The structure of complexes of HCl withN,N-dimethylformamide based on polarization measurements in the Raman spectra

Abstract

The Raman spectra of solutions of HCI in DMF were studied and the degree of depolarization of spectral lines was measured. Complexes of three types, 2DMF-HCI, DMF-HCI, and DMF-2HCI, are formed depending on the ratio of the components. Examination of the structure of the contour of the v(C=O) line showed that the acid-base interactions in the complexes occur through the O atom of the DMF molecule. On the basis of polarization measurements it was established that two DMF molecules in the 2DMF 9 HC1 complex are nonequivalent.Key words: dimethylformamide, hydrogen chloride, complexes; Raman spectra, degree of depolarization; solutions, acid-base interactions.Solutions of HCI in DMF are used as catalytic systems for a number of chemical reactions.l The efficiency of catalytic systems of such a type is determined by composition and structure of the DMF complexes with HC1. Previously, z the binary systems DMF--acid have been considered as solutions in which weak donoracceptor interactions play a significant role. Later, complexes 2DMF-HCI and DMF" HCI (1) with a strong quasi-symmetric H-bond as well as ionic pairs of composition DMF-2HCI (2) have been found 3 in solutions of HCI in DMF using the Multiple Attenuated Total Reflection (MATR) IR spectroscopy.Complex 1 is a quasi-ionic pair formed due to a strong quasi-symmetric H-bond between the O atom of the carbonyl group and the C1 atom. The formation of complex 2DMF" HCI (3) upon addition of one additional DMF molecule to complex 1 does not result in the cleavage of the strong quasi-symmetric H-bond between DMF and HCI. The two DMF molecules in 3 are nonequivalent. Previously, 4 the Raman spectra of complexes of such a type have been obtained for the first time and it was established that the formation of the complexes is accompanied by considerable changes in the frequencies and intensities of almost all lines of DMF molecules constituting them. In this work, Rarnan spectra of solutions of HCI in DMF were studied in a wider range of concentrations of the components and polarization measurements in the spectra were performed. ExperimentalThe procedures for purifying the reagents and preparing the solutions have been described previously)The Raman spectra of solutions of HCI in DMF were recorded on a DFS-24 spectrophotometer equipped with a double monochromator and an improved registration system. The 488 nm line of an LG-106M argon ion laser was used as the source of excitation; the other lines of the laser were suppressed by an interference filter. The polarization plane of linearly polarized laser light was rotated by 90 ~ with respect to the optical axis using a X/2 plate. In all experiments, the optical widths of the slits were 3 to 10 cm -t. To determine the relative degrees of depolarization of the lines (0) equal to the ratios of the line intensities obtained in the transversely and longitudinally polarized light, the spectrum of each solution was recorded 3 to 5 times in the correspondingly polarized light. The reproducibility of the intensity values was 10 to ...

Hydrogen bonding in benzenesulfonic and 4‐toluenesulfonic acids dissolved in N,N′‐dimethylformamide: an FT‐Raman study

“…The relatively low level of dissociation is quite surprising, taking into account the strength of the acid and the behaviour of DMF as a dissociating solvent in terms of both its donating power and dielectric constant. 24,25 However, as we have reported previously, 8 lithium triflate (another typical strong electrolyte) is strongly associated in DMF solutions and Burdin et al 9 could find no evidence for HCl dissociation in HCl/DMF solutions.…”

“…However, it almost disappears in the Raman spectrum of the most concentrated (5.03 M) solution, in good agreement with previous results. 9 The last band in this spectral region, at 638 cm 1 , is the 4-toluenesulfonate anion symmetric SO 3 bending, used here for band intensity normalization. Band-fitting of this spectral region (Fig.…”

“…Recently, Burdin et al 9 have published the Raman spectra, including polarization measurements, of HCl dissolved in DMF; they found three types of complexes, namely 2DMFÐHCl, DMFÐHCl and DMFÐ2HCl, depending on the molar ratio of the components. They report important changes in several DMF fundamentals promoted by the hydrogen bonding, including (C O) at 1672 cm 1 and s (C 0 -N-C 0 ) at 866 cm 1 .…”

Zn(II) Complexes Based on a Schiff Base: Mechanochromism- and Solvent Molecule-Dependent Acidochromism

“…We speculate that HCl destroyed the interaction between DMF and ligand molecules, which leads to the phase transition and the departure of partial DMF molecules. HCl molecules also interacted with the complex molecules and DMF molecules, and existed in 1-DMF-HCl . − Most of the DMF molecules remained after HCl fumigation due to their poor volatility. Therefore, 1-DMF-HCl cannot change to crystalline phase 1 and recover but remains in an amorphous state.…”

Complexes with strong symmetric hydrogen bonds and their solvation in the trifluoroacetic acid—N,N-dimethylformamide system studied by IR spectroscopy

“…The CA spectra of these solutions with equal concentrations of the salt and DMF coincide. The formation of the (A...H...A)-anions by reactions (5) and (6) is accompanied by a decrease in tl~e concentration of the free TFA molecules. In the DMF-containing system, two TFA molecules are required for the formation of the proton disobate, whereas only one TFA molecule is needed in the salt system.…”