Hydrogen bonding analysis of phosphoric acid-N,N-dimethylformamide mixtures

Ab initio molecular dynamics study of H-bonding and proton transfer in the phosphoric acid-N,N-Dimethylformamide system

Car-Parrinello molecular dynamics simulations of phosphoric acid (H₃PO₄)-N,N-dimethylformamide (DMF) mixtures over the whole composition range have been carried out. It has been found that the neutral molecules are the dominant species in this system. The concentration dependences of the average number of H-bonds per proton acceptor atom in P=O and C=O groups as well as per proton donor atom in DMFH⁺ ions towards phosphate species have been discussed. The H-bonding between components in all investigated mixtures of H₃PO₄ and DMF is possible. A significant fraction of the protonated DMF forms appears at phosphoric acid mole fraction higher than 0.37, indicating a high probability of proton transfer from phosphate species to oxygen atoms in C=O groups. The intermolecular proton transfer between phosphate species themselves is mainly observed when x_H3PO4 > 0.19. Satisfactory agreement with available experimental data for structural characteristics of the investigated system was obtained.

Computer simulation study of the intermolecular structure of phosphoric acid-N,N-dimethylformamide mixtures

The structures and energies of the complexes (H3PO4)2, H3PO4-DMF, and (H3PO4)2-DMF were analyzed at the B3LYP level of approximation. It was found that H-bonds form between H3PO4 and DMF molecules, but the strength of the H-bond depends strongly on its molecular environment. Effects of the solvent were taken into account via the CPCM approach. According to the B3LYP-СPCM calculations, the O···O distance in (H3PO4)2-DMF is shorter and its H-bonds are stronger than in the other complexes studied. In order to study the effects of concentration on the intermolecular structure, molecular dynamics simulations of H3PO4-DMF mixtures with mole fractions of acid of <0.1 were performed. The calculations indicated that the largest fraction of the acid protons are involved in hydrogen bonding with oxygen atoms of the DMF molecules. An increased probability of acid-acid hydrogen-bond formation at phosphoric acid mole fractions >0.06 was also noted.