Extraction of 7-aminocephalosporanic acid (7-ACA) has been investigated
using secondary and tertiary
amines and a quaternary ammonium salt (Aliquat-336) as the carriers.
The values of the distribution
coefficients have been reported in a range of aqueous-phase pH values
and concentrations of 7-ACA using
different carriers in n-butyl acetate as the diluent.
As expected, ion-pair extraction with secondary and
tertiary amines exhibits lowerings of the distribution coefficient with
increase of pH, whereas the ion
exchange extraction with quaternary ammonium chloride (Aliquat-366)
exhibits an opposite but more
pronounced pH dependence, providing at the same time higher values of
distribution coefficient at high
values of pH. Both the extraction principles can be exploited to
achieve extraction and reextraction of
7-ACA in the pH range of 5 to 8 in which it is relatively
stable.
The extraction equilibria of Cephalosporin antibiotics with Aliquat-336 (tricaprylylmethylammonium chloride) in various solvents were studied at pH values above the pK a2 values of the antibiotics. The reactive extraction, which is essentially an anion-exchange reaction, takes place in a 1:1 stoichiometry. The extraction equilibrium constants (K P ) could be correlated well with the hydrophobicity scale of the antibiotics. The equilibrium constants for coextraction of the buffer ions were found to be lower than those of the cephalosporin antibiotics, indicating the possibility of exploiting the reactive extraction technique for process application. The K P values obtained for a specific solute were also found to correlate well with the dipole moment of the solvents.
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