Oxidation—continued with hydrogen peroxide

The very sensitive ether peroxide test strips (Merckoquant, Art. No. 10011), available from E. Merck, Darmstadt, are used. If the test is still positive at this point, an additional 0.2 ml. of N-methyl morpholine is added. Stirring and heating at 75° are continued for another 5 hours. Remaining peroxide renders the work-up and drying of the product potentially hazardous. N-Methylmorpholine N-oxide (1) and hydrogen peroxide form a strong 1 1 complex. In the reaction with osmium tetroxide, this complex produces conditions similar to those of the Milas reaction,7 and some ketol formation may result. 

Photoreduction of ferric ion. Lunck and co-workers observed the enhanced rate of photo-oxidation of salicyclic acid by hydrogen peroxide in the presence of Fe(III) as well as the increased rate of photodecomposition of hydrogen peroxide in the presence of transition metal ions.23 The ferrous ion reacts with hydrogen peroxide, generating a second hydroxyl radical and ferric ion, and the cycle continues. 

Of the artificial chemiluminescent compounds, luminol (5-amino-2,3-dihydro-l,4-phthalazinedione) is the most popular, and has been applied not only in analytical chemistry but also in other fields. The luminol chemiluminescence is based on the light emission from an excited 3-aminophthalate ion generated by oxidation with hydrogen peroxide or atmospheric oxygen in the presence of bases and catalysts. This peculiar chemiluminescence property and its industrial value have attracted continuous interest and prompted many chemists to investigate its reaction in detail... 

A promising and cleaner route was opened by the discovery of titanium silica-lite-1 (TS-1) [1,2]. Its successful application in the hydroxylation of phenol started a surge of studies on related catalysts. Since then, and mostly in recent years, the preparation of several other zeolites, with different transition metals in their lattice and of different structure, has been claimed [3]. Few of them have been tested for the hydroxylation of benzene and substituted benzenes with hydrogen peroxide. Ongoing research on suppoi ted metals and metal oxides has continued simultaneously. As a result, knowledge in the field of aromatic hydroxylation has experienced major advances in recent years. For the sake of simplicity, the subject matter will be ordered according to four classes of catalyst medium-pore titanium zeolites, large-pore titanium zeolites, other transition metal-substituted molecular sieves, and supported metals and mixed oxides. 

An unavoidable by-product of the Swem reaction is the volatile dimethylsulphide which, on account of its unpleasant smell, is a reagent regulated by offensive odour control laws. This makes large scale chemistry problematic, especially in industry. To overcome this, several methods exist to perform the Swem oxidation under odourless conditions. For example, Node et al. outline a protocol for the Swem oxidation which uses dodecyl methyl sulfoxide in place of methyl sulfoxide,12 while Crich and co-workers have developed a fluorous Swem oxidation reaction that uses tridecafluorooctylmethyl sulfoxide 17,l3a,b This reagent can be recovered via a continuous fluorous extraction procedure and recycled by reoxidation with hydrogen peroxide. Additionally, the fluorous DMSO is crystalline, odourless and soluble in CH2CI2 to —45 °C. 

The importance of fully or partially hydrogenated isoxazolo[2,3-a]pyridines as intermediates in the synthesis of stereochemically complex molecules, particularly alkaloids, has led to a continued high level of interest in their preparation. The route of choice remains the 1,3-dipolar cycloaddition reaction between a tetrahydropyridine A-oxide, that is a nitrone, and a dipolarophile. A number of methods for the production of the nitrone for in situ reaction have been developed. They include the oxidation of the secondary amine, piperidine, with hydrogen peroxide in the presence of... 

In continuation of their stereochemical studies of sparteine N-oxides cf. Vol. 6, p. 91), Wiewiorowski and co-workers prepared 2-phenylsparteine N-16-oxide and its perchlorate salt (6) X-ray analysis of the salt shows that there is a strong hydrogen bond between the N-16 oxygen function and the N-1 proton/ Almost exclusive formation of the N-16-oxide in the reaction of 2-phenylsparteine with hydrogen peroxide is attributed to a greater accessibility of the N-16 atom to the reagent, although this site is protonated preferentially (Scheme 1). Previous views on the formation of N-oxides of sparteine and its derivatives have thus been revised protonation affects the rate of reaction, but does not influence the site at which oxidation occurs. 

LaLonde and Wong have continued their studies of thiaspirane bis-amine sulphoxides. Oxidation of the Nuphar alkaloid thiobinupharidine (15) with hydrogen peroxide gave a mixture of the syn-sulphoxide (16) and the anti-sulphoxide (17) configurations of the sulphoxide groups were assigned by... 

As with betaines and other amphoterics, efforts continue in the development of amine oxides with reduced levels of residual impurities. A process for preparing long monoalkyl-chain amine oxides with low nitrite and nitrosamine levels [41] and another process [42] involving the oxidation of Cjg-Cig dimethylamine with hydrogen peroxide in the presence of malic acid and diethylenetriaminepentaacetate (DTPA) have been described. The resulting amine oxide contains (the undesired) nitrite levels below 1 ppm [42]. 

First, the corresponding sulfide 2 has relatively low volatility and is not malodorous. Second, fluorous sulfide 2 can be easily separated from the reaction mixture by continuous fluorous/organic liquid-liquid extraction and then oxidized to 1 with hydrogen peroxide for reuse. In addition, sulfoxide 1 has similar reactivities and compatibility as DMSO with a variety of functional groups due to the relatively inert nature of the fluorous subunit. 

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