Oxidation of thiourea

In many cases, the a-haloketone does not appear to be an intermediate in this reaction, since reagents such as sulfur trioxide, sulfuric, or 60% nitric add lead to 2-aminothiazole but with lower yields (11 to 43%). Formamidine disulfide [-S-C(=NH)NH2]2, a product of the oxidation of thiourea, seems to be the intermediate in this reaction, since upon treatment with ketones, it gives 2-aminothiazole (604). However, the true mechanism of this reaction has not yet been completely elucidated. 

Thiourea dioxide, or formamidine sulfinic acid, is an oxygenated thiourea derivative synthesized by the oxidation of thiourea with hydrogen peroxide. It has the chemical formula (NH2)NHCS02H and is tautomeric. 

RATE AND ACTIVATION DATA FOR ONE-EQUIVALENT OXIDATIONS OF THIOUREAS... 

The stoichiometries of the oxidations of thiourea and thioacetamide, respectively, by alkaline ferricyanide are ... 

Oxidation of thiourea occurs fairly rapidly with H202 but more slowly with Fe111,69... 

Oxidation of thiourea adsorbed on Au(lll) and pc-Au electrode in 0.1 M HCIO4 has been investigated using CV, in situ Fourier transform infrared spectroscopy, and differential electrochemical mass spectrometry [165]. Two reaction mechanisms were proposed for the oxidation of the adsorbed and nonadsorbed thiourea. For both types of Au electrodes, similar results were obtained. 

Wang D, Gyorgy G, Hildenbrand K, von Sonntag C (1994) Free-radical-induced oxidation of phloro-glucinol - a pulse radiolysis and EPR study. J Chem Soc Perkin Trans 2 45-55 Wang W-F, Schuchmann MN, Schuchmann H-P, Knolle W, von Sonntag J, von Sonntag C (1999) Radical cations in the OH-radical-induced oxidation of thiourea and tetramethylthiourea in aque-ous solutions. J Am Chem Soc 121 238-245... 

Free radicals derived from thiourea have been proposed as intermediates in several oxidations of thiourea. However, the reactions have not yielded much information regarding the identity or thermochemistry of the species implicated. For example, oxidation by IrCl62- occurs with a second-order dependence on [thiourea], a complex pH dependence, and hints of copper catalysis (244). Oxidation by Cu-(me2-phen)2+ is suggested to be an inner-sphere mechanism (92). At this time it is difficult even to guess at the redox potential of the thiourea radical. 

Alkali chlorites, NaCl20, in the presence of cuprous salts, can also be used for this oxidation. Oxidation of thioureas with dichlorodicyanobenzoquinone in the presence of sodium hydroxide also affords carbodiimides. Reaction of dialkylthioureas with sodium amide in refluxing toluene affords carbodiimides 25. The use of sodium hydride instead of sodium amide gives higher yields. 

It is generally believed that the oxidation of thiourea and related compounds by aqua-metal ions involves an inner-sphere electron-transfer process, whereas an outer-sphere mechanism is more commonly associated with substitution-inert complexes. The stoichiometry of redox reactions with one-electron oxidizing agents is different for acid and alkaline media. The oxidation of both thiourea and thioacetamide by [Mo(CN)g] in the range 0.02 < [HCIO4] < 0.08 M proceeds in a 1 1 ratio, yielding the disulfide as a product (108) ... 

M. Hoffmann, J.O. Edwards (1977). Kinetics and mechanisms of the oxidation of thiourea and N,N -dialkylthioureas by hydrogen peroxide. Inorg. Chem., 16, 3333-3338. 

An example of a catalyzed reaction that has an obvious shift in mechanism is the oxidation of thiourea by H202(HofTmann and Edwards, 1977). The stoichiometry for this reaction is... 

The assumed3,53,54 sequential occurrence of these reactions both in this synthesis and in the direct oxidation of thioureas (39 being considered an isomerization product of 38) must now be regarded as doubtful the evidence is in better accord with the parallel independent formation of 38 and 39 (see Section e, immediately below). 

ESR spectroscopy/ In both cases, an intermediate Cr(V) species was detected. In the latter report, comparison was drawn with reactions where cysteine was employed as the reductant. The decomposition of manganic cysteinates follows a reaction rate law, expressed by the disappearance of the Mn(III) and Mn(IV) complexes, that is, second-order with respect to the absorbant complex species and zero-order in the reducing substrate. " The oxidation of thiourea by permanganate ions in aqueous acidic media was found to be autocatalytic. The presence of Mn " thiourea complex ions were detected and a mechanism was proposed to account for the stoichiometry of the oxidation process as well as the product distribution. [Ag(OH)4] is rapidly reduced by thiourea in accordance with the three-term rate law (10), where = 1.08 s , ki = 1.46 x 10 s", and... 

Formamidinesdulflnic acid, H2N—C(=NH)—SO2H, a well known reducing agent synthetized by H2O2 oxidation of thiourea, has been successfully employed under PTC conditions in the reduction of disulfides and sulfylimines to thiols and sulfides, respectively... 

Studies of oxidation reactions of differing substrate types have been described. The nature of oxidant species in HCIO4 and H2SO4 media has been examined by investigation of catalysis of the Ce -Hg reaction. It is suggested that at 2.OM-HCIO4 the iridium(iv) is hydrolysed with protonation constant of 0.4 for [Ir(H20)s0H] +. Most kinetic studies, however, refer to reaction of the hexachloro and hexabromo ions. The oxidation of thiourea (tu), iV,iV -dimethyl-thiourea (dmtu), and 2-imidazolidinethione (it) follows a rate law second order in [substrate] and first in [Ir "]. The rate of oxidation follows the reactivity trend established previously for aquo-metal ions. The mechanism proposed involves rapid pre-equilibria followed by disulphide radical formation,... 

Preparative Methods by the oxidation of thiourea or amino-iminomethanesulfinic acid (formamidinesulfinic acid) with peracetic acid. Many substituted aminoiminomethanesulfonic acids can be prepared in the same way. 2 Others have utilized hydrogen peroxide with sodium molybdate as a catalyst to oxidize the corresponding thioureas to a variety of monosubsUtuted aminoiminomethanesulfonic acids the substituents include phenyl, 2-methylphenyl, 4-fluorophenyl, / -propyl, cyclohexylmethyl, S-a-methylbenzyl, cyclooctyl, and benzhydiyl. ... 

Solubility partially sol cold water insol in organic solvents. Preparative Method prepared by oxidation of thiourea with hydrogen peroxide. ... 

Manganese(iii).— The rates of oxidation of thiourea derivatives and of benzene-1,2-dithiol by the [Mn(OH)] + ion have been shown to be controlled by the rate of substitution of the substrate at the ion, ... 

A transient red color observed during the oxidation of thiourea by nitrous acid to formamidine disulfide [(NH2)2CSSC(NH2)2] is the S-nitroso compound [(NH2)2CSNO]. The decomposition of this intermediate, equation (21), involves two pathways, one involving the reversible... 

The kinetics and mechanism of the oxidation of thiourea and AA -dialkylthioureas to their respective formamidine disulphide cations have been investigated. Details of product characterization have been provided. The observed rate law is of the form (tu = thiourea)... 

Formamidinesulfmic acid (obtained by the oxidation of thiourea with hydrogen peroxide) has been used to reduce disulfides to sulfides (see Eqs. 12.6 and 13.22) and N-tosylsulfilimines to sulfides (see Eqs. 12.7 and 13.23), under phase transfer catalytic conditions in the presence of hexadecyltributylphosphonium bromide [15]. Diphenyl, dibenzyl and dibutyldisulfides were reduced by this method to the corresponding sulfides in 72%, 62% and 90% yields respectively. Examples of the reduction of N-tosylsulfilimines are recorded in Table 12.4. 

Oxidation. Formamidino-disulphides (33) are formed by oxidation of thioureas... 

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