Search

Thermodynamic equilibrium constants of protonation of (acetato)(octakis)(4-tert-butylphenyl)- and (acetato)(octakis(3-trifluoromethylphenyl)tetraazaporphynato)manganese(III) in a trifluoroacetic acid–dichloromethane medium are determined via spectrophotometric titration using Hammett acidity function H0 for a mixed solvent. The effect of the higher basicity of the mono-protonated forms against that of the neutral forms is established and interpreted using literature data on tetraazaporphyrin analogs. The role of functional substitution and the electronic structure of coordination centers in the acid–base behavior of porphyrazine complexes is determined. The obtained data are important for developing the theory of reactivity of macroheterocyclic compounds and creating actual supramolecular 2D and 3D structures based on porphyrazines.

The effect of medium acidity on the rate constant (k) of the reactions of alkanes (AlkH), cycloalkanes (c-AlkH), and arenes (ArH) in sulfuric acid solutions with peroxy compounds (H2O2 or (NH4)2S2O8), complexes (Pd(II), Pt(III), Hg(II)), acids (H2CrO4, HNO3, H2SO4, HVO3), 1-adamantanol (AdOH), and formaldehyde (CH2O) was analyzed using the equation log k = C0 – m0H0, where Н0 is the Hammett acidity function, C0 is the intercept on the ordinate, and m0 is the slope of the line in the coordinates log k – H0. All the reactions can be divided into three groups depending on the slope value (1 ~ m0 ≤ 3.4) in accordance with the degree of protonation of the main species: single protonation (H2O2 or (NH4)2S2O8, Pd(II), Pt(III)) (group 1); protonation followed by dehydration (AdOH, H2CrO4, HNO3, H2SO4, as well as HVO3, and CH2O in reactions with ArH in 57–65% and 60–80% H2SO4, respectively) (group 2); and more profound double or triple protonation (Hg(II), HVO3, and CH2O in reactions with AlkH and c-AlkH in 84–90% and 88–93% H2SO4, respectively) (group 3). For the active oxidant species in the HVO3–H2SO4 system and in H2SO4 itself, the thermochemical characteristics of their reactions with 2,3-dimethylbutane were evaluated using the DFT B3LYP/6-311G(d,p) quantum-chemical method, and the possibilities of alternative reaction mechanisms were analyzed.

The results of a study into the acid-base surface properties of four silicon-containing ash samples obtained from the above-ground part of the field horsetail plant species ( E. arvense L. ) are presented. The samples were derived according to various schemes, comprising oxidative roasting both with and without preliminary treatments involving water and solutions of hydrochloric acid having a concentration of 0.1 and 1.0 mol/l. It was shown that the content of silicon dioxide in the samples varies from 33 to 98 % depending on the conditions of processing of raw materials. Preliminary processing of the raw material with an acid solution prior to roasting results in the formation of ash having a high silicon oxide content. The main impurity elements are calcium, potassium, magnesium, aluminum and iron. Samples prepared without preliminary treatment, as well as those treated with water, are characterised by a large amount of alkaline earth metal- and potassium oxides. A comparative characteristic of the surface condition of the obtained ash samples is given using pH measurements and the Hammett acidity function method. The pH measurements allow the integral acidity of the surface to be evaluated, while the Hammett method, based on the selective adsorption of acid-base indicators, is used to study the distribution of surface centres by acid-base properties. The pH values of the aqueous suspensions of neutral, alkaline or acidic samples are determined depending on the plant tissue processing scheme. It was found that the surface of the samples is characterised by the presence of Lewis acid- (pKa +16.8), Bronsted basic- (pKa +7.15; +9.45) and acid- (pKa +2.5) active sites, the amount of which is determined by the composition of the samples. The high content of Lewis acid sites in the ash is associated with silicon atoms. The number of Bronsted sites depends on the horsetail treatment scheme. On the surface of samples obtained by oxidative roasting and those pretreated with water, the number of Bronsted active sites at pKa +2.5 and pKa +9.45 is higher compared to ash isolated following hydrolysis with hydrochloric acid. A comparative characteristic of the distribution curves of acid-base centres of silicon-containing ash samples obtained from the above-ground parts of field horsetail and rice straw is given, indicating their similarity.

Herein, a simple method was developed for the first time to pretreat sulfonic acid resin-based catalysts using different solvents (such as n-hexane, toluene, acetone, methanol, dimethyl sulfoxide, and sulfolane), and the as-treated resins were applied in DMM carbonylation. Except for sulfolane, the treatment solvents with a higher dipole moment resulted in a higher turnover number (TON) but lower DMM conversion and MMAc selectivity. SAresin-sulfolane-393 K exhibited excellent activity and stability for 50 h with an STY of 3.15 mmolMMAc (gcat h)−1 and nearly 100% MMAc selectivity. The Arrhenius plot of SAresin-sulfolane-393 K was generated from the reaction rate data at various temperatures, and the apparent activation energy was calculated to be 18.39 kJ mol−1. Karl Fischer analysis, in situ FT-IR analysis of CO adsorption, and static CO adsorption method indicated that the residual H2O in SAresin was significantly reduced and the CO adsorption capacity was obviously enhanced. The nitrogen adsorption–desorption isotherms, FT-IR spectra, and SEM and EDX-mapping images of SAresin-sulfolane-393 K proved that a larger average pore diameter and pore volume were generated, and sulfolane indeed entered the resin and changed the chemical composition of SAresin. The FT-IR spectra of the pyridine pre-adsorbed samples and Hammett acidity function (H0) confirmed that SAresin-sulfolane-393 K exhibited a stronger acid strength. The unusual activity and stability of SAresin-sulfolane-393 K are attributed to its stronger acid strength, low H2O content and excellent CO adsorption capability.

—The reaction of 2-amino-1,4-naphthoquinones with ninhydrin at 50–60°C in acetic acid leads to 4b,11b-dihydroxy-4b,5-dihydrobenzo[f]indeno[1,2-b]indole-6,11,12(11bH)-triones. The products were isolated as hydrates, and, when heated in DMSO with methanesulfonic acid or in acetic acid in the presence of sulfuric acid, they converted into 13-R-benzo[f]isochromeno[4,3-b]indole-5,7,12(13H)-triones. The rate of the conversion of 4b,11b-dihydroxy-4b,5-dihydrobenzo[f]indeno[1,2-b]indole-6,11,12(11bH)-triones to 13-R-benzo[f]isochromeno[4,3-b]indole-5,7,12(13H)-triones in solutions of sulfuric acid in acetic acid is linearly related to the Hammett acidity function.

Nanoporous Na+-montmorillonite perchloric acid as a novel heterogeneous reusable solid acid catalyst was easily prepared by treatment of Na+-montmorillonite as a cheap and commercially available support with perchloric acid. The catalyst was characterized using a variety of techniques including X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), energy dispersive X-ray spectroscopy (EDX), pH analysis and determination of the Hammett acidity function. The prepared reagent showed excellent catalytic activity for the chemoselective conversion of alcohols and phenols to their corresponding trimethylsilyl ethers with 1,1,1,3,3,3-hexamethyldisilazane (HMDS) at room temperature. Deprotection of the resulting trimethylsilyl ethers can also be carried out using the same catalyst in ethanol. All reactions were performed under mild and completely heterogeneous reaction conditions in good to excellent yields. The notable advantages of this protocol are: short reaction times, high yields, availability and low cost of the reagent, easy work-up procedure and the reusability of the catalyst during a simple filtration.

The carboxyl-functionalized porphyrin entangled with benzimidazolium-based ionic liquid (CFPBIL) was successfully synthesized and characterized by FT-IR, FT-NMR and TGA analysis. The proton level was determined by the Hammett acidity function, and DR spectra have been supported to confirm the band gap of photocatalyst. The present study reveals the metal-free, conventional photocatalytic acetalization of furfural to biofuel components under visible light irradiations using carboxyl-functionalized porphyrin catalyst. The effect of different parameters on the photocatalytic reaction, catalyst loading, ratio of furfural:alcohol, duration and intensity of light were investigated. The model reaction of furfural and ethanol in a home-made photoreactor using a 5-W LED presented that a very high yield of furfural acetal (92%) could be obtained under optimized conditions. Moreover, the eco-friendly method of acetalization reactions with higher alcohols (1-butanol, 1-pentanol, 1-hexanol, 1-octanol) was carried out at optimized reaction conditions which also afforded good to excellent yield of the target products, demonstrating the potential of CFPBIL as a highly active, stable and recyclable heterogeneous photocatalyst. Moreover, physical properties of biodiesel–diesel blends comprising B10, B20 and B30 were determined and furfural acetals were found as a potential fuel additive.

Nanoporous Na + -montmorillonite perchloric acid (MPA) as a novel heterogeneous solid acid catalyst was easily prepared. The physico-chemical properties of the catalyst were analyzed by a variety of techniques including X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), energy dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET) and nitrogen adsorption-desorption measurements, pH analysis and Hammett acidity function. The prepared reagent showed excellent catalytic activity for the green one-pot, three component synthesis of 3-methyl-4-arylmethylene-isoxazol-5(4 H )-one, pyrano [2,3- d ] pyrimidinone and 5-arylidine barbituric acid derivatives in aqueous media. The remarkable features of the present protocol are availability and low cost of the starting materials, reusability of the catalyst, short reaction times and high yields of the products.

Tin dioxide-based aerogels were produced by supercritical drying of gels, synthesized using propylene oxide, in CO2 and isopropanol. Aerogels consisted of nanocrystalline cassiterite and had a specific surface area of 210–270 m2/g. Sulfation with sulfuryl chloride imparted superacidic properties to the aerogels (the Hammett acidity function H0 reached values within the range – 11.99 ≥ H0 ≥ –12.7). Superacid SnO2 aerogels demonstrated high catalytic activity in 1-hexene oligomerization and isomerization.

A simple method was developed for the synthesis of sulfated bismuth oxide nanorods decorated with niobia (S-Bi2O3@Nb2O5). The material was well characterized with the help of several techniques such as FTIR, Raman, UV-vis DRS, PXRD, SEM/EDX, Elemental mapping, TEM, TGA, and BET analyses. Bronsted and Lewis acidic sites of the catalyst were measured using Hammett indicator method and pyridine FTIR spectroscopy respectively. The value of Hammett acidity function (H0 = 1.38) indicated the presence of significant number of Bronsted acidic sites while intense peak at 1452 cm−1 in the pyridine FTIR revealed the existence of a large number of Lewis acidic sites on the surface of material. Catalytic potential of the material was explored by synthesizing a library of pyrazolylmethanes via multicomponent reaction and results were excellent in terms of high product yield (90–98%) and reduced reaction time period (4–12 min). Solvent free reaction, ambient temperature, recyclability of the catalyst (up to five cycles), low E-factor (3.32–4.26), high atom economy (95.87–96.61%) and overall efficiency (92.04%–98.36%) confirmed the greenness of the present protocol.

The neutral rhodium(III) mer-[Rh(C2O4)Cl(py)3] (1) complex was found to release oxalate in concentrated aqueous solutions of strong acids (HNO3, HClO4, and CF3SO3H), generating the heteroleptic cis-diaquacomplex cis,mer-[RhCl(H2O)2(py)3]2+ (3). The process proceeded via formation of intermediate complex 2 ([Rh(HC2O4)Cl(H2O)(py)3]+) with the monodentately coordinated oxalato ligand. The structure of the intermediate complex 2 was probed using density functional theory (DFT) calculations. Experimental 13C nuclear magnetic resonance (NMR) data on the kinetics of oxalate release at 25 °C were evaluated within a consecutive reaction model with two pseudo-first order stages. The logarithms of the rate constants linearly depended on the Hammett acidity function of the medium. Cationic cis-diaquacomplex 3 was found to act as an active water reduction catalyst (WRC) under visible light irradiation when paired with the [Ir(ppy)2bpy]+ photosensitizer (PS).

Efficient conversion of glucose to levulinic acid (LA) was achieved with –SO3H functionalized ionic liquids in combination with a catalytic amount of metal salts under environmentally benign mild reaction conditions. Ionic liquids having different Bronsted acidic functional groups were prepared in the laboratory. The acidity of these ionic liquids was determined on the basis of the Hammett acidity function using UV-Visible spectroscopy. These catalysts were then screened in the conversion of glucose to LA using a batch autoclave under autogenous pressure at a temperature range of 140 to 175 °C. The structure–activity relationship of these multifunctional ionic liquids was correlated based on the Hammett function (Ho) and the catalytic activity results obtained in terms of glucose conversion and LA yield. The catalytic activity of the functionalized ionic liquids decreased in the order: IL-SO3H > IL-COOH > IL-OH, which is in good agreement with their Bronsted acidity trends. Furthermore, a metal salt based Lewis acidic co-catalyst, with metal ions (Fe, Co, Ni, Cu and Zn), was used in combination with the laboratory prepared Bronsted acidic functionalized ionic liquids in the efficient conversion of glucose to LA. Among all the investigated catalyst and co-catalyst systems, the –SO3H functionalized ionic liquid with nickel sulfate (NiSO4·6H2O) showed the highest LA yield (56.33%) and selectivity (56.37%). The synergistic effect of the metal ions helps in improving the LA yield by 10% as observed in our investigations. The co-catalytic effect of the transition metal chlorides and metal nitrates was not obvious as compared to transition metal sulfates. The catalyst could be recovered easily and reused three times without significant loss of activity.

In the present study, three novel dicationic Bronsted acidic molten salts based on benzimidazole were synthesized and characterized by FT-IR, 1HNMR, 13CNMR and FESEM techniques. Topological analysis of the atoms in molecules (AIM), electron localization function (ELF), Mayer bond index and local aromaticity analysis were applied to study the theoretical and electronic structure of the presented molten salts molecules, and the nature of C-N, N-H, N-S, O-H, and H-Cl bonding was investigated. Antibacterial activities of the molten salts were tested against the Bacillus subtilis (Gram-positive) and Escherichia coli (Gram-negative) by the agar well diffusion method. The catalytic activity of the novel salts was also assessed using two different one-pot multi-component reactions in two various media (in the presence and absence of solvent) for the promotion of the synthesis of pyrano[2,3-d]-pyrimidinone and polyhydroquinoline derivatives. In this study, also the acidity of molten salts (by determination of their Hammett acidity function (H0) and potentiometric titration method) and its effect on their catalytic activity was investigated. Easy preparation of the reagents, reusability, green process, simple work-up procedure, high yields, and short reaction times are the most important advantages of the application of these salts as catalysts.

The synchronized transformation of molasses, sugarcane juice, glucose, fructose, and sucrose into water insoluble platform chemicals, has stand up as a resourceful exercise to eradicate the expensive separation steps. On the other hand, the existing processes involve both acid-catalyzed and hydrogenation processes. We report herein, new green approaches for sequential conversion of sugarcane biorefinery products into biofuels using metal free carboxyl acid functionalized ionic liquid entangled porphyrin (CAFILP) photo-catalyst. Both levulinic acid (LA) and hydroxymethyl furfural (HMF) are water soluble and difficult to separate from the reaction mixture. Remarkably, the reaction of mixture containing LA and HMF easily converted to ethyl levulinate that considerably increases the yield of levulinate by affording another transformation technique excluding the hydrogenation step. The photo-catalytic activity of CAFILP affords ethyl levulinate (94%) and HMF (70%) yield that matches the acidic strength articulated by the Hammett acidity function. Photo-catalyst CAFILP exhibited intense absorptions in the visible regions with low band gap (1.49 eV) for visible light absorption is a key step of photocatalytic performance to convert sugarcane bio-refinery products into biofuels. The yield of HMF/LA was the highest from molasses, comprising more fructose that facilitates faster conversion compare to other biomass sources. Other products of sugarcane bio-refinery like sugarcane juice, sucrose, glucose, and fructose also have potential to add value in the bioenergy chain, affording HMF as the main product using optimized reaction conditions in presence of CAFILP photo-catalyst. The reusability of photocatalyst (up to 5 runs) was confirmed by easy filtration with good photo-catalytic activity.

In this work, 1,4-sultone and benzimidazolium-based ionic liquids (ILs) with four different anions were synthesized, and their structures were confirmed by nuclear magnetic resonance (NMR) and elemental analysis (CHNS). The acidity of the synthesized ILs was studied using Hammett acidity function and COSMO-RS. The waste cooking oil was used as a raw material for biodiesel production and their different fatty acids were determined by gas chromatography coupled with flame ionization detector (GC-FID). These four ILs, as catalysts, were screened and comparatively IL 3-methyl-1-(4-sulfo-butyl)-benzimidazolium trifluoromethanesulfonate [BSMBIM][CF3SO3] was selected for further detailed optimization study. This IL experimental efficiency results supported the Hammett acidity function and COSMO-RS study. The catalyst performance was studied and optimised the different parameters. The catalyst efficiency was studied in one and two-step reactions. [BSMBIM][CF3SO3] as a catalyst showed the esterification of waste cooking oil up to 78.13% in a single step reaction. Potassium hydroxide was used in the second step to trans-esterify the waste cooking oil up to 94.52%. The catalyst was reused for seven times with high-yield production. The obtained biodiesel was characterized by GC, NMR, FTIR, thermogravimetric (TGA) and their physicochemical properties were compared with the already established standards. The kinetic study of this transesterification reaction was evaluated and followed the first-order reaction mechanism.

The concept of "pH memory" has been established in the literature for the correlation between the pH of a pre-lyophilization solution and the ionization state of freeze-dried powder (lyophile). In this paper, the concept of "pH memory" is explored for the system of an aqueous solution, a frozen solution, and a lyophile. Sodium and potassium phosphate buffers in the pH range of 5-9 were frozen and lyophilized with sulfonephthalein indicators as acidity probes, and their Hammett acidity functions were compared to the initial pH of the aqueous solution. The results show that the acidities of the lyophiles are somewhat changed compared to the initial pHs, but the acidities in the frozen state differ more substantially. The Hammett acidity functions of the frozen buffers were found to be markedly dissimilar from the initial pH, especially in the sodium phosphate frozen at 233K, where an increase in the initial pH led to a decrease in the Hammett acidity function of the frozen state at a certain pH range. The large acidification observed after freezing the sodium phosphate buffer was not detected in the lyophiles after the sample had been dried; the phenomenon is explained considering the formed crystals analyzed by X-ray powder diffraction. The results suggest that monitoring the final acidity of a lyophile is not sufficient to predict all the acidity changes throughout the whole lyophilization process. The importance of well-controlled freezing and lyophilization conditions follows from the results of the research.

Zwitterionic sulfamic acid functionalized nanoclay (MMT-ZSA) was prepared with montmorillonite K10 as template, 3- aminopropyltriethoxysilane as linker and chlorosulfonic acid as a SO 3 H source. The physical and chemical properties of zwitterionic nanoclay were characterized by the following instrumental techniques: FT-IR spectroscopy, elemental analysis, TGA, DTA, SEM, XRD, elemental analysis and Hammett acidity function techniques. The catalytic activity of MMT-ZSA was investigated in the synthesis of dihydropyrano[2,3-c]pyrazoles and spiro[indoline-3,4 ´ -pyrano[2,3-c]pyrazole] derivatives via the multicomponent reaction between hydrazine hydrate (or phenyl hydrazine), malononitrile, β -keto ester and carbonyl compounds (1,2-di ketones and benzaldehyde derivatives) under solvent-free conditions. Using this synthetic method, the title compounds were prepared in high to excellent yields and short reaction times. Other remarkable features include heterogeneous reaction conditions, a much milder procedure, and a wide range of functional group tolerance, high reaction rates, absence of any tedious workup or purification, and reusability of the catalyst. This synthetic protocol also avoids hazardous reagents/solvents and is thus an eco-friendly, alternative approach to the existing methods.

The valorization of hemicellulose into valuable chemicals, such as C5 sugars and furfural, in a one-pot fashion is crucial. In this work, acidic ionic liquids in the presence of water showed high yields of C5 sugars (>80%) with >99% conversion of hemicelluloses at 160 °C. With a water + toluene biphasic solvent system, within 4 h, an 85% furfural yield was obtained directly from hemicellulose in a one-pot fashion using a catalytic amount of 1-methyl-3-(3-sulfopropyl)-imidazolium hydrogen sulfate. It was seen that Bronsted acidic ionic liquids (BAILs) perform better than solid acid [Faujasite and Mordenite zeolites; ion exchange resin, Amberlyst-15] and mineral catalysts [HCl and H2SO4]. The higher activity of BAILs compared to solid acids and mineral acids was correlated to the Hammett acidity function (Ho) and ion-dipole type of interactions. The catalysts were characterized using NMR (1H and 13C), elemental analysis and TGA to confirm that they were stable under reaction conditions and were thus recyclable.

In this work, 1,4-disulfopiperazine-1,4-diium chloride ([Piper-(SO3H)2]·2Cl), as a novel Bronsted acidic ionic catalyst is synthesized and characterized using a series of techniques including FT-IR, TGA, DTA, SEM, pH analysis and Hammett acidity function. This substance can significantly catalyze the N-Boc protection of amines without solvent interference at room temperature. The advantages of this manner are chemoselectivity, short reaction times, suitable yields, excellent yields of the products, without solvent interference and ease of preparation as well as reusability of the catalyst.

The batch reaction experiments have been made for the first time to investigate the effect of ionic structure on the reactivity and selectivity of the trioxane-forming reaction catalyzed by a Bronsted-acidic ionic liquid (IL). The ILs considered include 1-cyclohexyl-2-pyrrolidinonium trifluoromethanesulfonate ([NCyP][TfO]), 1-cyclohexyl-2-pyrrolidinonium benzenesulfonate ([NCyP][BSA]), 1-cyclohexyl-2-pyrrolidinonium p -toluenesulfonate ([NCyP][ p -TSA]), 1-octyl-2-pyrrolidinonium 2,4-dinitrobenzenesulfonate ([NOP][DNBSA]), 1-octyl-2-pyrrolidinonium benzenesulfonate ([NOP][BSA]), 1-octyl-2-pyrrolidinonium methanesulfonate ([NOP][MSA]), and 1-octyl-2-pyrrolidinonium trifluoromethanesulfonate ([NOP][TfO]). It is found that the yield of trioxane in the reaction solution correlates inversely with the Hammett acidity function H 0 of the aqueous solution of the corresponding ILs. Variation of the cation structure from [NCyP] + to [NOP] + exerts little influence on the yield and the selectivity of trioxane in the reaction solution. Using [TfO] − or [DNBSA] − in place of [MSA] − or [BSA] − apparently increases the yield of trioxane, but only slightly increases the concentration of formic acid in the reaction solution. The continuous production experiments have been made to investigate the performance of [NOP][MSA], [NOP][DNBSA], [NCyP][TfO], and H 2 SO 4 as an extraction distillation agent. Such effect of [NCyP][TfO] considerably overrides that of H 2 SO 4 . The yield and the selectivity of trioxane are both increased when [NCyP][TfO] is used instead of H 2 SO 4 at a reaction time 5 h.

This manuscript explores the catalytic activity, selectivity and stability of Aquivion ® PFSA PW98 in the oligomerization of glycerol. Aquivion ® PFSA PW98 is a solid superacid catalyst with a Hammett acidity function of −12. Furthermore, the perfluorinated structure allows this polymer to stand quite high operating temperature (up to 150–160 °C) without loss in mechanical and chemical integrity which is of huge interest for glycerol conversion. In this context, we discovered that Aquivion ® PFSA PW98 was nearly fully selective to oligoglycerols up to 80% conversion of glycerol. The oligomerization degree of oligoglycerol and the regioselectivity of the reaction (linear vs branched and cyclic isomers) were fully analyzed by means of GC and SEC chromatographies. In contrast to conventional solid acid catalysts, Aquivion ® PFSA PW98 was found highly robust in glycerol and was sucessfully recycled at least 10 times without apparent decrease in activity or selectivity. A comparison with Nafion NR 50 is also included to shed light on the potential of Aquivion ® PFSA PW98 for acid-catalyzed conversion of glycerol.

A series of choline chloride-based deep eutectic solvents (ChCl-DESs) were synthesized and characterized, and their performance in the dissolution of cellulose was investigated. The hydrogen-bond donors significantly (β-value) affected the properties of ChCl-DESs, causing differentiated dissolution performances. ChCl- imidazole (Im) showed the highest Hammett acidity function (1.869), hydrogen bond basicity (0.864), and dipolarity/polarizability effect (0.382) among the ChCl-DESs. The ChCl-Im showed the lowest pseudo-activation energy for viscous flow (31.76 kJ mol-1) among the ChCl-DESs. The properties of ChCl-Im caused the highest solubility of cellulose (2.48 wt.%) relative to the other ChCl-DESs. Polyethylene glycol (PEG), as a co-solvent, significantly (β-value) enhanced the accessibility of ChCl-Im to cellulose by breaking the supramolecular structure of cellulose, promoting its dissolution. The decrystallization of ChCl-Im-coupled PEG approximately doubled the dissolving capabilities, and the solubility increased by more than 80% in comparison with only ChCl-Im. The cellulose was directly dissolved by ChCl-Im-coupled PEG, and no other derivatives were produced.

Solutions of three Good’s buffers (HEPES, MOPS, and MES), both pure and mixed with sodium phosphate buffers (Na-P), are investigated in terms of the freezing-induced acidity changes in their operational pH ranges. The Good’s buffers have the tendency to basify upon freezing and, more intensively, at lower pHs. The acidity varies most prominently in MES, where the change may reach the value of two. Importantly, the Good’s buffers are shown to mitigate the strong acidification in the Na-P buffer. Diverse concentrations of the Good’s buffers are added to cancel out the strong, freezing-induced acidity drop in 50 mM Na-P that markedly contributes to the solution’s acidity; the relevant values are 3 mM HEPES, 10 mM MOPS, and 80 mM MES. These buffer blends are therefore proposed to be applied in maintaining approximately the acidity of solutions even after the freezing process and, as such, should limit the stresses for frozen chemicals and biochemicals.

[AAE]X composed of amino acid ester cations is a sort of typically &ldquo, bio-based&rdquo, protic ionic liquids (PILs). They possess potential Br&oslash, nsted acidity due to the active hydrogens on their cations. The Br&oslash, nsted 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&ndash, 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&middot, L&minus, 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.

The increase in energy demand and depletion of fossil fuels are among major issues of modern society. Valorization and transformation of raw materials in products of industrial value represents a challenge. This justifies the growing interest of scientific research towards the identification of suitable media and methodologies able to pursue above goals, paying attention to matter of sustainability. On this subject, we studied sulfonic-acid functionalized diimidazolium salts as catalysts for the conversion of fructose and sucrose to 5-hydroxymethylfurfural (5-HMF) in an ionic liquid mixture. In general, using these salts allowed us to obtain 5-HMF in good yields from both substrates in mild conditions. Indeed, at 60 °C and in the presence of 20 mol % of catalyst, 5-HMF yields of 60 and 30 % were obtained from fructose and sucrose, respectively. The catalytic system was recycled and used up to six times observing no appreciable loss in yield for the first four cycles. Moreover, we gathered mechanistic information by in situ 1H NMR monitoring the dehydration of fructose. To dissect the role of acidity on the reaction, we determined the Hammett acidity function of each salt. Comparison of these results with yields and reactivity observed in the presence of related monocationic salts and with a dicationic salt bearing only one sulfonic acid group allowed stating that the reactivity observed is the result of the combined action of acidity and structural features of the catalysts. Overall, the approach proposed here could contribute to pave the way to increase sustainability in the raw material valorization processes.

International audience; Two sets of activating solutions with increasing sodium hydroxide contents were prepared either with or without silicates. Their buffer capacities, i.e. their ability to resist changes in pH, were determined and compared using the Hammett acidity function, a measure of acidity appropriate for concentrated solutions. This is the first time the Hammett acidity function of sodium silicate solutions has been measured. The effects of the buffer capacity and of the initial Hammett acidity function on the reactivity of metakaolin-based pastes were assessed using isothermal conduction micro-calorimetry. The reactivity of metakaolin in sodium hydroxide solutions is shown to be directly related to the initial Hammett acidity function, whereas for sodium silicate mixtures, the buffer capacity is a more pertinent parameter. The mechanism deduced for the role of hydroxide ions during geopolymerization also highlights the role of silicate species as a hydroxide reservoir that nurtures the dissolution process.

The conversion of cellulose into valuable chemicals has attracted much attention, due to the concern about depletion of fossil fuels. The hydrolysis of cellulose is a key step in this conversion, for which Bronsted acidic ionic liquids (BAILs) have been considered promising acid catalysts. In this study, using BAILs 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. The glucose yields exceeded 10% when the H0 values of the BAIL aqueous solutions were below 1.5. The highest glucose yield was about 36% in 1-(1-octyl-3-imidazolio)propane-3-sulfonate (Oimps)/sulfuric acid (H2SO4) aqueous solution. A long alkyl side chain on the imidazolium cation, which increased the hydrophobicity of the BAILs, enhanced the glucose yield.

Regarding the subject of waste products/materials, recycling or reusing has had a pivotal role on account of environmental and economic reasons. As a consequence, the essential task, nowadays, can be invention of new and practical pathways to reuse or even recycle them. In this framework, until now, recycling of some waste products such as tile wastes has not been taken into consideration; so, we were prompted by the possibility of recycling tile wastes in the catalytic direction. To this end, we use them as cost-effective, available, and nontoxic support materials for the heterogenization of sulfuric acid, in order to prepare the novel nano-ceramic tile waste supported sulfonic acid catalyst (nano-ceramic tile waste-SO3H or n-CTW-SA). This solid acid catalyst was well characterized through FT-IR, XRD, FE-SEM, EDX, TEM, TGA, BET, BJH, pH analysis and Hammett acidity function. The as-prepared nano-ceramic tile waste supported sulfonic acid catalyst proved to be an active heterogeneous catalyst in multicomponent reactions (MRCs) for the rapid and efficient one-pot synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles in high yields and selectivity. In comparison with some other homogeneous and heterogeneous catalysts, nano-ceramic tile waste supported sulfonic acid displayed a greater activity. Moreover, being highly stable, inexpensive, accessible, retrievable, reusable, and having low toxicity are some other beneficial points of this catalyst.

Nano-zirconia-supported sulfonic acid [nano-ZrO2-SO3H (n-ZrSA)] is synthesized by immobilizing sulfonic acid groups on the surface of nano zirconium dioxide to produce a novel heterogeneous reusable solid acid nanocatalyst. This new nanocatalyst is characterized by FT-IR spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), the Hammett acidity function and pH analysis. The introduced nano-zirconia-supported sulfonic acid is used as an efficient and recyclable catalyst for different heterocyclic multicomponent reactions such as the synthesis of hexahydroquinoline, 1,8-dioxo-decahydroacridine, polyhydroquinoline and 1,8-dioxo-octahydroxanthene derivatives. Optimization of the reaction conditions was studied using a central composite design (CCD) which is one of the most widely used response surface methodologies. The newly prepared heterogeneous solid acid nanocatalyst is easily separated and reusable for five cycles without any apparent loss of its catalytic activity, which confirmed the stability of the covalent bonding of the sulfonic acid groups. n-ZrSA has advantages such as its low cost, low toxicity, ease of preparation, good stability, high reusability and operational simplicity.

A highly efficient and retrievable titanium dioxide-based nanocatalyst has been synthesized by covalent grafting of chlorosulfonic acid on amine-functionalized titania as a novel inorganic–organic hybrid heterogeneous nanocatalyst, which was characterized by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The acid strength of the catalyst was determined by pH analysis and the Hammett acidity function. The potential of the resultant nanocatalyst was effectively evaluated for the chemoselective oxidation of sulfides to sulfoxides and thiols to disulfides using 30% H2O2 as an oxidant at room temperature under solvent-free conditions, which led to high conversion rates and yields. Optimization of the reaction conditions was studied by central composite design (CCD), which is one of the most widely used response surface methodologies. The catalyst can be easily recycled up to 10 times without significant decrease in catalytic activity, which makes it a promising catalyst for practical and large-scale applications. This work is the first report that uses 2,4-toluene diisocyanate as a linker for immobilizing liquid acid on a support.

In this work, O-sulfonated poly(vinylpyrrolidonium) hydrogen sulfate ([PVP-SO3H]HSO4) has been prepared as a powerful recyclable solid acid catalyst and characterized using a variety of techniques including elemental analysis, FT-IR, TGA, SEM, XRD, pH analysis and Hammett acidity function. After preparation and identification the mentioned solid acid with wide acidic functional group sites, is utilized as a highly efficient catalyst for the synthesis of tetrahydrobenzimidazo[2,1-b]quinazolin-1(2H)-ones, 1-(benzothiazolylamino)phenylmethyl-2-naphthols and 2H-indazolo[2,1-b]phthalazine-1,6,11(13H)-triones in the absence of solvent. These eco-friendly protocols offer some advantages such as green and cost-effective procedures with excellent yields, shorter reaction times, simpler work-up, recovery, and reusability of a metal-free solid acid heterogeneous catalyst.

1,4-Disulfo-1,4-diazabicyclo[2.2.2]octane-1,4-diium dihydrogen sulfate {DABCO(HSO3)2(HSO4)2} as a new ionic liquid, is prepared and characterized by using different methods including FT-IR, NMR, Mass and SEM analysis as well as determination of the Hammett acidity function. This reagent can be used as an efficient catalyst for the promotion of the synthesis of 2H-indazolo[2,1-b]phthalazine-1,6,11(13H)-trione derivatives as important biologically active compounds with pharmaceutical properties. All reactions are performed in the absence of solvent using small amounts of the catalyst. Easy preparation of the catalyst, simple and easy work-up, mild reaction conditions, green process, excellent yields and short reaction times are the most important advantages this of method.

Succinimidinium N -sulfonic acid hydrogen sulfate is prepared as a new ionic liquid and characterized with a variety of techniques including FT-IR, 1 H and 13 C NMR, SEM, mass spectra method as well as Hammett acidity function. After identification, this reagent was used as an efficient catalyst for the multi-component synthesis of 2 H -indazolo[2,1- b ]phthalazine-trione derivatives. The simple work-up, mild reaction conditions, excellent yields and relatively short reaction times are the notable advantages of this protocol. In addition, the ionic liquid could be recycled several times without appreciable reduction in its catalytic activity.

A novel Bronsted solid acid named poly(vinylpyrrolidonium) hydrogen phosphate ([PVP-H]H2PO4) has been prepared by using H3PO4 and poly(vinylpyrrolidone) as green and commercially available reagents. The prepared reagent was characterized using a series of techniques including Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, energy-dispersive X-ray analysis (EDAX), pH analysis, and Hammett acidity function. The mentioned solid acid with wide acidic functional group sites can be utilized as a highly efficient, heterogeneous, and reusable catalyst for preparation of 2-amino-3-cyano-5-oxo-5,6,7,8-tetrahydro-4H-benzopyrans using aldehydes, dimedone, and malononitrile. Also, this catalyst can be reused for several times without loss of catalytic activity.

Succinimidinium N-sulfonic acid hydrogen sulfate ([SuSA-H]HSO4) as a new ionic liquid is prepared and characterized using a variety of techniques, including infrared spectra (FT-IR), 1H and 13C NMR, scanning electron microscopy, a mass spectra method, as well as by Hammett acidity function. The prepared reagent is efficiently able to catalyze the preparation of 5-arylmethylene-pyrimidine-2,4,6-triones via the condensation of aldehydes and barbituric acid. Further studies showed that the condensation of aldehydes with barbituric acid and malononitrile leading to pyrano[2,3-d]pyrimidinone derivatives can also be efficiently promoted in the presence of this reagent. The present methodology offers several advantages, including ease of the preparation and handling of the catalyst, simple and easy work-up, short reaction times, high yields of the products and recyclability of the catalyst.

A green approach for the promotion of the synthesis of Hantzsch products using poly(vinylpyrrolidinium) perchlorate {[PVPH]ClO4} as a new modified polymeric catalyst in the absence of solvent is reported. The title catalyst is easily prepared and characterized using a variety of techniques including infrared spectra, X-ray diffraction, thermal gravimetric analysis, scanning electron microscopy, pH analysis, and Hammett acidity function. Some of the advantages of this novel synthetic method are: easy preparation of the catalyst, short reaction times, high to excellent yields of the products, simple and easy work-up procedure, and reusability of the catalyst.