Active oxygen reaction with activators

The method of photosensitized oxygenation was successfully applied in the preparation of alcohols 265-270 from sylvestrene (264),207 and seems to be the most simple and successful method for the preparation of optically active rose oxides (272,273) from (+)- or (—)-citronellol C271).177 It may also be used for the preparation of certain organo-metallic hydroperoxides. Thus, the triphenyl-tin derivative of tri-methylethylene (274) undergoes a photosensitized oxygenation reaction with a rate similar to that of tetramethylethylene, giving rise to the hydroperoxides 275 and 276 219... 

The Type II photo-oxygenation reactions with which we are concerned occur by a completely different mechanism. The main feature of these reactions is that an activated oxygen is formed during the reaction, which can react stereoselectively with certain substrates to give the addition products. Today, we have reason to believe that the activated oxygen is the excited singlet oxygen, 02. 

Reactions at G-5. The C-5 atom of hydantoins can be considered as an active methylene group, and therefore is a suitable position for base-cataly2ed condensation reactions with aldehydes (44). 2-Thiohydantoins give the reaction more readily than their oxygen counterparts ... 

Many waste-rock or overburden disposal systems result ia compacted dumps having uncontrolled distribution of fines. In such dumps, solution distribution is poor and there is Htde oxygen for reaction with the sulfides. Methods for managing these dumps to maximize copper recovery have been actively pursued. 

Any substance capable of reacting with free radicals to form products that do not reinitiate the oxidation reaction could be considered to function as free-radical traps. The quinones are known to scavenge alkyl free radicals. Many polynuclear hydrocarbons show activity as inhibitors of oxidation and are thought to function by trapping free radicals [25]. Addition of R to quinone or to a polynuclear compound on either the oxygen or nitrogen atoms produces adduct radicals that can undergo subsequent dimerization, disproportionation, or reaction with a second R to form stable products. 

Catalysis plays an important part in the hydrazine/oxygen reaction. Copper salts were formerly added for this purpose, but in recent years certain organic substances, e.g. quinhydrone, have been employed and a number of proprietary activated hydrazines have been available. These are useful at low temperatures above 150°C scavenging rates with normal hydrazine are such that no great benefit is achieved by their use. 

The anion of DMSO undergoes a phenylation reaction with aryl halides under sunlight stimulation38. The presence of benzhydryl methyl sulfoxide (maximum yield 5%) in all runs, the sunlight activation, the order of reactivity of halobenzenes (I > Br > Cl), the inhibition of the reaction with oxygen, all hint at the SRN139-44 mechanism (Scheme 3). 

The oxidation reaction is generally described with Pt or Pd as catalyst, eventually on active coal, in aqueous alkaline solutions at temperature from 40°C to 100°C. The oxidation reaction is mostly carried out with oxygen or with an oxygen-containing gas such as air [17,18]. 

The cyclopropanation of 1-trimethylsilyloxycyclohexene in the present procedure is accomplished by reaction with diiodomethane and diethylzinc in ethyl ether." This modification of the usual Simmons-Smith reaction in which diiodomethane and activated zinc are used has the advantage of being homogeneous and is often more effective for the cyclopropanation of olefins such as enol ethers which polymerize readily. However, in the case of trimethylsilyl enol ethers, the heterogeneous procedures with either zinc-copper couple or zinc-silver couple are also successful. Attempts by the checkers to carry out Part B in benzene or toluene at reflux instead of ethyl ether afforded the trimethylsilyl ether of 2-methylenecyclohexanol, evidently owing to zinc iodide-catalyzed isomerization of the initially formed cyclopropyl ether. The preparation of l-trimethylsilyloxybicyclo[4.1.0]heptane by cyclopropanation with diethylzinc and chloroiodomethane in the presence of oxygen has been reported. "... 

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