Correlation analysis of ?arylic strengthening? of the extraction capacity of bidentate organophosphorus extractants

Abstract

This paper is devoted to the so-called effect of “anomalous arylic strengthening” (AAS) observed upon extraction of a series of elements, mainly actinides and lanthanides, by bidentate neutral organophosphorus compounds (BNOPC). This “anomalous” effect is an increase in the extraction capacity of a reagent when alkyl substituents at the phosphorus atom are replaced with more electronegative aryl groups. The influence of phenyl substituents at the phosphorus atom on the reactivity of organophosphorus compounds of various types was considered. Based on the data on electronic effects of substituents, hypotheses were formulated about the reasons for AAS involving phenyl groups that are biphilic because they have substituents capable of manifesting both donor and acceptor properties depending on several factors such as,e.g., the nature of the reaction center, the character of the attacking reagent, the nature of the solvent,etc. When a strong complex of a metal with a phenyl substituted reagent of BNOPC is formed during extraction, the phenyl groups become donating, and additional strengthening of the complex appears.