Microwave-assisted, regioselective, Petasis olefination of unsymmetrical oxalates. Formation of pyruvate-based enol ethers and enamines

The Petasis olefination of unsymmetrical oxalates and oxalate monoesters/monoamides (tert-BuO₂CC(O)X, where X = OR, NR₂) is highly regioselective and provides pyruvate-based enol ether and enamine derivatives. The olefination step occurs under conventional thermal conditions, but is dramatically improved--shorter reaction times and higher yields--when promoted by microwave irradiation.     

The tautomerism of heteroaromatic compounds with 5-membered rings—XI 4-Hydroxyisoxazoles-4-isoxazolinones

Four 4-hydroxyisoxazoles together with model compounds have been investigated by UV, IR and NMR spectroscopy and by pK_a measurements, 4-Hydroxyisoxazoles exist predominantly in the hydroxy-form in a wide range of media.     

Fifth and sixth order PECE algorithms based on g-splines with improved stability characteristics

In this note fifth and sixth order PECE algorithms are presented. The corrector formulae are derived by using natural g-splines. The resulting PECE algorithms which use the Schoen predictor have larger regions of absolute stability and smaller truncation errors than the Krogh and Schoen algorithms of corresponding order.     

Optical-model analysis of 7Li + 25Mg and 7Li + 27Al elastic scattering at 89 MeV

The elastic scattering angular distributions for ⁷Li + ²⁵Mg and ⁷Li + ²⁷Al were measured at $\text{E(}{}^7\text{Li}\text{) = 89}\text{MeV}$ over angular ranges of 8–55° c.m. and 8–64° c.m. Previously published measurements for ^{24, 26}Mg at 89 MeV and ²⁴Mg at 34 MeV are reanalyzed. The cross sections were analysed using a 6-parameter phenomenological Saxon-Woods potential. No discrete ambiguities were found but the usual continuous ambiguities exist. The data were also analysed with double folded real potentials generated using the M3Y effective interaction. The folded potential must be multiplied by about 0.6 to fit the data. The extent to which ⁷Li optical-model potentials are determined and suggestions for further work on the normalization of the folded potential are discussed.     

Determination of small quantities of xanthate

A new spectrophotometric method for the determination of very small amounts of xanthate in solutions, particularly cyanide solutions from gold-extraction plants, is described. It is based on the formation and extraction of copper(II) xanthate. The coefficient of variation is 1.0% at the 40-ppm level and 3.4% at the 4-ppm level and the lower limit of determination is approximately 0.5 ppm. Copper(II) xanthate normally decomposes into copper(I) xanthate and dixanthogen, but in the proposed method the decomposition is delayed.     

Injectives of strongly hereditary relative homological algebras

IfR is a strongly hereditary relative homological algebra of Abelian groups which contains the torsion split sequences, then theR-injectives can be completely characterized. IfR is a relative homological algebra with enough projectives and enough injectives, which contains the torsiol split sequences, then equivalent conditions forR to be strongly hereditary are given.     

Shock measurement with non-contacting fiber optic levers

The displacement, velocity, and acceleration performance limits of a non-contacting fiber optic lever vibration transducer are quantified. Performance characteristics are experimentally verified and measurements of displacement, velocity, and acceleration obtained from impacted plates are compared with those obtained by using conventional accelerometers. It is shown that all relevant transducer quantities, i.e., absolute maximum and minimum levels, dynamic range, and frequency response, lend themselves to quantification (or optimization) on a single graphic representation. The transducer is particularly useful for measuring high frequency shock parameters.