Irradiation, under pressure

Figure 4. System used for irradiation under pressure.

Method A A solution of the azidoquinoline (5 mmol) in 3M KOMe in MeOH (40 mL) and dioxane (40 mL) was irradiated under N2 using a water-cooled, 125-W medium-pressure Hg lamp until all the azide [as measured by the disappearance of u(N3) at 2120 cm" 1 or by TLC] had reacted (4-10h). The photolysate was left to stand at 20 C for 24h then neutralized cautiously by the addition of 4M IICI in MeOH. The solvent was removed under reduced pressure and the crude product was purified initially by column chromatography on alumina (Type H, toluene), then finally by crystallization (petroleum ether). 

The imine 13 (1.0-2.0 g) in benzene or CH2C12 (200-300 mL) was irradiated under N2 in an immersion apparatus equipped with a 400-W high-pressure Hg lamp and a Pyrex filter and cooled internally with running water. When TLC showed that all the starting material had been consumed (1 -3 h) the solvent was removed under reduced pressure and the residue was chromatographed (silica gel. CH2C12). 

A solution of a 3-azidopyridine (0.5-1.0 g) in a mixture of MeOH (75 mL) and dioxane (75 mL) containing NaOMe (2.5-3.0g, large excess) was irradiated under N2 with a 400-W high-pressure Hg lamp with a Pyrcx filter. When TLC indicated that no azidopyridine was left (1 —2 h), the solvents were removed in vacuo, ice-water (10-25 mL) was added to the residue and the mixture was extracted with hexane. The extract was washed with H20, dried and evaporated under reduced pressure and the residue was chromatographed (Sephadex, hexane) to give the products as colorless oils. 

Rhodium and cobalt carbonyls have long been known as thermally active hydroformylation catalysts. With thermal activation alone, however, they require higher temperatures and pressures than in the photocatalytic reaction. Iron carbonyl, on the other hand, is a poor hydroformylation catalyst at all temperatures under thermal activation. When irradiated under synthesis gas at 100 atm, the iron carbonyl catalyzes the hydroformylation of terminal olefins even at room temperatures, as was first discovered by P. Krusic. ESR studies suggested the formation of HFe9(C0) radicals as the active catalyst, /25, 26/. Our own results support this idea, 111,28/. Light is necessary to start the hydroformylation of 1-octene with the iron carbonyl catalyst. Once initiated, the reaction proceeds even in the... 

Quite recently this reaction was revisited by Kappe [91] et al. who reinvestigated the Biginelli synthesis under the action of microwave irradiation under a variety of different conditions. At atmospheric pressure in ethanol solution there is no difference from conventional heating. Under pressure the yield is reduced and byproducts are formed. In an open system rate and yield enhancements are significant and this is rationalized by the rapid evaporation of the solvent which means that this is in fact a solvent-free reaction. This was confirmed by running the reaction without solvent under the action of microwaves and with thermal heating. (Scheme 8.65)... 

Prednisone (136) irradiated at 254 nm with a low-pressure mercury lamp in dioxane gave lumiprednisone (138). Further irradiation under the same condi-... 

High Pressure. Irradiation under high pressure increases the crosslinking yield of some polymers (64-66). This has mechanistic implications which need to be further explored. 

The photochemical step could also be accomplished by adding Mo(CO)e, EtjN and EtgO to a photochemical immersion well, and irradiating under an inert atmosphere with a Hanovia medium pressure 450W mercury vapor lamp for 20-30 min. Commercially available immersion wells generally require > 800 mL of solvent in order to work effectively (so that the solvent is level with the lamp), and the submitters have found that the more concentrated solution reported here (ca. 450 mL) is more effective. 

To a solution of diallyl ether (11. X = O 980 mg, 0.01 mol) in anhyd Et20 (140 mL) was added CuOTf (36 mg, 0.1 mmol). This homogeneous solution was irradiated under a N2 atmosphere with a medium-pressure Hg lamp for 20 h. After completion of the reaction the Et20 solution was poured into a mixture of crushed ice and 30% NH4OII (100 mL) and shaken well. The two layers were separated and the Et20 layer dried (MgS04). Distillation gave 12 (X = O) yield 51 mg (52%) bp 115-118 °C. 

Aldehyde or ketone (3 mmol), ammonium acetate (3 mmol, 231 mg), basic alumina (3 g) and active methylene compound 2 (3 mmol) were mixed thoroughly in a mortar. The reaction mixture was placed in a beaker and irradiated under the conditions shown in Table. The progress of reaction was monitored by TLC using petroleum ether-CH2Cl2 (30 70) as eluent. The mixture was extracted into CH2C12 then filtered and washed with water. The solvent was removed under reduced pressure by rotatory evaporator. Further purification by column chromatography on silica gel gave the desired product. 

A crystalline salt of 1 and 2 (20 mg) was crushed and spread between two Pyrex plates and this was irradiated with a 400-W high-pressure mercury lamp for 20 h under an argon atmosphere. The irradiation vessel was cooled from the outside by tap water. After the irradiation, the reaction mixture was analyzed by NMR. The only peaks observable were those for the starting materials (1 and 2) and a cross photoadduct (3) (47% conversion, 39% yield). In a separate experiment, 105 mg of the salt was irradiated under similar conditions. The product 3 could be isolated simply by fractional recrystallization from ethanol (15 mL). Polymeric products (6 mg) first separated and then 18 mg (17% yield) of nearly pure 3 separated as a pale brown powder mp 215-225 °C. 

Crystals of 1 were ground to a fine powder ill a mortar. The powder (210 mg) was placed between two Pyrex disks (8 cm diameter) and irradiated under a nitrogen atmosphere for 10 h at 0°C (ice-water) by using a 400-W high-pressure mercury lamp as a light source. The separation between the lamp and the sample was approximately 5 cm. The reaction mixture was separated by preparative TLC to give 178 mg of the recovered 1 and 31 mg ( 100% yield) of a dimeric product, 4-(2-hydroxy-2,2-di-p-tolylethyl)-4,-methylbenzophenone 2. This was recrystallized from hexane-ethyl acetate (10 1, v/v) to give colorless crystals mp 53-55 °C. 

A suspension of powdered 1 1 inclusion complex of (-)-la and 2a (3.07 g, 4.41 mmol) in water (120 mL) containing hexadecyltrimethylammonium bromide (0.1 g) as a surfactant was irradiated under stilling for 16 h with 100-W high-pressure Hg-lamp. The reaction mixture was filtered, dried and chromatographed on silica gel using AcOEt-toluene (1 9) as an eluent to give (+)-3a of 97% ee after distillation at 180°C/2mmHg as colorless oil. 

Achiral 1 crystallizes from EtOH-CH2Cl2 in a chiral structure of space group P21. The monomer was suspended in a mixture of methanol-water (10%) and irradiated under continuous stirring with a 450-W immersion high-pressure Hano-via Hg-lamp at -2 °C for periods of 20-60 h. Dimer 2 mp (racemic dimer) 170 °C [a]D 114° (100% ee). 

Photodimerisation of cyclopent-2-enone. cis,tra.ns,cis-3,3,8-Tetramethoxy-tricyclo[5.3.0.02 6]decane and c s,. ra.ns,c s-tricyclo[5.3.0,02 6]decane-3,10-dione. Place a solution of 49.9 g (0.61 mol) of cyclopent-2-enone in 800 ml of methanol (distilled from solid potassium hydroxide) in a photochemical reactor vessel of 1-litre capacity equipped with a 100-W medium pressure mercury arc lamp surrounded by a Pyrex cooling jacket (Section 2.17.5, p. Ill), flush the magnetically stirred solution with nitrogen for 10 minutes and then irradiate under nitrogen overnight. Filter the white crystalline solid which separates and continue irradiating until no further crystalline material separates from the methanol solution. About 21.5 g of material is obtained after approximately 40 hours irradiation. Crystallisation from methanol gives cis,trans,cis-3,3,8,8-tetramethoxytricyclo[5.3.0.02,6]decane as white plates, m.p. 173-174 °C. The yield is 19.3 g (30%). 

An alternative concept is the so-called direct absorption concept, which applies solar-receiver reactors. According to this concept a solar reformer was developed by DLR in the SOLASYS project (Tamme, 2003) based on earlier experiences in the projects SCR and CAESAR (Bauer, 1994). It allows the concentrated radiation to penetrate through a transparent aperture into the reformer, where it is absorbed directly by the irradiated absorber. The reaction gases pass through the absorber which serves simultaneously as a heat transfer unit and as support for the catalyst. The quartz window, used as aperture closure, enables the reformer to be operated under pressure. A schematic of the solar receiver is shown in Figure 3 (right). The reformer was operated up to 0.9 MPa and 780°C. The pilot reformer was tested at a power level of about 300 kW(th) at the solar tower of the Weizmann Institute of Science in Rehovot, Israel. In a follow-up project SOLREF (Moller, 2006), the operation conditions will be about 1.5 MPa and 950°C. 

---