David G. Hehemann

Reactions of Per-O-Acetylated Carbohydrate Triflates With Halide Ions

Abstract The reactions of bromide, chloride, and iodide ions with 1,3,4, 6-tetra-O-acetyl-2-O-(trifluoromethylsulfonyl) -α-D-glucopyranose (2) and with 1, 3, 4, 6-tetra-O-acetyl-2-O-(trifluoromethylsulfonyl)-β-D-mannopyranose (3) gave good to excellent yields of the corresponding deoxyhalogeno sugars. In contrast, when the gluco triflate 2 and tetra-butylammonium fluoride were heated under reflux in benzene, only 5-(acetoxymethyl)-2-formylfuran (13) was formed. Reaction of the manno triflate 3 under similar conditions produced 1, 3,4, 6-tetra-O-acetyl-2-deoxy-2-fluoro-β-D-gluco-pyranose (17), 1. 3, 4. 6-tetra-O-acetyl-2-deoxy-β-D-erythro-hex-2-eno-pyranose (18), 4,6-di-O-acetyl-1, 5-anhydro-2-deoxy-D-erythro-hex-l-enitol-3-ulose (19), and 1, 2, 3, 4, 6-penta-O-acetyl-β-D-glucopyranose (20). The mechanisms of the reactions of The triflates 2 and 3 with fluoride ion are discussed.

Wet-Chemical Synthesis of Thin-Film Solar Cells

We have been working on the development of wet-chemical processing methods that can be used to create thin film photovoltaic solar cells. Electrochemically deposition methods have been used to produce copper indium diselenide (CIS) thin films on molybdenum coated polymer substrates. CIS has an extremely high optical absorption coefficient, excellent radiation resistance, and good electrical conductivity and thus has proved to be an ideal absorber material for thin film solar cells. A series of compositionally different p-type CIS films were produced by using different electrochemical deposition potentials. Cadmium sulfide (CdS) window layers were deposited directly on these CIS films using a chemical bath process. CdS is a naturally ntype wide-bandgap semiconductor which has good transparency and is well lattice-matched to CIS. Zinc oxide thin films were grown by electrochemical deposition directly on the CdS films. ZnO is a transparent and conductive thin film that serves as the top contact of the cells. The structural and elemental properties of the individual ZnO, CdS and CIS films were characterized by x-ray diffraction and energy dispersive spectroscopy. The electrical behavior of the CdS on CIS junctions was determined using current versus voltage measurements. We will discuss the performance of these devices based on the physical properties of the component films and the processing methods employed in their fabrication.

A MECHANISTIC STUDY OF THE PHOTOCHEMISTRY OF CARBOHYDRATE P-TOLUENESULFONATES

Abstract Photolysis of 1,2:3,4-di-O-isopropylidene-6-O-(p-tolylsulfonyl)-α-D-galactopyranose (5) in methanol under nitrogen in the presence of sodium hydroxide or diazabicyclo[2.2.2]octane (3, DABCO) produces toluene and 1,2:3,4-di-O-isopropylidene-α-D-gatactopyranose (6). Electron transfer from DABCO or hydroxide ion to singlet excited 5 to generate a radical anion is the first step in this reaction. The radical anion rapidly fragments to give the p-tolylsulfonyl radical (2) and deprotonated 6, which accepts a proton from the solvent. The p-tolylsulfonyl radical (2) then abstracts a hydrogen atom from the solvent to give p-toluenesulfinic acid, a compound that is converted to the p-toluenesulfinate anion (8) under the basic reaction conditions. Photolysis of 8 completes the reaction sequence by forming toluene.

Synthesis and Structural Characterization of a Novel Indium Mercapto Derivative [ClIn(SCH2(CO)O)2]2-[(4-MepyH)2]2+

The synthesis and structural characterization of a novel In(III) complex is described. The reaction between InCl3 with sodium mercapto-acetic acid (NaSCH2(CO)OH) in 4-methylpyridine (CH3(C5H5N), (4-Mepy)) at 25°C affords [ClIn(SCH2(CO)O)2]2-[(4-MepyH)2]2+ (1). X-ray diffraction studies of (1) show it to have a distorted square-pyramidal geometry with the [(-SCH2(CO)CO-)] ligands in a trans conformation. The compound crystallizes in the P1(No. 2) space group with a = 7.8624(6) Å, b = 9.950(1) Å, c = 13.793(2) Å, α = 107.60(1)°, β = 90.336(8)°, γ = 98.983(9)°, V = 1014.3(4) Å3, R(F°) = 0.037 and Rw = 0.048.