Sodium Analogue Research Articles

New synthetic strategies leading to [RNPNR]- anions and the isolation of the [P(Nt-Bu)3]3- trianion.

New and straightforward synthetic paths for the syntheses of [RNPNR]- anions (R = t-Bu (1) or CPh3 (6)) in the form of their tmeda- or thf-coordinated lithium salts are described. The attempts to isolate the sodium analogue [(Ph3CNPNCPh3)Na·(thf)x] (8) remained unsuccessful probably due to its high reactivity although its formation in the reaction of the parent cis-[(Ph3CNP)2(Ph3CNH)2] (5) with 2 eq. of sodium naphthalenide was corroborated by NMR spectroscopy. Importantly, when an excess of sodium naphthalenide was used in the reaction with 5, [(Ph3C)Na(thf)3] (9) was obtained along with a complex mixture of other by-products indicating the cleavage of the C-N bond in the starting material. Furthermore, the synthesis and the structural characterization of the [P(Nt-Bu)3]3- trianion as its trilithium salt [P(Nt-Bu)3Li3]2 (10) has been successfully achieved.

In-Situ and Real-time Monitoring of Mechanochemical Preparation of Li2 Mg(NH2 BH3 )4 and Na2 Mg(NH2 BH3 )4 and Their Thermal Dehydrogenation.

For the first time, in situ monitoring of uninterrupted mechanochemical synthesis of two bimetallic amidoboranes, M2 Mg(NH2 BH3 )4 (M=Li, Na), by means of Raman spectroscopy, has been applied. This approach allowed real-time observation of key intermediate phases, and a straightforward follow-up of the reaction course. Detailed analysis of time-dependent spectra revealed a two-step mechanism through MNH2 BH3 ⋅NH3 BH3 adducts as key intermediate phases which further reacted with MgH2 , giving M2 Mg(NH2 BH3 )4 as final products. The intermediates partially take a competitive pathway toward the oligomeric M(BH3 NH2 BH2 NH2 BH3 ) phases. The crystal structure of the novel bimetallic amidoborane Li2 Mg(NH2 BH3 )4 was solved from high-resolution powder diffraction data and showed an analogous metal coordination to Na2 Mg(NH2 BH3 )4 , but a significantly different crystal packing. Li2 Mg(NH2 BH3 )4 thermally dehydrogenates releasing highly pure H2 in the amount of 7 wt.%, and at a lower temperature then its sodium analogue, making it significantly more viable for practical applications.

Lithium salt of biphenyl tetracarboxylate as an anode material for Li/Na-ion batteries

Electrochemical lithiation/delithiation and sodiation/desodiation studies are carried out on lithium [1,1′-biphenyl]-3,3′,4,4′-tetracarboxylate (Li4-BPTC). Although four Li+ can be inserted, only two Li+ was reversible yielding a capacity of 110, 122 and 107mAhg−1 (after 50 cycles) at a current density of 40, 80 and 160mAg−1 respectively. As sodium analog of Li4-BPTC is unstable in the ambient conditions, Li4-BPTC was tested in sodium half-cell and a reversible capacity of 107mAhg−1 was obtained even after 200 cycles at 160mAg−1 rate. The exchange of Li+ by Na+ in Li4-BPTC electrode during the electrochemical sodiation/desodiation was confirmed by ICP-OES and XPS studies.

Reversible Na-Ion Uptake in Si Nanoparticles

Na ion batteries attract significant research interest since they provide potentially high energy density while using low cost and abundant sodium as the active ion. Si has been extensively investigated for its operation as anode in lithium based batteries since it has a high theoretical lithiation capacity up to Li4.4Si. However, the sodium analogue with successful reversible electrochemical sodiation of Si has not been reported yet. Si sodiation is anticipated to be different with respect to phase behaviour, insertion voltages and kinetic barriers when compared to Li ion, for instance because of the difference in ionic radius of Na+ (0.97 Å) and Li+(0.68 Å). From thermal synthesis of Na-Si materials it is known that NaSi is the most Na rich phase for Na-Si binary compounds, which would enable a sizeable capacity of 954 mAh/g. Anticipating that nanoscaling is of advantage for the kinetics of ion insertion and extraction, we studied Si particles with much reduced size (~ 20 nm) containing a large fraction of amorphous Si. The nano particles were obtained from Expanding Thermal Plasma Chemical Vapour Deposition (ETPCVD) of silane. The materials consist of aggregated individual nano particles with a very thin silicon oxide layer that forms after contact with air. The work presented here reports, to our knowledge for the first time, reversible electrochemical Na ion uptake in these Si based materials for a significant capacity. The desodiation capacity is stable around 260 mAh/g, while the initial sodiation shows a large irreversible Na loss attributed to SEI formation. The experiments show that during Na insertion a two phase equilibrium may be present between NaSi and Si: x Na + Si -> x NaSi + (1-x) Si, where the NaSi becomes amorphous. For desodiation a sloping voltage profile is observed indicative of a solid solution behaviour. Therefore we propose that desodiation occurs as NaSi -> Na1-xSi + x Na, where the Na1-xSi phase remains amorphous. After 100 cycles all Si has been transformed to amorphous phases, and no crystalline nano Si particles remain. In conclusion, nanoparticles containing both amorphous and crystalline Si, produced by ETPCVD, demonstrate an excellent reversible capacity of 279 mAh/g for Si at 10 mA/g and a capacity retention of 248 mA/g after 100 cycles at 20 mA/g. Significant reversible capacities can be achieved at high dis-/charge rates as well. Nanoscaling benefits the Na insertion and extraction kinetics in Si although reversible Na uptake and release for the full theoretical capacity has not been reached. Initial amorphous and crystalline Si are performing an equally active role in the electrochemical sodiation. Coexistence of Si and NaSi may occur during Na insertion into amorphous Si and on the surface of the Si crystallites; while a solid solution desodiation reaction is evidenced when Na is being extracted. Y. Xu, E. Swaans, S. Basak, H. W. Zandbergen, D. M. Borsa, F. M. Mulder, Adv. Energy Mater. 2015, doi 10.1002/aenm.201501436 early view Figure 1

Synthesis and Evaluation of NaMPO4 (M=Fe, Mn, Co) Framework Polyanion Cathodes for Sodium-Ion Batteries (SIB)

Polyanion compounds are attractive for use as cathode materials because they generally have higher potentials for a given Mn+/(n+1)+ redox couple in comparison to the oxide analogue.1 In addition, the strong bonding within the polyanion group provides similar safety characteristics to oxides even though they exhibit higher working potentials.2 The phospho-olivine LiFePO4 has been thoroughly investigated as a cathode material for use in lithium-ion batteries since its introduction in 1997.3 It has been determined that NaMPO4 (M = Fe and Mn) compounds prefer the electrochemically inactive maricite structure and not the olivine structure when using conventional synthesis methods,4 which has left the research community seeking unorthodox methods to access the olivine phase.5 , 6 Herein we report on a NaCoPO4 (NCP) polymorph (Red-phase) that has previously only been observed as an impurity while attempting to synthesize other polymorphs.7 The Red-phase was synthesized by a microwave-assisted solvothermal process using tetraethylene glycol as the solvent. Ex-situ XRD and XANES measurements indicate that during cycling the structure undergoes reversible changes and the Co2+/3+ redox couple is partially active near 4.4 V vs. Na. The silicate family of cathode materials is rich in polymorphism8 and has also been thoroughly investigated for use in lithium-ion batteries. Among the polymorphs investigated is Pn­-Li2MnSiO4 9 that was accessed by ion-exchange of the parent Pn­-Na2MnSiO4 compound. Yet, minimal work has been reported on the sodium analogue.9 , 10 Considering the air sensitivity reported of the lithium version,11 herein we report preliminary results on the effect of air exposure on the electrochemistry of Pn­-Na2MnSiO4. § cjohnson@anl.gov Acknowledgements Work supported by U. S. DOE, Office of Science under Contract No. DE-AC02-06CH11357. We also thank the Argonne LDRD program office for additional support.

Advanced Processing and Electrochemical Analysis of Novel Sodium-Rich Anti-Perovskites Via Conventional Sintering and Spark Plasma Sintering Methods

Interest in non-flammable solid-state battery electrolytes continues to grow as they hold promise for batteries with increased safety, reliability, and energy density. They are nonflammable, stable over a wide temperature range, have a large electrochemical window, and potentially allow for the use of metallic Li anodes [1]. One particular solid-state electrolyte is the Lithium-rich anti-perovskite (LiRAP) with the formula Li3OX where X is a halogen or a mixture of halogens. Conductivities of >1 mS/cm were previously reported [2]. Interest in the material grew as the conductivity varied with different processing conditions thus opening the door to improvement with structura tweaking and optimization [3]. Whenever new a lithium compound is discovered in the battery field, interest in a sodium analog also arises. Na-ion batteries are considered a possible lower-cost alternative to lithium ion batteries due to the abundance of sodium. The conductivity of various Na-rich anti-perovskite (NaRAP) compounds with varying halogens were also previously reported [4]. Here we compare different synthesis methods for the Na3OBr compound, namely conventional cold-pressed sintering and spark plasma sintering. Spark plasma sintering enables a shorter processing time and more tightly-packed, dense pellets [5]. We report that the Na ionic conductivity for Na3OBr remained at similar values regardless of the synthesis method. Acknowledgements This work was supported by the National Science Foundation under grant number ACI-1053575.

LiMnTiO4 with the Na0.44MnO2 Structure as a Positive Electrode for Lithium-Ion Batteries

A metastable polymorph of LiMnTiO4 with the Na0.44MnO2 structure has been synthesized via ion-exchange from its sodium analogue, NaMnTiO4. The structure was determined from a combination of X-ray and Neutron Powder Diffraction data. LiMnTiO4 has the Pbam space group, with a = 9.074(5), b = 24.97(1) and c = 2.899(2) Å. The shapes and dimensions of the channels are slightly modified as compared to NaMnTiO4 with displaced alkali metal positions and occupancies. LiMnTiO4 was cycled vs Li at room temperature and up to 0.89 lithium ions can be reversibly inserted into the structure, with a discharge capacity of 137 mAh/g after 20 cycles at C/20. At 60°C all the lithium is removed at the end of the first charge at C/20, with subsequent cycles showing reversible insertion of 1.06 Li-ions.

Syntheses and Characterization of 1,4‐Phenylenebisphosphonates, A[HO3PC6H4PO3H2] (A = Li, K, Rb, Cs, Tl, Ag and NH4) and Crystal Structure of 1,4‐Phenylenebisphosphonic Acid

AbstractSeven 1,4‐phenylenebisphosphonates of monovalent ions, A(HO3PC6H4PO3H2) (A = Li, K, Rb, Cs, Tl, Ag and NH4), were synthesized and characterized by single‐crystal X‐ray diffraction, spectroscopic and thermal methods. These compounds and the reported sodium analogue have four structure types. The sodium compound, one‐dimensional lithium compound and pillared‐layered cesium compounds have different structure types, whereas the potassium, rubidium, thallium, ammonium and silver compounds have a pillared ladder‐like structure. They undergo initial thermal decomposition in the range of 120–270 °C. Moreover, the single crystal X‐ray structure of 1,4‐phenylenebisphosphonic acid was determined.

Electrochemical Behavior of Some Sodium Nickel Oxides for a Sodium-Ion Battery

Sodium-ion batteries have been considered as a cheap alternative to lithium-ion batteries. Electrode materials for a sodium-ion battery and a lithium-ion battery have interesting similarities and differences in materials characteristics and electrochemical properties. Layered lithium nickel oxide, LiNiO2 has been developed to achieve a high capacity battery, but it shows interslab cation mixing and poor thermal stability. Li2NiO2 has also been studied mainly as a cathode additive to compensate the lithium loss at the anode side owing to the SEI formation. It can provide a large irreversible charging capacity at the first cycle, but it exhibits a significant oxygen evolution upon charging. In this study, we report electrochemical properties of their sodium analogues for a sodium-ion battery. The materials were prepared via solid state reactions and characterized with powder XRD and SEM. Electrochemical properties of them are examined with coin half- and full-cells, and further characterized with ex-situ electrode XRD analysis. The experimental data was correlated to DFT+U calculations. Details on the materials and electrochemical properties will be presented at the meeting.

A Viable Hydrogen Storage and Release System Based on Cesium Formate and Bicarbonate Salts: Mechanistic Insights into the Hydrogen Release Step

AbstractAqueous solutions of cesium formate and bicarbonate represent an effective hydrogen storage–delivery couple that undergoes either release or take up of hydrogen in the presence of {RuCl2(mTPPTS)2}2 (TPPTS=triphenylphosphine trisulfonate) and excess mTPPTS ligand, with no other additives required. Cesium salt solutions offer the advantage of improved volumetric and gravimetric H2 density compared to their sodium and potassium analogs, owing to their high water solubility. Details of the equilibrium between formate and bicarbonate, which constitutes an important parameter for the applicability of this H2 storage/release cycle, were determined. H2 production is readily tunable by controlling the operating pressure. This behavior was also rationalized through the identification of catalytic intermediates under various conditions. High concentration formate and bicarbonate solutions were used during the tests and the bidirectional catalytic system could be recycled without loss of activity or replacement of solvent. A tentative mechanism is proposed for the formate dehydrogenation step. Among the identified hydride species, the pentacoordinated [RuH(H2O)(TPPTS)3] complex was indispensable for promoting the formate dehydrogenation reaction.

Electrical conductivity of molten cesium chloride–dysprosium(III) chloride system

Electrical conductivity of the molten binary CsCl–DyCl3 system has been measured in the temperature range of 898–1233K. There were given equations of temperature dependences of specific and molar conductivities of melts for 0≤xDyCl3≤1. Dependence of the CsCl–DyCl3 system conductivity on the melt composition was compared with sodium and potassium analogues as well as CsCl–light lanthanide ones (La–Pr). It was found that the minimum of molar conductivity in the CsCl–DyCl3 system is at typical composition of the melt (xDyCl3=0.40–0.50) but further increase of the melt conductivity is apparently weaker. The results have been briefly commented in terms of literature findings on the lanthanide halides–alkali metal halide system structure.

Synthesis, Structure, and Na-Ion Migration in Na4NiP2O7F2: A Prospective High Voltage Positive Electrode Material for the Na-Ion Battery

In the recent hunt for novel Na-ion cathode hosts, a variety of sodium analogues of classic Li-ion structures have been thoroughly explored. However, Na-ion analogues generally possess modified structures and dissimilar Na-ion energetics compared to their Li-ion analogues due to the large size of Na+ (102 pm) vs Li+ (76 pm), often resulting in sluggish Na+ kinetics. Materials development targeted toward new and different specific host structures possessing optimum properties for Na-ion migration is crucial. Here, we report the first sodium metal fluoropyrophosphate Na-ion host with a three-dimensional framework—Na4NiP2O7F2—which is predicted to have a high voltage (∼5 V) based on its Ni2+/3+/4+ redox couple and composition. Structure solution from single crystal diffraction data combined with atomistic simulation computation suggests the presence of low activation energy Na-ion migration pathways (<0.6 eV) in all three dimensions. The particularly low barrier of 0.36 eV calculated for migration along the [010] direction is in full accord with temperature dependent ionic conductivity measurements that yield an experimental value of 0.32 eV. Spacious Na-ion pathways endow the material with good ionic conductivity as determined by ac impedance spectroscopy, and facile exchange of three Na+ ions for Li+ is observed at slightly elevated temperatures. Furthermore, the polycrystalline material exhibits excellent thermal stability under ambient atmosphere up to 600 °C, crucial for the safe operation of a Na-ion battery.

Synthesis and Catalytic Performance of Na2HfM(PO4)3 and Ag2−xNaxHfM(PO4)3 (M = Fe and Al and 0.07 ≤ x ≤ 0.13)

Materials belonging to NASICON family of compositions Na2HfM(PO4)3 and Ag2−xNaxHfM(PO4)3 (M = Fe and Al and 0.07 ≤ x ≤ 0.13) are prepared by sol-gel and ion exchange methods, respectively. The IR spectra are characterized by bands belonging to PO4 groups. The band gap energy of all compositions is obtained from their UV-vis DRS profiles. All these materials are used as catalysts in the degradation of methylene blue and methyl orange under visible light irradiation. The silver compounds have shown good catalytic activity compared to their sodium analogues. The catalysts are stable even after the third cycle of photodegradation.

Comparative Studies of Li Versus Na System: Phase Diagram and New Polyanion Cathodes

“Abundance” is the important key word in materials development. This is particularly the case for energy storage sector, where materials themselves function as a storage host; the amount of materials directly link to the amount of energy stored in a device. At the present stage, Na-ion batteries in not a strong competitor for Li-ion chemistry by only considering large abundance compared to the well established state-of-art Li-ion power packs. However, it has rapidly attract many material scientist; both weak Lewis acidity and large polarizability of Na-ion allow fast charge transfer reaction at electrode/electrolyte interface and in bulk diffusion.1,2Furthermore, unlike an incremental progress of the mature Li-ion systems, the research of the immature Na-ion systems based on Na-ion intercalation is likely to discover new electrodes with ordered functional structure due to difference of ionic radius of Na and 3d transition metal, which may enable Na-ion batteries to surpass the Li-ion batteries. Abundance of Na should not be compensated for by combination with rare transition metals, thereby Fe is definitely the best to functionalize as a redox center.In spite of the great success of olivine LixFePO4, the sodium analogue NaxFePO4 with the same structure has turned out to be unsuitable for an electrode with completely different phase diagram3. The existence of an intermediate phase at x = 2/3 in Na case, which is very stable up to 500°C, is somehow anticipated to relax the large lattice strain between x= 0 and x = 1 phases. However, even with the existence of an intermediate phase at Na2/3FePO4 one notices that the expansion from FePO4 to Na2/3FePO4 is still quite large (12.8%), nearly 2 times that for Li x FePO4 to change from x=0 to 1, which may disturb to sustain a coherent interface for smooth electrode reaction. Although switch to Na from Li is the conceptually obvious way to follow, simple extension by just replacing lithium to sodium does not always lead to similar performances, and in many cases ended up with in failure. Therefore, strategies should be directed toward specific exploration of new materials suitable for sodium system. One of our recent achievements was new material, Na2FeP2O7, with high rate performance and extreme thermal stability4, and Sumitomo electric company chose Na2FeP2O7 in parallel with NaCrO2as cathode materials for their prototype Na-ion battery pack, but its operating voltage was limited below 3.0 V versus Na.Maximizing the redox function of Fe has been intensively studied in the lithium system, from which we can expect to realize ~3.6 V operation in Na system5. However, the present status is still far from this. Operating voltage and reversible capacity of various known iron based cathode for sodium-“ion” (cathode functions as whole sodium source) battery system are summarized in Figure 1. Here, we report a log-awaited new sodium battery material to reach primary target of >3.6 V operation and capacity around 120 mAh/g (dashed circle in Figure 1) being able to lead to energy density of >450 Wh/kg, which is comparable to those of LiMn2O4 (430 Wh/kg) and LiFePO4 (500 Wh/kg) in lithium system6. M. Okoshi, Y. Yamada, A. Yamada, H. Nakai, J. Electrochem. Soc. 160 A2160 (2013)S. P. Ong, V. L. Chevrier, G. Hautier, A. Jain, C. Moore, S. Kim, X. Ma, G. Ceder, Energy Environ. Sci. 4 3680 (2011)J. Lu, S. C. Chung, S. Nishimura, A. Yamada, Chem. Mater. 25 4557 (2013)P. Barpanda, T. Ye, S. Nishimura, S. C. Chung, Y. Yamada, M. Ohkubo, H. Zhou, A. Yamada, Electrochem. Comm. 24 116 (2012)T. Ye, P. Barpanda, S. Nishimura, N. Furuta, S. C. Chung, A. Yamada, Chem. Mater. 25 3623 (2013)A. Yamada, P. Barpanda, S. Nishimura, G. Oyama, Patent JP-2013-187914 (2013)

Growth and characterization of struvite-Na crystals

Sodium magnesium phosphate heptahydrate [NaMgPO4·7H2O], also known as struvite-Na, is the sodium analog to struvite. Among phosphate containing bio-minerals, struvite has attracted considerable attention, because of its common occurrence in a wide variety of environments. Struvite and family crystals were found as urinary calculi in humans and animals. Struvite-Na crystals were grown by a single diffusion gel growth technique in a silica hydro gel medium. Struvite-Na crystals with different morphologies having transparent to translucent diaphaneity were grown with different growth parameters. The phenomenon of Liesegang rings was also observed with some particular growth parameters. The powder XRD study confirmed the structural similarity of the grown struvite-Na crystals with struvite and found that struvite-Na crystallized in the orthorhombic Pmn21 space group with unit cell parameters such as a= 6.893Å, b=6.124Å, c=11.150Å, and α=β=γ=90°. FT-IR spectra of struvite-Na crystals revealed the presence of functional groups. The TGA, DTA and DSC were carried out simultaneously. The kinetic and thermodynamic parameters of dehydration/decomposition process were calculated. The variation of dielectric constant with frequency of applied field was studied in the range from 400Hz to 100kHz.

Counterion effects in the preparation of aldehyde–bisulfite adducts

The identification and development of an aldehyde–bisulfite adduct as an isolable starting material in the synthesis of the CETP inhibitor Evacetrapib are described. The physical properties of the sodium and potassium analogs are compared, and the extension of the scope of this study to include an investigation into the solid state properties of a range of sodium and potassium bisulfite adducts of commonly encountered aldehydes is discussed.

New dicoumarol sodium compound: crystal structure, theoretical study and tumoricidal activity against osteoblast cancer cells

BackgroundEnormous interest had been paid to the coordination chemistry of alkali and alkaline metal ions because of their role inside body viz; their Li+/Na+ exchange inside the cell lead to different diseases like neuropathy, hypertension, microalbuminuria, cardiac and vascular hypertrophy, obesity, and insulin resistance. It has been presumed that alkali metal ions (whether Na+ or K+) coordinated to chelating ligands can cross the hydrophobic cell membrane easily and can function effectively for depolarizing the ion difference. This unique function was utilized for bacterial cell death in which K+ has been found coordinated valinomycin (antibiotic).ResultsDistinct sodium adduct (1) with dicoumarol ligand, 4-Hydroxy-3-[(4-hydroxy-2-oxo-4a,8a-dihydro-2H-chromen-3-yl)-phenyl-methyl]-chromen-2-one (L) is isolated from the saturated solution of sodium methoxide. Single crystal X-ray diffraction studies of the adduct reveals that sodium is in the form of cation attached to a methoxide, methanol and a dicoumarol ligand where carbonyl functional groups of the coumarin derivative are acting as bridges. The sodium compound (1) is also characterized by IR, 1H-NMR, and 13C{1H}-NMR spectroscopic techniques. The composition is confirmed by elemental analysis. DFT study for 1 has been carried out using B3LYP/6-13G calculations which shown the theoretical confirmation of the various bond lengths and bond angles. Both the compounds were studied subsequently for the U2OS tumoricidal activity and it was found that L has LD50 value of 200 μM whereas the sodium analog cytotoxicity did not drop down below 60%.ConclusionA sodium analogue (1) with medicinally important dicoumarol ligand (L) has been reported. The crystal structure and DFT study confirm the formation of cationic sodium compound with dicoumarol. The ligand was found more active than the sodium analog attributed to the instability of 1 in solution state. Coumarin compound with sodium was observed to be less cytotoxic than the ligand, its LD50 value never dropped below 60%.

Reversible sodiation in maricite NaMn1/3Co1/3Ni1/3PO4 for renewable energy storage

Battery technology is now at a point where water based sodium batteries may take a place in large-scale applications such as electrical grid stabilization. The starting point for new aqueous based sodium battery technology is to understand the fundamental differences between lithium versus sodium in similar host materials synthesized via non-ceramic synthetic approaches. The new sodium phosphate host compound, NaMn1/3Co1/3Ni1/3PO4, has been synthesized using sol–gel and combustion routes. The framework of sodium phosphate with a maricite structure is analogous to olivine based lithium phosphate compound, except the M(1) and M(2) sites have reverse occupancies. Physical and electrochemical characterization indicate that the combustion synthesized sodium analogue is fully reversible (electrochemically intercalating and de-intercalating sodium ions) in water based NaOH electrolyte for multiple cycles.

Theoretical study of C60(OH)20 and C60(OH)18 fullerenols and B12(OH) 12 2− , Si20O30(OH)20, and Ti20O30(OH)20 polyhydroxyl clusters and their Li-substituted derivatives

The equilibrium geometric parameters and the energetic characteristics of fullerenol molecules C60(OH)20 and C60(OH)18 and fullerenol-like inorganic clusters B12(OH)122−, Si20O30(OH)20, and Ti20O30(OH)20 and their derivatives C60(OH)20 − n(OLi)n, C60(OH)18 − n(OLi)n, B12(OH)12 − n(OLi)n2−, Si20O30(OH)20 − n(OLi)n, and Ti20O30(OH)20 − n(OLi)n, in which the H atoms of all or one-half of hydroxyl groups are replaced by Li atoms, have been calculated by the density functional theory B3LYP/6-31G* method. It has been found that partial energies ΔE(H/Li) per single substitution of Li for H in the reactions C60(OH)20 + nLiAc → C60(OH)20 − n(OLi)n + nHAc and C60(OH)18 + nLiAc → C60(OH)18 − n(OLi)n + nHAc (Ac is acetate) and the energies averaged over the entire series of changes in n, as well as over its first and second halves, do not exceed a few kilocalories per mole. It has been predicted that at least one-half (or more than one-half) of OH groups can be replaced by OLi without noticeable changes in energy; however, with a further increase in n, substitutions become endothermic and require ever-increasing energy inputs. In the completely hydroxylated closo-dodecaborane dianion with an icosahedral [B12] cage and more polar B-O-H bonds, analogous H/Li substitutions are slightly exothermic so that the reaction can proceed somewhat smoother and further (toward larger n values) than in fullerenols, other conditions being the same. In the inorganic clusters Si20O30(OH)20 and Ti20O30(OH)20 with the [Si20] and [Ti20] cages, respectively, and with even more polar Si-O-H and Ti-O-H moieties, the substitutions are even more exothermic (their partial energies ΔE(H/Li) increase to 4–6 kcal/mol). For sodium and potassium analogues, the qualitative pattern persists, but H/Na and H/K substitutions are somewhat less exothermic than the H/Li substitutions. The results are compared to the data of previous calculations of stepwise H/Li and H/Na substitutions in the reactions C60(OH)24 + nLAc → C60(OH)24 − n(OL)n + nHAc (L = Li, Na).

Liquid-phase oxidation of propylene glycol using heavy-metal-free Pd/C under pressurized oxygen

The liquid-phase oxidation of propylene glycol using Pd/C undoped with any heavy metal such as tellurium in the presence of aqueous NaOH under pressurized oxygen resulted in a significant production of lactic acid and a minimal amount of hydroxyl acetone, although, under these conditions, sodium lactate as sodium analogue of lactic acid has been known to easily convert to sodium pyruvate. The advantageous effect of doping Pd/C with a heavy metal, which has been reported for various catalytic reactions in an aqueous phase, was not observed in the present oxidation. Previous papers have reported that oxidation using heavy-metal-free Pd/C and Pd/C doped with a heavy metal at atmospheric pressure and a pH 8 produced pyruvic acid via the formation of hydroxyl acetone and lactic acid, respectively, and that Pd/C doped with a heavy metal rather than Pd/C was suitable for the formation of pyruvic acid from propylene glycol. However the results of the present study show that the use of pressurized oxygen conditions as used in the present study can result in the exclusion of doping with a heavy metal in the preparation of the catalyst, which is amenable to green chemistry.