Immersion well irradiation apparatus

The apparatus is dried in an oven at 140° overnight and cooled under nitrogen or argon prior to the irradiation. A Vycor filter sleeve and a 450-watt medium-pressure mercury lamp are placed in the immersion well. The Vycor filter, the quartz immersion well (catlog No. 19434), the 450-watt mercury lamp (catalog No. 679A36), and the requisite transformer are all available from Hanovia Lamp Division, Canrad-Hanovia Inc., 100 Chestnut Street, Newark, New Jersey 07105. 

The irradiation light source is a Hanovia 450 W medium-pressure Hg vapour lamp placed in a quartz immersion well. The reaction solution is contained in a 150 ml quartz semicircular flask mounted as closely as possible to the immersion well. No light filter is used. The entire apparatus is immersed in a large Dewar flask charged with dry ice-isopropanol with the bath temperature maintained between —60 and —40°C during irradiation. 

A solution of 2,2,7,7-tetramethylcyclohepta-3,5-dienone (1.0 g, 6.1 mmol) in acetone (450 mL) was placed under an atmosphere of Nj und was irradiated with a 450-W Hanovia Hg-vapor lamp in an immersion-well apparatus fitted with a Vycor filter. The course of the reaction was followed by removing small aliquots at various intervals. After 55 min the reaction was virtually complete. The solvent was evaporated on a rotary evaporator to give 0.7 g of a nonpolymeric residue, which was subjected to preparative scale GC. The title compound was obtained as a colorless oil. 

Likewise, explorative studies are conveniently carried out in very simple apparatus. This may be built with the lamp(s) outside a reaction vessel (made of a material transparent to the desired wavelength, e.g., Pyrex absorbs below ca. 300 nm), including test tubes, and irradiating by means of some external low-pressure lamps (10-20 W, see above). Alternatively, with the lamp inside, a vessel fitted with a refrigerated immersion well (of the correct material) is used in which is inserted a mercury arc (125 or 400 W - the former is sufficient for the great majority of cases). 

Experimental details 01 A solution of 260 (0.24 mmol) and 259 (0.49 mmol) in toluene (20 ml) was irradiated at —10 °C with a high-pressure mercury lamp (150 W) at = 300 nm (Duran filter) in an immersion well apparatus (Figure 3.9). The solvent was then removed in vacuo and the residue containing the crude product was purified by column chromatography to give 261 in 56% yield. The diastereomeric ratio of oxetane isomers was determined using 1H NMR. 

Small (1-5 g) scale UV photolysis of air sensitive compounds can be performed in quartz Schlenk tubes, or in conventional Schlenkware with the use of a UV transparent quartz stopper. The latter apparatus is easily adapted to low temperature irradiations. Large scale (10-50 g) UV photochemical reactions use quartz immersion well reactors. Medium pressure Hg-arc lamps are the preferred radiation sources for synthetic applications. ... 

A solution of 2.1d (300 mg, 0.69 mmol) in 400 mL of anhydrous methylene chloride was purged with deoxygenated nitrogen for 1 h and then irradiated under a positive pressure rf nitrogen for 40 min. The irradiation was carried out in an immersion well apparatus with a Pyrex filter and a 400 W medium-pressure Hg arc-lamp. After rotary evaporation of the solvent, the crude product was flash chromatographed (silica gel 60 230-400 mesh) using hexane/ethyl acetate (94 6) as eluant. The chromatography yielded 151 mg (70%) of 2.1e,... 

A suspension of 0.25 g (1.2 mmol) of 2.11d in 300 mL of cyclohexane was placed in a cylindrical immersion well apparatus to which a distillation head and a cooler were fitted. The suspension was first boiled until ca 30 mL of solvent had passed over and then cooled while magnetically stirring and passing through a slow stream of dry nitrogen. When cooled to room temperature, the solution was irradiated by means of a 125 W medium-pressure mercury arc for 30 min. Evaporation, extraction with 15 mL of cyclohexane, filtration and evaporation gave 0.22 g (90%) of product as an oil. 

A solution of 0.5 g (16.6 mmol) of 2.12b in 300 mL of benzene was irradiated for 1 h in an immersion well apparatus at room temperature by means of a 125 W high-pressure mercury arc. The solution was then filtered over 20 g of active alumina, which was further... 

The dimerization of vinyl acetylene presented by H. Hopf requires the presence of benzophenone as triplet sensitizer. Either by irradiation in sealed glass tubes or by using a low temperature immersion well apparatus 1,2-diethynylcyclobutane is formed in good yields. Note that the analogous dimerization of 1,3-butadiene yields similar products beside vinylcyclohexane and cyclooctadiene depending on the triplet energy of the sensitizer. 

Three 100 mL, one-necked flasks with 24/40 ground glass joints and a 4 L beaker (25 cm high and 18 cm in diameter) are employed for the photolysis together with a Hanovia 450 W medium-pressure mercury lamp and immersion well apparatus. A Pyrex filter cylinder is used. Into each flask is added 100 mg (0.96 mmol) of cyclooctatetraene. Each flask is sealed under vacuum by first being cooled in a dry ice/acetone bath followed by subsequent application of 0.05 mm vacuum. The lamp well is immersed in the center Of the beaker filled with water maintained at 70 °C. The beaker is surrounded by aluminum foil which serves as a reflector. The flasks containing the cyclooctatetraene are placed in the water in proximity to the lamp well and irradiated at 70 °C for 60 h. 

A solution of 1.0 g (2.7 mmol) of 7.1b in 250 mL of spectral grade acetone was irradiated (immersion well apparatus, Pyrex filter sleeve, Hanovia 450 W medium-pressure mercury lamp) under a nitrogen atmosphere until capillary gas chromatography indicated little... 

A mixture of 250 mg 3,3-dimethyl-1,5,5-triphenyl-2-aza-l,4-pentadiene (0.80 mmol), 550 mg m-methoxyacetophenone (3.7 mmol) and 450 mL dry -BuOH was put into a quartz immersion well apparatus with a Pyrex filter. The solution was purged with argon for 1 h and was irradiated with a 400-W medium-pressure mercury arc lamp for 6 h. After completion of the irradiation, the solvent and the sensitizer were removed under reduced pressure, the residue was chromatographed with hexane/Et20 (99 1) as an eluent to afford 65.0 mg benzaldehyde, and 13.0 mg of cyclopropylimine as a colorless oil, in a yield of 5%. Further elution with Et20 yielded 25 mg of a highly polar material. Final elution with EtOH afforded 148 mg l,l-dimethyl-3,3-diphenyl-2-propenylamine, in a yield of 81%. 

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