Quartz lamps

Conformational factors in the photolysis of N-acylimidazoles leading to Norrish type II products or cyclobutanols have been discussed in reference [7]. 7V-Acylimidazoles have been irradiated in tetrahydrofuran using a low-pressure mercury lamp (quartz well,... 

Spectrophotometer with ultraviolet (UV) lamp Quartz cuvettes, 1.00 0.01-cm path length... 

The [2 + 2]-photocycloaddition chemistry of a,(3-unsaturated lactones has been widely explored. The factors governing regio- and simple diastereoselectivity are similar to what has been discussed in enone photochemistry (substrate class Al, Section 6.2). The HT product is the predominant product in the reaction with electron-rich alkenes [84]. A stereogenic center in the y-position of ot,P-unsaturated y-lactones (butenolides) can serve as a valuable control element to achieve facial diastereoselectivity [85, 86]. The selectivity is most pronounced if the lactone is substituted in the a- and/or P-position. The readily available chiral 2(5H)-furanones 79 and 82 have been successfully employed in natural product total syntheses (Scheme 6.30). In both cases, the intermediate photocycloaddition product with 1,2-dichloroethylene was reductively converted into a cyclobutene. In the first reaction sequence, the two-step procedure resulted diastereoselectively (d.r. = 88/12) in product 80, which was separated from the minor diastereoisomer (9%). Direct excitation (Hg lamp, quartz) in acetonitrile solution was superior to sensitized irradiation (Hg lamp, Pyrex) in acetone, the former providing the photocycloaddition products in 89% yield, the latter in only 45%. Cyclobutene 80 was further converted into the monoterpenoid pheromone (+)-lineatin (81) [87]. In the second reaction... 

SCHEME 29.3 Photochemical electrocyclization applied to the synthesis of helicenes. A Hanovia 450 W medium-pressure mercury vapor lamp (quartz well) was used for UV irradiation. 

Glass Bulb T3 Quartz Lamp Quartz Tube Metal Sheath ... 

Pieces of optical fiber 300 W Xe arc lamp Quartz fibers coated with Ti02 layer Acetone [56]... 

If the components are colourless, their separation can often be followed by working in a quartz (or special glass) tube which is placed in the light of a mercury lamp. The separate zones are then often revealed by their fluorescence. 

Quartz glass Quartz-halide bulbs Quartz halogen lamp Quartzite... 

Lighting. An important appHcation of clear fused quartz is as envelop material for mercury vapor lamps (228). In addition to resistance to deformation at operating temperatures and pressures, fused quartz offers ultraviolet transmission to permit color correction. Color is corrected by coating the iaside of the outer envelope of the mercury vapor lamp with phosphor (see Luminescent materials). Ultraviolet light from the arc passes through the fused quartz envelope and excites the phosphor, produciag a color nearer the red end of the spectmm (229). A more recent improvement is the iacorporation of metal haHdes ia the lamp (230,231). 

Figure 1. A, Dewar flask B, sintered glass filter C, metal cooling coil D, water inlet E, water outlet F, reaction vessel < , quartz immersion well /f, pyrex filter /, lamp ...

Photolysis of a dioxane solution of (2) using a 250 watt quartz lamp also provides 16a,17a-methylene-20-ketones (4). ... 

A solution of 500 mg 3 -acetoxypregn-5-en-20-one-[17a,16a-c]-A -pyrazoline in 100 ml of anhydrous dioxane is stirred with a magnetic stirrer and irradiated in a water-cooled quartz reactor with a high pressure Biosol Philips 250 W quartz lamp for 1 hr. The solvent is removed at reduced pressure and the residue is chromatographed on alumina (activity III). Elution with petroleum ether-benzene (3 1) gives 0.2 g (42%) of 3 -acetoxy-16a,17a-methylene-pregn-5-en-20-one mp 193-193.5° after two recrystallizations from methylene dichloride-ethyl acetate. 

A solution of 0.17 g (51) in 160 ml benzene is stirred magnetically and irradiated for 6 hr with a Hanau NK 6/20 low-pressure mercury lamp (main emission at 2537 A) placed in a central water-cooled quartz tube. Cyrstalliza-tion of the crude product gives 0.15 g (52) (88%). 

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