Peroxygen intermediates

2 Percarboxylic acids. This group of compounds, often simply called peracids, represents the main means used to date of activating H2O2 towards electrophilic oxidations, such as epoxidation, Bayer-Villiger oxidation and heterocyclic A-oxidation. 

For most carboxylic acids, a strong acid catalyst must be added in order to achieve an acceptable rate of reaction sulphuric, or sulphonic acids, the latter in resin-bound form, or phosphonic acids can be used. A few acids are strong enough to catalyse their own peracid formation, notably formic and trifluoroacetic. The reaction may be speeded up by increasing the temperature, subject to safety considerations (see section 9.4). 

Peracids themselves are very weakly acidic, with most pKa values in the range 7.5-8.5 cf. most parent acids at 2-5) [13]. For example, peracetic acid has pKa of 8.2, compared to acetic acid at 4.8. 

1 Lower aliphatic acids. The two peracids most relevant to industry are performic and peracetic. Performic acid is always generated in situ by the above reaction, as it is not sufficiently stable to isolate as an equilibrium mixture. Peracetic acid can, however, be used in a variety of forms including in situ generation, pre-formed equilibrium mixtures, distilled aqueous solution and solvent-extracted products. 

In situ generation is a convenient method for substrates which tolerate the acidity required to catalyse the equilibrium. Faster reaction can be achieved using the strongest pre-formed products, manufactured from 85% H2O2, which typically contain 35-40% peracetic acid with about 45% acetic acid, under 15% water, under 5% residual H2O2 and 1% sulphuric acid or less. In the latter case, the mineral acidity can be sup- 

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An unstable intermediate peroxygenated compound is also always formed. This gives a blue coloration to fresh guaiacum tincture and is possibly analogous to Caro s acid.2... 

Secondary amines can be oxidized at the N-H bond to hydroxylamines and nitroxides, and via nitrones via C-N oxidation. Nitrones are valuable intermediates in the production of isoxazolines. Initial C-N oxidation of secondary amines gives imines which can react further to oxaziridines. The latter can be converted to nitrones, and both to amides. Primary amines are oxidized at the N-H bond to mono-substituted hydroxylamines, which are readily converted further to nitroso and nitro compounds by the more activated peroxygen... 

A dimethylzinc/air-generated tetrahydrofuran radical reacted with aldehyde to give the a-hydroxylated 3-addition product, which was isolated as the keto-lactone after Jones oxidation. It was proposed that the initial THF a-radical that was generated was able to react with molecular oxygen to generate an a-peroxygenated THF p-radical as the key intermediate <04TL795>. 

At least some of the ways toward which other chemicals have turned to capture the researcher s attention are clearly shown in a few specific examples. Functionality in the new product is most important where the ultimate application involves its use as an intermediate or as a monomer. Development of bisphenol, epichlorohydrin, and peroxygenated compounds are examples resting upon this type of situation. Our own diallylmelamine is a similar example. 

Then, the effects of ligands of cobalt(II) complexes in the above reaction was examined and was found that various bis(l,3-diketonato)cobalt(II), especially Co(modp)2, were effectively employed as catalysts. Preparation of a peroxy compound directly from olefin has been considered to be difficult because of its unstability. The present peroxygenation reaction, however, provides a facile and efficient method for the direct introduction of dioxygen function into the carbon-carbon double bond of olefmic compounds under mild conditions (Table 4). In addition, the triethylsilyldioxy derivative here is expected to be a potentially useful synthetic intermediates. 

The reaction may involve intermediate formation of hydrogen peroxide, but the mechanism has not been fully established.) Peroxygens such as H2O2 [362] and calcium peroxide [363] can be added to improve the recovery of gold. In some cases, aeration is difficult owing to the viscosity of the ore slurry, and these may require use of a peroxygen as the sole oxidant [364]. 

In the reaction pathway, the imininm ion formed from corresponding a,P-unsaturated aldehyde with the chiral amine is subject to nucleophilic attack by the peroxide, leading to an enamine intermediate (Schane 1.64). Formation of the epoxide then takes place by attack of the nucleophilic enamine carbon atom on the electrophilic peroxygen atom. 

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