Oxidation by-products

However, thermolysis of the phosphonium salts (X=+PPh3) leads directly to the indolic products without need of acid catalyst or PPh3, and thus may not proceed via a normal Wittig pathway. Alternatively, Hughes has effected a solid-phase version of this reaction employing a polymer-hound phosphonium salt and potassium tert-butoxide as base <96TL7595>. In this case, the phosphine oxide by-product remains bound to the polymer resin. 

The HiPOx process achieved >99.9% reduction in MTBE concentration and easily met the treatment goal of reducing the concentration of MTBE to below 5 pg/L. However, significant concentrations of MTBE degradation intermediates and oxidation by-products were present in the final effluent. TBA was produced early during the chemical oxidation process. Its concentration was diminished by further oxidation, reaching below its regulatory limit of 12 pg/L in two of the three... 

A model calculation showed that the HiPOx system may have been fully successful in limiting bromate formation under the chosen oxidant doses if the influent bromide concentration was 0.56 mg/L or less. Since a bromide concentration of 0.56 mg/L is still extremely high for a drinking water source, the HiPOx system appears to hold promise for destroying MTBE and its oxidative by-product TBA while controlling bromate formation, even in waters that have high bromide concentrations.101... 

Nitration of ketones or enol ethers provides a useful method for the preparation of a-nitro ketones. Direct nitration of ketones with HN03 suffers from the formation of a variety of oxidative by-products. Alternatively, the conversion of ketones into their enolates, enol acetates, or enol ethers, followed by nitration with conventional nitrating agents such as acyl nitrates, gives a-nitro ketones (see Ref. 79, a 1980 review). The nitration of enol acetates of alkylated cyclohexanones with concentrated nitric acid in acetic anhydride at 15-22 °C leads to mixtures of cis- and rrans-substituted 2-nitrocyclohexanones in 75-92% yield. 4-Monoalkylated acetoxy-cyclohexanes give mainly m-compounds, and 3-monoalkylated ones yield fra/w-compounds (Eq. 2.40).80... 

Without cooling, the temperature rises above 70° and the precipitate becomes deep rose from oxidation by-products. This color, however, does not seem to affect the yield or purity of the dichloroaniline to any great extent. 

The oxidation of cobalt metal to inactive cobalt oxide by product water has long been postulated to be a major cause of deactivation of supported cobalt FTS catalysts.6 10 Recent work has shown that the oxidation of cobalt metal to the inactive cobalt oxide phase can be prevented by the correct tailoring of the ratio Ph2cJPh2 and the cobalt crystallite size.11 Using a combination of model systems, industrial catalyst, and thermodynamic calculations, it was concluded that Co crystallites > 6 nm will not undergo any oxidation during realistic FTS, i.e., Pi[,()/I)i,2 = 1-1.5.11-14 Deactivation may also result from the formation of inactive cobalt support compounds (e.g., aluminate). Cobalt aluminate formation, which likely proceeds via the reaction of CoO with the support, is thermodynamically favorable but kinetically restricted under typical FTS conditions.6... 

Edlund et al. (10) published a protocol similar to Vyverman et al. (8), but recommend gently oxidizing diatoms overnight in cold 30% H202 at step 5 instead of boiling. At step 6, Edlund et al. (10) prefer to rinse the material with distilled water six times, each rinse followed by 6 h of settling to remove oxidation by-products. 

The lluorous biphasic technique has also been applied to the Wittig reaction, one of the most effective methodologies for the production of C=C double bonds [13] (Scheme 10.11). One of the major drawbacks of this reaction is the separation of the alkene from the phosphine oxide by-product. This is commonly achieved via recrystallization or column chromatography, but recently it has been shown... 

Site-specific risk analysis of oxidation by-product emissions, including dioxins and nitrated polyaromatic hydrocarbons. 

The reaction of fuming nitric acid with 2-methyl-2-butene (3) is reported to yield 2-methyl-3-nitro-2-butene (4). The reaction of alkenes with fuming nitric acid, either neat or in chlorinated solvents, is an important route to unsaturated nitrosteroids, which assumedly arise from the dehydration of /3-nitroalcohols or the elimination of nitric acid from /3-nitro-nitrate esters. Temperature control in these reactions is important if an excess of oxidation by-products is to be avoided. 

D.M. (1990) Transformations of iron oxide by-products during the Becher process. The Aus. IMM Proceedings No. 1 53-59... 

No secondary wastes or off-gases are produced, and oxidation by-products are nontoxic. 

Since ascorbate reduces photooxidation of lipid emulsions and multivitamin preparations (see Figure 4) [19], Lavoie et al. [34] studied the formation of oxidative by-products of vitamin C in multivitamins exposed to light. They found that the loss of ascorbic acid in photoexposed multivitamin preparations was associated with the generation of products other than dehydroascorbate and 2,3-diketogulonic acid, which are the usual products of vitamin C oxidation. The authors showed that hydrogen peroxide at concentrations found in TPN solutions induced the transformation of dehydroascorbate into new, biologically active compounds that had the potential to affect lipid metabolism. They believe that these species have peroxide and aldehyde functions [35]. 

The gas phase oxidation of benzene with air is an important process for the production of maleic anhydride, which is the major partial oxidation product, besides products of complete oxidation. By-products are benzo-quinone, in particular at low conversion, and fumaric acid which is formed at the high conversion levels used in industrial installations [28]. Only traces of phenol and other by-products are formed. The important catalysts are based on V2Os and a maximum yield of 60—80% maleic anhydride is obtained at 350—500° C. 

Uses- no information at our disposal Remark According to Ref 5, TNBzlN is a precursor of the White CompoundSee 2,2 -Azoxybis (4,6-dinitrobenzoic acid) under Dinitrobenzoic Acid] an oxidative by-product in the manuf of TNT by continuous method... 

The expln mentioned above occurred during faulty manual removal of white compound , an insoluble TNT oxidation by-product, which has periodically coated the nitrator cooling coils (the chemical structure and mode of formation of this material are given under the section on Chemical Reactions and Derivatives ). It was found (Ref 21) that its formation resulted from high carry-back of TNT oxidation products from one of the nitrators in stage 3 to stage 2. This again pointed to the desirability of cleaner separation of acid and nitrobody, since white compd deposition was not a problem in plants where better separation occurred... 

The high decomposition rate of pollutants is dependent on the high value of the molar extinction coefficient at 254 nm, the quantum yield of M, and the concentration of oxidation by-products. 

Scavengers include overdosed hydrogen peroxide, humic substances, carbonate ions, bicarbonate ions, and oxidation by-products. Free-radical scavengers are compounds that consume chemical species that have at least one unpaired electron. 

Deethylatrazine, deisopropylatrazine, and acetamido-s-triazines are the primary oxidation by-products of atrazine by UV/Q3. UV photolysis of atrazine... 

The one-step hydroxylation ofbenzene represents an attractive alternative pathway for the direct synthesis of phenol and many studies are performed using different processes among which the photocatalytic reaction [45,46]. One of the main problem is the low selectivity of the process due to the higher reactivity of phenol towards the oxidation than benzene with the formation of oxidation by-products. In order to avoid these secondary products and to obtain the separation of the phenol from the oxidant reaction environment the use of a membrane system coupled with the photocatalytic process seems a useful solution. 

The product aluminum trialkoxides are then stripped in a flash evaporator to remove solvent and oxidation by-products described earlier. The light hydrocarbon solvent is separated... 

Sulfonamides may be directly synthesized from sulfonic acid salts by treatment with triphenylphosphine ditriflate followed by an amine <2004JA1024>. This procedure, that avoids the generation of sulfonic acids, converts sulfonic acid salt 129 to sulfonamide 130 in 81% yield (Equation 92). Problems associated with the removal of triphenylphosphine oxide by-products can be alleviated by performing the reaction with polystyrene-supported phosphine. 

Low MW organics O3/UV SBBPR, LVP lamp, 100 W. Compounds with 1 to 6 C atoms. Phenol oxidation. By-product identification. TOC removal 169... 

For the same air feed rate, the smaller the bubble size in the reaction, the greater the quantity of highly oxidized by-products formed. This decrease in reaction efficiency was qualitatively explained in terms of the rate of surface renewal at the gas-liquid interface. The above authors also reported that increased pressures also reduced the efficiency of the reaction. 

Slowly add acetone (400 mL) to this flask to precipitate crude product. Filter off the precipitate. This contains a significant amount (15-25%) of phosphine oxide by-product. 

Polymer-supported Wittig reagents have recently been developed as an extension to the traditional reagents.29 For example, polystyryldiphenylphosphine has been developed in an attempt to replace the use of triphenylphosphine in the preparation of phosphoranes (see Protocol 1). The hope is that these polymer-bound regents will overcome the practical problem of removing the triphenylphosphine oxide by-product formed in Wittig reactions. Polymer supported phosphonates and Wittig substrates have also been prepared for use in solid phase synthesis and combinatorial chemistry.30... 

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