PALLAS System

CompuDrug Ltd.—the PALLAS System— including programs for for pifa> ogD predictions, metabolism and toxicity, and high pressure liquid chromatography (HPLC) development (118)... 

The use of palladium(II) sulfoxide complexes as catalyst precursors for polymerization has met with mixed results thus a report of a palla-dium(II) chloride-dimethyl sulfoxide system as a catalyst precursor for phenylacetylene polymerization suggests similar results to those obtained using tin chloride as catalyst precursor (421). However, addition of dimethyl sulfoxide to solutions of [NH fPdCh] decreases the activity as a catalyst precursor for the polymerization of butadiene (100). Dimethyl sulfoxide complexes of iron have also been mentioned as catalyst precursors for styrene polymerization (141). 

Metal membranes. Since Thomas Graham [1866] discovered that metallic palladium absorbs a large amount of hydrogen, the metal hydride system of which palla um is an important example has been extensively studied. Hydrogen dissolved in a metal hydride system (according to the mechanism to be describ below) is considered to behave in an atomic or ionic form which is more reactive than molecular hydrogen in a gas phase. 

The first asteroid was discovered serendipitously by the Italian astronomer Giuseppe Piazzi (1746-1826) on the night of January 1,1801. This asteroid, subsequently called Ceres after the Roman goddess of com and harvests, has a diameter of 584 mi (940 km) and is the largest asteroid in our solar system. The next three largest asteroids, Pallas, Juno, and Vesta, were discovered in 1802,1804, and 1807. 

Even in the early days of homogeneous hydrocyanation the reaction of norbor-nene with hydrogen cyanide in the presence of tetrakisftriphenyl phosphite)palla-dium(O) 12 indicated the influence of steric factors, since exo-5-cyanobicy-clo[2.2.1]heptane (Structure 10) is obtained stereospecifically. This result was confirmed in similar reactions showing that the entering cyano group is directed into the exo-position of the norbomene system [28]. This is due to the complexa-tion of the palladium(O) center to the exo-face of norbomene. Recent experiments have also utilized the bicyclic system to demonstrate asymmetric hydrocyanation induced by chiral palladium diphosphine complexes. Depending on the applied ligand system 11-17, an enantiomeric excess (ee) up to 40% is obtained [25]. 

A triple point exists at which there is a equilibrium between the G, LE, and LC phases. At this point, A e = Harkins and Boyd estimated that the coexistence curves meet at 17°C at an area of 44 and Pallas and Pethica report the intersection at 38 4 and 17 + 2°C. The triple-point temperature can be located directly in fluorescence measurements by determining the temperature at which a third phase appears when the temperature of a two-phase system is lowered at a fixed area. 

In 1998, Guitian, Perez and co-workers reported that the cyclotrimerization of benzyne (1) to triphenylene (56) is efficiently catalyzed by palladium(O) complexes (Scheme 11) [39]. This was the first time an aryne had been the substrate in a metal-catalyzed process. The success of the reaction was based on a judicious choice of the reaction conditions, particularly with regard to the catalytic system and the method of generating the aryne. Some significant results of this seminal study are shown in Table 1. After some preliminary experiments in which nickel complexes were used as catalysts (entry 1), it was found that nucleophilic palla-dium(O) complexes efficiently promote the desired [2+2+2] cycloaddition of the strongly electrophilic substrate 1 (entries 2-6) [40]. At the same time, a systematic study of benzyne generation conditions showed that Kobayashi s method... 

The Heck reaction was the first catalytic application examined for palla-dium/NHC complexes. A high degree of efficiency was observed for chelating bis-carbene/palladium complexes in this transformation. The reactions involving butyl acrylate with aryl halides were efficiently mediated by such complexes at catalyst loadings as low as 10" mol%. Unactivated chlorides required, however, a catalyst loading up to 1 mol%. The impressive stability of the catalytic system under harsh reaction conditions and its reactivity profile were described as quite impressive [32,56]. 

Hexafluorophosphoramide. Panaris and Pallas [61] described the use of hexafluorophosphoramide as an SEC solvent. It is a common solvent for nylons 6,11 and 12 at temperatures below 100°C, and its RI differs from nylons sufficiently to give a good response (RI = 1.459 at 25°C). It was purified by distillation under argon and used at 85°C. The linearity of response was checked, and it was ascertained that there was no adsorption of nylon on to the columns. Polystyrene is also soluble in it, and therefore calibration could be carried out with polystyrene standards. Results obtained were compared with those determined in benzene at 25°C by classical methods. Its use in other polymer systems is being considered. 

Palla, B.J., Shah, D.O., 2000. Stabilization of high ionic strength slurries using the symergistic effects of a mixed surfactant system. J. Colloid Interface Sci. 223, 102—111. 

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