Peracid procedure

Oxaziridines are generally formed by the action of a peracid on a combination of a carbonyl compound and an amine, either as a Schiff base (243) or a simple mixture. Yields are between 65 and 90%. Although oxygenation of Schiff bases is formally analogous to epoxidation of alkenes, the true mechanism is still under discussion. More favored than an epoxidation-type mechanism is formation of a condensation product (244), from which an acyloxy group is displaced with formation of an O—N bond. 

Formation of mixtures of (E)- and (Z)-oxaziridines from sterically defined Schiff bases fits a two step mechanism through (244) (70CC745). 

Preparation of spirooxaziridines from cyclic ketones poses no problems nor does oxaziridine synthesis from cyclic Schiff bases, which was preferably carried out with pyrro-lines to give, for example (245) (59JCS2102) and, in connection with tranquilizer synthesis, with heterocyclic seven-membered rings to give, for example, (246) (63JOC2459). 

Compound (247) is one of the rare examples of an oxaziridine having an orthoacid carbon in the ring (71TL4519). The formation of (248) demonstrates how far oxaziridine synthesis can be extended into the field of unconventional chemicals (80IC1330). 

Mixtures of a nitrile and hydrogen peroxide are of interest in a commercial hydrazine synthesis (Section 5.08.5) (72TL633). 

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Oxaziridine formation by photoisomerization of nitrones was discovered almost simultaneously with the peracid procedure (58JOC65l>. The t-butyl nitrones of benzaldehyde and 4-nitrobenzaldehyde yielded about 90% of oxaziridines (254) and (255) on UV irradiation. 

Oxaziridines bearing no substituent at nitre en were not, until recently, prepared by the peracid procedure. They became available only after the discovery of a novel oxaziridine synthesis, which instead of formally adding oxygen to a C=N double bond consisted in adding an imino group to a C=0 double bond. The first compound of this type was prepared by Schmitz and Ohme ° in 1961 by treating cyclohexanone with an alkaline solution of hydroxylamine-O-sulfonic acid. S,3-Pentamethyleneoxaziridine (34) was formed (ca. 50% yield) in an extremely fast reaction. Analogous compounds were prepared from methyl ethyl ketone and benzaldehyde (yields ca. 30%). 

As noted in the introduction, epoxidation by the peracid procedure suffers from a number of drawbacks associated with the use of a volatile acid catalyst. Fortunately, as outlined here, research activity in this area has been vibrant, and flie processor has been offered a wide variety of new alternatives for fatty epoxide production. 

Another method of preparing mercuric acetate is the oxidation of mercury metal using peracetic acid dissolved in acetic acid. Careful control of the temperature is extremely important because the reaction is quite exothermic. A preferred procedure is the addition of approximately half to two-thirds of the required total of peracetic acid solution to a dispersion of mercury metal in acetic acid to obtain the mercurous salt, followed by addition of the remainder of the peracetic acid to form the mercuric salt. The exothermic reaction is carried to completion by heating slowly and cautiously to reflux. This also serves to decompose excess peracid. It is possible and perhaps more economical to use 50% hydrogen peroxide instead of peracetic acid, but the reaction does not go quite as smoothly. 

Although the three-membered rings with two heteroatoms were discovered only after 1950, they are accessible by very simple procedures familiar to the chemists decades before. The most common starting materials, peracids and N-haloamines, were available to the chemist before 1900 preparation, as well as isolation, follows standard procedures. 

The reaction of peracids with ketones proceeds relatively slowly but allows for the conversion of ketones to esters in good yield. In particular, the conversion of cyclic ketones to lactones is synthetically useful because only a single product is to be expected. The reaction has been carried out with both percarboxylic acids and Caro s acid (formed by the combination of potassium persulfate with sulfuric acid). Examples of both procedures are given. 

Provided an excess of the hydroperoxide is not used, sulfoxides are obtained in essentially quantitative yields in short reactions times, usually 0.7-2.5 h (42). The method is uncomplicated and can be carried out on the benchtop. The long shelf-life of 1 (> 3 months) adds to the convenience of this procedure. A wide variety of functional groups is tolerated on R and R. The reaction affords nearly pure sulfoxides without contamination from sulfones. The product is obtained simply be evaporating the solvent and tert-butyl alcohol. This method avoids aqueous workup, which is often required when peracids are used (43), and is thus convenient for water-soluble sulfoxides. 

Reaction of 3,5-disubstituted-1,2,4-trioxolanes (89) with oxidants (usually under basic conditions) leads to carboxylic acids (Equation (14)). This reaction is often carried out as the work up procedure for alkene ozonolysis, avoiding the need to isolate the intermediate ozonide. Typical oxidants are basic hydrogen peroxide or peracids and this type of oxidative decomposition is useful for both synthetic and degradative studies. 

Commercial 40% (w/w) peracetic acid is available from the Becco Sales Corporation, Buffalo 7, New York. The use of a 3.3 molecular proportion of the peracid results in slightly higher and more consistent yields of product than when the theoretical 3.0 proportion is employed. The procedure gives the same yield (percentage) of product when using proportionately smaller quantities of reactants. 

Among the oxidative procedures for preparing azo compounds are oxidation of aromatic amines with activated manganese dioxide oxidation of fluorinated aromatic amines with sodium hypochlorite oxidation of aromatic amines with peracids in the presence of cupric ions oxidation of hindered aliphatic amines with iodine pentafluoride oxidation of both aromatic and aliphatic hydrazine derivatives with a variety of reagents such as hydrogen peroxide, halogens or hypochlorites, mercuric oxide, A-bromosuccinimide, nitric acid, and oxides of nitrogen. 

Oxidation of N, -substituted pyrazoles to 2-substituted pyrazole-] -oxides using various peracids facilitates the introduction of halogen at C i, followed by selective nitration at C4. The halogen aiom at C3 or C5 is easily removed by sodium sulfite and acts as a protecting group. Formaldehyde was used to direct the selective introduction of electrophiles at C in a simple one-pot procedure. 

Diels-AUer reactions. This diene can serve as a precursor to the highly oxygenated cyclohexane derivative shikimic acid (3), as shown in Scheme 1. Oxidative desilylation of the Diels-Alder adduct 2 could not be effected with peracids, but was effected by cis-dihydroxylation (Upjohn procedure, 7, 256-257) followed by p-elimination of (CH3)3SiOH with TsOH. Introduction of the 4a,5P diol system was effected indirectly from the 4a,5a-epoxide in several steps, since direct hydrolysis of the epoxide resulted in a mixture of three triols.1... 

Oxidative functionalization of imidazoles is typically not preparatively useful. However, an optimized procedure for direct peracid oxidation of azoles to N-hydroxyazoles was reported [95JCS(P1)243], with imidazoles affording dioxygenated products. In contrast, imidazoles are conveniently converted to imidazole-2-thiones with phenyl chlorothionoformate [95SL239]. 

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