Amine oxidation with peracids

Aliphatic amines have been oxidized with peracids. 

Owiag to the lower basicity of the parent amines, aromatic amine oxides cannot be formed directiy by hydrogen peroxide oxidation. These compounds may be obtained by oxidation of the corresponding amine with a peracid perbenzoic, monoperphthaUc, and monopermaleic acids have been employed. 

Direct oxidation of primary amines with peroxide oxidants does not provide appreciable yield of hydroxylamines. As was mentioned above, oxidation of secondary amines usually proceeds smoothly giving moderate to good yields of iV,iV-disubstituted hydroxylamines. Oxidation of sterically hindered secondary amines such as 125 (equation 88) can also be done with peracids . Further oxidation of the resulting Af,A-disubstituted hydroxylamines 126 with an excess of m-chloroperbenzoic acid is known to end up with the corresponding nitroxyl radicals of type 127 (equation 88) ° although the reaction can be stopped at the hydroxylamine stage. 

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. 

Some aromatic amines may be oxidized to azoxy compounds with peracids... 

Primary aromatic amines may be oxidized with Caro s acid or a variety of peracids (Eq. 4). 

The oxidation of aromatic amines with peracids had been the subject of some dispute. It has now been demonstrated that simple oxidation of aromatic amines with peracids produces azoxy compounds without the intermediate formation of azo compounds [71]. To be sure, small amounts of azo compounds were isolated from the reaction mixture, but this was considered a side reaction. 

This mechanism is the same as that of 9-24 the products differ only because tertiary amine oxides cannot be further oxidized. The mechanism with other peracids is probably the same. Racemic p-hydroxy tertary amines have been resolved by oxidizing them with /-BuOOH and a chiral catalyst—one enantiomer reacts faster than the other.424 This kinetic resolution gives products with enantiomeric excesses of >90%. 

Pyridine A-oxides are formed by the treatment of pyridines with peracids (74)— (75). Typical conditions are MeC02H/H202 at 100°C or m-ClC6H4C03H/CHCl3 at 0°C. The pyridine nitrogen atom reacts less readily with peracids than do aliphatic tertiary amines, as expected. Large a-substituents and any electron-withdrawing substituents slow the reaction thus the A-oxidation of 2,6-diphenylpyr-idine proceeds in poor yield, and efficient conversion of pentachloropyridine to the A-oxide requires a powerful oxidant such as peroxytrifluoroacetic acid. 

It is well known that other non-metal oxides can react with hydrogen peroxide to form similar compounds which can be viewed as inorganic peracids. Such species include boron(III), arsenic(III) and selenium(IV). For example, selenium dioxide can be used as a catalyst for epoxidations or amine oxidations through perselenous acid (Figure 2.29).86... 

Aqueous or alcohol solutions of amine oxides are normally obtained by oxidizing tertiary amines with either hydrogen peroxide or a peracid.4 For example, N,N-dimethyldodecyl-amine oxide has been prepared by treating N,N-dimethyl-dodecylamine with aqueous hydrogen peroxide.5 The procedure illustrated in this preparation permits the oxidation of tertiary amines with /-butyl hydroperoxide in organic solvents under relatively anhydrous conditions.6 In this procedure the reaction time is short and the method is as convenient as the use of aqueous hydrogen peroxide or a peracid as the oxidant. Furthermore, isolation of the anhydrous amine oxide is often relatively simple. 

Barton oxidation was the key to form the 1,2-diketone 341 in surprisingly high yield, in order to close the five-membered ring (Scheme 38). The conditions chosen for the deprotection of the aldehyde, mercuric oxide and boron trifluoride etherate, at room temperature, immediately led to aldol 342. After protection of the newly formed secondary alcohol as a benzoate, the diketone was fragmented quantitatively with excess sodium hypochlorite. Cyclization of the generated diacid 343 to the desired dilactone 344 proved very difficult. After a variety of methods failed, the use of lead tetraacetate (203), precedented by work performed within the stmcmre determination of picrotoxinin (1), was spectacularly successful (204). In 99% yield, the simultaneous formation of both lactones was achieved. EIcb reaction with an excess of tertiary amine removed the benzoate of 344 and the double bond formed was epoxidized with peracid affording p-oxirane 104 stereoselectively. Treatment of... 

Sulfoxides, prepared by the oxidation of sulfides with NaI04 or peracid, undergo elimination to give the alkenes at temperatures similar to the amine oxides (Scheme 4.12). 

The rapid development of chiral phosphine derivatives of ferrocene was undoubtedly due to their application in catalysis. In contrast, chiral sulfur compounds from lithiated iV,iV-dimethyl-l-ferrocenylethylamine were only prepared about 15 years later [140], For the synthesis of such derivatives, the lithiated amine is treated with disulfides as shown in Fig. 4-24, top (and analogously, diselenides [141]). The sulfides obtained are easily oxidized by peracids or NaI04 to the corresponding sulfoxides. As sulfur becomes a new center of chirality by the oxidation, diastereoisomeric sulfoxides are formed in ratios depending on the oxidant [140]. If chiral oxaziridines [106, 142] are used as oxidizing agents, the diastereoisomeric ratio is appreciably... 

Triazin-3-amines with an unsubstituted or a monosubstituted amino group are oxidized by peracids to give the 2-oxides 4, while the AvV-dialkyl-l,2,4-triazin-3-amines afford the 1-oxides.237 Oxidation of l,2,4-triazin-3-amine 2-oxide (4 R1 = R2 = R3 = H) with hydrogen peroxide in polyphosphoric acid at 24 °C gives l,2,4-triazin-3-amine 2,4-oxide (36%), the first monosubstituted 1,2,4-triazine di-iV-oxide.238... 

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