Synthesis of halide glasses by reactive processing of sol-gel materials

This paper aims to introduce fluoride materials, their conventional processing and how sol-gel processing can be used both to simplify processing and to improve properties. A multistep process incorporating sol-gel synthesis and reactive treatment is used to prepare a monolithic ZBLA fluoride glass. The first step is synthesis of a porous, monolithic, atomically homogeneous hydrous oxide gel containing zirconium, barium, lanthanum, aluminum and possibly sodium as components (ZBLA or ZBLAN). The second step is a relatively low-temperature reactive treatment of the gel with a fluorinating agent to achieve a porous fluoride glass. Subsequently, the gel is viscous sintered to a dense glass. The present status and future challenges in the preparation of optical-quality fluoride glasses via this method will be presented.     

Design, synthesis, and evaluation of a novel class of enantioselective electrophilic fluorinating agents: N-fluoro ammonium salts of cinchona alkaloids (F-CA-BF(4))

The first enantiopure N-fluoro quaternary ammonium salts of cinchona alkaloids as enantioselective fluorinating agents are reported. A one-step transfer-fluorination on the naturally occurring cinchona alkaloids gave the fluorinating agents F-CA-BF(4). This new generation of fluorinating agents exhibited asymmetric induction up to 61% on fluorination of enolates and silyl enol ethers of 2-methyl-1-tetralone.     

悬浮体进样/氟化电热蒸发(ETV)/ICP-AES直接测定二氧化钛粉末中痕量钇

以聚四氟乙烯(PTFE)悬浮体为氟化剂,悬浮体制样/氟化辅助电热蒸发(ETV)/ICP-AES直接测定TiO₂陶瓷粉末中痕量杂质钇;考察了影响基体和待测元素的蒸发过程的各种因素;对比研究了待测元素和基体的氟化蒸发行为;实现了基体和待测元素的预分离,显着降低了基体效应。本法的检出限为0.26μg/L,相对偏差为3.8%(n=5,c=0.5mg/L).     

A thermoanalyser for studies in an atmosphere of a gaseous fluorinating agent

A thermoanalyser for studies in an atmosphere of a strong fluorinating agent has been designed. A methodology for simultaneously obtaining DTA and TG/DTG curves of physicochemical processes over a wide range of temperatures in environments of gaseous fluorine, hydrogen fluoride and chlorine trifluoride, as well as under vacuum and hydrogen, has been developed. The construction of the thermoanalyser is described in detail. To illustrate the capabilities of the thermoanalyser a study of the thermal behaviour of M₂IrCl₆ complexes with gaseous fluorine is presented.     

Discovery of 4-tert-butyl-2,6-dimethylphenylsulfur trifluoride as a deoxofluorinating agent with high thermal stability as well as unusual resistance to aqueous hydrolysis, and its diverse fluorination capabilities including deoxofluoro-arylsulfinylation with high stereoselectivity

Versatile, safe, shelf-stable, and easy-to-handle fluorinating agents are strongly desired in both academic and industrial arenas, since fluorinated compounds have attracted considerable interest in many areas, such as drug discovery, due to the unique effects of fluorine atoms when incorporated into molecules. This article describes the synthesis, properties, and reactivity of many substituted and thermally stable phenylsulfur trifluorides, in particular, 4-tert-butyl-2,6-dimethylphenylsulfur trifluoride (Fluolead, 1k), as a crystalline solid having surprisingly high stability on contact with water and superior utility as a deoxofluorinating agent compared to current reagents, such as DAST and its analogues. The roles of substituents on 1k in thermal and hydrolytic stability, fluorination reactivity, and the high-yield fluorination mechanism it undergoes have been clarified. In addition to fluorinations of alcohols, aldehydes, and enolizable ketones, 1k smoothly converts non-enolizable carbonyls to CF(2) groups, and carboxylic groups to CF(3) groups, in high yields. 1k also converts C(=S) and CH(3)SC(=S)O groups to CF(2) and CF(3)O groups, respectively, in high yields. In addition, 1k effects highly stereoselective deoxofluoro-arylsulfinylation of diols and amino alcohols to give fluoroalkyl arylsulfinates and arylsulfinamides, with complete inversion of configuration at fluorine and the simultaneous, selective formation of one conformational isomer at the sulfoxide sulfur atom. Considering the unique and diverse properties, relative safety, and ease of handling of 1k in addition to its convenient synthesis, it is expected to find considerable use as a novel fluorinating agent in both academic and industrial arenas.     

对映选择性亲电氟化反应研究进展

含氟有机化合物, 特别是手性氟化物在医药、农药及功能性材料等相关领域的作用备受注目. 尽管在分子中有立体选择性地引入一个氟原子一直是有机化学家面临的一个挑战性问题, 近年来在化学家们的不断努力下, 对映选择性氟化反应研究取得重要进展. 高光学活性的手性氟化物可通过手性亲电氟化试剂诱导的立体选择性氟化反应, 基于底物的手性氟化反应以及手性催化剂诱导的不对称催化氟化反应等来制备. 特别是, 手性金属配合物和有机催化剂诱导的不对称催化氟化反应被广泛应用于各类手性氟化物的合成, 已成为不对称氟化反应研究的热点. 全面介绍对映选择性亲电氟化反应研究概况和最新进展, 讨论各种不对称氟化反应的特点及应用范围.     

Ordering the relative power of electrophilic fluorinating,trifluoromethylating, and trifluoromethylthiolating reagents: A summary of recent efforts

Electrophilic fluorination and fluoroalkylation are one of the most promising and efficient strategies in the synthesis of organofluorine compounds. The rapid progress of this field has been made possible by the emergence of a wide variety of power-variable, readily prepared, and easy-to-handle electrophilic fluorinating and fluoroalkylating reagents. Understanding the relative power of these reagents is thus vital for their use in synthetic transformations. This digest will outline some recent efforts to quantitatively ordering the relative power of electrophilic fluorinating, trifluoromethylating, and trifluoromethylthiolating reagents.     

Reaktion von Lanthanfluorid mit Halogenalkanen

Reactions of Lanthanum Fluoride with Halogenoalkanes Reactions are reported on lanthanum fluoride as a fluorinating reagent and as a catalyst for the fluorination and dismutation of halogenoalkanes. Carbon tetrachloride, monofluorotrichlormethane, and chloroform are partially fluorinated by lanthanum fluoride. In the presence of HF, lanthanum fluoride acts as catalyst the fluorine transfer to CCl₄, CHCl₃ and C₂F₃Cl₃. Monofluorotrichloromethane, difluorodichloromethane, and trifluorotrichloroethane dismutate on lanthanum fluoride. Results on the thermal decomposition of the above-mentioned fluorochloroalkanes are communicated.     

Recent advances in the synthesis of fluoroalkylated compounds using fluoroalkyl anhydrides

Fluoroalkyl-containing organic compounds have exhibited wide applications in the field of pharmaceuticals, agrochemicals and materials science due to their outstanding properties such as biological activity, metabolic stability, lipophilicity, excellent chemical and thermal stability. Therefore, various synthetic strategies have been developed for the construction of fluoroalkyl-containing compounds, using highly active fluorinating reagents and fluorinated building blocks. Recently, the use of easily available and inexpensive trifluoroacetic anhydride (TFAA) and its anhydride analogues has attracted great attention to access numerous fluoroalkyl-containing compounds through cyclization and coupling reactions. In this review, we summarized the recent advances in the synthesis of fluoroalkylated compounds using fluoroalkyl anhydrides as reagents. This review aims to provide a reference for researchers on how to develop new synthetic straregies of fluorine-containing organic compounds and achieve kilograms or even tons preparation of fluorine-containing organic compounds using fluoroalkyl anhydrides.     

Thermal behavior of blends based on a thermoplastic-modified epoxy resin with a crosslinking density variation

The thermal behavior of blends based on a polystyrene (PS) and several epoxy-amine systems where amino groups were provided by a monoamine (MA) and a diamine (DA) mixed in different proportions was investigated. This way, the crosslinking density of epoxy-amine polymer was controlled and continuously changed from a linear polymer (epoxy-MA) to a highly crosslinked polymer (epoxy-DA). The effect of the MA–DA proportion and PS modifier on the thermal stability, glass transition, and polymerization reaction was studied by differential scanning calorimetry and thermogravimetric analysis. The MA–DA ratio and modifier proportion did not affect the reaction heat but affected the reactivity. The thermal stability and glass transition temperature increased by increasing the DA proportion in the blend as a result of the higher degree of crosslinking. A study of miscibility of blends based on glass transitions was performed. The thermoplastic-modified materials generally showed two glass transitions with values close to the those of the pure materials, indicating that the mixtures were separated into phases.     

N-Fluoro-(3,5-di-tert-butyl-4-methoxy)benzenesulfonimide (NFBSI): A sterically demanding electrophilic fluorinating reagent for enantioselective fluorination

We disclose here a novel electrophilic fluorinating reagent, N-fluoro-(3,5-di-tert-butyl-4-methoxy)benzenesulfonimide (NFBSI) as a sterically demanding analogue of popular fluorinating reagent, N-fluorobenzenesulfonmide (NFSI). NFBSI improves the enantioselectivity of the products as much as 18% for the cinchona alkaloid-catalyzed enantioselective fluorination of silylenol ether compared to the use of NFSI.     

Slurry sample introduction with fluorinating electrothermal vaporization for the direct ICP-AES determination of boron in plant leaves

Summary The slurry sample introduction with fluorinating electrothermal vaporization has been applied to ICP-AES for the determination of boron in plant leaves. The main working parameters for ETV-ICP-AES, such as r.f. power, gas flow rate, drying temperature and atomization temperature have been studied. The concentration of the fluorinating agent polytetrafluoro-ethylene was examined for the boron determination. The matrix concentrations of Na, K, Ca and Mg up to 5 mg/ml do not interfere with the fluorinating vaporization of boron. Several plant samples were analysed with the standard addition method. A good agreement of analytical results between this method and a spectrophotometric method was obtained. The determined value of boron in NBS SRM 1573 tomato leaves coincides with literature values.     

Photoredox Activation of SF6 for Fluorination

We report the first practical use of SF₆ as a fluorinating reagent in organic synthesis. Photoredox catalysis enables the in situ conversion of SF₆, an inert gas, into an active fluorinating species by using visible light. Under these conditions, deoxyfluorination of allylic alcohols is effected with high chemoselectivity and is tolerant of a wide range of functional groups. Application of the methodology in a continuous‐flow setup achieves comparable yields to those obtained with a batch setup, while providing drastically increased material throughput of valuable allylic fluoride products.     

The consequences of cation-radical fluorination theory—II : Fluorination pathways with less-reactive reagents

The fluorination of benzene with caesium tetrafluorothallate and of pyridine or benzo[b] furan with caesium tetrafluorocobaltate gives sequences of polyfluoroaromatics with vicinal fluorines. Polynuclear aromatics are fluorinated by caesium or potassium tetrafluorocobaltate to give products containing little or no hydrogen, whereas the stronger fluorinating agent cobalt trifluoride gives products which contain much hydrogen. These two previously unexplained features are rationalized by a mechanism which involves 1,2-migrations of fluorine in cyclohexadienyl-type radicals or cations, and is backed up by CNDO/2 calculations. This rationalization implies significantly different rates of atom or ion migrations through the lattices of the different solid fluorinating agents.     

Elimination of porosity in heavily rare-earth doped sol–gel derived silicate glass films

The combination of spin-coating and rapid thermal annealing is a very important sol–gel technique to prepare high quality silicate glass films, widely used in the fabrication of waveguides, photonic bandgap structures and other film-based optical devices. This work found that high rare-earth concentrations will seriously affect the optical quality of the films prepared by the spin-coating/rapid thermal annealing process, with pores with hundreds of nanometres in size being found in heavily rare-earth doped aluminosilicate glass films, causing significant light scattering. However, it was also found that a new recipe using acetylacetone was able to dramatically eliminate these pores and to improve the film optical quality, even for rare-earth concentrations as high as 15 mol%. This result will be useful for the fabrication of sol–gel derived devices based on rare-earth doped silicate glass films like active waveguides, functional films and photonic bandgap structures.     

Thermal characterization of benzylcellulose derivatives prepared from bleached pinus kraft pulp

The thermal characterization (DSC and TG) of benzylcellulose derivatives prepared from the benzylation of bleached Pinus Kraft pulp is described in this paper. The objective of this study was to examine the changes in glass transition temperature (T _g) and the thermal stability of the benzylated product as a function of the benzylation extent (degree of substitution). The DSC analysis showed that the benzylcelluloses can display glass transition temperature at two different regions and that thermal stability is slightly higher than that of the parent cellulose. This revised version was published online in August 2006 with corrections to the Cover Date.     

New Technique for Fourier Transform Thermal Analysis

A new technique for the simultaneous measurement of higher order harmonic of temperature wave under temperature scan was proposed. The mathematical rule for the propagation of harmonies in the film shaped specimen was examined and the principle of Fourier transform thermal analysis was theoretically and experimentally justified. This principle applied to a technique called ‘Fourier transform thermal analysis’, makes it possible to determine simultaneously thermal diffusivity, heat capacity per unit volume and thermal conductivity as a function of frequency and temperature. The results on thermoplastics were shown and the glass transition and the crystallization were discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Magnesium isotope ratio measurements by negative thermal ionisation mass spectrometry using molecular fluoride ions

A new technique for accurate Mg isotope ratio measurements has been developed with MgF₂ as sample compound. With the help of a fluorinating agent negatively charged MgF₃ molecular ions were formed in the ion source of a thermal ionisation mass spectrometer. An evaporation study has been performed and the results clearly show that Mg is evaporated from the filament as MgF₂ molecules. The MgF₂ technique has been applied in the certification of a candidate ²⁶Mg-enriched Spike Isotope Reference Material. The result from this new technique has been compared with results obtained for the same material using ICP-MS.     

Photoredox-catalyzed deoxyfluorination of activated alcohols with Selectfluor®

Herein we disclose a deoxyfluorination of alcohols with an electrophilic fluorine source via visible-light photoredox catalysis. This radical-mediated C–F coupling is capable of fluorinating secondary and tertiary alcohols efficiently, complementing previously reported nucleophilic deoxyfluorination protocols.