Ozone-Silica gel

HYDROXYLATION Benzeneseleninic anhydride. Diperoxo-oxohexamelhyl-phosphoramidomolybdenum(Vl). Hydrogen peroxide. Iodosobenzene. Oxygen. Ozone-Silica gel. Perchloryl fluoride. 

Oxirane hydroperoxides, 94 Oxyamination, 256 Oxy-Cope rearrangement, 302-303 Oxygen, 258-260 singlet, 261, 271 Oxygenation, 80-81 Oxymercuration, 222, 223, 224 Ozone, 269-271 Ozone-Silica gel, 271-273... 

IIYDROXYLATION Oz.onc. Ozone-Silica gel. Pertritiuoroacetic add. > <-HYI)ROXYLATION Osmium lctroxidc-/-Butyl hydroperoxide. Thallium acetate. IIYDROXYMEI IIYI ATION 1 ri- biilyllincarhinol. 

Compounds containing susceptible C—H bonds can be oxidized to alcohols. " Nearly always, the C—H bond involved is tertiary, so the product is a tertiary alcohol. This is partly because tertiary C—H bonds are more susceptible to free-radical attack than primary and secondary bonds and partly because the reagents involved would oxidize primary and secondary alcohols further. In the best method, the reagent is ozone and the substrate is absorbed on silica gel. Yields as high as 99% have been... 

TERTIARY ALCOHOLS FROM HYDROCARBONS BY OZONATION ON SILICA GEL 1-ADAMANTANOL... 

A Welsbach T-816 Ozonator purchased from the Welsbach Corporation, Philadelphia, Pennsylvania, was used. The oxygen stream was dried by passage through dry silica gel and molecular sieves and then introduced into the ozonator with the operating voltage set at 115 V., the gas pressure at 8 p.s.i.g., and the gas flow rate at 1 1. per minute. The resulting ozone flow rate was 0.00245 mole per minute, as determined by titration of a potassium iodide trap. ... 

In the apparatus used by the checkers, the internal temperature was between —45° and - 65° while ozone was being passed through the silica gel. The use of lower bath temperatures results in the adsorption of a greater quantity of ozone on the silica gel consequently shorter reaction times and higher conversions may be realized in the ozonation. However, since ozone liquifies at —112°, there is a serious danger of explosion. 

The ozone flow is stopped when the silica gel reaches a constant, dark blue color. The time required for saturating the silica gel with ozone depends on the type of silica gel used and on whether it has been dried (Note 2). 

Ozone is strongly endothermic (A(g) +142.2 kJ/mol, 2.96 kJ/g) and the pure solid or liquid materials are highly explosive. Evaporation of a solution of ozone in liquid oxygen causes ozone enrichment and ultimately explosion [1], Organic liquids and oxidisable materials dropped into liquid ozone will also cause explosion of the ozone [2], Ozone technology and hazards have been reviewed [3], a safe process to concentrate ozone by selective adsorption on silica gel at low... 

Silica gel at —78°C adsorbs 4.5 wt% of ozone, and below this temperature the... 

For the anodic substitution of unactivated CH-bonds, some fairly selective reactions for tertiary CH-bonds in hydrocarbons and y—CH-bonds in esters or ketones are available [85-87]. However, in some cases, a better control of follow-up oxidations remains to be developed. Chemically, a number of selective reactions are available, such as the ozone on silica gel for tertiary CH-bonds [88], the Barton or Hoffmann-LoefHer-Freytag reaction for y-CH-bonds [89], and for remote CH-bonds, Cprop)2NCl/H [90, 91], photochlorination of fatty acids adsorbed on alumina [92] or template-directed oxidations [93]. 

Photolytic. A carbon dioxide yield of 46.5% was achieved when aniline adsorbed on silica gel was irradiated with light (X >290 nm) for 17 h (Freitag et al., 1985). Products identified from the gas-phase reaction of ozone with aniline in synthetic air at 23 °C were nitrobenzene, formic acid, hydrogen peroxide, and a nitrated salt having the formula [CeHsNHsl NOs" (Atnagel and Himmelreich, 1976). A second-order rate constant of 6.0 x 10 " cmVmolecule-sec at 26 °C was reported for the vapor-phase reaction of aniline and OH radicals in air at room temperature (Atkinson, 1985). 

Photolytic. Fluorene reacts with photochemically produced OH radicals in the atmosphere. The atmospheric half-life was estimated to range from 6.81 to 68.1 h (Atkinson, 1987). Behymer and Hites (1985) determined the effect of different substrates on the rate of photooxidation of fluorene (25 tig/g substrate) using a rotary photoreactor. The photolytic half-lives of fluorene using silica gel, alumina, and fly ash were 110, 62, and 37 h, respectively. Gas-phase reaction rate constants for OH radicals, NO3 radicals, and ozone at 24 °C were 1.6 x lO , 3.5 x 10 and <2 x 10in cmVmolecule-sec, respectively (Kwok et al., 1997). 

While primary aliphatic amines are converted to nitro compounds on reaction with ozone these reactions are accompanied by numerous by-products.Such side-reactions are largely suppressed by first dissolving the amine onto silica gel followed by passing a stream of 3 % ozone in oxygen through the solid at -78 °C under anhydrous conditions, where yields of between 60 and 70 % are reported. This route has been used to synthesize the energetic cyclopropane (65) from the diamine (64) (Table 1.7). ... 

---