Reactions Of Cations Research Articles

Adsorption of Pb (II) ions on variable charge oxidic calcined substrates with chemically modified surface.

The paper describes lead ion adsorption on variable charge oxidic calcined substrates with chemically modified surfaces. Amphoteric oxides of iron, aluminum, titanium, and manganese, change their surface electric charge after acid or alkaline treatment, letting cationic or anionic adsorption reactions from aqueous solutions. This property allows using them as adsorbing substrate for heavy metals retention in water treatment systems. Substrate was prepared by extruding cylindrical strips from a saturate paste of the oxidic lithological material-OLM; dries it up and thermally treated by calcination. The study was performed by triplicated trial, on batch mode, using 2 grams samples of treated with NaOH 0.1N and non-treated substrate. Lead analysis was performed by AAS-GF. Freundlich and Langmuir models were used to fit results. Comparing differential behavior between treated and non-treated substrates showed the variable charge nature of the OLM. Results show L-type isotherms for the adsorption of Pb(II) ions on the activated substrate, suggesting good affinity between Pb(II) ions and OLM's surface. Average value of adsorption capacity ( K) for activated substrate (1791.73±13.06), is around four times greater than the non-activated substrate (491.54±31.97), during the adsorption reaction, 0.35 and 0.26 mmolH + of proton are produced on the activated and non-activated substrate respectively using a 1 mM Pb(II) solution and 72.2 and 15.6 mmolH + using a 10 mM Pb(II) solution. This acidification agrees with the theoretic model of transitional metals chemisorption on amphoteric oxides, present in lithological material used for the preparation of adsorbent substrates, confirming the information given by the L-type isotherms. Results suggest that these variable charge oxidic adsorbent substrate show great potential as an alternative technique for water treatment at small and medium scale using granular filtration system. The easiness and low price make them suitable to apply in rural media where no treating water systems is available.

The Sensitivity of Structure to Ionic Radius and Reaction Stoichiometry: A Crystallographic Study of Metal Coordination and Hydrogen Bonding in Barbiturate Complexes of All Five Alkali Metals Li-Cs.

A systematic study has been conducted on barbiturate complexes of all five alkali metals, Li-Cs, prepared from metal carbonates or hydroxides in an aqueous solution without other potential ligands present, varying the stoichiometric ratio of metal ion to barbituric acid (BAH). Eight polymeric coordination compounds (two each for Na, K, and Rb and one each for Li and Cs) have been characterised by single-crystal X-ray diffraction. All contain some combination of barbiturate anion BA- (necessarily in a 1:1 ratio with the metal cation M+), barbituric acid, and water. All organic species and water molecules are coordinated to the metal centres via oxygen atoms as either terminal or bridging ligands. Coordination numbers range from 4 (for the Li complex) to 8 (for the Cs complex). Extensive hydrogen bonding plays a significant role in all the crystal structures, almost all of which include pairs of N-H···O hydrogen bonds linking BA- and/or BAH components into ribbons extending in one dimension. Factors influencing the structure adopted by each compound include cation size and reaction stoichiometry as well as hydrogen bonding.

Enhancing cathodic redox of metal-organic frameworks through biomimetic O2 adsorption

The energy density of conventional Li-ion/ Li-metal batteries is being approached their limitation due to the reliance on transition metal cationic redox. Although the anionic redox reactions of organic ligands in metal-organic cathode materials offer high specific capacity, they encounter substantial hurdles such as low redox potential and limited cyclability. To address this fundamental dilemma, we developed a biomimetic approach by designing metal-organic Fe2(dobdc) (Fe-MOF-74) with a channel framework structure that mimics the strong adsorption of methemoglobin for peroxide/superoxide species. When FeII2(dobdc) adsorbs O2 in unsaturated coordination, FeIII2(O2)2(dobdc) containing dispersed superoxide is formed and demonstrate a high specific capacity of 250.2 mAh g−1 in the voltage range of 2.0–4.5 V, making it a promising candidate for using as the high-energy-density cathode in Li-metal battery. Both experimental and computational evidence confirms that confined structure and biomimetic design enable FeIII2(O2)2(dobdc) cathode materials to realize synergistic electrochemical reactions of metal cations (Fe3++ e−↔ Fe2+) and oxygen anions (O2−+ e−↔ O22−) with high discharge voltages and high reversibility. This biomimetic design, along with confined structure strategies, opens a new pathway for discovering effective electrode materials with diverse Li-ion storage models.

Dual‐Wavelength Vat Photopolymerization 3D Printing with Hybrid Acrylate‐Epoxy Resins: Influence of Resin Composition on Microstructure and Mechanical Properties

Dual‐wavelength vat photopolymerization 3D printing represents a convenient technology for the fabrication of objects with heterogeneous and locally controlled mechanical properties. By using two λ‐orthogonal cross‐linking reactions, it is possible to produce soft and stiff photopolymers with a single resin vat by switching the light source. Herein, hybrid acrylate‐epoxy resins are selectively cured by using either visible or UV light. At 405 nm, a free radical curing of the acrylate monomers is induced while irradiation with 365 nm triggers an additional cationic ring opening reaction of the epoxy monomer yielding interpenetrating photopolymer networks. In a comprehensive approach, the influence of the resin composition and the applied wavelength on cure kinetics, film morphology, (thermo)mechanical properties, and printability are studied. Fully separated as well as homogenous network morphologies are obtained depending on the ratio between acrylate and epoxy monomers, cure rate and applied light source (405 vs 365 nm). In general, glass transition temperature, stiffness, and tensile strength of the photopolymers increase with rising epoxy content. In contrast, a higher epoxy concentration in combination with a higher amount of the cationic photoinitiator compromises on the system's orthogonality, giving rise to the important role of the resin composition in dual‐wavelength vat photopolymerization 3D printing.

Leveraging the Activated Monomer Mechanism to Create Grafted Polymer Networks in Epoxide–Acrylate Hybrid Photopolymerizations

Hybrid epoxide–acrylate photopolymerization enables the temporal structuring of polymer networks for advanced material properties. The ability to design polymer network architectures and to tune mechanical properties can be realized through the control of the cationic active center propagation reaction (active chain end mechanism) relative to the cationic chain transfer reaction (activated monomer mechanism). Grafted polymer networks (GPNs) can be developed through the covalent bonding of epoxide chains to acrylate chains through hydroxyl substituents, making hydroxyl-containing acrylates a promising class of chain transfer agents. This work demonstrates the formation of these GPNs and explores the physical properties obtained through the control of hydroxyl content and hybrid formulation composition. The GPNs exhibit a lower glass transition temperature than the neat epoxide network and result in a more homogeneous network. Further investigations of hydroxyl-containing acrylates as chain transfer agents will generate a wider range of physical property options for photopolymerized hybrid coatings, sealants, and adhesives.

Mechanistic Studies on Rhodium-Catalyzed Chemoselective Cycloaddition of Ene-Vinylidenecyclopropanes: Water-Assisted Proton Transfer.

Rhodium-catalyzed cycloaddition reactions are a powerful tool for the construction of polycyclic compounds. Combined experimental and DFT studies were used to investigate the temperature-controlled chemoselectivity of cationic rhodium-catalyzed intramolecular cycloaddition reactions of ene-vinylidenecyclopropanes. After a series of mechanistic studies, it was found that trace amounts of water in the reaction system play an important role in generating the product with endo double bond located on a five-membered ring and revealed that trace amounts of water in the reaction system, including the rhodium catalyst, substrate and solvent, were sufficient to promote the formation of the product with endo double bond located on a five-membered ring, and additional water could not further accelerate the reaction. DFT calculation results show that the addition of water indeed significantly lowers the energy barrier of the proton transfer step, making the formation of the product with endo double bond located on a five-membered ring more likely to occur and confirming the rationality of water-assisted proton transfer occurring in the selective access to the product with endo double bond located on a five-membered ring.

From the Iron Pentacarbonyl Cation to Heteroleptic η6-arene Carbonyls and bis-η6-arene Cations.

Partial ligand substitution at the iron pentacarbonyl radical cation generates novel half-sandwich complexes of the type [Fe(η6-arene)(CO)2]⋅+ (arene=1,3,5-tri-tert-butylbenzene, 1,3,5-trimethylbenzene, benzene and fluorobenzene). Of those, the bulkier 1,3,5-tri-tert-butylbenzene (mes*) derivative [Fe(mes*)(CO)2]⋅+ was fully characterized by XRD analysis, IR, NMR, cw-EPR, Mössbauer spectroscopy and cyclic voltammetry as the [Al(ORF)4]- (RF=C(CF3)3) salt. Chemical electronation, i. e., the single electron reduction, with decamethylferrocene generates neutral [Fe(mes*)(CO)2], whereas further deelectronation under CO-pressure leads to a dicationic three-legged [Fe(mes*)(CO)3]2+ salt with [Al(ORF)4]- counterion. The full substitution of the carbonyl ligands in [Fe(CO)5]⋅+[Al(ORF)4]- mainly resulted in disproportionation reactions, giving solid Fe(0) and the dicationic bis-arene salts [Fe(η6-arene)2]2+([Al(ORF)4]-)2 (arene=1,3,5-trimethylbenzene, benzene and fluorobenzene). Only by employing the very large fluoride bridged anion [F-{Al(ORF)3}2]-, it was possible to isolate an open shell bis-arene cation salt [Fe(C6H6)2]⋅+[F-{Al(ORF)3}2]-. The highly reactive cation was characterized by XRD analysis, cw-EPR, Mössbauer spectroscopy and cyclic voltammetry. The disproportionation of [Fe(C6H6)2]⋅+ salts to give solid Fe(0) and [Fe(C6H6)2]2+ salts was analyzed by a suitable cycle, revealing that the thermodynamic driving force for the disproportionation is a function of the size of the anion used and the polarity of the solvent.

Molecular geochemistry of radium: A key to understanding cation adsorption reaction on clay minerals

Adsorption reactions of various cations on clay minerals have different effects on their environmental behaviors depending on the molecular-scale adsorption structure. Some cations form outer-sphere complexes via hydration, while others create inner-sphere complexes through dehydration. This preference dictates their environmental impact. However, the factors controlling these complex formations remain unclear. Furthermore, research on the adsorption preferences of radium (Ra) is lacking. Thus, this study conducted the first EXAFS study of Ra2+ adsorbed on clay minerals and showed that Ra2+ forms inner-sphere complexes on vermiculite, which can be surprising because Ra2+ is a divalent cation and prefers to be hydrated. In order to investigate the factors controlling the complex formations, this study conducted systematic EXAFS measurements and DFT calculations for alkali and alkaline earth metal cations. The results showed the importance of the size-matching effect between the adsorbed cation and the cavity of the tetrahedral sheets and that the complex formation can be estimated by the combination of the ionic radius and hydration enthalpy of the adsorbed cation. Furthermore, this study also analyzed environmental core samples. Their results showed the fixation of Ra2+ by clay minerals and the controlling factors can effectively predict cation environmental behavior.

Realization of Selector‐Memory Bi‐Functionality with Self‐Current Regulation Utilizing Poly‐Crystalline Based GST Electrolyte for Memristor Hardware Development

AbstractConductive bridge random‐access memory (CBRAM) are two terminal devices that offer excellent switching performance. In addition, CBRAM shows various switching modes, including volatile threshold switching (TS) and nonvolatile threshold switching (N‐TS). These properties expand its applications to memory, selector, biological synapses, and neurons. However, due to the uncontrollable behavior of stochastic switching between TS and N‐TS in CBRAM devices, a novel approach is needed to improve the switching performance of CBRAM. Moreover, conventional devices that have different stacking between TS and N‐TS increase fabrication cost and worsen the device yield. Here, the selector‐memory bi‐functionality with self‐current regulation effect of Ag‐inserted Ge2Sb2Te5 (GST) thin films is demonstrated. Selector‐memory bi‐functionality, having TS behavior with an adjustable on/off current, with confined conductive filaments (CFs) improves the uniformity and reduces the fabrication cost by implementing TS/N‐TS in a single stack. From the material analysis, it becomes evident that confined Ag‐based CFs within GST films are key factors for realizing selector‐memory bi‐functionality. The selector‐memory bi‐functionality is achieved through the reaction of Ag metal cations with non‐bonded Te atoms in GST film depending on field polarity. These results suggest that the Ag‐inserted GST film contributes to the development of large‐scale nonvolatile memory and neuromorphic application.

Elution of Divalent Cations from Iron Ore Mining Waste in an Indirect Aqueous Mineral Carbonation for Carbon Capture and Storage

Mining waste is generated in vast quantities globally, which can have negative environmental consequences. This study highlights the utilization of iron ore mining waste as feedstock material in the preparatory step of an indirect aqueous mineral carbonation for carbon sequestration. The role of reactive cations (Ca2+, Mg2+, and Fe2+) was investigated in view of their elution behavior to improve carbonation efficiency. An elution experiment was carried out for the divalent cations using different acids (oxalic, HCl, acetic, and formic acid) at different concentration solutions (up to 1.5 M) and times (up to 100 min) at ambient temperature. The initial analysis confirmed the presence of divalent cations in the sample. The elution approach at ambient temperature resulted in the elution efficiency of Fe2+ (30.4%), Mg2+ (54%) using oxalic acid, and Ca2+ (98%) using HCl at a relatively short time between 50 and 100 min. It was found that for the iron ore mining waste, oxalic acid and HCl were best suited as elution agents for the Fe2+ and Mg2+, and Ca2+, respectively. The CO2 sequestration potential was calculated to be 131.58 g CO2/kg residue. A further carbonation step using a complexing agent (1,10 phenanthroline) confirmed the formation of siderite and magnesite along with phenanthroline hydrates. Findings have shown that the indirect mineral carbonation of the iron mining waste with complexing agent might improve carbonation efficiency, thus indicating that this material is useful for long-term carbon capture and storage applications.

F-Block reactions of metal cations with carbon dioxide studied by inductively coupled plasma tandem mass spectrometry.

f-Block chemistry offers an opportunity to test current knowledge of chemical reactivity. The energy dependence of lanthanide cation (Ln+ = Ce+, Pr+, Nd+-Eu+) and actinide cation (An+ = Th+, U+-Am+) oxidation reactions by CO2, was observed by inductively coupled plasma tandem mass spectrometry. This reaction is commonly spin-unallowed because the neutral reactant (CO2, 1Σ+g) and product (CO, 1Σ+) require the metal and metal oxide cations to have the same spin state. Correlation of the promotion energy (Ep) to the first state with two free d-electrons with the reaction efficiency indicates that spin conservation is not a primary factor in the reaction rate. The Ep likely influences the reaction rate by partially setting the crossing between the ground and reactive states. Comparison of Ln+ and An+ congener reactivity indicates that the 5f-orbitals play a small role in the An+ reactions.

Reaction of size-selected iron-oxide cluster cations with methane: a model study of rapid methane loss in Mars' atmosphere.

We report gas-phase reactions of free iron-oxide clusters, FenOm+, and their Ar adducts with methane in the context of chemical processes in Mars' atmosphere. Methane activation was observed to produce FenOmCH2+/FenOmCD2+ and FenOmC+, where the reactivity exhibited size and composition dependence. For example, the rate coefficients of methane activation for Fe3O+ and Fe4O+ were estimated to be 1 × 10-13 and 3 × 10-13 cm3 s-1, respectively. Based on these reaction rate coefficients, the presence of iron-oxide clusters/particles with a density as low as 107 cm-3 in Mars' atmosphere would explain the rapid loss of methane observed recently by the Curiosity rover.

Activation of small molecules by ambiphilic NHC-stabilized phosphinoborenium cation: formation of boreniums with B-O-C, B-O-B, and B-O-P structural motifs

The reactivity of the phosphinoborenium cation supported by a 1,3,4,5-tetramethylimidazolin-2-ylidene ligand toward small molecules was explored. The phosphinoborenium cation exhibited dual Lewis acid–base properties due to the presence of the...

Structural and Electrochemical Investigation of 3D Tunnel Type Li0.44MnO2 Cathode Material for Secondary Li-Ion Batteries

The design of new cathode materials remains a key goal in the development of (post) Li-ion batteries. In that regard, densely packed structures like Li0.44MnO2 are judicious for study. The presence of Mn as a transition metal makes it more attractive due to its sustainable nature, low cost, elemental abundance, structural diversity/polymorphism, and rich oxidation states (2+ to 7+) offering tunable redox potential [1]. Here, we have investigated Mn-based tunnel-type Li0.44MnO2 oxide for secondary LIBs. i) Li44MnO2 (LMO) was prepared by a soft chemical method using the corresponding sodium manganese oxide (Na0.44MnO2) as a parent compound [2]. The crystal structure of Li0.44MnO2 maintains the parent Na0.44MnO2-type tunnel structure which is analogous to Na4Mn4Ti5O18 having an orthorhombic (s.g. Pbam) crystal system [3]. To understand redox chemistry, this material was studied for both cationic (Mn) and anionic (O) redox reactions using ex-situ X-ray photoelectron spectroscopy. The lithium (de)insertion mechanism of Li0.44MnO2 was explored involving ab initio calculations and in-situ X-ray diffraction experiments. Combined with electrochemical measurements, structural characterizations, and first principles DFT calculations revealed the capacity correlated strongly with both cationic and anionic redox reactions. ii) We have studied the phase transition of Li44MnO2 from a 3D tunnel-type structure to a cubic spinel structure by in-situ X-ray diffraction and Raman spectroscopy. The mechanism of transformation was elucidated by employing transmission electron microscopy. In this case, diffusion-less transformation occurs involving the rearrangement of atoms during heating [4]. An increase in the average redox potential from the pristine orthorhombic phase to the final spinel phase was observed by electrochemical studies. iii) Further to improve the electrochemical performance of Li0.44MnO2, Ti was used as a dopant. The Li0.44[Mn1-xTix]O2 (x=0, 0.11, 0.22, 0.33, 0.44, 0.56) series were obtained with chemical ion exchange from Na precursors. The Na precursors (Na0.44[Mn1-xTix]O2) were prepared via a simple solid-state route. Ti-substituted compositions exhibited similar crystal structures to their parent LMO i.e. orthorhombic framework with Pbam symmetry. A tunnel-type morphology was observed in all cases. The electrochemical performance of Ti-substituted LMO as cathode material for LIBs was studied in a half-cell configuration. The structure and electrochemical properties of Ti-doped LMO, reaching the highest capacity of 128 mAh/g, will be described. Keywords: batteries; cathode; tunnel type manganese oxides; phase transformation; doping

Electrochemistry and Organic Synthesis: New Adventures with Olefin Coupling Reactions and Electrode Surfaces

Electrochemistry has long offered opportunities to explore new modes of reactivity, new approaches for introducing selectivity into synthetic reactions, and new strategies for the synthesis of everything from complex molecules to complex, addressable molecular surfaces. In the talk to be given, two aspects of our efforts along these lines will be detailed. In the first, we will take a look at recent efforts to use anodically-generated reactive intermediates to convert readily available small molecules into functionalized synthetic building blocks and natural product derivatives. Key to these efforts are oxidation reactions that generate reactive radical cation and radical intermediates. In one application, newly available chiral lactols synthesized using methodology developed by the Lin (Cornell) and Miller (Yale) groups are being transformed into C-glycoside and aza-C-glycoside derivatives. The reactions take advantage of oxidation reactions of either enol ether or vinylsulfide groups. The cyclization reactions and the subsequent deprotection strategy needed for converting the cyclization products into a useful synthetic building block will be highlighted. In a second application of an anodic cyclization, the role of thioamides in reactions targeting the chrysosoporazine family of natural products will be discussed. The reactions seek to provide an efficient method for converting lignin derived building blocks into molecules that reduce the efflux of anticancer drugs from cells. Initial cyclization attempts utilizing amide based N-radicals and anodic olefin coupling reactions were not successful. Those reactions consistently led to over-oxidation of the products that contain a highly electron-rich aryl ring. The use of thio-amide derived radicals provides a method to circumvent this problem.In the second topic to be discussed, the question of how one might begin to induce asymmetry into such electrochemical cyclizations will be highlighted. The chemistry focuses on efforts to influence the course of both electrochemical oxidation and reduction reaction and non-redox based transition metal catalyzed reactions with the surface of an electrode.

Manganese-Based Tunnel and Layered Oxide Cathodes for Secondary Alkali-Ion Batteries

Designing new cathode materials remains crucial in developing (post) Li-ion batteries. Mn-based oxide cathodes have received wide attention due to their sustainable nature, low cost, elemental abundance, structural diversity/polymorphism, and rich oxidation states (2+ to 7+), offering tunable redox potential [1]. Here, we have investigated different oxide-based cathode insertion compounds for secondary metal-ion batteries.i) We have demonstrated tunnel-type sodium insertion material Na44MnO2(NMO) as an intercalation host for Li-ion and K-ion batteries. The solution combustion synthesized Na0.44MnO2 assuming an orthorhombic structure (space group Pbam), exhibited rod-like morphology. After electrochemical ion exchange from NMO, we obtained Na0.11K0.27MnO2 (NKMO) and Na0.18Li0.51MnO2 (NLMO) cathodes for K-ion batteries and Li-ion batteries, respectively [2]. These new compositions, NKMO and NLMO, showed excellent cycling stability with capacities of ∼74 and 141 mAh g–1 (first cycle, C/20 current rate). The underlying mechanistic features concerning charge storage and structural modifications in these cathode compositions were probed by combining ex-situ structural, spectroscopy, and electrochemical tools [3].ii) Using composite formation, we have tried to improve the P2-type layered material. Here, the stable Na7(Li1/18Mn1/18Ni3/18Fe2/18χ1/18)O2–xNa2MoO4 biphasic composite was synthesized using Mo doping. Overall, the redox chemistry was investigated using various spectroscopy techniques to prove the net capacity resulted from both cationic and anionic redox reactions [4]. Keywords: energy storage; batteries; cathode; manganese oxides; intercalation; doping

Accessing Indenoazulenes via a Gold‐Catalysed Cyclisation of Cycloheptatrienyl‐Substituted 1,5‐Diynes

AbstractHerein we report that cycloheptatrienyl‐substituted 1,5‐diynes with aromatic backbones undergo a gold‐catalysed 5‐endo‐dig cyclisation to give 11H‐indeno‐[2,1‐a]azulenes at room temperature. This methodology complements the established range of aromatic structures obtained from gold‐catalysed conversions of differently substituted 1,5‐diynes accessed via highly reactive cationic intermediates. We have demonstrated the scope of the reaction and have assessed the possibility of further functionalisation of the indenoazulene scaffold. Additionally, we have studied the optical and electrochemical properties as well as the frontier molecular orbitals of this structural motif by both spectroscopic and theoretical means.

Gas-phase ion chemistry of [B12X12]2− (X = F, Cl, Br, I, CN). A brief review of twelve years of researching twelve−vertexed dianions and their fragments

The closo-dodecaborate dianions [B12X12]2− (X = halogen, CN) have been recognized in recent years for their outstanding physical and chemical properties. Gas-phase ion chemistry and spectroscopy have contributed to the understanding and further development of their record stability, which is applied to stabilize highly reactive cations. Fragment ions generated by collision induced dissociation provide access to a large variety of boron-based structures previously not available in the condensed phase and have challenged common chemical concepts (e.g., the discovery of “superelectrophilic anions”). This has opened new avenues for noble gas chemistry and direct functionalization of alkyl groups with covalently bound “charge tags”. Furthermore, the interactions with neutral molecules in the gas phase, e.g., host-guest chemistry, complements the fundamental understanding of solvation effects in solution and association with large neutral molecules, which is highly relevant for the biochemical applications of these compounds. Future perspectives, in particular the special role of these ions and their fragments in preparative mass spectrometry, are discussed.

New Protocol for the Synthesis of S-Thioesters from Benzylic, Allylic and Tertiary Alcohols with Thioacetic Acid.

A new one-pot solvent-less reaction to convert benzylic, allylic, ferrocenyl or tertiary alcohols into S-thioesters, bench-stable and less odorous precursors of the corresponding thiols, which is based on reactions in neat thioacetic acid in the presence of tetrafluoroboric acid, is presented. Reaction monitoring by NMR and GC of the benzyl alcohol conversion indicated the intermediate formation of benzyl acetate and benzyl thionoacetate (PhCH2 OC(S)CH3 ) prior to the slower conversion to the final S-benzyl thioacetate product. Increasing the HBF4 concentration enhanced the reaction rate, giving good to excellent yield (up to 99 %) for a large scope of alcohols. Control experiments, with support of DFT calculations, have revealed a thermodynamically favorable, though requiring HBF4 -activation, disproportionation of CH3 C(O)SH to CH3 C(O)OH and CH3 C(S)SH, the latter immediately decomposing to H2 S and (MeC)4 S6 but also generating the hitherto unreported [MeC(O)C(Me)S]2 (μ-S)2 . Kinetic investigations demonstrated that the rate of benzyl alcohol conversion is second-order in [PhCH2 OH] and second order in [HBF4 ], while the rate of conversion of the benzyl acetate intermediate to S-benzyl thioacetate is second order in [PhCOOMe] and fourth order in [HBF4 ]. The DFT calculations rationalize the need to two alcohol molecules and two protons to generate the reactive benzyl cation.

Impact of ionic liquid's cation alkyl chain length and reaction time on cellulose nanocrystals preparation

Traditional methods to obtain cellulose nanocrystals typically involve mechanical and chemical processes and develop an improved process in terms of efficiency, sustainability, and the quality of CNCs produced are interesting. In this sense, we aimed to prepare cellulose nanocrystals (CNCs) from the hydrolysis of microcrystalline cellulose using protic ionic liquids (PILs), named 3-diethylamino-propylammonium hexanoate ([DEAPA][Hex]), 3-dimethylamino- 1-propylammonium hexanoate ([DMAPA][Hex]), and propylammonium hexanoate ([PA][Hex]) at different reaction times. The PILs demonstrated efficiency in producing cellulose nanocrystals, regardless of the cation size and reaction times. However, as expected the properties of the CNCs varied depending on the studied condition. The highest yield was observed in DMAPA[Hex], with a 34 % conversion. Crystalline indices decreased independent of the cation sizes and reaction times. Thermal stabilities were shifted to higher temperatures up to 92 ºC probably due to PILs cation sizes. In contrast, increasing reaction times decreased nanocrystals’ thermal stabilities up to 51ºC. So, protic ionic liquids (PILs) can be considered more environmentally friendly or sustainable solvents compared to traditional organic solvents for preparing cellulose nanocrystals. In the present work, it is reported an alternative method for obtaining CNCs and additionally provide the best preparation conditions for achieving important properties of this nanomaterial, with the potential for various applications.