Effect of Metal Ion Hydration on the Interaction between Sodium Carboxylates and Aluminum(III) or Chromium(III) Ions in Aqueous Solution

Abstract

The interaction between sodium octanoate, decanoate, and dodecanoate and aluminum(III) and chromium(III) has been studied in water at natural pH values, starting well below the surfactant critical micelle concentration, using electrical conductivity, turbidity, and potentiometric measurements. With decanoate or dodecanoate, maximum interaction occurs at 3:1 stoichiometry, corresponding to charge neutralization. Although the solutions become turbid with both metal ions, indicating phase separation, differences are observed and attributed to the fact that aluminum(III) is relatively labile to substitution and rapidly replaces its water ligands, whereas chromium(III) is substitution inert. This shows up in well-defined floc formation with Al(3+), whereas Cr(3+) suspensions do not precipitate, probably because that replacement of coordinated water by carboxylate ligands is impeded. This can be overcome by increasing temperature, and differences in the thermal behavior with Al(3+) and Cr(3+) are suggested to be due to increased involvement of substitution reactions in the latter case. The effect of octanoate on the trivalent metal ions is less clear, and with Cr(3+) interaction only occurs when the carboxylate is in excess. Hydrophobic interactions between alkyl chains play a major role in driving phase separation. At high surfactant concentrations, the solid phases do not dissolve, in contrast to what is observed with the corresponding alkylsulfates. This has implications for use of these systems in metal separation through froth flotation. The concentration of metal ions in supernatant solution has been determined for sodium dodecanoate and sodium dodecylsulfate with Al(3+) and Cr(3+) over the whole surfactant concentration range by inductively coupled plasma-mass spectrometry (ICP-MS). From this, association constants have been determined and are found to be larger for the carboxylate than the alkylsulfate, in agreement with the greater Lewis basicity of the -CO(2)(-) group.

The formation of host–guest complexes between surfactants and cyclodextrins

“…In the case of ionic surfactant-based solutions, electrical conductivity has been successfully used for determination of critical micelle concentration and degree of counter ion dissociation of micelles [138][139][140], or in the case of multicomponent systems, such as polymer-surfactant or multivalent salt-surfactant, polymer saturation points [141] and critical aggregation concentrations (see, e.g., [142]). That is, even in systems where the interpretation becomes rather complicated as a consequence of multiple contributions for the overall ionic conductance, electrical conductivity measurements may discriminate between structural or configurational changes as a consequence of counterions release (or charge neutralization followed by structural re-arrangements) or by significant changes in the size of ionic species.…”

Interactions between cationic surfactants and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin tetrasodium salt as seen by electric conductometry and spectroscopic techniques

“…In fact, for the C 12 TAB the cmc in the presence of porphyrin increase by increasing the temperature following the general trend; however, the cmc of C 16 TAB remains unchanged with temperature, suggesting that the increase in the thermal energy of the system is used to favor the micellization by keeping its value approximately constant. This occurs when, in a given system, there are slow or weak interactions among different species [35]. However, it should be stressed that the increase of  values by increasing the temperature suggests the formation of micelles with a lower aggregation number [36].…”

Synthesis, structure, and spectral and electrochemical properties of chromium(iii) tris-(8-hydroxyquinolinate)

“…24 In addition, while Al(III) complexes fairly rapidly undergo ligand exchange, the 3d 3 electronic configuration of chromium(III) makes its complexes kinetically inert to substitution, with rates at least a million times slower than those of the corresponding aluminium(III) complexes. 23,25,26 Chromium(III) complexes also show interesting electronic spectral properties, involving metal based quartet and doublet states, together with ligand based π,π* states, and, possibly, charge transfer states, as demonstrated by detailed UV/visible absorption, 27 luminescence spectra, 28,29 and photophysical studies. 30,31 In one case, electrogenerated chemiluminescence has been observed with a chromium(III) complex.…”