The mechanism of the elimination kinetics of 2-bromo-2-butene in the gas phase

The kinetics of the gas phase elimination of 2-bromo-2-butene were determined in a static system over the temperature range of 340–380°C and pressure range of 37–134 torr. The reaction in seasoned vessels, even in the presence of a free radical inhibitor, is catalyzed by hydrogen bromide. Under maximum catalysis of HBr, the kinetics were found to be of order 1.0. The reaction, when maximally catalyzed with HBr, appears to undergo a molecular elimination of HBr which follows first-order kinetics. The products are 1,2-butadiene and hydrogen bromide. The rate coefficients. under maximum catalysis, are given by the Arrhenius equation log ??₁(s^?1) = (13.57 ± 0.56) ? (200.4 ± 6.8) kJ mol^?1 (2.303RT)^?1. The catalyzed pyrolysis of 2-bromo-2-butene appears to proceed through a six-membered cyclic transition-state type of mechanism.     

A matricial extension of the Helson-Sarason theorem and a characterization of some multivariate linearly completely regular processes

We generalize the theorems of Helson-Szegö and Helson-Sarason for matricial measures. We study two-weighted inequalities for the Hilbert transform in [0, 2π] and in R and give a characterization for the positivity of the angle between past and future of multivariate weakly stationary stochastic processes, in the discrete and the continuous case. We also characterize the multivariate weakly stationary stochastic processes that are linearly completely regular and study the rate of convergence of the maximal correlation coefficient.     

Aryl-aryl bond formation by the fluoride-free cross-coupling of aryldisiloxanes with aryl bromides

The prevalence of the biaryl structural motif in biologically interesting and synthetically important molecules has inspired considerable interest in the development of methods for aryl-aryl bond formation. Herein we describe a novel strategy for this process involving the fluoride-free, palladium-catalysed cross-coupling of readily accessible aryldisiloxanes and aryl bromides. Using a statistical-based optimisation process, preparatively useful reaction conditions were formulated to allow the cross-coupling of a wide range of different substrates. This methodology represents an attractive, cost-efficient, flexible and robust alternative to the traditional transition-metal-catalysed routes typically used to generate molecules containing the privileged biaryl scaffold.     

A primal-dual interior-point algorithm for quadratic programming

In this paper we propose a primal-dual interior-point method for large, sparse, quadratic programming problems. The method is based on a reduction presented by Gonzalez-Lima, Wei, and Wolkowicz [14] in order to solve the linear systems arising in the primal-dual methods for linear programming. The main features of this reduction is that it is well defined at the solution set and it preserves sparsity. These properties add robustness and stability to the algorithm and very accurate solutions can be obtained. We describe the method and we consider different reductions using the same framework. We discuss the relationship of our proposals and the one used in the LOQO code. We compare and study the different approaches by performing numerical experimentation using problems from the Maros and Meszaros collection. We also include a brief discussion on the meaning and effect of ill-conditioning when solving linear systems.This work was partially supported by DID-USB (GID-001).     

The gas-phase elimination kinetics of 3-buten-1-methanesulphonate and 3-methyl-3-buten-1-methanesulphonate

The elimination kinetics of the title compounds were carried out in a static system over the temperature range of 290–330°C and pressure range of 29.5–124 torr. The reactions, carried out in seasoned vessels with allyl bromide, obey first-order rate law, are homogeneous and unimolecular. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for 3-buten-1-methanesulphonate, log k₁(s^?1) = (12.95 ± 0.53) ? (175.3 ± 5.9)kJ mol^?1(2.303RT)^?1; and for 3-methyl-3-buten-1-methanesulphonate, log k₁(s^?1) = (12.98 ± 0.40) ? (174.7 ± 4.5)kJ mol^?1(2.303RT)^?1. The olefinic double bond appears to assist in the rate of pyrolysis. The mechanism is described in terms of an intimate ion-pair intermediate. © 1995 John Wiley & Sons, Inc.     

Diagnostic criteria for characterization of mechanisms corresponding to the second reduction polarographic wave of carbonyl compounds in acidic medium

Expressions of i-E funtions are developed, either by the reaction layer approach or from the assumption that the reactions take place at the surface of the electrode, for different possible mechanisms corresponding to the second reduction polarographic wave of carbonyl compounds in acidic medium.Diagnostic criteria for their characterization are presented and applied to the pyridine-4-aldehyde reduction. Close agreement between the experimental and theoretical results is obtained for a mechanism with a reversible transfer reaction followed by a protonation reaction of the compound formed.     

Derivation and experimental verification of approximate explicit equations in differential pulse polarography: Part I. First order processes

An approximate method applicable to electrochemical processes either coupled or not to first order chemical reactions in differential pulse polarography is proposed. A program has been prepared in order to enable the authors to interpret DP polarograms. The method has been tested with the aid of well-known oxidation and reduction processes. The utility of the method is shown, particularly in those cases involving overlapping DP polarographic waves. Applications to determinations of kinetic parameters and quantitative analysis have also been made.     

New oxidized isocularine alkaloids from sarcocapnos plants

Structures 1a, 3 and 6 were deduced for the new oxoisocularine alkaloids, oxosarcophylline, yagonine and aristoyagonine, respectively, on the basis of spectroscopic studies and synthesis.     

Temperature dependence of the rho-meson mass and width

It is shown, to leading order in the virial expansion, that unitarity of the ππ scattering amplitude implies that if the ρ-meson widthΓ _ρ(T) increases with temperature, then the ρ-meson massM _ρ(T) must also increase. The temperature dependence ofM _ρ(T) is explicitly obtained from a simple, but physically motivated, parametrization of theI=J=1 ππ scattering amplitude.