Study of the structure of H2SO4-amine Primene 81R and Fe(III)-amine Primene 81R sulphate compounds by infrared spectroscopy

The primary amine Primene 81R extracts sulphuric acid from aqueous solutions to form the corresponding sulphate and bisulphate salts. The infrared study shows that in the sulphate salt, the sulphate group presents a Td symmetry, whereas the amine bisulphate presents a C-3v symmetry for the bisulphate group. The former of the above compounds, the amine sulphate, is complexed to Fe(III) in sulphate media, and two complexes ale extracted depending on temperature. At 8 degrees C or lower temperatures a complex with the stoichiometric formula 4(RNH3)(2)SO4 (Fe(OH)SO4)(2) is formed, whereas at 50 degrees C or higher temperatures the complex with the stoichiometric formula 3(RNH3)(2)SO4 (Fe(OH)SO4)(2) is formed. The infrared spectrum of both complexes is very similar and it is consistent with a weaker interaction between the protons associated with the amine group and the anion, and with a change in the symmetry of the sulphate group respect to the symmetry presented in the amine sulphate salt.