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Thomas Welton

Publications and source records attributed to Thomas Welton.

7 recordsLinked to original sources
PubMed2007

Decolorization of ionic liquids for spectroscopy.

It has been widely recognized that although ionic liquids should be colorless, they are frequently not. Colored samples appear to be pure by most analytical techniques (e.g., NMR spectroscopy, mass spectrometry, HPLC, and ion chromatography), and there have been many attempts to identify the source of color in our own laboratories and others-after 20 years the best that can be said is that the impurities are at a very low level (probably parts per billion) with very high molar extinction coefficients. In this paper, we do not identify these impurities but describe a practical method for removing them for spectrochemical applications. We clearly note that the method is not "green", but we anticipate that it will only be applied to the small volumes of ionic liquids required for fundamental spectroscopic studies in academia but not in industrial processes.

Journal Article↗
PubMed2004

Chiral ionic liquids as stationary phases in gas chromatography.

Recently, it has been found that room-temperature ionic liquids can be used as stable, unusual selectivity stationary phases. They show "dual nature" properties, in that they separate nonpolar compounds as if they are nonpolar stationary phases and separate polar compounds as if they are polar stationary phases. Extending ionic liquids to the realm of chiral separations can be done in two ways: (1) a chiral selector can be dissolved in an achiral ionic liquid, or (2) the ionic liquid itself can be chiral. There is a single precedent for the first approach, but nothing has been reported for the second approach. In this work, we present the first enantiomeric separations using chiral ionic liquid stationary phases in gas chromatography. Compounds that have been separated using these ionic liquid chiral selectors include alcohols, diols, sulfoxides, epoxides, and acetylated amines. Because of the synthetic nature of these chiral selectors, the configuration of the stereogenic center can be controlled and altered for mechanistic studies and reversing enantiomeric retention.

Chromatography, Gas↗
PubMed2002

Characterizing ionic liquids on the basis of multiple solvation interactions.

Room-temperature ionic liquids (RTILs) are useful in many chemical applications. Recent publications have attempted to determine the polarity of RTILs using empirical solvent polarity scales. The results have indicated that most RTILs have similar polarities. Nevertheless, RTILs are capable of behaving quite differently when used as solvents in organic synthesis, matrixes in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, liquid-liquid extraction, and as stationary phases in gas chromatography. The work presented in this study uses a linear free energy approach to characterize 17 RTILs on the basis of their distinct multiple solvation interactions with probe solute molecules. This model provides data that can be used to help identify the interactions and properties that are important for specific chemical applications.

Alkanes↗
PubMed2002

A highly selective arene hydrogenation catalyst that operates in ionic liquid.

The synthesis and structural characterization of [Ru(eta(6)-p-cymene)(eta(2)-TRIPHOS)Cl][PF(6)] is described. The complex is a highly active, homogeneous arene hydrogenation catalyst that is selective toward the hydrogenation of aromatic rings in preference to alkenes, as demonstrated by the hydrogenation of allylbenzene to allylcyclohexane. The catalyst operates in both dichloromethane and ionic liquids and undergoes no decomposition in the latter solvent.

Journal Article↗
PubMed1998

Dithiocarbamate-Functionalized Dendrimers as Ligands for Metal Complexes.

Zeroth- and first-generation poly(amido)amine dendrimers have been functionalized with dithiocarbamate end groups and reacted with ruthenium complexes, to form metallodendrimers. Monomeric ruthenium dithiocarbamate complexes were also prepared as model compounds and their spectroscopic data compared with those of the metallodendrimers. The novel compounds were characterized using NMR spectroscopy ((1)H and (13)C) and mass spectrometry. The compound [Ru(S(2)CNMe(2))(PPh(3))(eta(5)-C(5)H(5))] has also been characterized crystallographically.

Journal Article↗