Unexpected differences in the alpha-halogenation and related reactivity of sulfones with perhaloalkanes in KOH-t-BuOH

Most alkyl phenyl sulfones are readily alpha-chlorinated with CCl(4) and alpha-brominated with CBrCl3 in KOH-t-BuOH via radical-anion radical pair (RARP) reactions. While isopropyl mesityl sulfone (4) is easily alpha-chlorinated with CCl(4), it was completely recovered when treated with the more reactive CBrCl3. Subsequent investigations showed the latter result to be due to the poor acidity of 4 together with the rapid depletion of CBrCl3 and KOH by their reaction with each other, and led to a variety of other important results. 4-Hydroxyphenyl isopropyl sulfone (6) is unreactive with either CCl4 or CBrCl3 in KOH-t-BuOH, its phenoxide anion strongly reducing the electronegativity of the sulfonyl group, thereby inhibiting alpha-anion formation. This effect is reversed by the electron-withdrawing influence of two alpha-phenyls, so that benzhydryl 4-hydroxyphenyl sulfone (8) is readily alpha-halogenated in KOH-t-BuOH with CCl4 or CBrCl3. On further contact with KOH-t-BuOH the alpha-halogenated sulfones from 8 are decomposed into benzophenone and phenol. While the alpha-halogenated derivatives of 4-methoxyphenyl benzhydryl sulfone (9) are stable to base, they are decomposed even under mildly acidic conditions into 4-methoxyphenyl 4-methoxybenzenethiolsulfonate (9c), phenol, and benzophenone. Mono-alpha-halogenation of benzyl phenyl sulfone (10) enhances the rate of the subsequent halogenation, so that alpha,alpha-dihalogenation is attained while much substrate is still present and the mono-alpha-halogenated product is not detected. The ease of reductive debromination of alpha-bromo sulfones with Cl3C- was correlated with the stability of the formed alpha-anions, explaining the success with alpha-bromobenzylic sulfones but failure with alpha-bromoalkyl sulfones. In the presence of air and the absence of competing halogenation, formation of the alpha-anions of alkyl aryl sulfones is quickly accompanied by oxidative cleavage by atmospheric O2, leading to the formation of arenesulfonyl alcohols, arenesulfonyl halides, and haloarenes.     

Efficient Continuous Wave-laser emission of Pr3+-doped fluorides at room temperature

We report, to our knowledge for the first time, Continuous Wave (CW) laser emission at room temperature of Pr:LiYF₄ (Pr.YLF) at six wavelengths: 522, 545, 607, 639.5, 720 and 907.4 nm. The pump source was an argon-ion laser tuned to a wavelength of = 457.9 nm. The maximum output powers at 522 nm (³P_i ³H₅) and 639.5 nm (³P₀ ³F₂) were 144 and 266 mW, respectively. We also observed CW laser action of Pr:GdLiF₄ (Pr: GLF) at = 639 nm and of Pr:KYF₄ (Pr: KYF) at = 642.5 nm.     

Self-starting mode locking of a Nd:glass fiber laser by use of the third-order nonlinearity of low-temperature-grown GaAs

We present a diode-pumped Nd:glass fiber laser, emitting at 1060 nm, that is passively mode locked by fast nonlinear loss in low-temperature-grown GaAs (LT-GaAs). This new mode-locking mechanism is based on intensity-dependent defocusing in LT-GaAs that occurs after nonresonant generation of free carriers by two-photon absorption. Mode locking is self-starting and produces pulses as short as 4.1 ps.     

The IEA/DOE/SNL on-line hydride databases

A series of comprehensive hydride databases have been constructed and made freely available on the Internet (URL http://hydpark.ca.sandia.gov). They include extensive listings of alloys reported to hydride, detailed engineering properties on selected hydrogen-storage elements and alloys and a hydride-applications database. These databases and an associated reference database are described, along with other hydride information available on the web site. The databases were created under the auspices of the International Energy Agency (IEA) with financial support from the U.S. Department of Energy (DOE) and Internet service support from the Sandia National Laboratories (SNL). Received: 21 August 2000 / Accepted: 6 November 2000 / Published online: 9 February 2001     

A Simple Algorithm for Solving Small,Fixed-Charge Transportation Problems

The solution of the classical transportation problem (as generally presented) can be mastered very quickly. The fixed-charge problem is another matter. The reason is that the introduction of fixed costs in addition to variable costs results in the objective function being a step function. Fixed-charge problems are usually solved, therefore, by using sophisticated computer software. This paper deviates from that approach. It presents a low-tech. algorithm for the solution of small, fixed-charge problems.     

Orthogonal reactivity in boryl-substituted organotrifluoroborates

A method was developed for the hydroboration of alkenyl-containing organotrifluoroborates to generate dibora intermediates. The reactivity differences between organotrifluoroborates and trialkylboranes facilitated the cross-coupling of the borane moiety of these intermediates in a highly chemoselective fashion with aryl halides, leaving the trifluoroborate intact for subsequent transformation. A one-pot hydroboration/two-directional cross-coupling sequence was also demonstrated, providing the fully elaborated products in good yields. These conditions were also amenable in the cross-coupling of trialkylboranes to halo-containing organotrifluoroborates. The stability of the trifluoroborate moiety to these conditions allows simple and efficient strategies for complex molecule construction.     

Diffractive Scattering of Virtual Photons on Nuclei and Its Interference with the Muon-Induced Bremsstrahlung Process

Physics of Atomic Nuclei - Investigation of lepton propagation through matter is of importance for cosmic-ray physics and neutrino astronomy. The diffractive scattering of virtual photons is...     

Ternäre Chloride in den Systemen NaCl/HoCl3 und NaCl/ErCl3

Ternary Chlorides in the Systems NaCl/HoCl₃ and NaCl/ErCl₃ Phase diagrams of the systems NaCl/HoCl₃ and NaCl/ErCl₃ were determined by means of DTA and high-temperature XRD. There exist compounds Na₃LnCl₆, NaLnCl₄ (Ln ? Ho, Er) and NaHo₂Cl₇. NaHoCl₄ undergoes a phase transition at 374°C from the NaGdCl_4? to the NaErCl_4? type of structure. The thermodynamic functions for the formation of the compounds from NaCl and LnCl₃ were determined by solution calorimetry and e.m.f. measurements in galvanic cells for solid electrolytes. The compounds NaLnCl₄ are the most stable ones.     

Laser emission of erbium-doped fluoride bulk glasses in the spectral range from 2.7 to 2.8 mum

We report on the laser emission of erbium-doped fluoride glasses in the spectral range from 2.7 to 2.8 mum . The pump source was a fiber-coupled InGaAs semiconductor laser emitting near lambda(p)~970 nm . The laser performance of bulk samples with various ErF(3) contents was investigated with respect to the optimum doping concentration, which is estimated to be higher than 8 mol. %. A maximum output power of P(out) > 160 mW and a slope efficiency of eta = 10% were achieved. Results are compared with previously published data on erbium-doped ZBLAN fiber and LiYF(4) crystal lasers.