Ozone, on silica gel

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

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]. 

Uncatalysed cleavage of epoxides has been reported [e.g. tetrahydro-(39)- dihydro-(64 X = OH)]," and oxidation of tetrahydrogeranyl acetate with ozone on silica gel yields dihydro-(65 R = H) predominantly with some 8-acetoxy-6-methyloctan-2-one (cf. Vol. 7, p. 7)." ... 

Alebic-Juretic, A., T. Cvita, and L. Klasinc, Heterogeneous Polycyclic Aromatic Hydrocarbon Degradation with Ozone on Silica Gel Carrier, Environ. Sci. Technol., 24, 62-66(1990). 

Branched acyclic alkanes also exhibit a slightly different behavior toward ozone on silica gel.105 Although tertiary alcohols are usually the main products, C—C bond cleavage to yield ketones always occurs and may become the predominant reaction. Atomic oxygen generated by microwave discharge of a C02/He mixture is a more selective reagent in the transformation of these compounds to tertiary alcohols.106... 

Ozone on silica gel has been used to hydroxylate alkanes and unactivated C—H bonds.The example shown in equation (67) illustrates the application to a steroid, which was achieved in 51% yield at a respectable 11% conversion with regard to ozone. ... 

Dry ozonization is also an efficient proc ure for oxidation of aliphatic primary amines into nitro groups, with yields of about 70%. Arylamines are also oxidized to nitro aronutics, albeit witii low yields. Ozone on silica gel has also been shown to oxidize arenes in some cases. ... 

The heat of adsorption of ozone on silica gel was calculated for various conditions with the help of the Clausius-Clapeyron equation (Figure 3). In the region of temperature and ozone concentration of most interest, the heat of adsorption is about 5400 cal. per gram-mole of ozone. 

Method I (Figure 7). [Step 1—Start]. Adsorb ozone on silica gel from the stream of oxygen plus ozone. 

Figure 6. Adsorption of ozone on silica gel at a concentration of 2 weight % in oxygen...

Step 1. Adsorb ozone on silica gel from the stream of oxygen plus ozone, first purging the relatively small amount of carrier gas blown out initially from the silica gel bed through an ozone decomposition catalyst to the atmosphere (or to a gas holder if the carrier gas is valuable), then recycling the oxygen back to the ozonizer. 

Ozone on silica gel introduces a 25-hydroxy-substituent into suitable compounds with a cholestane side-chain. By using the la,3/8-diacetoxy-6/8,7a-dibromo-derivative (383), prepared from the known 6-ene, the 25-hydroxylated compound was obtained as the only product (11% conversion). Trifluoroacetylation followed by dehydrobromination afforded the 5,7-diene (385), which was transformed into la,25-dihydroxy-vitamin D3 by the usual method. 

Alebic-Juretic, A., Cvitas, T., and Klasmic, L. (1990) Heterogeneous polycyclic aromatic hydrocarbon degradation with ozone on silica-gel carrier. Environ. Sci. TechnoL, 24, 62-66. 

Ozonation of Heteroatoms. Phosphines are converted to phosphine oxides and phosphites to phosphates by ozone. These reactions are quite general and a wide range of sub-stitutents can be tolerated. Phosphine oxides also can be produced by the ozonation of alkylidenetriphenylphosphoranes or of thio- or selenophosphoranes. Organic sulfides are converted to sulfoxides and sulfones by ozonation. Tertiary amines are converted to amine oxides, while nitro compounds can be produced in modest yields by ozonation of primary amines. This preparation of nitroalkanes compares well with alternate approaches using peroxides, peroxy acids, permanganate, or Monoperoxysulfuric Acid, but ozonation on silica gel has proven to be superior (see Ozone-Silica Get). Selenides are converted to selenoxides by ozone and this reaction is often used to achieve overall production of unsaturated carbonyl compounds. An example is shown in eq 25. ... 

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