Detailed analysis of the charge transfer complex N,N‐dimethylaniline–SO₂ by Raman spectroscopy and density functional theory calculations

Abstract

Although the amine sulfur dioxide chemistry was well characterized in the past both experimentally and theoretically, no systematic Raman spectroscopic study describes the interaction between N,N-dimethylaniline (DMA) and sulfur dioxide (SO 2 ). The formation of a deep red oil by the reaction of SO 2 with DMA is an evidence of the charge transfer (CT) nature of the DMA-SO 2 interaction. The DMA-SO 2 normal Raman spectrum shows the appearance of two intense bands at 1110 and 1151 cm −1 , which are enhanced when resonance is approached. These bands are assigned to ν s (SO 2 ) and ν(φ -N) vibrational modes, respectively, confirming the interaction between SO 2 and the amine via the nitrogen atom. The dimethyl group steric effect favors the interaction of SO 2 with the ring π electrons, which gives rise to a π -π * low-energy CT electronic transition, as confirmed by time-dependent density functional theory (TDDFT) calculations. In addition, the calculated Raman DMA-SO 2 spectrum at the B3LYP/6-311++g(3df,3pd) level shows good agreement with the experimental results (vibrational wavenumbers and relative intensities), allowing a complete assignment of the vibrational modes. A better understanding of the intermolecular interactions in this model system can be extremely useful in designing new materials to absorb, detect, or even quantify SO 2 .

Recent advances in linear and nonlinear Raman spectroscopy. Part V

“…The FT‐IR and FT‐Raman spectra of 4‐hydroxy‐3‐(3‐oxo‐1‐phenylbutyl)‐2 H ‐1‐benzopyran‐2‐one (Warfarin) were measured and calculated by Amalanathan, Joe and Kostova . Ando, Matazo and Santos carried out a systematic Raman experimental and theoretical spectroscopic study of the interaction between N , N ‐dimethylaniline (DMA) and sulfur dioxide (SO 2 ), where the formation of a deep red oil by the reaction of SO 2 with DMA is an evidence of the charge transfer nature of the DMA–SO 2 interaction . Anto and coworkers measured and analyzed the FT‐IR and FT‐Raman spectra of phenylphosphate disodium salt, and they also measured the SERS spectrum as a silver colloid .…”

New experimental data for absorption of SO2 into DMA solution

“…The result of present research was also compared to the other investigations in the pool of literature available (Table ). Ando et al explained the charge transfer of complex DMA and SO 2 system through Raman spectroscopy. Absorption of SO 2 into DMA solution gives an ionic liquid (dimethyl ammonium N,N ‐dimethyl amino sulfinate) .…”

“…Ando et al explained the charge transfer of complex DMA and SO 2 system through Raman spectroscopy. Absorption of SO 2 into DMA solution gives an ionic liquid (dimethyl ammonium N,N ‐dimethyl amino sulfinate) . The present work showed that DMA solution can be used as an efficient absorbent for SO 2 removal.…”

The solvation inhomogeneity of sulfur dioxide in 1‐butyl‐3‐methylimidazolium thiocyanate ionic liquid probed by Raman spectroscopy

“…The charge transfer interaction from a Lewis base to SO 2 causes a partial filling of the S = O antibonding π* orbitals, and as a consequence, the S = O bond orders decrease. Therefore, the charge transfer extent to SO 2 can be monitored by vibrational spectroscopic techniques by the direct analysis of its stretching vibrational modes . Furthermore, such charge transfer interaction is associated to a highly allowed electronic transition in the near ultraviolet or visible region, permitting the use of resonance Raman spectroscopy technique.…”

“…Furthermore, such charge transfer interaction is associated to a highly allowed electronic transition in the near ultraviolet or visible region, permitting the use of resonance Raman spectroscopy technique. In fact, a huge resonance Raman enhancement is associated to the ν s (SO 2 ) in SO 2 complexes, making the spectral analysis much simpler as other Raman bands are not enhanced in the same extent …”