Chemo- and Site-Selective Electro-Oxidative Alkane Fluorination by C(sp3)−H Cleavage

Electrochemical fluorinations of C(sp³)−H bonds with a nucleophilic fluoride source have been accomplished in a chemo- and site-selective fashion, avoiding the use of electrophilic F⁺ sources and stoichiometric oxidants. The introduced metal-free strategy exhibits high functional group tolerance, setting the stage for late-stage fluorinations of biorelevant motifs. The synthetic utility of the C(sp³)−H fluorination was reflected by subsequent one-pot arylation of the generated benzylic fluorides.     

Artificial Caries Lesion Characteristics after Secondary Demineralization with Theobromine-Containing Protocol

Developing artificial caries lesions with varying characteristics is needed to adequately study caries process in vitro. The objective of this study was to investigate artificial caries lesion characteristics after secondary demineralization protocol containing theobromine and fluoride. Sixty bovine enamel slabs (4 × 3 mm) were demineralized using a Carbopol-containing protocol for 6 days. A baseline area (2 × 3 mm) was protected with acid-resistant nail varnish, after which specimens were exposed for 24 h to a secondary demineralization protocol containing acetic acid plus one of four fluoride/theobromine combinations (n = 15): theobromine (50 or 200 ppm) and fluoride (0 or 1 ppm). Specimens were sectioned and analyzed using transverse microradiography for changes in mineral content, lesion depth, and surface layer mineralization. Data was analyzed using paired t-test and analysis of variance followed by Bonferroni test at 0.05 significance level. After secondary demineralization, fluoride-containing groups had significantly deeper lesions (p = 0.002 and 0.014) compared to the group with 0 ppm fluoride and 50 ppm theobromine. Mineral content and lesion depth were significantly different compared to baseline for all groups. Theobromine did not show an added effect on mineral uptake. Theobromine-containing groups exhibited particularly deep lesions with a more uniform mineral profile in the presence of fluoride.     

Unexpected Radical Telomerisation of Vinylidene Fluoride with 2-Mercaptoethanol

The radical telomerisation of vinylidene fluoride (VDF) with 2-mercaptoethanol as chain transfer agent (CTA) was studied to synthesise fluorinated telomers which bear a hydroxy end-group, such as H(VDF)_nS(CH₂)₂OH, under thermal (di-tert-butyl peroxide as the initiator) or photochemical initiations. A careful structural study of a typical H-VDF-S(CH₂)₂OH telomer was performed by ¹H and ¹⁹F NMR spectroscopy. These analytical methods allowed us to explore the selective addition of the thiyl radical onto the hydrogenated side of VDF, and the telomer containing one VDF unit was obtained selectively. Surprisingly, for higher [VDF]_o initial concentrations, a monoadduct telomer was produced as well as PVDF homopolymer. This feature was related to the fast consumption of the CTA. The kinetics of radical telomerisation led to a quite high transfer constant of the CTA (40 at 140 °C) that evidences the formation of a monoadduct as the only telomer formed.     

Recent progress in the synthesis of sulfonyl fluorides for SuFEx click chemistry

Since the sulfur(VI) fluoride exchange reaction (SuFEx) was introduced by Sharpless and co-workers in 2014, this new-generation click chemistry has emerged as an efficient and reliable tool for creating modular intermolecular connections. Sulfonyl fluorides, one of the most important sulfur(VI) fluoride species, have attracted enormous attention in diverse fields, ranging from organic synthesis and material science, to chemical biology and drug discovery. This review aims to introduce seminal and recent progresses on the synthetic methods of sulfonyl fluorides, which include aromatic, aliphatic, alkenyl, and alkynyl sulfonyl fluorides. While not meant to be exhaustive, the purpose is to give a timely overview and insight in this field, and stimulate the development of more efficient synthetic methods of sulfonyl fluorides.     

Electrochemical Fluorination of Dithiocarbonates Using a Triarylamine Mediator

Electrochemical oxidation of O-(4-chlorobenzyl) S-methyl dithiocarbonate using tris(2,4-dibromophenyl)amine as a redox mediator was studied by cyclic voltammetric measurements. The triarylamine mediated anodic fluorodesulfurization of O-(4-chlorobenzyl) and O-(4-bromobenzyl) S-methyl dithiocarbonates provided 4-chloro- and 4-bromobenzyl fluorides, respectively in moderate yields. On the other hand, similar anodic fluorination of O-(2-phenethyl) S-octyl dithiocarbonate and O-(4-bromophenyl) S-methyl dithiocarbonate afforded 2-phenethyl trifluoromethyl ether and difluoro(methylthio)methyl 4-bromophenyl ether, respectively. Mechanistic aspects are also discussed.     

On the reactivity of naphthalene and biphenyl dianions: tying up loose ends concerning an SN2‐ET dichotomy in alkylation reactions

Naphthalene and biphenyl dianions are interesting compounds that can be obtained by double reduction of the corresponding arenes in solution with certain alkali metals. These dianions are highly reactive and rather elusive species with very high laying and highly delocalized electrons. They share many aspects of the reactivity of the alkali metal they originated from and consequently behave primarily as strong electron transfer (ET) reagents. We report here kinetic evidence for a different type of reactivity in their alkylation reactions with alkyl fluorides. By using cyclopropylmethyl fluoride (c‐C₃H₅CH₂F) as a very fast radical probe, we were able to settle that this alkylation does not involve the classical electron transfer reaction followed by radical coupling between diffusing radicals, but supports the alternative S_N2 concerted mechanism, discerning thus this mechanistic S_N2‐ET dichotomy. Copyright © 2015 John Wiley & Sons, Ltd.     

The Activation of Sulfur Hexafluoride at Highly Reduced Low‐Coordinate Nickel Dinitrogen Complexes

The greenhouse gas sulfur hexafluoride is the common standard example in the literature of a very inert inorganic small molecule that is even stable against O₂ in an electric discharge. However, a reduced β‐diketiminate nickel species proved to be capable of converting SF₆ into sulfide and fluoride compounds at ambient standard conditions. The fluoride product complex features an unprecedented [NiF]⁺ unit, where the Ni atom is only three‐coordinate, while the sulfide product exhibits a rare almost linear [Ni(μ‐S)Ni]²⁺ moiety. The reaction was monitored applying ¹H NMR, IR and EPR spectroscopic techniques resulting in the identification of an intermediate nickel complex that gave insight into the mechanism of the eight‐electron reduction of SF₆.     

A Borinic Acid Polymer with Fluoride Ion‐ and Thermo‐responsive Properties that are Tunable over a Wide Temperature Range

A new type of smart borinic acid polymer with luminescence and multiple stimuli‐responsive properties is reported. In DMSO with small amounts of water, the homopolymer PBA shows a tunable upper critical solution temperature (UCST). As the amount of water increases from 0 to 2.5 % (v/v), the UCST rises linearly from 20 °C to 100 °C (boiling point of water). Thus, the thermal responsive behavior can be tuned over a wide temperature range. Furthermore, polymer solutions in DMSO show a reversible response to fluoride ions, which can be correlated to the presence of the Lewis acidic borinic acid groups. Upon addition of fluoride, the polymer becomes soluble because the functional R₂BOH groups are converted into ionic [R₂BF₂]^? groups, but turns insoluble again upon addition of H₂O, which reverses this process.     

XMgO·YMg(OH)_2吸附剂除氟机理及其净化水的水质研究

研究了XMg O·YMg(OH)2对水中氟离子的吸附性能,考察了吸附时间、吸附剂用量、含氟水p H值、温度、含氟水初始浓度等因素对吸附的影响。实验结果表明,在较宽的p H(3.4~8.4)值和水温(22~51℃)范围内,XMg O·YMg(OH)2对水中氟离子具有极强的吸附能力,室温下0.4g XMg O·YMg(OH)2可将100m L浓度为30mg F-1·L-1含氟水处理为符合含氟标准的饮用水。氟离子在XMg O·YMg(OH)2上的吸附速率较大,30min内基本达到吸附平衡,吸附平衡符合Langmuir方程,在50min内达到饱和吸附,室温下饱和吸附量为13.46mg·g-1。净化水呈微碱性,含有5.68~15.07mg·L-1Mg2+,有益于人体健康。吸附饱和后的XMg O·YMg(OH)2经焙烧再生,除氟率可达81%。