Triphenylborane methanolysis and equilibrium association between triphenylborane or diphenylborinate esters and alcohols

Abstract

the nitrone spin trap PBN.2a For example, ferf-butylethylene gives a radical yield of 0.1% using the BHT method; PBN gives a radical yield of 0.004% with this olefin, confirming our suggestion24 that PBN traps radicals with about 1 % efficiency in these ozone systems.21"This work demonstrates the usefulness of BHT as a "spin trap". Carbon-centered radicals can be converted to peroxyl radicals in the presence of oxygen, and BHT traps these radicals with high efficiency. The use of BHT in place of a nitrone spin trap clearly conveys some advantages: BHT yields a stable, diamagnetic species that can be quantified by normal chromatographic methods, rather than by ESR. While the identification of the radical that is trapped by BHT using GC/MS is not trivial, our data do show that this identification can be made (at least for simple R groups) using GC/MS in collaboration with NMR.NMR spectra, and Figure 3,13C NMR spectra of compounds 1 and 2a (3 pages). Ordering information is given on any current masthead page.

Heat Capacities and Excess Enthalpies of 1-Ethyl-3-methylimidazolium-Based Ionic Liquids and Water

“…The pK a 's of the acids of interest are shown in Table 6. The pK a of trifluoromethanesulfonic acid is - 11,42 indicating that it should have weak interactions with water, which is consistent with the experimental endothermic excess enthalpy (H E < 1373 J · mol -1 ). The ethylsulfuric acid has a larger pK a of -3.14, 43 31 The structures of the respective acids are very similar, and the pK a 's are virtually the same; 44,45 however, the excess enthalpies are very different.…”

Conducting Poly(anilineboronic acid) Nanostructures: Controlled Synthesis and Characterization

“…However, in the case of methanol, PABA appears to remain in self-doped state containing anionic tetrahedral boron and remains soluble even after purification with 0.5 M HCl. These results suggest that the tetrahedral boronate structure containing methanol and fluoride is stabilized likely due to the higher association constant of boron for methanol [23] and fluoride or synergy effect of both, and stays intact even after purification with 0.5 M HCl. The XPS and 11 B NMR results indicate that the different doping mechanisms resulting from the interaction of the solvent with boronic acid is responsible for the different nanostructures observed, and that the external doping by HCl, which occurs in the precipitation and purification step, is an important factor in producing the nanofiber morphology.…”

“…The 11 B NMR spectrum of the monomer in methanol ( Figure 1a) shows a single resonance with a chemical shift at 29.3 ppm indicating that boron exists primarily in the neutral trigonal form (Scheme 1, 2 and 3 ). [23] However, in the presence of sodium fluoride (Figure 1b), an additional resonance signal is observed approximately 25 ppm upfield indicative of the formation of tetrahedral anionic boronate (Scheme 1, 4 and 5). [19] Following the addition of an oxidizing agent and completion of the polymerization reaction, the 11 B NMR spectrum was taken again (Figure 1c-e).…”

“…[22] Aromatic boronic acids are also known to complex reversibly with aliphatic alcohols where the equilibrium constant for boronic acid-alcohol complex decreases with increasing steric size of the alcohol (i.e., methanol > ethanol > 1-propanol). [23] Based on this chemistry, we hypothesized that it should be possible to synthesize self-doped, alcohol-soluble PABA and to manipulate the solubility and morphology by converting between internal doping involving anionic boronate groups and external doping in the presence of anions in solution and under conditions where boronic acid groups are uncharged. In previous studies, nanostructures such as nanoparticles, nanofibers and nanotubes have been prepared using templates, surfactants, polyacids, etc.…”

Supramolecular anion binding by the [ZnCl(HpztBu)3]+ cation (HpztBu = 5-tert-butylpyrazole)

“…7): Within the halides and oxyanion series, there is a direct correlation between δ NH and the pK a of the conjugate acid of each anion (Fig. 7), which follow the following trends in aqueous solution: [13][14][15] HCl (Ϫ7) > HBr (Ϫ9) > HI (Ϫ11) HNO 3 (ca. Ϫ1) > HClO 4 (ca.…”