W-Halogenation

OPHTHALMOSCOPE 25 VOLT COMPACT W/HALOGEN LIGHTS POLARIZED FILTER 6540014587337 EA 133.50 ... 

Ziessel110 reported on Ir(m) complexes, including [(CH3)5C5Ir(bpy)Cl]+, [(CH3)5C5Ir(bpy)H]+, and [(CH3)5C5Ir(phen)Cl]+, where bpy = bipyridine and phen = 1,10-phenanthroline, which displayed activity for the water-gas shift reaction under illumination. Catalysts were tested in a 15 ml of phosphate (0.1 mol/L) buffer solution, and conditions were Pco = 1 atm T = room temperature [complex] = 4.8 x 10-4 mol/L 250 W halogen lamp excess 1.2 x 10-2 mol/L pyridine in 0.5 ml of CH3CN added. Activity results are reported in Table 29. 

W halogen lamp as light source. As per the case 9, the isolated yields for the substituted organic sulfides R= COCH3 96% and R= OCH3 90%. 

Dye-sensitized photooxygenation of oxazoles (242) in aprotic solvents with 650 W halogen lamp leads to unstable 1,2,4-dioxazolines (244) via intermediate cyclic peroxides (243) (Scheme 49) <90JCS(Pl)10n, 91JCS(P2)1085>. 

So far, we have only considered light of a single wavelength. Illuminants are described by their power spectrum. The power spectrum of several different illuminants are shown in Figure 3.18. The data was measured by Funt et al. (1998) with a Photoresearch PR-650 spectrometer. Figure 3.18 shows the power spectrum of a Sylvania 75 W halogen bulb, a... 

Synthesis of single crystals of TBPDA (Cgo)2 was described elsewhere [4], Photoconductivity was excited by white light of a 150 W halogen tube. Photoconductivity was characterized by current T running through indium contacts attached to one of the faces of the samples with silver paste. The contacts were under direct voltage of 10-50 V. Current values were measured with a charge amplifier connected with PC. The cell filled with the sample was put in a resonator of a standard Radiopan SE/X 2547 spectrometer. 

Photo-oxidation of citronellol in polystyrene beads [120]. A sample of 3.0 g of polystyrene beads (commercial, cross-polymerized with 1% of divinylbenzene) was treated with a solution of 2 mg of tetraphenylporphyrin and 780 mg (5 mmol) of citronellol in 20 mL of ethyl acetate in a petri-dish (30 cm diameter). After 2h in a ventilated hood, the solvent has evaporated and the petri-dish was covered with a glass plate and irradiated for 5 h with a 150 W halogen lamp. The solid support was then washed with 3 x 20 mL of ethanol, the combined ethanol fractions were rota-evaporated and 900 mg of the hydroperoxide mixture (96%) was isolated as a slightly yellow oil. The hydroperoxides were quantitatively reduced to the corresponding allylic alcohols by treatment with sodium sulfite. One of these products is used in the industrial synthesis of rose oxide. 

A design based on a similar concept was published by Castner et al. (1990) the following year. This cell (Figure 23) also incorporates a pressed catalyst wafer, but heating was by 500-W halogen bulbs. The cell could operate from 77 to 923 K and from high vacuum (10, s mbar) to 1 bar the window material was Mylar . 

In an analogous manner the indole double bond in VIII/203 was opened oxidatively (02, rose Bengal, 200 W halogen lamp, CH3OH/CH2Cl2, 25, 5 h) and the desired eight-membered lactam VIII/204 was isolated in 82% yield [118]. Compound VIII/204 is an intermediate in a synthetic approach to the potent antitumor antibiotic mitomycin A (see Chapter VIII.2). 

Carbonyl compounds rapidly equilibrate with their enols, a process called tautomerism. Although enol tautomers are normally present to only a small extent at equilibrium and can t usually be isolated in pure form, they nevertheless contain a highly nucleophilic double bond and react rapidly with electrophiles. For example, ketones and aldehydes are rapidly halogenated at the a position by reaction with CI2, Brg, or I2 in acetic acid solution. Alpha bromination of carboxylic acids can be similarly accomplished by the Hell-Volhard-Zelinskii (HVZ) reaction, in which an acid is treated with Br2 and PBrs. The w-halogenated products can then undergo base-induced E2 elimination to yield ar,j8-unsaturated carbonyl compounds. 

Two moles of methylenetriphenylphosphorane are reacted with one mole of a dihalogen compound. In the first step methylenetriphenylphosphorane is C-alkylated yielding an to-halophosphonium salt, which subsequently reacts with a second mole of methylenetriphenylphosphorane forming a transylidation equilibrium with methyltriphenylphosphonium halide and an w-halogenated ylide. This compound undergoes intramolecular C-alkylation, in the course of which the resulting exocyclic phosphonium salt... 

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