Structure of complexes in the H2SO4-2-pyrrolidone system as determined by IR-spectroscopy and quantum-chemical calculations

摘要

Specific features of complexation in solutions of a strong dibasic acid in the H2SO4-2-pyrrolidone (Pyr) system (in the range of compositions of 0-100% H2SO4) are studied using multiple frustrated total internal reflection IR spectroscopy. The conclusions drawn on the structure of the complexes formed in such solutions are confirmed by quantum-chemical calculations of the mPyr center dot nH(2)SO(4) (m, n = 1, 2) heteroassociates and by comparison of their calculated and measured vibrational spectra. It is found that, in the investigated solutions, four types of acid-base complexes, with various degrees of proton transfer in the OHO bridge, are formed: (AHA)(-) anions with quasi-symmetric H-bonds, solvated by acid molecules, or entering into the composition of PyrH(+) center dot (AHA)(-) ion pairs; quasi-ion pairs with incomplete proton transfer to the base molecule of 1: 1 and 2: 2 compositions; and 2Pyr center dot H2SO4 complexes with two O-H center dot center dot center dot O bridges of molecular type. The main differences in the mechanisms of the acid-base interactions in the H2SO4-Pyr system as compared to the CH3SO3H-Pyr system result from the participation of two OH-groups of H2SO4 molecule in these interactions. Therefore, two types of quasi-ion pairs and complexes of 2Pyr center dot H2SO4 composition are formed.