Stoichiometric Amount Of Water Research Articles

Pyrrole Compounds from the Two-Step One-Pot Conversion of 2,5-Dimethylfuran for Elastomer Composites with Low Dissipation of Energy.

A one-pot, two-step process was developed for the preparation of pyrrole compounds from 2,5-dimethylfuran. The first step was the acid-catalyzed ring-opening reaction of 2,5-dimethylfuran (DF), leading to the formation of 2,5-hexanedione (HD). A stoichiometric amount of water and a sub-stoichiometric amount of sulfuric acid were used by heating at 50 °C for 24 h. Chemically pure HD was isolated, with a quantitative yield (up to 95%), as revealed by 1H-NMR, 13C-NMR, and GC-MS analyses. In the second step, HD was used as the starting material for the synthesis of pyrrole compounds via the Paal-Knorr reaction. Various primary amines were used in stoichiometric amounts. 1H-NMR, 13C-NMR, ESI-Mass, and GC-Mass analyses confirmed that pyrrole compounds were prepared with very good/excellent yields (80-95%), with water as the only co-product. A further purification step was not necessary. The process was characterized by a very high carbon efficiency, up to 80%, and an E-factor down to 0.128, whereas the typical E-factor for fine chemicals is between 5 and 50. Water, a co-product of the second step, can trigger the first step and therefore make the whole process circular. Thus, this synthetic pathway appears to be in line with the requirements of a sustainable chemical process. A pyrrole compound bearing an SH group (SHP) was used for the functionalization of a furnace carbon black (CB). The functionalized CB (CB/SHP) was utilized in place of silica, resulting in a 15% mass reduction of reinforcing filler, in an elastomeric composite based on poly(styrene-co-butadiene) from solution anionic polymerization and poly(1,4-cis-isoprene) from Hevea Brasiliensis. Compared to the silica-based composite, a reduction in the Payne effect of about 25% and an increase in the dynamic rigidity (E' at 70 °C) of about 25% were obtained with CB/SHP.

Acidity of Carboxylic Acid Ligands Influences the Formation of VO2(A) and VO2(B) Nanocrystals under Solvothermal Conditions.

Vanadium dioxide (VO2) can adopt many different crystal structures at ambient temperature and pressure, each with different, and often desirable, electronic, optical, and chemical properties. Understanding how to control which crystal phase forms under various reaction conditions is therefore crucial to developing VO2 for various applications. This paper describes the impact of ligand acidity on the formation of VO2 nanocrystals from the solvothermal reaction of vanadyl acetylacetonate (VO(acac)2) with stoichiometric amounts of water. Carboxylic acids examined herein favor the formation of the monoclinic VO2(B) phase over the tetragonal VO2(A) phase as the concentration of water in the reaction increases. However, the threshold concentration of water required to obtain phase-pure VO2(B) nanocrystals increases as the pKa of the carboxylic acid decreases. We also observe that increasing the concentration of VO(acac)2 or the concentration of acid while keeping the concentration of water constant favors the formation of VO2(A). Single-crystal electron diffraction measurements enable the identification of vanadyl carboxylate species formed in reactions that do not contain enough water to promote the formation of VO2. Increasing the length of the carbon chain on aliphatic carboxylic acids did not impact the phase of VO2 nanocrystals obtained but did result in a change from nanorod to nanoplatelet morphology. These results suggest that inhibiting the rate of hydrolysis of the VO(acac)2 precursor either by decreasing the ratio of water to VO(acac)2 or by increasing the fraction of water molecules that are protonated favors the formation of VO2(A) over VO2(B).

Lewis Acid Regulated Divergent Catalytic Reaction between Quinone Imine Ketals (QIKs) and 1,3‐Dicarbonyl Compounds: Switchable Access to Multiple Products Including 2‐Aryl‐1,3‐Dicarbonyl Compounds, Indoles, and Benzofurans

AbstractA catalytic Lewis acid regulated reaction between quinone imine ketals (QIKs) and 1,3‐dicarbonyl compounds provides a divergent and tunable approach to a variety of skeletons, including a series of 2‐aryl‐1,3‐dicarbonyl compounds, indoles, and benzofurans. The use of lithium chloride and ferrous bromide gives C3‐ or C2‐alkylation products of the QIKs. The combination of ferrous bromide and trifluoromethanesulfonic acid delivers indole derivatives. Sequential hydrolysis and C3‐alkylation occur in the presence of ytterbium (III) trifluoromethanesulfonate and stoichiometric amounts of water. When the reaction is performed with trifluoromethanesulfonic acid and stoichiometric amounts of water, benzofuran is obtained. This protocol utilizes mild conditions, exhibits regio‐ and chemoselectivity, and has broad functional group tolerance.magnified image

Synthesis of C12A7 calcium aluminate aerogels

Calcium aluminate aerogels with mayenite stoichiometry C12A7 were prepared for the first time. The surface area of amorphous aerogel obtained after hydrolysis with stoichiometric amount of water was about 330 m2/g after the supercritical drying and 170 m2/g after calcination at 500 °C. The latter sample mostly consisted of 10–20 nm amorphous platelets. The mayenite phase was observed after the supercritical drying only if overstoichiometric amount of water was used for hydrolysis. Diphenyloxyl nitroxyl radicals were observed on the surface of calcined C12A7 aerogels after diphenylamine adsorption. Their formation on the surface of the samples calcined at 500 °C suggests that mayenite cages capable of stabilizing active forms of oxygen are present on the surface of the amorphous aerogels.

One step stereoselective synthesis of oxazoline-fused saccharides and their conversion into the corresponding 1,2-cis glycosylamines bearing various protected groups.

Herein we disclosed a straightforward synthesis of oxazoline-fused saccharides (oxazolinoses) from peracetylated saccharides and benzonitriles under acidic conditions with stoichiometric amounts of water. The density functional theory (DFT) calculations have revealed the origin of the stereoselectivity and the key role of water in promoting the departure of the acetyl group at C-2. The resulting oxazolinoses can be concisely converted into the corresponding 1,2-cis glycosylamines bearing various protected groups, allowing the access to schisandrin derivatives.

DBU‐Promoted Synthesis of 1,3‐Benzoxazines from Geminal Dibromo Olefins: Applications to the Construction of o‐Amido Phenacyl Bromides

AbstractHerein we demonstrated an approach for the synthesis of 1,3‐benzoxazines through 1,8‐Diazabicyclo(5,4,0)undec‐7‐ene (DBU) promoted annulation of geminal dibromoolefins. The key features of this work include good reaction yield, high regioselectivity, mild reaction condition, metal‐free approach, and broad scope. Synthetic application for some of the products is extended to achieve α‐bromomethyl Ketones (Phenacyl bromides) via ring opening sequence using stoichiometric amount of water and DMSO as solvent. We also successfully demonstrated the applicability to gram scale synthesis and one‐pot strategy. This protocol serves as an alternative approach to the conventional reaction of α‐bromination of ketones.

Sol-gel Syntheses of Photocatalysts for the Removal of Pharmaceutical Products in Water

A screening study on seven photocatalysts was performed to identify the best candidate for pharmaceutical products degradation in water. Photocatalysts were deposited as thin films through a sol-gel process and subsequent dip-coating on glass slides. The efficiency of each photocatalyst was assessed through the degradation of methylene blue first, and then, through the degradation of 15 different pharmaceutical products. Two main types of synthesis methods were considered: aqueous syntheses, where the reaction takes place in water, and organic syntheses, where reactions take place in an organic solvent and only a stoichiometric amount of water is added to the reaction medium. Photocatalysts synthesized via aqueous sol-gel routes showed relatively lower degradation efficiencies; however, the organic route required a calcination step at high temperature to form the photoactive crystalline phase, while the aqueous route did not. The best performances for the degradation of pharmaceuticals arose when Evonik P25 and silver nanoparticles were added to TiO2, which was synthesized using an organic solvent. In the case of methylene blue degradation, TiO2 modified with Evonik P25 and TiO2 doped with MnO2 nanoparticles were the two best candidates.

Ni-catalyzed hydroboration and hydrosilylation of olefins with diboron and silylborane

Herein we report a Ni-catalyzed formal hydroboration of olefins, which afforded anti-Markovnikov-type alkylboranes with B2pin2 and a stoichiometric amount of water. Formal hydrosilylation using air- and moisture-sensitive silylboranes also proceeded under optimized conditions. The reaction with trans-stilbene and D2O resulted in 1,2-H migration, which suggested that the reaction proceeded via β-hydride elimination and reinsertion mechanisms.

Novel Highly Luminescent Amine-Functionalized Bridged Silsesquioxanes.

Amine-functionalized bridged silsesquioxanes (BSs) were synthesized from bis[(3-trimethoxysilyl)propyl] amine via a solvent-mediated route. BS-1 and BS-2 were obtained at neutral pH with sub- and stoichiometric amounts of water, respectively, and high tetrahydrofuran content. BS-3 was prepared with hyperstoichiometric water concentration, high tetrahydrofuran content, and hydrochloric acid. BS-4 was synthesized with hyperstoichiometric water concentration, high ethanol content, and sodium hydroxide. BS-1 and BS-2 were produced as transparent films, whereas BS-3 and BS-4 formed white powders. Face-to-face stacking of flat or folded lamellae yielded quasi-hydrophobic platelets with emission quantum yields of 0.05 ± 0.01 (BS-1 and BS-2) or superhydrophilic onion-like nanoparticles with exciting emission quantum yields of 0.38 ± 0.03 (BS-3) and 0.33 ± 0.04 (BS-4), respectively. The latter two values are the largest ever reported for amine-functionalized siloxane-based hybrids lacking aromatic groups. Fast Grotthus proton hopping between = / = NH groups (BS-3) and = N−/ = NH groups (BS-4), promoted by H+ and OH− ions, respectively, and aided by short amine-amine contacts provided by the onion-like morphology, account for this unique optical behavior.

Oxidation-Resistant Nano-Reinforced PC-refractories of Modified Phenolformaldehyde Resin. Part 2. Modification of Phenolformaldehyde Resins with Silicon Alkoxide Sols1

Coking of phenolformaldehyde resins (PFRs) modified with various silicon-alkoxide sols produced structurally varied carbon binders with cavities filled by entrained sols, depending on the structures of the silicon-alkoxide hydrolysis products. The physicomechanical properties improved if PFRs modified with silicon-alkoxide sols were used. Sols with the stoichiometric amount of water hydrolyzed the silicon alkoxide more effectively.

Metal-Free Markovnikov-Type Alkyne Hydration under Mild Conditions.

A Markovnikov-type alkyne hydration protocol is presented using 20% CF3SO3H (TfOH) as the catalyst under unprecedented mild conditions applicable to various alkynes, including terminal arylalkynes, terminal nonfunctionalized aliphatic alkynes, and internal alkynes with excellent regioselectivity in good to excellent yields (average yields >85%). The reaction procedure operates under mild conditions (25-70 °C), with broad functional group compatibility, and uses only slightly more than a stoichiometric amount of water in the absence of any transition metal. The success of this protocol hinges upon the utilization of trifluoroethanol as the solvent.

Titanium oxo/alkoxo clusters with both phosphonate and methacrylate ligands.

The clusters Ti5O(OiPr)11(OMc)(O3PR)3 (OMc = methacrylate; R = Et, CH2CH2CH2Br) and Ti10(OiPr)16(OMc)4(O3PCH2CH=CH2)10 were obtained when Ti(OiPr)4 was reacted with the corresponding bis(trimethylsilyl) phosphonate and methacrylic acid. Oxo clusters of the composition Ti6O4(OiPr)10(OMc)2(O3PR)2, with a variety of groups R (Et, Ph, CH=CH2, CH2Ph, CH2CH=CH2, CH2CH2CH2Br, CH2CH2CN, CH2C(O)Me, CH2CH2OC(O)C(Me)=CH2), were formed instead, when a stoichiometric amount of water was added to the reaction mixture.Graphical abstract

Copper-catalyzed regioselective synthesis of furan via tandem cycloaddition of ketone with an unsaturated carboxylic acid under air.

A catalytic decarboxylative annulation has been developed for the regioselective synthesis of trisubstituted furans by the cycloaddition of ketones with α,β-unsaturated carboxylic acids under ambient air. A library of furan derivatives were obtained in good yields from the readily available substrates in the combination of a catalytic amount of Cu-salt and a stoichiometric amount of water. Water plays a crucial role in this catalytic transformation.

Effect of Sol Formation Conditions on the Structure and Properties of Anhydride-Cured Epoxy-Siloxane Composites

We used the sol–gel method to obtain anhydride-cured epoxy-siloxane composites. We show that increasing the sol holding time and using a stoichiometric amount of water for hydrolysis of the ethoxysilanes results in an increase in the crosslink density of the epoxy-siloxane composites, and we observe a relative increase in the glass transition temperature.

Synthesis and characterization of new, liquid, branched poly(methylvinylborosiloxanes)

Abstract New liquid branched poly(methylvinylborosiloxanes) (br-PMVBS) of random structure were synthesized in three steps. By reacting boric acid with an excess of dimethyldichlorosilane (Me2SiCl2) in dry ether a “borosiloxane precursor”: tris(chlorodimethylsilyl) borate B(OSiMe2Cl)3 was prepared. In the second step of synthesis ether solution of B(OSiMe2Cl)3 was added to a mixture of appropriate organic chlorosilanes (Me2SiCl2, MeViSiCl2, MeSiCl3, and Me3SiCl) and all reagents were reacted with stoichiometric amounts of water, in the presence of pyridine (as an acceptor of HCl), in dry ether, at low temperature (usually at -10 to 0 C). In order to fully react (“to block”) trace silanol groups, reactions of intermediate PMVBS with additional batches of Me3SiCl were carried out in the third step, C5H5N·HCl was filtered off and washed with a dry ether. The solvent was distilled off from filtrates and low molecular weight siloxane oligomers were removed by a vacuum distillation at 130-150 C. Chemical structures of br-PMVBS were confirmed by elemental analysis and spectroscopic methods (FTIR, emission atomic spectroscopy ICP-AES, and NMR: 1H, 29Si and 11B). On the basis of analysis of their 29Si-NMR spectra the microstructure of polysiloxane chains was proposed. The prepared br-PMVBS had in their structures: triple branching borosiloxane units: BO1.5 and in some cases methylsiloxane moiety CH3SiO1.5 (T). They contained linkages: Si-O-Si, Si-O-B, vinyl(methyl)siloxane functional groups (CH2=CH)MeSiO (Dvi), dimethylsiloxane mers (CH3)2SiO (D), and non-reactive trimethylsiloxy terminal groups (CH3)3SiO0.5 (M), but they did not have: hydroxyl functional groups: Si-OH and B-OH, and sensitive to water B-O-B linkages. Molecular weights of br-PMVBS (Mn = 1500-3300 g/mol; Mw = 3800-7400 g/mol) and their polydispersity (Mw/Mn = 2.0-2.5) were determined by a size exclusion chromatography (SEC).

Direct Proof for a Lower Reactivity of Monomeric vs. Dimeric Oxidovanadium Complexes in Alcohol Oxidation

Abstract Previous attempts to synthesize and isolate (thiobisphenolate) vanadium(V) dioxido complexes had always provided their dimers containing [O=V(μ‐O)2V=O]2+ cores, and these also dominate the solution reactivity. Hence, the behavior of their parent monomers, which represent the major species in solution, has remained uncertain. Herein we report the development of a synthetic route that allowed for the successful isolation, spectroscopic investigation, and structural characterization of the monomer PPh4[SLVO2] (3) [SL2– = 2′2‐thiobis(2, 4‐di‐tert‐butylphenolate)]. For this purpose PPh4[SLVOCl2] (1) had to be accessed first in order to convert it to the ethoxido compound PPh4[SLVO(OEt)2] (2), which is more prone to hydrolysis. Treatment of 2 with stoichiometric amounts of water followed by immediate cooling to –30 °C led to crystals of 3. After its dissolution NMR spectra were recorded that were identical with those obtained after dissolution of its dimer, thus confirming the monomer/dimer equilibrium postulated previously. The molecular structure of 3 revealed the absence of a V···S interaction, which, however, stabilizes its dimer, and thus suggested the employment of a bisphenolate ligand lacking a bridging sulfur atom to obtain an analogue, which does not undergo dimerization in solution. In EtL2– the sulfur atom is replaced by an ethylmethine unit and indeed the corresponding complex NBu4[EtLVO2] (4) proved to be stable as a monomer. Investigation of its potential as a catalyst for the oxidative dehydrogenation of 9‐fluorenol confirmed a much lower reactivity in comparison to dimeric complexes, which is discussed.

Synthesis and Structures of ansa‐Titanocene Complexes with Diatomic Bridging Units for Overall Water Splitting

The synthesis of a series of ansa-titanocene dichlorides [Cp'2TiCl2] (Cp' = bridged η(5)-tetramethylcyclopentadienyl) and the corresponding titanocene bis(trimethylsilyl)acetylene complexes [Cp'2Ti(η(2)-Me3SiC2SiMe3)] is described. The ethanediyl-bridged complexes [C2H4(C5Me4)2TiCl2] (2-Cl2) and [C2H4(C5Me4)2Ti(η(2)-Me3SiC2SiMe3)] (2-btmsa; btmsa = η(2)-Me3SiC2SiMe3) can be obtained from the hitherto unknown calcocenophane complex [C2H4(C5Me4)2Ca(THF)2] (1). Furthermore, a heterodiatomic bridging unit containing both, a dimethylsilyl and a methylene group was introduced to yield the ansa-titanocene dichloride [Me2SiCH2(C5Me4)2TiCl2] (3-Cl2) and the bis(trimethylsilyl)acetylene complex [Me2SiCH2(C5Me4)2Ti(η(2)-Me3SiC2SiMe3)] (3-btmsa). Besides, tetramethyldisilyl- and dimethylsilyl-bridged metallocene complexes (structural motif 4 and 5, respectively) were prepared. All ansa-titanocene alkyne complexes were reacted with stoichiometric amounts of water; the hydrolysis products were isolated as model complexes for the investigation of the elemental steps of overall water splitting. Compounds 1, 2-btmsa, 2-(OH)2, 3-Cl2, 3-btmsa, 4-(OH)2, 3-alkenyl and 5-alkenyl were characterised by X-ray diffraction analysis.

Application of computational chemistry methods to obtain thermodynamic data for hydrogen production from liquefied petroleum gas

The objective of this study was to estimate thermodynamic data, such as standard enthalpy, entropy and Gibbs free energy changes of reaction and, consequently, chemical equilibrium constants, for a reaction system describing the hydrogen production from Liquefied Petroleum Gas (LPG). The acquisition of those properties was made using computational chemistry methods and the results were compared with experimental data reported in the literature. The reaction system of steam reforming of LPG was reported as a set of seven independent reactions involving the chemical species n-C4H10, C3H8, C2H6, C2H4, CH4, CO2, CO, H2O, H2 and solid carbon. Six computational approaches were used: Density Functional Theory (DFT) employing Becke's three parameter hybrid exchange functional, and the Lee-Yang-Parr correlation functional (B3LYP) using the 6-31G++(d,p) basis set and the composite methods CBS-QB3, Gaussian-1 (G1), Gaussian-2 (G2), Gaussian-3 (G3) and Gaussian-4 (G4). Mole fractions of the system components were also determined between 873.15 and 1173.15 K, at 1 atm and a feed with a stoichiometric amount of water. Results showed that the hybrid functional B3LYP/6-31G++(d,p), G3 and G4 theories were the most appropriated methods to predict the properties of interest. Gaussian-3 and Gaussian-4 theories are expected to be good thermodynamic data predictors and the known efficient prediction of vibrational frequencies by B3LYP is probably the source of the good agreement found in this study. This last methodology is of special interest since it presents low computational cost, which is important when more complex molecular systems are considered.

Structural properties of trans hydrido–hydroxo M(H)(OH)(NH2CMe2CMe2NH2)(PPh3)2 (M = Ru, Os) complexes and their proton exchange behaviour with water in solution

We report the synthesis of Ru(II) and Os(II) trans hydrido-hydroxo complexes by reacting the unsaturated amido complexes MH(NHCMe2CMe2NH2)(PPh3)2 (M = Ru, Os) with stoichiometric amounts of water. Proton exchange is rapid at room temperature between the amine/water/hydroxide moieties which leads to signal averaging of the NMR properties which can be slowed at low temperature in order to see resonances of separate complexes. These compounds can also be cleanly converted back to their starting complexes by dehydration in the presence of 3 Å molecular sieves. X-ray crystal structures of these Ru(II) and Os(II) trans hydrido-hydroxo complexes reveal that the unit cell contains an additional molecule of water trapped in the crystal lattice which hydrogen bonds with a neighbouring hydroxo ligand, forming a water bridged dimer in the solid state. Although there are many cases of oxidative addition of water to transition metal complexes, relatively few cases are well characterized where water addition occurs via metal-ligand cooperation (bifunctional addition) without altering the oxidation state of the metal center.

Single-step solvothermal synthesis of mesoporous Ag–TiO2–reduced graphene oxide ternary composites with enhanced photocatalytic activity

With growing interest in the photocatalytic performance of TiO2-graphene composite systems, the ternary phase of TiO2, graphene, and Ag is expected to exhibit improved photocatalytic characteristics because of the improved recombination rate of photogenerated charge carriers and potential contribution of the generation of localized surface plasmon resonance at Ag sites on a surface of the TiO2-graphene binary matrix. In this work, Ag-TiO2-reduced graphene oxide ternary nanocomposites were successfully synthesized by a simple solvothermal process. In a single-step synthetic procedure, the reduction of AgNO3 and graphene oxide and the hydrolysis of titanium tetraisopropoxide were spontaneously performed in a mixed solvent system of ethylene glycol, N,N-dimethylformamide and a stoichiometric amount of water without resorting to the use of typical reducing agents. The nanocomposites were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, along with different microscopic and spectroscopic techniques, enabling us to confirm the successful reduction of AgNO3 and graphite oxide to metallic Ag and reduced graphene oxide, respectively. Due to the highly facilitated electron transport of well distributed Ag nanoparticles, the synthesized ternary nanocomposite showed enhanced photocatalytic activity for degradation of rhodamine B dye under visible light irradiation.