Photoreactors immersion well

The reaction was carried out in an immersion-well photoreactor with a medium-pressure. 80-W Hg lamp in a water-cooled double jacket (quartz and Simax glass, sintered-glass inlet at the bottom of the reactor), and equipped with a dry icc cooled spiral cooler with an hydraulic seal. A mixture of 3,4,4-trifluoro-5.5-dimethyl-4.5-dihydrofuran-2(3//)-one (3 67 mg, 40 mmol) and solvent (2 mol) was irradiated for 10 h at 18-20 C in a stream of argon. The low-boiling part of the mixture was fractionally distilled off and the product was isolated by preparative GC (polybutane-1,4-diol succinate, 500 cm, 160-200 C) vicld 50-65%. 

The most commonly used type of photoreactor is an immersion well, in which the light source is placed in the center of the reaction mixture. However, during scale-up, it is very difficult to reproduce the same ratio of area irradiated to volume of reactant. 

Photochemistry can also be carried out in a photoreactor of external configuration,158 This arrangement is very simple the solution is held outside the source of irradiation. One option is to use an immersion well as shown in Figure 3.9, but the sample is placed in a separate vessel nearby. The whole setup can be immersed in a thermostated water or methanol bath to control the temperature of the reaction mixture. An external... 

In an atmosphere of argon, a solution of 13.5 g (88%, 94 mmol) of S.6b and 300 mg (11 mmol) of copper (I) trifluoromethanesulfonate benzene complex (CuOTf) in 120 mL of dry diethyl ether is irradiated in a Pyrex photoreactor with a water cooled quartz immersion well by a high-pressure mercury lamp (HPK 125 W, Fa. Philips). After the reaction is complete (monitored by GLC), the mixture is concentrated in vacuo and purified by column chromatography (cyclohexane/ethyl acetate 2 3) to give 10.5 g (64% from... 

The solution of 5.08 g 2-methyl-4-nitroimidazole in 200 mL 42% tetrafluoroboric acid was cooled to -10°C to this cooled solution was added 5.08 g zinc dust (78 mmol) in portions of 0.1 g with rapid stirring. Each addition was made only after the prior portion had dissolved and the temperature had fallen to at least -5°C. The addition took about 1 h. Small aliquots were removed, diluted with water, and examined by UV. Total loss of the chromophore at 310 nm indicated the completion of reduction. Then a solution 2.04 g sodium nitrite (44 mmol) in 10 mL water was added dropwise. The resulting solution of the diazonium salt was diluted to 380 mL with cold 42% tetrafluoroboric acid and was irradiated under argon in a Pyrex immersion-well photoreactor using a 400-W high-pressure mercury lamp (Riko 400-HA). After 90 min, the diazonium chromophore at 280 nm had disappeared. The solution was cooled to - 10°C with dry ice, neutralized slowly with 25% aqueous sodium hydroxide to pH 5-6, and extracted with EtOAc (5 x 200 mL). The combined extracts were dried over Na2S04 and evaporated. The residual material was purified on 100 mL silica gel with EtOAc as an eluent to give 1.06 g 4-fluoro-2-methylimidazole, in a yield of 27%, m.p. 142-144°C. 

The industrial PNC process is based on the development of efficient photoreactors. Toray designed an immersion lamp with a high radiation efficiency and capacity as well as long life. In order to remove the short-wave radiation below 365 nm (which contributes to tar formation on the lamps) either an absorbent is added to the cooling water, or the light source is surrounded by a glass filter264. 

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