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

Abstract

Solutions of benzenesulfonic acid (BSA) and monohydrated 4-toluenesulfonic acid (PTSA) in dimethylformamide (DMF) were studied by FT-Raman spectroscopy in the concentration range 1.0-5.0 mol dm −3 . Spectra in the region of the acid S -OH and benzenesulfonate anion SO 3 − stretching bands were analysed using band-fitting procedures in order to ascertain the degree of acid dissociation. In BSA solutions, this parameter changes from 0.34 (1.02 M solution) to 0.11 (5.01 M solution) despite the strong character of the acid. Interaction of DMF with undissociated BSA produces a new band in the n(C -N -C ) Raman spectral region near 866 cm −1 , displaced −11.0 cm −1 and assigned to DMF molecules hydrogen-bonded to BSA. In PTSA solutions, hydrogen bonds are formed with the oxonium ion (H 3 O + ) dissociated from the acid. In this case, the displacement observed is only −7.0 cm −1 , indicating a weaker interaction. From the concentration of hydrogen-bonded DMF, the mean number of hydrogen-bonds participating in bonding with each solvent molecule can be calculated. This number changes, in BSA solutions, from ca. 0.5 in the less concentrated solutions up to ca. 1.0 in the most concentrated. This result supports the conclusion that BSA-DMF complexes of fixed stoichiometry are not present in the range of concentrations studied here. On the contrary, the oxonium ions form a stable complex of stoichiometry (DMF) 2 ·H 3 O + which does not change with the acid concentration.

Precipitation of monodisperse ZnO nanocrystals via acid-catalyzed esterification of zinc acetate

“…2 ) stretching bands, appearing at 1125 and 1037 cm 21 , respectively, 34 disappear after the washing procedure. This result also indicates that insoluble zinc tosylate was not formed.…”

Microwave assisted organocatalytic synthesis of 5-hydroxymethyl furfural in a monophasic green solvent system

“…While in case of IPA, yield of HMF showed similar trend the requirement of PTSA was 50% less in IPA as compared to DMF for >98% conversion which can be attributed to the formation of a stable complex between PTSA and DMF. 30 Besides, the existence of DMF in two resonance forms of amide structures can be said to favor hydrogen bonding with the acidic part of PTSA thereby possibly resulting in lower availability of PTSA as a proton source for fructose dehydration. Optimal PTSA concentrations were found to be 0.10 g ml À1 and 0.20 g ml À1 in IPA and DMF, respectively for obtaining maximum of HMF yield and fructose conversion.…”

Concentration and pH dependent SERS spectra of sulfanilic acid sodium salt on colloidal silver particles

“…[25] The asymmetric S O vibration is observed at 1176 cm −1 in the IR and at 1180 cm −1 in the Raman spectrum. [26] The SO 3 symmetric stretching vibration [27,28] is seen at 1048 cm −1 for benzene sulfonate and at 1035 cm −1 for sulfanilic acid. [11] For the title compound, the vibrations at 697, 492 (IR), 675 and 510 cm −1 (DFT) are assigned as the deformation bands of the SO 3 group.…”