Hydrogen peroxide thiocyanate oxidation

N 24.12% brick red solid mp, decomps when heated over 300°. Insol in w and the usual organic solvents as well as weak acids and alkalies. Comm prepn (Ref 3) is from thiocyanic acid and/or thiocyanates either by anodic oxidation or by interaction with hydrogen peroxide or halogens. The yield is impure because it contains both H and O. The S content varies between 45 and 55%. Lab prepn of the pure polymer is by reacting the Na salt of 5-chlor-3-mercapto 1,2,4-thiodiazols with either acet, ethanol or w (Refs 1 2)... 

On the basis of these results it can be stated that the fast oxidation of thiocyanate by peroxy acids gives rise to the induced reduction of hydrogen peroxide. In order to elucidate the mechanism of this interesting reaction let us have a look at reactions of thiocyanate with peroxy compounds of different types. 

More decisive evidence is provided by the interconvertibility of N-aryl-JV-arylamidinothioureas (28) and Hector s bases by oxidation-reduction.63, B4,67b The former compounds are accessible (as salts) (i) by the condensation of arylthioureas (24) with arylcyanamides (23),63 (ii) by the extrusion of sulfur from the recently described40,41 s-diaryldithioformamidine hydrobromidesB4a (22), (tit) by the oxidation of arylthioureas (24) with 0.5 moles of hydrogen peroxide in the presence of mineral acids,B4a and (iv) by the mild reduction of Hector s bases by hydrogen sulfide in acid media.B4a The first of these four reactions limitB the structure of the products to the three alternatives 25, 28, and 30. Of these, 25 is excluded by the non-identity of the product with authentic67 N-phenyl-i -phenylamidinothiourea (25 R = Ph). The monosulfide structure (30) is not reconciled as readily with the observedB4a hydrolytic fission of the products into diaryl-guanidines (29) and thiocyanic acid as is structure 28. Indeed, as in the case of thioamides and nitriles (see Section II, C, 1), the present condensation may involve the primary formation of an intermediate diimido-monosulfide (30) and its isomerization to 28. 

Small amounts of hydrogen peroxide in raw milk can activate the lactoperoxidase-catalyzed oxidation of thiocyanate to produce a bacterial inhibitor (Hogg and Jago 1970). Inhibitory compounds resulting from oxygen metabolism can produce initially slow starter culture growth in industrial dairy fermentations if the milk has been excessively agitated. 

Methanesulfonic acid, dimethyl sulfoxide and dimethyl sulfone are potential intermediates in the gas phase oxidation of dimethylsulfide in the atmosphere. We nave measured the rate of reaction of MSA with OH in aqueous solution using laser flash photolysis of dilute hydrogen peroxide solutions as a source of hydroxyl radicals, and using competition kinetics with thiocyanate as the reference solute. The rate of the reaction k (OH + SCN ) was remeasured to be 9.60 1.12 x 109 M 1 s 1, in reasonable agreement with recent literature determinations. The rates of reaction of the hydroxyl radical with the organosulfur compounds were found to decrease in the order DMSO (k = 5.4 0.3 x 109 M-i s 1) > MSA (k = 4.7 0.9 x 107 M l S 1) > DMS02 (k = 2.7 . 15 x 107 M 1 s ). The implications of the rate constant for the fate of MSA in atmospheric water are discussed. 

MPO (Myeloperoxidase) [EC 1.11.1.7] catalyzes the hydrogen peroxide dependent two-electron oxidation of halides (CD, I, Br ) and thiocyanate to the corresponding hypohalous acids and hypothiocyanate which are cytotoxic to invading pathogens. In addition, MPO is capable of the singleelectron oxidation of a wide variety of aromatic alcohols and amines. " ... 

Oxidations of thiocyanate ion by nitrous and nitric acids and by peroxomono-sulphate and peroxodisulphate are considered under the oxidants (p. 293 and 350). Oxidation by hydrogen peroxide and by iodine will be considered here. 

Note. If the total Fe content of a solution containing both Fe(III) and Fe(II) is required, the latter must be oxidized by heating with a small amount of ammonium persulphate or hydrogen peroxide. Before the addition of thiocyanate, the solution must be cooled. 

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