Silica irradiation

Peroxy anions or entities cannot be detected by any currently known technique unless the 0-0 bond is activated. One method is ionizing radiation. In the case of high purity fused silica irradiating with y- and x-rays led to peroxy radicals ( ) and dangling bonds at the three-fold coordinated silicon which were fully characterized using EPR (16.17) ... 

Although for a different reaction, the cracking of cumene, a similar difference in behavior was found by Traynard and Orsini (94) for two silica-aluminas of different purities. After bombardment to about 2 X IQi nvt (fast) the purer of the two was less active after irradiation than before (ratio = ca. 0.3) while the less pure was more active (ratio = ca. 2). When the principal impurities of the second (Zn and V) were added to the first, the irradiated sample was then more active (ratio = ca. 1.7). A very pure silica, irradiated to 8 x lO nvt, showed no measurable cumene cracking activity, although there was evidence (discoloration) of some reaction of cumene with the catalyst (10). 

Phenol-silica/irradiation y-Diketones and pinacols by redoxdimerization of ketones... 

The irradiation of tetra-/-butylcyclopentadienone with 254 nm light at 77 K produced a tricyclopentanone which, upon extended irradiation, lost carbon monoxide. Tetra-f-butyltetrahedrane was formed. This derivative of the second fundamental hydrocarbon of molecular formula (CH), namely tetrahedrane, is stable at room temperature and could be isolated after chromatography on silica gel in crystalline form (G. Maier, 1978). 

Total frequencies of environmental illness are difficult to measure. When causes can be identified, however, scientists observe that frequencies of occurrence of a particular illness vary directly with the severity and extent of exposure. Particularly frequent in the workplace are skin lesions from many different causes and pulmonary diseases related to the inhalation of various dusts, such as coal dust (black lung), cotton dust (brown lung), asbestos fibers (asbestosis), and silica dust (silicosis). Environmental agents can also cause biological effects without overt clinical illness (for example, chromosome damage from irradiation). 

Detection and result The chromatogram was dried in a stream of warm air for 10 min, immersed in the reagent solution for 3 s and then subjected to intense UV radiation (high pressure lamp, A = 365 nm) for up to 10 min. Terephthalic (hRf 0 - 5), pimelic (hRf 55), suberic (hRf 60), sebacic (hRf 65 — 70) and benzoic acids (hRf 70 — 75) together with sorbic, malic, adipic, citric, tartaric, lactic and fumaric acids only exhibited a reaction on silica gel layers at higher concentrations. 4-Hydroxybenzoic, salicylic and acetylsalicylic acids fluoresced light blue after irradiation. The detection limit per chromatogram zone was 0.5 pg for salicylic acid and more than 5 pg for benzoic acid. 

Irradiations of Testosterone Acetate (114), —In t-Butanol. 1.25 g of (114) in 250 ml t-butanol is irradiated for 32 hr at 30° under nitrogen with a Hanau Q81 high-pressure mercury lamp placed in a central water-cooled Pyrex immersion well with acetone filter. The solvent is evaporated in vacuo and the residue chromatographed on 125 g silica gel with benzene-ethyl acetate (4 1) to yield 0.29 g 17 -hydroxy-la,5 -cyclo-10a-androstan-2-one acetate [(118) 23%] mp 164-165°, after crystallization from acetone-hexane [a]i3 37 (CHCI3) 0.14 g cyclopentanone (120) (11%) mp 106-107° [aJo 38° (CHCI3) and 0.58 g starting material [(114) 46%]. Ratio (118) (120) - 2 1. 

With 2537 k-Light. 1 g (140) in 140 ml anhydrous dioxane is irradiated for 20 hr at room temperature with a Hanau NK 6/20 low-pressure mercury lamp placed in a central water-cooled quartz finger. 0.19 g of (141) crystallize from the crude reaction mixture as described above. Chromatography of the residual material on silica gel with benzene-ethyl acetate (4 1) gives 0.29 g of B-nortestosterone acetate [(142) 28.5 %] and starting material (140). 

Variations on this theme have been reported. One example utilized silica gel and urea with 95 and 82 under microwave irradiation to afford dihydropyridines 96 in 3-5 minutes and in 70-90% yield. 

Dibenz[c,/][1,2]oxazcpine-ll-carbonitrile isomerizes to the TV-oxide acridine-9-carbonitrile 10-oxide on heating in aprotic solvents. Attempted chromatography on silica gel or alumina columns gave a mixture of the oxepino[2,3-6]quinolinecarbonitrile 2, the oxoazepinoindolecarbo-nitrile 3 and the benzo[c]-2-aza-l,6-oxa[10]annulenecarbonitrile 4. Only these types of compounds were isolated when 2,7-dimethylacridine 10-oxide was irradiated.6... 

A solution of a phenantbridine 5-oxide (0.20 g) in benzene (200 mL) was irradiated at 17 C with a Helios Italquartz 125-W medium-pressure arc until TLC showed that the reaction was complete. The solution was evaporated under reduced pressure and the residue was chromatographed (silica gel, cyclohexane/ EtOAc then CHCl,). 

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). 

The pyridinium salt 3 (0.427 g, 1.81 mmol) in H20 (1 L) was irradiated for 40 min with a high-pressure Hg lamp. The resulting solution was treated with 2M HC1 to pH 1 and then extracted with CHd3 under Nj. The extract was dried (MgS04) and evaporated in vacuo and the residue was chromatographed (silica gel) yield 0.157g (63%) mp 35-39 C. 

An ice-cold solution of a dia/atricydoheptene 1 (0.5-1.5 mmol) in McCN (300 mL) was irradiated with a 30-W low-pressure Hg lamp for 10-15 min. The solvent was removed under reduced pressure and the residue was chromatographed (silica gel. Et20/hexane 1 1) to give the yellow product, which was re-crystallized (i-Pr20). 

A solution of a 4-azidoquinoline (0.5-0.6 g) and NaOMe (0.3 0.35 g, large excess) in a mixture of MeOH (75 mL) and dioxane (75 mL) was irradiated for 20-30 min with a 400-W high-pressure Hg lamp under N2. A further quantity of NaOMe (1.0-2.0 g) was added and the solution stirred at 20 C for 7-8 h and then concentrated in vacuo. The residue was treated with ice-water (30 mL) and the mixture was extracted with Et20. The extract was washed with sat. brine, dried and evaporated under reduced pressure. The residue was chromatographed (silica gel, Et20) to give the 3//-1,4-benzodiazepine as a yellow oil. 

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