First Monte-Carlo modelling of global beryllium migration in ITER using ERO2.0

ERO2.0 is a recently developed Monte-Carlo code for modelling global erosion and redeposition in fusion devices. We report here on the code's application to ITER for studying the erosion of the beryllium (Be) first wall armour under burning plasma steady state diverted conditions. An important goal of the study is to provide synthetic signals for the design of two key diagnostics: the main chamber visible spectroscopy and the laser in-vessel viewing systems. The simulations are performed using toroidally symmetric plasma backgrounds obtained by combining SOLPS simulations extended to the wall using the OSM-EIRENE-DIVIMP edge code package. These are then further combined with a shadowing model using magnetic field line tracing to provide a three-dimensional correction for the flux patterns. The resulting plasma wetted area, which amounts to ∼10% of the total first wall area, is in excellent agreement with shadowing calculations obtained with the SMITER field line tracing code. The simulations reveal that the main Be erosion zones are located in regions intersected by the secondary separatrix, in particular the upper Be panels, which are close to the secondary X-point. For the particular high-density Q = 10 background plasma case studied here, ∼80% of the eroded Be is found to re-deposit on main chamber surfaces. The rest migrates in almost equal parts to the inner and outer divertor and is deposited close to the strike lines.     

A study of the structural and thermodynamic properties of water by the molecular dynamics method

The thermodynamic and structural properties of four rigid water models were studied by the molecular dynamics method over a wide temperature range. Two three-center (SPC/E and TIP3P) and two five-center (ST4 and TIP5P) models were considered. The results discussed include the boiling and condensation temperatures, VT phase transition diagrams, three-dimensional spatial distributions of atoms, the temperature dependences of the total energy, density, heat capacity, the number of H-bonds per molecule, the distribution of H-bonds over the ∠HOO angle, the self-diffusion coefficient, and the radial distribution functions. The boiling points of all the models did not correspond to 100°C and were noticeably different from each other. The condensation points were also different. The data on the structural parameters led us to conclude that the TIP5P model reproduced the local structure of water most correctly. However, if the reproduction of the local structure is not a necessary condition, less resource consuming three-center models can be used.     

Regio- and stereoselective addition of methane- and bromomethanesulfonyl bromides to 1-phenylthiotricyclo[4.1.0.0<Superscript>2,7</Superscript>]heptane

1-Phenylthiotricyclo[4.1.0.0^2,7]heptane reacted with MeSO₂Br and BrCH₂SO₂Br directly at mixing at 20°C in CH₂Cl₂ along a ionic (electrophilic with respect to bromine) mechanism affording a product of an antistereoselective addition to the central bicyclobutane C¹–C⁷ bond of the norpinane structure. The reaction product contains the exo-oriented sulfonyl group in the geminal position to the SPh substituent. The structure of the adduct with MeSO₂Br in a single crystal was determined by XRD analysis.     

Mechanistic and computational study of a palladacycle-catalyzed decomposition of a series of neutral phosphorothioate triesters in methanol

The methanolytic cleavage of a series of O,O-dimethyl O-aryl phosphorothioates (1a?g) catalyzed by a C,N-palladacycle, (2-[N,N-dimethylamino(methyl)phenyl]-C1,N)(pyridine) palladium(II) triflate (3), at 25 °C and sspH 11.7 in methanol is reported, along with data for the methanolytic cleavage of 1a?g. The methoxide reaction gives a linear log k2?OMe vs sspKa (phenol leaving group) Br?nsted plot having a gradient of βlg = ?0.47 ± 0.03, suggesting about 34% cleavage of the P?OAr bond in the transition state. On the other hand, the 3-catalyzed cleavage of 1 gives a Br?nsted plot with a downward break at sspKa (phenol) 13, signifying a change in the rate-limiting step in the catalyzed reaction, with the two wings having βlg values of 0.0 ± 0.03 and ?1.93 ± 0.06. The rate-limiting step for good substrates with low leaving group sspKa values is proposed to be substrate/pyridine exchange on the palladacycle, while for substrates with poor leaving groups, the rate-limiting step is a chemical one with extensive cleavage of the P?OAr bond. DFT calculations support this process and also identify two intermediates, namely, one where substrate/pyridine interchange has occurred to give the palladacycle coordinated to substrate through the S═P linkage and to methoxide (6) and another where intramolecular methoxide attack has occurred on the P═S unit to give a five-coordinate phosphorane (7) doubly coordinated to Pd via the S? and through a bridging methoxide linked to P and Pd. Attempts to identify the existence of the phosphorane by 31P NMR in a d4-methanol solution containing 10 mM each of 3, trimethyl phosphorothioate (a very slow cleaving substrate), and methoxide proved unsuccessful, instead showing that the phosphorothioate was slowly converted to trimethyl phosphate, with the palladacycle decomposing to Pd0 and free pyridine. These results provide the first reported example where a palladacycle-promoted solvolysis reaction exhibits a break in the Br?nsted plot signifying at least one intermediate, while the DFT calculations provide further insight into a more complex mechanism involving two intermediates.     

Experimental and computational determination of Brønsted coefficients for equilibrium transfer of the O,O‐dimethyl phosphorothioyl group between oxyanion nucleophiles

An experimental determination of the β^Eq value for equilibrium transfer of the O,O‐dimethyl phosphorothioyl group between oxyanion nucleophiles in water and methanol at 25 °C is presented. The respective β^Eq values in the two solvents are experimentally the same at ?1.45 ± 0.08 and ?1.39 ± 0.12. Based on the observation that the Brønsted correlation for the nucleophilic reaction of phenoxides in water with substrate 1d (dimethyl 4‐nitrophenyl phosphorothioate, pK_a^HOAr of 7.14) is linear over the entire range of phenoxides employed (5.53 ≤ pK_a^Nu ≤ 12.38), the reaction for phenoxide nucleophiles displacing phenoxide leaving groups is probably concerted. The obtained data allow one to calculate, for a symmetrical transition state involving 2,4,5‐trichlorophenoxide as a nucleophile and leaving group, an approximately 60% P–OAr cleavage and about 40% P–Nuc bond formation. A computational method is presented for the rapid prediction of the β^Eq values for such processes in water and methanol, and the results are compared with known values from the literature. Copyright © 2011 John Wiley & Sons, Ltd.     

Structure and properties of Ti1 − x CrxSe2 substitutional solid solutions

Titanium diselenide TiSe₂ is doped for the first time with an acceptor impurity through substitution of Cr³⁺ ions for Ti⁴⁺ ions in the host lattice. The structure and electrical resistivity of the TiSe₂-based solid solutions are investigated in the vicinity of the compensation point, and the influence of the compensation point on the stability of the charge-density-wave state is analyzed. It is demonstrated that disorder in the guest sublattice does not lead to Anderson localization of charge carriers.     

Methanolysis of thioamide promoted by a simple palladacycle is accelerated by 10(8) over the methoxide-catalyzed reaction

Palladacycle 1 catalyzes the methanolytic cleavage of N-methyl-N-(4-nitrophenyl)thiobenzamide (4) via a mechanism involving formation of a Pd-bound tetrahedral intermediate (TI). The rate constant for decomposition of the complex formed between 1, methoxide, and 4 is 9.3 s(-1) at 25 °C; this reaction produces methyl thiobenzoate and N-methyl-4-nitroaniline. The ratio of the second-order rate constant for the catalyzed reaction, given as k(cat)/K(d), relative to that of the methoxide-promoted reaction is 3 × 10(8), representing a very large catalysis of thioamide bond cleavage by a synthetic metal complex.     

Electrosynthesis of cyclopropanes at the electrolysis of solutions of methyl esters of Di- and trichloroacetatic acids in aprotic media in the presence of acrylonitrile

The potentiostatic (galvanostatic) electrolysis of methyl esters of trichloroacetic acid on mercury (steel) cathodes in the cathodic compartment of a diaphragm cell in the presence of acrylonitrile affords a mixture of two stereoisomers of methyl ester of 1-chloro-2-cyanocyclopropanecarboxylic acid. The process involves a stage of dehalogenation of the original methyl ester followed by the reaction of the formed anion with acrylonitrile and proceeds more efficiently on a mercury cathode in the dimethylformamide medium with the current efficiency of 94% and the substance yield of 25%. In contrast to methyl trichloroacetate, the electrolysis of methyl dichloroacetate proceeds by an indirect mechanism involving its deprotonation on the steel cathode and by the cleavage of the C-Cl bond on the mercury cathode. In both cases, the acrylonitrile addition leads to formation of the corresponding cyclopropane structures. Moreover, the process is the most efficient on the steel cathode in the MeCN medium. In the latter case, the current efficiency of methyl ester of 1-chloro-2-cyanocyclopropanecarboxylic acid is 31% and substance yield is 41%. Peculiarities of these processes are discussed.