S. G. Sysoeva

IR Study of ion-molecular interactions in a DMF-HCl system

The Multiple Attenuated Total Reflection (MATR) IR-spectra of HCl solutions in DMF (0–48.55% HCl) were recorded and analyzed in the range of 900–4000 cm−1. Depending on the ratio of compounds, a variety of complexes (2 DMF) · HCl (1), DMF · HCl (2), DMF · (2 HCl) (3) are formed in the system. The concentrations of the complexes were measured. Complex2 possesses a quasi-ionic structure Me2NHCO...H...Cl. The addition of a DMF molecule to complex2 with formation of complex1 does not result in destruction of the quasi-ionic structure of the DMF-HCl bond. In excess HCl, this structure is decomposed and the complex with the ion pair structure Me2NHCOH+ (ClHCl)− is formed.

IR SPECTROSCOPIC STUDY OF ION-MOLECULAR INTERACTIONS IN THE METHANESULFONIC ACID-N, N-DIMETHYLFORMAMIDE SYSTEM

Complex formation in the methanesulfonic acid (MSA)-DMF system was studied by Multiple Attenuated Total Reflectance (MATR) IR spectroscopy at 30°C within the composition range from neat MSA up to neat DMF. Depending on the ratio of components, two types of complexes with a strong quasi-symmetrical H bond (1 and2) are formed. The uncharged complex1 is a quasi-ion pair with the (O…H…O) bridge. Complex2 is formed by a protonated DMF molecule and the (A…H…A)− anion bound as an ion pair. It is established that complexes1 are solvated by DMF molecules in an excess of a base. Solvation or2 in an excess of an acid corresponds to a change from contact to contact-separated ion pairs. Continuous absorption spectra of charged and uncharged complexes1 and2 were obtained. The schemes of acid-base interactions in the MSA-DMF and HCl-DMF systems were compared.

The acidity scale of HCl solutions in N,N-dimethylformamide

The scale of the thermodynamic acidity of HCl solutions in DMF has been measured at 25 and 39.5 °C up to 15 mol L−1 acid concentration by the indicator method. It is shown that in the HCl-DMF system the ionization of the nitroaniline-derived indicators occurs by the ion pair mechanism. Within the temperature range studied acidity is independent of temperature. Indicators of the nitroaniline series are used.

Acidity function of methanesulfonic acid solutions in DMF

The acidity function of solutions of methanesulfonic acids (MSA) in DMF and H2O were measured by the indicator method at 25 °C in the 0–100% concentration range. A higher ionizing activity of HCl complexes with DMF as compared to that of similar MSA complexes was established. The relative ionizing activity of MSA molecules, H5O2+ ions, and ion pairs between MSA and DMF was determined.

Acidity function scale for H2SO4 solutions in phenol-acetone solvents with low water content at 25°C

The indicator method was employed to measure the acidity function H0S of H2SO4 solutions in solvents consisting of an equimolar mixture of phenol and acetone with 0.8% water (from 3.6·10−4 to 2.6·10−2 M H2SO4) and 2.5% water (from 4.3·10−4 to 0.32 M H2SO4) and of phenol and acetone in a molar ratio of 1:1.5 with 0.67% water (from 1.63·10−4 to 7.77·10−2 M H2SO4) and 2.09% water (from 4.49·10−4 to 0.35 M H2SO4) at 25°C. The indicators employed were 4- and 2-nitroaniline.

Acidity function of HCl solutions in mixtures of H2O with γ-butyrolactam

Conclusions1.The values of log (CB/CBH+) of 4-, 2-, and 2,6-dichloro-4-nitroanilines in the H2O-HCl-γ-butyrolactam (BL) system were obtained at 25°C, at various BL and HCl concentrations under conditions wherein BL is either nonionized, partially or completely ionized.2.It was shown that if BL is either completely nonionized or completely ionized, the Ho of an aqueous solution and the HoS of a solution of HCl in a H2O-BL mixture are equal at the same H5O2+ concentrations on a molar ratio scale.

Effect of 1,1,2,2-tetrachloroethane on IR spectra of HCl complexes withN,N-dimethylformamide and 1-methyl-2-pyrrolidone formed by a strong quasi-symmetric hydrogen bond

The effect of 1,1,2,2-tetrachloroethane (TCE) on the IR spectra of HCl complexes withN,N-dimethylformamide (DMF) and 1-methyl-2-pyrrolidone (N-MP) with strong quasisymmetric hydrogen bonds was studied using Multiple Attenuated Total Reflection (MATR) IR spectroscopy. The addition of TCE does not change the background absorption spectra, but results in a change in the extinction coefficients of some bands of these complexes. The analysis of the spectra shows that the HCl−DMF complexes interact only with one molecule of TCE, and the HCl−N-MP complexes interact with two molecules of TCE. It is shown that the neutral component of the system (TCE) has no effect on the parameters of the strong quasi-symmetric H-bond in the complexes studied.

Solvent effect on catalytic properties of the HCI-DMF-1,1,2,2-tetrachloroethane system

Ionization of 2- and 3-nitroanilines was studied in HCl-DMF-1,1,2,2-tetrachloro-ethane (TCE) solutions at 25 °C. The ionization capability of the medium and basicity constants pKi of indicators change depending on the ratio of the components. The numerical values of pKi are found to depend on the analytical composition of the DMF-TCE solvent. The solvent effect on pKi is associated with a change in the solvation of the nonionized form of the indicators.

The acidity functionsH 0 s of HCl solutions in EtOH with low water content

The acidity functionsH0s of HCl solutions in EtOH-H2O solvents containing 1.09, 3.0, and 5.0% water have been measured at 25 and 40 °C by the indicator method. The concentration of HCl changes from 10−2 to 36m. Nitroanilines, for which a protonation mechanism is realized in the studied systems, were used as indicators.For each solvent,H0s is temperature independent atmHCl < 4, and acidity atmHCl > 4 mol L−1 increases more rapidly at 25 °C than at 40 °C. The acidity functions of aqueous and water-ethanol solutions of HCl were compared, and the concentrations of proton solvates of different compositions and their relative protonating ability were evaluated.

Hammett acidity function of water-salt solutions of strong acids

The values of the acidity function H0s of HCl-KCl-H2O solutions (mKCl=2.73, 3.61) at 25°C were determined by the indicator method. An infinitely dilute solution of the acid in a H2O-KCl mixture of fixed composition is the standard state for H0s. A method for calculation of H0s of water-salt solutions of strong mineral acids was proposed.