Merry-go-round apparatus

Photolysis of [[(C6H5)(CH3)Si] LM(CH3)Si]TO, THF solutions of the polymers, which were obtained from reactions such as those described earlier, in quantities sufficient to produce an absorbance of 1 at Xmax under nitrogen at 88.6 kPa were irradiated in quartz cuvettes in a merry-go-round apparatus at 300 nm for periods of 1-60 s. A sample of authentic [(C6H5)(CH3)Si] of almost identical molecular weight was also irradiated at the same time for a comparative study. Typical results are illustrated in Figures 1 and 2. 

Irradiations were conducted at 366 nm (Corning 7-83 filter combination) in a merry-go-round apparatus in which the samples rotated about a stationary 450-Watt Hanovia medium pressure lamp for constant light exposure. The samples consisted of degassed 5 ml solutions of the photoinitiators in neat MMA contained in Pyrex tubes. Two initiator concentrations were utilized 1.05 x 10and 4.11 x 10 which corresponded to 16 and > 99% light absorption, respectively. Samples were irradiated to about 7% monomer conversions which required 15 min for the optically dense solutions and 30 min for the tubes with low initiator concentration. The resulting poly-... 

Procedures. Continuous irradiations of halocarbon solutions were conducted with monochromatic radiation in a merry-go-round apparatus (12) or in a Schoeffel reaction chemistry system. Reactions were followed through analysis for remaining halocarbon or analysis of chloride ions produced by the photoreactions. Dark controls were used in all cases to correct for thermal production of chloride ions. Ferrioxalate actinometers were used to determine the irradiance (16). The irradiance at the photoreaction cell surface was typically about 10 nanoeinsteins/cm2,s. The Fe(II) concentrations were determined by using a modified version of the ferrozine procedure described by Stookey (17). Electronic absorption spectra were obtained by using a Shi-madzu model 265 spectrophotometer. 

A solution of bicyclo[2.2.2]oct-5-en-2-one (410 mg, 3.36 mmol) in acetone (30 mL) was placed in three quartz tubes, degassed by bubbling Nj through the solution for 15 min, and irradiated with RPR 253.7 nm lamps in the merry-go-round apparatus. After 4 h, one tube was analyzed by GC (6ft UCW 98 column at 100 C) to show that the reaction was 70% complete. The remaining two tubes were photolyzed for an additional 3 h. The solvent was evaporated on a rotary evaporator under vacuum and the crude oil (240 mg) was distilled with a micro still to give the product as a clear, colorless oil yield 92.2 mg (34%). 

Figure 3.30 Merry go round apparatus. Reproduced by permission of Ace Glass Inc...

Experimental details 55 The quantum yields of the reactions shown in Scheme 6.98 were obtained by simultaneous irradiation of the corresponding 4-nitroanisole amine solutions in methanol water (20 80, v/v) and actinometer (Section 3.9.2) solutions (aqueous potassium ferrioxalate) in UV cells, placed in a merry-go-round apparatus (Figure 3.30). The samples were irradiated by passing the light from a... 

Experimental details. Actinometry measurements can be performed in a merry-go-round apparatus (Figure 3.30) or on an optical bench (Figure 3.28). 

From the scheme described in Fig. 3, it is evident that quantum yield measurements in solids are the first step toward understanding mechanisms of solid-state photoreactions. Such measurements, however, have not been done frequently, because they require special precautions and apparatus (34). Recently we have found that quantum yields for some solid-state photoreactions can be conveniently estimated by the usual merry-go-round technique (11,29). The procedure is very simple dissolve a sample with ether in a Pyrex tube, evaporate the solvent to leave a coated crystalline film whose surface area is adjusted to be constant as precisely as possible, and then irradiate after degassing on a merry-go-round apparatus. The obtained quantum yields may not be very precise because of the reflection of light from the crystal surface and a variable surface area, but their reproducibilities are confirmed to be quite satisfactory (usually 5 %). 

I.J di tipn. Solutions were irradiated in sealed borosilicate or quartz test tubes held in a merry-go-round apparatus ensuring uniform illumination. A Rayonet Model RPR-100 photoreactor (Southern New England Ultraviolet Co., Hamden, CT) equipped with 16 RPR-3500 "blacklight lamps or 16 RPR-3000 "sunlight lamps was used in preliminary laboratory studies of PCB photolability. For solution phase experiments a 1.0 mg/L petroleum ether solution of Aroclor 1254 was studied. Periodically, irradiated samples were subjected to direct analysis by capillary electron capture gas liquid chromatography (EC-GLC). The photolability of PCB on surfaces was determined by irradiation of neat Aroclor 1254 thin films (18 ug/cm ) on glass Petri plates fitted with borosilicate glass covers. After irradiation plates were withdrawn from the photoreactor and the PCB residue dissolved in 2 X 5 mL of hexane for EC-GLC analysis. 

Quantum Yield Determinations. All quantum yields were obtained by irradiating degassed samples in borosilicate glass test tubes in a merry-go-round apparatus. The ruthenium complex samples were irradiated with the 436-nm line of a Hanovia medium pressure (450 W) mercury lamp Corning filters 3-73 and 5-58 were used to isolate this line. Light intensities were measured using the Reinecke s Salt Actinometer. 

Irradiation. Samples (uniformly 5.0 nL) were Irradiated In boro-slllcate glass test tubes (Pyrex 9820) sealed with foil-wrapped stoppers. Tubes were held In a merry-go-round apparatus and Irradiated In a Rayonet RPR-100 photo-reactor (Southern New England Ultraviolet Company, Hamden, CT) equipped with 16 RPR-3500 lamps. 

A soln. of startg. a-diazo-p-diketone in acetonitrile (or THF) treated with 3 eqs. diallylamine, and irradiated in two quartz tubes for 2 h at 254 nm in a merry-go-round apparatus fitted with 12 Philips TUV 15 lamps - N,N-diallyl-2-methylacetoacet-amide. Y 65%. F.e. and with ring contraction s. J. Cossy et al., Synthesis 1988, 720-21. 

Comparative photochemical researches can be accomplished with the so called merry go round apparatus, which consists of several reaction cells circularly placed around a central cylindrical lamp an uniform irradiation is ensured by the continuous rotation of the cells around the lamp. 

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