simultaneously. Electrochemical measurements of silver physical development in a hydroquinone/Phenidone physical developer with silver ion complexed with thiocyanate proceed as a catalytic electrode process [39]. 

Physical development can occur on nuclei with the simultaneous reduction of silver ion and oxidation of the developing agent. The two partial processes can also be separated in a model cell so that the effect of solution composition on the separate anodic and cathodic parts can be seen (Figure 14). Kawashima et al. [59]... 

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