Lamps reaction vessel system

Chemat and his coworkers [92] have proposed an innovative MW-UV combined reactor (Fig. 14.7) based on the construction of a commercially available MW reactor, the Synthewave 402 (Prolabo) [9[. It is a monomode microwave oven cavity operating at 2.45 GHz designed for both solvent and dry media reactions. A sample in the quartz reaction vessel could be magnetically stirred and its temperature was monitored by means of an IR pyrometer. The reaction systems were irradiated from an external source of UV radiation (a 240-W medium-pressure mercury lamp). Similar photochemical applications in a Synthewave reactor using either an external or internal UV source have been reported by Louerat and Loupy [93],... 

Figure 1.7 Checking that the conditions for a successful photochemical reaction are met. To use this system (1) Insert into the frame the range of active wavelengths (up to the longest wavelength where the reagent absorbs significantly two representative examples are shown). (2) Check whether this fits with the lamp chosen, the solvent and the material from which the reaction vessel, cooling well, etc. are constructed.

The reaction vessel and photolysis lamp lay within a cylindrical MgO reflector and the system could be heated to 420 K. The lamp was filled with a mixture of a few Torr of Ni in 100 Torr of Kr. Flash energies of 500-1000 J were provided by charging a 5 /iF capacitor to the appropriate voltage. The light output fell to half its peak intensity in less than 10 /is and was effectively zero after 30 jus. 

A solution of cyclonona-1,2-diene (180 mg, 1.48 mol, prepared from cyclooctene ) and benzene (260 mg, 3.33 mmol) was placed into a 3.7-LVycor tube, the bottom portion of the tube was cooled to — 78 C, and the system was degassed by evacuating to ca. 0.15 Torr and backflushing with Nj several times. After evacuation to 0.15 Torr, the tube was allowed to warm to rt and was irradiated for 4.5 d in a Rayonet photoreactor fitted with 2537-A lamps. The reaction vessel was then cooled to — 78 °C and vented to N, and the product was collected with pentane. The pentane solution was filtered through neutral alumina and was concentrated under reduced pressure at 0"C to give 165 mg (92%) of a clear oil. Capillary GC analysis indicated 97% conversion to four major products. These were isolated on a preparative scale and identified as follows bicyclo[4.3.0]non-l(9)-ene (11 4%, / = 3.41 min) c -bicyclo(4.3.0]non-2-ene (9, 2%, / = 3.67 min) bicyclo[4.3.0]non-l-ene (10, 5%, = 3.90 min) and the product 3 yield 160 mg... 

This report summarizes conventional methods for UV irradiation of air sensitive organometallic compounds at ambient or subambient temperatures. Of the irradiation sources available (l ) the medium pressure Hanovia 450 W arc lamp systems (2) are of moderate price, reliable, and versatile in our experience. Caution Powerful arc lamps can cause eye damage or blindness within seconds and UV protective goggles (available from most scientific supply houses) must be worn. Never look directly at the radiation source. For safety of other workers lamps should be enclosed in a vented box with baffles. If Pyrex transmits enough UV radiation for an efficient reaction, as for photochemical reactions of metal-metal bonded complexes (3), then conventional Schlenkware can be used for photolysis and no special glassware is needed. Since a 2 mm thick wall of Pyrex transmits only 10% of the UV light at 300 nm, UV transparent quartz reaction vessels are often needed for photoreactions of mononuclear organometallic complexes. 

The instruments needed for the determination of antimony comprise an atomic absorption spectrometer with electrodeless Sb discharge lamp and potentiometric recorder, a hydride system with quartz cuvette and polypropylene reaction vessel, a pressure decomposition system with a temperature-controlled heating block, and an evaporation apparatus together with various adjustable micropipettes. 

Ikeda et al. [80] have reported a photochemical entry to spiro-(3-lactams 27 (Scheme 8) by the irradiation of a solution of 2 - (/V - ac y I - /V-al k y I a m i n o) eye I o h e x -2-enone 26 in acetone with a 300 W high pressure mercury lamp in a pyrex vessel under nitrogen. The reaction occurred with the intervention of the 1,4-diradical intermediate formed via abstraction of a hydrogen on the N-acyl group by the (3-carbon atom of the ot,(3-enone system. 

Wetmore and Taylor (47) investigated the methylamlne photolysis and found the decomposition rate of the Hg-photosensitized reaction equal to that of the direct one where a plug of gold wire was interposed between the vacuum system and the photolysis cell to exclude Hg. It seems possible though that Hg was present in both cases. Photolyses carried out with the light of low-pressure Hg arc lamps were, at least in part, Hg-sensltlzed if the contamination of the photolysis vessels by the Hg vapor present in the vacuum system was not rigorously excluded. This holds true especially for the early work. 

Prior to each reaction test and spectroscopic measurement, the sample was treated with 100 Torr oxygen (1 Torr = 133.3 N m ) at 673 K for 1 h, followed by evacuation at 673 K for 1 h. The photooxidation of propene was performed with a conventional closed system (123 cm ). The sample (200 mg) was spread on the flat bottom (12.6 cm ) of the quartz vessel. Propene (100 pmol, 15 Torr) and oxygen (200 pmol, 30 Torr) were introduced into the vessel, and the sample was irradiated by a 200 W Xe lamp. After collecting the products in gas phase, the catalyst bed was heated at 573 K in vacuo to collect the products adsorbed on the catalyst by a liquid nitrogen trap. These products were separately analyzed by GC. The results presented here are the sum of each product yield. 

Insoluble brown reaction products (presumably phenolic tars) were deposited on the surfaces of the reactor vessel and lamp well. This expected phenomenon plus the high solvent absorbence demanded a careful reactor selection and photolysis system design. 

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