Comparison of theoretical and experimental investigation of protonation process of some thiones in acid media

PM3 semiempirical method was used for quantum chemical investigation in order to investigate the electronic properties and to determine the protonation centre in 1,2,4-triazoline-3-thione molecule. Confirmation of protonation center in acid media of investigated compounds was made using the values of atomic charges, as well as, proton affinity values. The results from semiempirical calculations indicated that the protonation center in the thione molecule was the sulphur atom. The behavior of thiones was investigated in mineral acid media using UV spectroscopy. The influence of the strength of the acid and its anion on the protonation process was discussed using three different mineral acids (perchloric, hydrochloric and phosphoric acid) for protonation. The protonation process in perchloric and hydrochloric acid took place in one step, while in phosphoric acid was not finished even when its concentration was to the highest degree. The dissociation constants of protonated forms (pKBH + ) and the solvation parameter m* values were calculated in accordance with "excess acidity" function method (Cox and Yates) using the absorbance data from the experimental and reconstructed spectra (Characteristic Vector Analysis (CVA)). The determined pKBH + values in hydrochloric acid had more negative value than those obtained in perchloric acid media. The pKBH + values were in agreement with the literature data for this class of compounds.

А singe isomer rotary switch demonstrating anti-Kasha behaviour: Does acidity function matter?

A novel rotary switch, overcoming the disadvantages of the hydrazone based switches with competitive proton acceptor sub-rotors, has been designed. The new compound contains pyridyl ring and COOH group as...

The Proton Dissociation of Bio-Protic Ionic Liquids: [AAE]X Amino Acid Ionic Liquids

[AAE]X composed of amino acid ester cations is a sort of typically “bio-based” protic ionic liquids (PILs). They possess potential Brønsted acidity due to the active hydrogens on their cations. The Brønsted acidity of [AAE]X PILs in green solvents (water and ethanol) at room temperature was systematically studied. Various frameworks of amino acid ester cations and four anions were investigated in this work from the viewpoint of structure–property relationship. Four different ways were used to study the acidity. Acid dissociation constants (pKa) of [AAE]X determined by the OIM (overlapping indicator method) were from 7.10 to 7.73 in water and from 8.54 to 9.05 in ethanol. The pKa values determined by the PTM (potential titration method) were from 7.12 to 7.82 in water. Their Hammett acidity function (H0) values (0.05 mol·L−1) were about 4.6 in water. In addition, the pKa values obtained by the DFT (proton-transfer reactions) were from 7.11 to 7.83 in water and from 8.54 to 9.34 in ethanol, respectively. The data revealed that the cationic structures of [AAE]X had little effect and the anions had no effect on the acidity of [AAE]X. At the same time, the OIM, PTM, Hammett method and DFT method were reliable for determining the acidic strength of [AAE]X in this study.

Direct Synthesis of Dimethyl Ether from Syngas on Bifunctional Hybrid Catalysts Based on Supported H3PW12O40 and Cu-ZnO(Al): Effect of Heteropolyacid Loading on Hybrid Structure and Catalytic Activity

The performance of bifunctional hybrid catalysts based on phosphotungstic acid (H3PW12O40, HPW) supported on TiO2 combined with Cu-ZnO(Al) catalyst in the direct synthesis of dimethyl ether (DME) from syngas has been investigated. We studied the effect of the HPW loading on TiO2 (from 1.4 to 2.7 monolayers) on the dispersion and acid characteristics of the HPW clusters. When the concentration of the heteropoliacid is slightly higher than the monolayer (1.4 monolayers) the acidity of the clusters is perturbed by the surface of titania, while for concentration higher than 1.7 monolayers results in the formation of three-dimensional HPW nanocrystals with acidity similar to the bulk heteropolyacid. Physical hybridization of supported heteropolyacids with the Cu-ZnO(Al) catalyst modifies both the acid characteristics of the supported heteropolyacids and the copper surface area of the Cu-ZnO(Al) catalyst. Hybridization gives rise to a decrease in the copper surface area and the disappearance of the strong acidic sites typical of HPW nanocrystals, showing all hybrids similar acid sites of weak or medium strength. The activity of the hybrids was tested for direct DME synthesis from syngas at 30 bar and 250 °C; only the hybrids with HPW loading higher than 1.4 monolayers showed activity for the direct synthesis of DME, showing that the sample loaded with 2.7 monolayers of heteropolyacid had higher activity than the reference hybrid representative of the most widely applied catalysts based on the combination of Cu-ZnO(Al) with HZSM-5. In spite of the high activity of the hybrids, they show a moderate loss in the DME production with TOS that denotes some kind of deactivation of the acidity function under reaction conditions.

Preparation and Characterization of a Novel Room Temperature Dicationic Ionic Liquid and its Application in the Synthesis of Xanthenediones Under Solvent-Free Conditions

Aim and Objective: In the present work, 1, 1’-sulfinyldiethylammonium bis (hydrogen sulfate) as a novel room temperature dicationic ionic liquid was synthesized and used as a catalyst for xanthenediones synthesis. Material and Method: The dicationic ionic liquid has been synthesized using ethylamine and thionyl chloride as precursors. Then, by the reaction of [(EtNH2)2SO]Cl2 with H2SO4, [(EtNH2)2SO][HSO4]2 was prepared and after that, it was characterized by FT-IR, 1H NMR, 13C NMR as well as Hammett acidity function. This dicationic ionic liquid was used as a catalyst for the synthesis of xanthenediones via condensation of structurally diverse aldehydes and dimedone under solvent-free conditions. The progress of the reaction was monitored by thin layer chromatography (ethyl acetate/n-hexane = 3/7). Results: An efficient solvent-free method for the synthesis of xanthenediones has been developed in the presence of [(EtNH2)2SO][HSO4]2 as a powerful catalyst with high to excellent yields, and short reaction times. Additionally, recycling studies have demonstrated that the dicationic ionic liquid can be readily recovered and reused at least four times without significant loss of its catalytic activity. Conclusion: This new dicationic ionic liquid can act as a highly efficient catalyst for xanthenediones synthesis under solvent-free conditions.

Brønsted acidic ionic liquids for cellulose hydrolysis in an aqueous medium: structural effects on acidity and glucose yield

Using Brønsted acidic ionic liquids with various structures, their acidic catalytic activity for cellulose hydrolysis assisted by microwave irradiation was assessed using the Hammett acidity function (H0) and theoretical calculations.