Basic Solvents Research Articles

Accessing 2,1-borazaronaphthols: self-arylation of 1-alkyl-2-aryl-3-bromo-2,1-borazaronaphthalenes.

Unlike their B-alkyl counterparts, brominated N-alkyl B-aryl 2,1-borazaronaphthalenes undergo a self-arylation reaction in the presence of a catalytic amount of palladium and base, in which the azaborine serves as both the electrophile and the nucleophile. The products of the self-arylation are air- and moisture-stable 2,1-borazaronaphthols, previously only observed in basic alcoholic solvents. The steric encumbrance of the azaborine appears to prevent formation of the corresponding boron acid anhydride, allowing access to a family of 2,1-borazaronaphthol derivatives.

The Lewis base-catalyzed silylation of alcohols--a mechanistic analysis.

Reaction rates for the base-catalyzed silylation of primary, secondary, and tertiary alcohols depend strongly on the choice of solvent and catalyst. The reactions are significantly faster in Lewis basic solvents such as dimethylformamide (DMF) compared with those in chloroform or dichloromethane (DCM). In DMF as the solvent, the reaction half-lives for the conversion of structurally similar primary, secondary, and tertiary alcohols vary in the ratio 404345:20232:1. The effects of added Lewis base catalysts such as 4-N,N-dimethylaminopyridine (DMAP) or 4-pyrrolidinopyridine (PPY) are much larger in apolar solvents than in DMF. The presence of an auxiliary base such as triethylamine is required in order to drive the reaction to full conversion.

Nanoparticle Electrocatalysts for the Oxidation of Waste Lignin

Lignin is a large organic molecule and a primary waste from the pulping industry and biorefineries [1, 2]. Currently, lignin has little value other than as a fuel to generate heat. Lignin can, however, be used as a renewable raw material for a variety of value-added chemicals. Unfortunately, catalytic processes are difficult to implement for the degradation of waste lignin because selective oxidation is difficult and these processes produce an unacceptable amount of solid residue like char [2, 3].Electrochemical processes, on the other hand, have several advantages over catalytic processes, including the use of mildly basic solvents as electrolytes, and control over the rate of reaction and the products. Thus, the electrochemical oxidation of waste lignin would be an ideal process to utilize this renewable raw material.While there have been efforts related to the electrochemical oxidation of lignin, most work has focused either on expensive platinum electrodes or on low surface area, large metal electrodes. However, nanoparticle electrocatalysts can be developed that enhance the rate of electrochemical reaction through enhancement of electrocatalyst surface area and porosity.We will report on our efforts to develop nanoparticle electrocatalysts with specific compositions and architectures for the electrochemical oxidation of lignin in weak alkaline solution. For example, Ni-Cu alloy nanoparticle electrocatalysts are suitable for the electro-oxidation of lignin in basic solution, as shown in Figure 1. Figure 1. Electrochemical oxidation of lignin on Ni-Cu alloy nanoparticle electrocatalysts. Baseline is 1 M NaOH in the absence of lignin. As shown in Figure 1, oxidation peaks in the presence of lignin occur around 0.03 V and 0.45 V vs. NHE that do not occur in the absence of lignin. Figure 1 indicates that lignin may undergo a complicated, multi-step oxidation process. For example, lignin may oxidize to one product at a lower potential, and that product may in turn oxidize to yet another product at higher potential. The oxidation potential and oxidation time (i.e., charge passed) affects the product distribution.One of the most important aspects of the electrochemical oxidation of lignin in alkaline solution is the identification of the oxidation products. We will present GC/MS data that identify lignin oxidation products. This process could provide an economic way of reducing the organic waste from the pulping and biorefinery industries. References. 1. A. French, “’Lignin’ May Be the Magic Word,” Innovation: America’s Journal of Technology Commercialization, June/July 2011.2. C. Grestini, “Conversion of Lignin: Chemical Technologies and Biotechnologies,” EuroBioRef Summer School, Universita Degli Studi di Roma, Castro Marina, Lecce, Italy, September 21, 2011.3. M. P. Pandey and C. S. Kim, “Lignin Depolymerization and Conversion: A Review of Thermochemical Methods,” Chemical Engineering and Technology, 34, 327-331 (1999)

Basic Molten Salt Route to Prepare Porous SrTiO3 Nanocrystals for Efficient Photocatalytic Hydrogen Production

AbstractSrTiO3 nanocrystals with porous structures were synthesized by a basic molten salt method. TEM images confirmed that the SrTiO3 nanocrystals possess a cellular morphology. High‐resolution TEM and selected‐area electron diffraction (SAED) analysis proved the existence of pores even in single crystals. Time‐dependent observations indicated that the formation of pores in the SrTiO3 nanocrystals resulted from the phase transformation of the TiO2 precursor in the basic solvent, and the process follows the dissolution–nucleation–aggregation growth mechanism. More importantly, the porous structure of the SrTiO3 nanocrystals is retained after the removal of the basic solvent by cool‐water washing, as the cool water can efficiently dissipate the heat of dissolution for the dissolution of the strong base into the water. The as‐prepared porous SrTiO3 nanocrystal photocatalysts exhibited a high rate of photocatalytic H2 evolution, which is attributed to their large specific surface area and good crystallinity.

Ionic Liquid-Based Aqueous Biphasic Systems with Controlled Hydrophobicity: The Polar Solvent Effect

Recovery of ionic liquids (IL) is necessary and urgent because of increasing production costs and potential environmental pollution. Dipolar aprotic solvents (dimethyl sulfoxide, DMSO; N,N-dimethylformamide, DMF; and N,N-dimethylacetamide, DMCA) and polar protic solvents (methanol, ethanol, and n-butanol) were used as cosolvents and antisolvents, respectively. These compounds have crucial effects on the separation and purification of ILs. We determined the effect of different polar solvents on the formation of aqueous biphasic systems (ABSs) using K3PO4 to control the hydrophobicity of 1-alkyl-3-methylimidazolium chloride ([Cnmim]Cl). Phase equilibria of the ABSs comprising IL + K3PO4 + water in the presence of the polar solvents were obtained at 298 K and at atmospheric pressure. In general, the IL aptitude that induced the formation of ABS in the presence of the polar solvents increased with decreasing hydrogen bond basicity and polarizability of the polar solvents in the following order: none < methano...

A new one-pot synthesis of novel hetarylazo-heterocyclic colorants and study of their solvatochromic properties

A simple synthetic strategy for synthesis of new series of hetarylazo-heterocycles is described. The effects of solvent on their electronic absorption spectra were analyzed using Kamlet–Taft equation. The results of fitting coefficients indicated that the solvatochromism of the studied compounds is mainly due to the solvent polarity rather than the solvent basicity and acidity.

The effects of pH and hydrogen bonds on photophysical properties of N-(4-bromobenzyl) substituted hydroxystilbazolium hemicyanine and merocyanine

Photophysical properties of (E)-1-(4-bromobenzyl)-4-(4-hydroxy-3-methoxystyryl) pyridinium bromide existing in equilibrium of its protonated (BSHB) and deprotonated (BS) forms at different pH were characterized by UV–Vis spectroscopy, and steady-state, and time-resolved fluorescence techniques.Absorption, steady-state, and time-resolved emission spectra, and synchronous scanning spectra were used to explain the observed phenomena. The pKa of BSHB in the ground state was determined. We also found that the deprotonated form – BS, being a weak base, is protonated upon addition of water. The pKa* of BSHB in the excited state was determined in two different ways giving different results. This inspires the discussion on the applicability of the use of the thermodynamic Förster cycle for calculation of the excited-state pKa* for hydroxystilbazolium dyes.Solvatochromism of both BSHB and BS in polar aprotic and protic solvents was analyzed using the four-parameter Catalán solvent scale and the Δf scale. This analysis indicates that both compounds in their emissive states have benzenoid-like (or zwitterionic for BS) structure in protic solvents. However, in aprotic polar solvents the contribution of the zwitterionic structure to their emissive state is reduced in favor of the quinoid structure.Importantly, the Catalán scale shows a strong influence of solvent basicity (hydrogen-bond accepting ability) on the absorption properties of BSHB, indicating strong stabilization of its ground and vertical excited state by hydrogen-bonded complexes. Contrary to BSHB, the absorption spectra of BS are affected by solvent acidity. Hydrogen – bonded complexes stabilize the ground state of this compound, although their energy decreases strongly upon excitation. The hydrogen-bonded complexes influenced the structures of both compounds in their excited states.

Preparation of Lignin-Based Quaternary Amine Anion Exchangers in NaOH Solutions and their Characteristics

A lignin-based quaternary amine anion exchanger (LQAE) modified from raw lignin was synthesized after the reaction with epichlorohydrin and triethylamine using an NaOH solution as the basic solvent. The reaction mechanism of the experiment was explored and validated. Effect of reaction conditions on the preparation of LQAE were investigated. The performance of the LQAE was characterized by FTIR, SEM, and elemental analysis. The adsorption rate and yield were the measurable indicators, and when the NaOH concentration was 6 M, the nitrate adsorption capacity and the yield were 36.7 mg nitrate/g anion exchanger lignin and 123.6%, respectively.

Acidity constant and solvatochromic behavior of some pyrazolo[1,5-a]pyrimidin-2-amine derivatives

The UV–visible electronic spectra of some azo compounds of pyrazolo[1,5-a]pyrimidin-2-amine have been studied. The solvatochromic behavior of these compounds was investigated by studying their spectra in pure organic solvents of different polarities such as cyclohexane carbon tetrachloride, chloroform, ethanol and DMF. These exhibits a red shift in its λmax with increase relative permittivity of medium changing from cyclohexane→carbon tetrachloride→chloroform→ethanol→DMF. The acid dissociation constants of these compounds were determined in aqueous–organic solvent mixtures such as acetone, methanol, ethanol and DMF. The ionization constants of the dyes in question depend largely on both the proportion and the nature of the organic solvent basicity contribute the major effects on the ionization process. In general, pKa values in all compounds decrease with increase relative permittivity of the medium. The acidity of studied azo compounds increases in the following order:p-NO2<m-CF3<p-F<p-Cl<p-H<p-CH3.

One of the Distinctive Properties of Ionic Liquids over Molecular Solvents and Inorganic Salts: Enhanced Basicity Stemming from the Electrostatic Environment and “Free” Microstructure

The basicity of ionic liquids (ILs) underlies many important IL-based processes including the dissolution and conversion of cellulose, the capture of CO2, and metal catalysis. In this work, we have disclosed the nature of the basicity of ILs, i.e., the difference between the basicity of IL and the basicity of the molecular solvent and inorganic salt, through a quantitative electrostatic and electronic analysis of the molecular surface for the first time. The results reveal one of the distinctive properties of ILs (enhanced basicity over molecular solvents and inorganic salts with the same basic site) stemming from their special electrostatic environment and microstructure. The enhancement is significant, from either the electrostatic aspect or the covalent aspect of basicity. The peculiar electrostatic environment of ILs leads to stronger basicity than similar molecular solvents, and the relatively freer microstructure of ILs contributes to the enhancement of basicity over their inorganic analogues. These results are highly instructive for better understanding the unique value of ILs and designing novel ILs to improve the efficiency of basicity-related processes.

Effect of solvent properties on reaction of isocyanates with mercaptans

Generalization of data on the reaction rate of catalyzed process between mercaptans and phenyl isocyanate in various media led to the conclusion that the reaction rate increased due to the specific, especially nucleophilic, solvation. The primary reaction stage is the formation of a complex between the acidic mercaptan and a base, a catalyst (triethylamine) or basic solvent.

Preferential Solvation of Some Sulfonamides in Propylene Glycol + Water Solvent Mixtures According to the IKBI and QLQC Methods

The preferential solvation parameters, which represent differences between the local and bulk mole fractions of the solvents near to the solute, in solutions of some sulfonamides in propylene glycol + water binary mixtures are derived from their thermodynamic properties by means of the inverse Kirkwood−Buff integrals (IKBI) and the Quasi-Lattice Quasi-Chemical (QLQC) method. From solvent effect studies, it is found that sulfonamides are sensitive to solvation effects; the preferential solvation parameter, δxPG,S, is negative in water-rich mixtures but positive in compositions from 0.20 to 1.00 in mole fraction of propylene glycol according to IKBI method and positive in all co-solvent compositions if the QLQC method is considered. It is conjecturable that in water-rich mixtures, hydrophobic hydration around the aromatic ring and/or other non-polar groups plays a relevant role in the solvation. The greater solvation by propylene glycol mixtures of similar solvent compositions and in co-solvent-rich mixtures could be due mainly to polarity effects and acidic behavior of the sulfonamides, in contrast to the more basic solvent propylene glycol.

Dipolarity versus Polarizability and Acidity versus Basicity of Ionic Liquids as a Function of Their Molecular Structures

The four empirical solvent polarity parameters according to the Catalán scale--solvent acidity (SA), solvent basicity (SB), solvent polarizability (SP), and solvent dipolarity (SdP)--of 64 ionic liquids (ILs) were determined by the solvatochromic method. The SA parameter was determined solely by using [Fe(II)(1,10-phenanthroline)2(CN)2] (Fe), the SB parameter by using the pair of structurally comparable dyes 3-(4-amino-3-methylphenyl)-7-phenylbenzo[1,2-b:4,5-b']difuran-2,6-dione (ABF) and 3-(4-N,N-dimethylaminophenyl)-7-phenylbenzo[1,2-b:4,5-b']-difuran-2,6-dione (DMe-ABF), and the SP and SdP parameters by using the homomorphic pair of 4-tert-butyl-2-(dicyanomethylene)-5-[4-(diethylamino)benzylidene]-Δ(3)-thiazoline (Th) and 2-[4-(N,N-dimethylamino)benzylidene]malononitrile (BMN). The separation of SP and SdP for a set of 64 various ILs was performed for the first time. Correlation analyses of SP with physicochemical data related to ionization potentials of anions of ILs as well as with theoretical data show the correctness of the applied method. The found correlations of the Catalán parameters with each other and with the alkyl-chain length of 1-alkyl-3-methylimidazolium-type ILs gives new information about interactions within ILs. An analytical comparison of the determined Catalán parameters with the established Kamlet-Taft parameters and the Gutmann acceptor and donor numbers is also presented.

H- and Fe-modified zeolite beta catalysts for preparation of trans-carveol from α-pinene oxide

The isomerisation of α-pinene oxide has been intensively investigated for selective preparation of campholenic aldehyde, a compound used in the synthesis of fragrances. Selective preparation of another product of α-pinene oxide rearrangement, trans-carveol, still remains a challenging task. Trans-carveol is a highly valuable compound used in perfume bases, food flavour compositions and as an active pharmaceutical substance in chemoprevention of mammary carcinogenesis.In the present work zeolite beta with different SiO2/Al2O3 molar ratios was modified by iron, characterised and tested per se and in the modified form for trans-carveol preparation from α-pinene oxide. The isomerisation reaction was carried out in a polar basic solvent N,N-dimethylacetamide at 140°C. The activities and selectivities of the catalysts were correlated with their acid properties and with the iron content.

A facile method for the fabrication of covalently linked PAH/PSS layer-by-layer films

We report a facile method for the fabrication of robust polyelectrolyte multilayers including strong polyanions. Covalently cross-linked PAH/PSS [PAH: poly(allylamine hydrochloride); PSS: poly(sodium-p-styrene sulfonate)] multilayered films are fabricated using a traditional layer-by-layer technique, followed by post-infiltration of a bifunctional photoactive molecule 4,4′-diazido-2,2′-stilbenedisulfonic acid disodium (DAS) and subsequent photochemical cross-linking. The stability of the cross-linked multilayers was enhanced significantly. Over 90% of the cross-linked multilayers were preserved in a basic solution or good solvent of the polyelectrolyte, forming a clear comparison with the un-crosslinked multilayers, which almost completely decomposed under the circumstances mentioned above.

Thermodynamics of solvation of pyridine in methanol-acetonitrile binary solvents

Heats of solution of pyridine (PY) over a range of compositions of methanol-acetonitrile (MeOH-AN) mixed solvents are measured at 298.15 K by calorimetry. Standard enthalpies of transferring PY from MeOH into its mixtures with AN are calculated from the obtained data. It is established that upon moving from methanol to acetonitrile, the solvation of PY becomes less exothermic, and marked changes in the energetics of amine solvation are observed at mole fraction ζAN = 0.8–1.0. It is shown that pyridine resolvates in the given range of mixed solvent compositions, predominantly through resolvation of the nitrogen atom in the amine group as a result of a considerable increase in the basicity of the mixed solvent. It is established that in the 0.0–0.8 range of AN mole fractions, PY molecules are predominantly solvated by MeOH molecules.

Structure of the Streptococcus pneumoniae Surface Protein and Adhesin PfbA

PfbA (plasmin- and fibronectin-binding protein A) is an extracellular Streptococcus pneumoniae cell-wall attached surface protein that binds to fibronectin, plasmin, and plasminogen. Here we present a structural analysis of the surface exposed domains of PfbA using a combined approach of X-ray crystallography and small-angle X-ray scattering (SAXS). The crystal structure of the PfbA core domain, here called PfbAβ, determined to 2.28 Å resolution revealed an elongated 12-stranded parallel β-helix fold, which structure-based comparisons reveal is most similar to proteins with carbohydrate modifying activity. A notable feature of the PfbAβ is an extensive cleft on one face of the protein with electrochemical and spatial features that are analogous to structurally similar carbohydrate-active enzymes utilizing this feature for substrate accommodation. Though this cleft displays a combination of basic amino acid residues and solvent exposed aromatic amino acids that are distinct features for recognition of carbohydrates, no obvious arrangement of amino acid side chains that would constitute catalytic machinery is evident. The pseudo-atomic SAXS model of a larger fragment of PfbA suggests that it has a relatively well-ordered structure with the N-terminal and core domains of PfbA adopting an extend organization and reveals a novel structural class of surface exposed pneumococcal matrix molecule adhesins.

Enthalpy characteristics of dissolution of L-tryptophan in water + formamides binary solvents at 298.15 K

Enthalpies of dissolution of L-tryptophan in aqueous solutions of formamide (FA), N-methylformamide (MFA), and N,N-dimethylformamide (DMF) are measured according to calorimetry at the concentration of amides x2 = 0−0.4 mole fraction. Standard values of enthalpies of dissolution and transfer ΔtrHo of L-tryptophan from water to binary solvent, as well as enthalpy coefficients of pair-wise interactions hxy of L-tryptophan with formamide molecules are calculated. The effect the composition of a waterorganic mixture has on the enthalpy characteristics of L-tryptophan is considered. The relation of ΔtrHo of L-tryptophan with the structure of amides is shown. A quantitative estimation of the contributions to the energy of L-tryptophan-formamide pair-wise interactions determined by polarity/polarizability, acidity, and basicity of organic solvent is performed using the four-parameter Kamlet-Taft correlation equation.

Selective Preparation of trans-Carveol over Ceria Supported Mesoporous Materials MCM-41 and SBA-15

Ce-modified mesoporous silica materials MCM-41 and SBA-15, namely 32 wt % Ce–Si–MCM-41, 16 wt % Ce–H–MCM-41 and 20 wt % Ce–Si–SBA-15, were prepared, characterized and studied in the selective preparation of trans-carveol by α-pinene oxide isomerization. The characterizations of these catalysts were performed using scanning electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorption and FTIR pyridine adsorption. Selective preparation of trans-carveol was carried out in the liquid phase in a batch reactor. The activity and the selectivity of catalyst were observed to be influenced by their acidity, basicity and morphology of the mesoporous materials. The formation of trans-carveol is moreover strongly influenced by the basicity of the used solvent and in order to achieve high yields of this desired alcohol it is necessary to use polar basic solvent.

A PPy-B15C5 modified lanthanum (III) electrode in acetonitrile and its thermodynamic application

Polypyrrole modified electrode prepared by electropolymerization of pyrrole in the presence of a complexing ligand, benzo-15-crown-5 (B15C5), was prepared and investigated as a La3+-selective electrode in acetonitrile. The potentiometric response of the electrode was linear within the La3+ concentration range 1×10−4 to 1×10−1M with a Nernstian slope of 19.5mV decade−1 in AN. The electrode was applied to study the complexation of the lanthanum (III) ion in acetonitrile with other basic solvent molecules (D) such as dimethyl sulfoxide, N,N-dimethylformamide, propylene carbonate, N,N,Diethylaniline and methanol. The successive complex formation constant (βi) and Gibbs energies of transfer (ΔGtr) of La3+ in AN in relation to such D were obtained.