Darwin B. Dahl

Enantiomeric separation of sulfonium ions by capillary electrophoresis using neutral and charged cyclodextrins.

Capillary zone electrophoresis was successfully applied, for the first time, to the chiral separation of structurally related sulfonium ions, using sodium phosphate buffer pH 2.5 with β-cyclodextrin (β-CD) or sulfated-β-cyclodextrin (S-β-CD) as the chiral selector with tetrabutylammonium bromide (TBA). For this study, a series of structurally related sulfonium ions in which one of the alkyl chains varied in length were synthesized from a common sulfide. The resolution of the ions was found to be dependent on the type of cyclodextrin used, the presence or absence of TBA, and the structure of the sulfonium ion. β-CD was found to be effective only for ions containing two aromatic groups, while the S-β-CD was effective only for ions containing one aromatic group. The chiral separation of thiophenium ions was also studied under the conditions established. Chiral separation of sulfonium ions in a binary buffer system containing methanol was explored as well. Separations were achieved for all but one sulfonium ion and one thiophenium ion. The data presented show the effectiveness of the enantiomeric separation using CZE with cyclodextrin-modified buffer for these types of ions.

The Pd(II)-catalyzed homogeneous isomerization of hexenes

Abstract The isomerization of linear hexenes in alcoholic media, catalyzed by low concentrations of PdCl 2 in the presence of CuCl 2 , has been examined. Effects of reagent concentrations, alcohol and temperature are noted. Values of the rate and equilibrium constants for the ten rate-determining steps have been calculated for reactions in methanol at 30°C. The turnover number for the π-complex group is 48,100 ± 3,800 h −1 . No skeletal isomerization is detected. These isomerizations appear to proceed through π-allylic intermediates.

Capillary zone electrophoretic separation of sulfonium and thiophenium ions

Capillary zone electrophoretic separation of sulfonium and thiophenium ions using phosphate buffer with TBA, pH 2.5, was investigated. Following their synthesis, 13 ions were synthesized and separated by this procedure. The benefits of speed and resolution has shown this method to be superior to that of conventional liquid chromatographic separation procedures.

Isomerization and oxidation of linear hexenes with methanolic Pd(II)

Abstract 1-Hexene, cis -2-hexene and trans -2-hexene all oxidize at the same rate at 30°C to yield 60–62% 2-hexanone along with 3-hexanone and hexanal. trans -3-Hexene reacts similarly, with the product mixture only slightly enriched (by ≈ 5%) in 3-hexanone. Under typical oxidation conditions with 0.010 M of PdCl 2 and CuCl 2 present these hexenes are shown to isomerize rapidly to an equilibrium mixture. The overall oxidation turnover number (TN) is ≈ 10, while for 1-hexene the isomerization TN under these conditions is approximately 3100.