Distribution behavior of L-tryptophane by extraction with di(2-ethylhexyl)phosphoric acid

To demonstrate that the proton-transfer reaction occurs in the extraction o f alpha-amino acid and to explain the complicated phenomenon present in the extraction of L-tryptophane, a series of extraction equilibrium experiment for t-tryptophane with di(2-ethyIhexyI) phosphoric acid (D2EHPA) dissolved in n-octane (System A) and a mixture of n-octane and n-octanol (System B) using L-tryptophane (L-Trp) as a model amino acid were carried out. The eff ects of L-tryptophane (L-Trp) concentration, D2EHPA concentration, n-octano l concentration, and pH on the extraction distribution ratio are discussed in detail. In System A, in the 1.0 < pH < 3.5 range, distribution ratio D i ncreases with an increase of pH, but changes slightly in the 3.5 < pH < 5.0 range. The data indicate the formation of both (1:1) and (1:2) L-tryptopha ne-D2EHPA (dimeric) complexes, and the complexes tend to cluster together, away from the low-polarity bulk solvent. The infrared spectrogram of the or ganic-phase-loaded solute illustrates that the pH condition has little effe ct on the structure of complex. In System B, both the (1:1) and(I:2) L-tryp tophane-D2EHPA (dimeric) complex form, but they do not cluster together bec ause of the diluent that improves the polarity of the bulk solvent. The pro ton-transfer reaction is again demonstrated in the extraction of alpha-amin o acid with D2EHPA. Expressions of the equilibrium distribution are propose d.