Methylene blue, oxidation

The catalysis by Mo(VI) of the oxidation of N2H5 to N2 by methylene blue depends on the steps given above, Mo(VI) being regenerated by methylene blue oxidation of the Mo(V) dimer . The latter reaction was studied independently and... 

Photosensitized oxidation offurans.3 The endoperoxide (2) formed in photosensitized (methylene blue) oxidation of 3-substituted or 3,4-disubstituted furans in acetone at -40° rearranges at 20° to 4-hydroxy-2-butenolides in 30-97% yield. Example ... 

Lactones. Photosensitized (methylene blue) oxidation of 3-alkyl-1,2-cyclohex-anediones (1) results in 8-kcto carboxylic acids (2) in high yield. They are converted by reduction and lactonization into 8-lactones (3). The method is attractive for substrates bearing labile, unsaturated side chains. 

Kinetic Analysis of the Methylene Blue Oxidations of Thiols... 

The observed rate laws for the methylene blue oxidations of both mercaptoethanol and dithioerythritol at the different pH s are consistent with the mechanisms proposed for these oxidations. The most significant effect of the pH on the reaction is that of establishing the relative amounts of thiol and sulfide ion. Initiation of the chain sequence by the reaction of a sulfide ion with MB+ would be expected to be more rapid, and therefore the overall oxidation. faster, if the pH of the medium is increased. However, at the higher pH s where the relative amount of undissociated thiol is small, the reaction rate diminishes indicating not only that the thiol is likely a reactant in the overall reaction but that it is involved in a rate limiting step of the reaction at higher pH s. While not as supportive as the... 

The effects of pH, ionic strength, reagent concentration ratios and deuterium substitution of the sulfur-bonded hydrogens on both the rates and rate laws for the methylene blue oxidations of mercaptoethanol and dithioerythritol have been determined. A free radical chain mechanism consistent with the observed kinetic behavior of the oxidation reactions is proposed. A key feature of the proposed mechanism is the formation of the sulfur-sulfur linkage of the disulfide in the reversible formation of a disulfide radical anion (RSSR) as a chain propagating step in the chain sequence. 

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