Phenylthiourea, oxidation

In contrast to the formation of Hector s base (3a) by the oxidation of 1-phenylthiourea, oxidation of l-phenyl-3-methylthiourea and 1,3-diphenylthiourea give thiadiazole (86 ... 

The oxidation of acetylthiourea and phenylthiourea to afford the corresponding 1,2,4-thiadiazoles has been reported using [bis(acyloxy)iodo]arenes as the oxidants. The proposed mechanism involves the formation of a polyvalent iodine compound 74. After the elimination of iodobenzene, the 1,6-dip he nyl-dithioformamidine 75 is formed, which is set up to undergo a further oxidation to give the bis 3,5-diamino-l,2,4-thiadiazole 76 (Scheme 7) <2003T7521>. 

S- and Se-donor ligands. The e.s.r. and electronic spectra of [Co(sacsac)2] and [Co(sacsac)2L] (sacsac = dithioacetylacetonate, L = py or piperidine) have been studied, and a polarographic study of [Co(sacsac)J (n = 2 or 3) in acetone has shown the complexes to have a well-defined capacity to accept one or two electrons in a reversible stepwise manner. The magnitude of the potentials and their reversible nature suggest that isolation of cobalt-sacsac complexes of low formal oxidation states should be possible." Co complexes of l,5-bis-(2-methylmercaptoethylthio)pentane are both hydrated and polymeric, and thermal decomposition in air or nitrogen leads to oxida tion to Co . Ethylenethiourea (etu) and tetramethylthiourea (tmtu) form the complexes [Co(etu) ](N03)2 and [Co(tmtu) ](C10 )2, which are tetrahedral, and [Co(etu)2(N03)2] and [Co(tmtu)2(N03)2] which have distorted octahedral co-ordination. 3-Diphenylphosphinothioyl-l-phenylthiourea, -1,1-diethyl-thiourea, and -1,1-dimethylthiourea form complexes with Co in which the ligands are bidentate. ... 

Monosubstituted amino groups (e.g. anilino) in amidinothioureas can participate in this cyclization, as shown by the ready oxidation of l-(2V,jV -diphenylamidino)-3-phenylthiourea (98 R = H, Ar = Ph) (and its analogs) to 5-anilino-2-phenyl-3-phenylimino-AM,2,4-thia-diazoline (99 R = H, Ar = Ph).116 This reaction, in which the alternative cyclization to benzothiazoles might be expected to predominate,68... 

A,TV-Dimethyl-A -phenylthiourea has been shown to coordinate to Rh111 as an N—S bidentate involving four-membered chelate ring formation.154 N-Substituted thioamides also may bond in this manner.155 156 l-Amidino-2-thioureas (44) may behave either as N—S or as N—N bidentates, with this donor choice being dependent mainly on pH and the nature of the metal ion.157 As N—S donors they are known to stabilize lower oxidation states.158 As part of a study on Mo—S-containing complexes as models for redox-active molybdoenzymes, Dilworth et al. have shown that some p-(substituted)phenylhydrazines may coordinate as N—S bidentates in three different ways to one metal atom.159 The three diazenido, diazene and hydrazonido forms vary in their degree of deprotonation and therefore their anionic nature. 

The reaction of thiourea126 with Methylene Blue (MB) is enhanced by an addition of mercaptosuccinic acid. The oxidation of phenylthiourea with MB127 is unaffected by the addition of the corresponding disulfide. The reactions exhibited a zero-order dependence on MB and a first-order dependence on the thiourea. The kinetic features have been explained in terms of reaction between half-reduced MB radical and the thiourea molecule. 

In the case of aniline, a weak base, no substitution occurs and (64) is obtained (75BCJ310). Oxidation of 1-phenylthiourea (66) with H2O2 gives Hector s base (3a Scheme 33). This... 

The preparations of 1,2,4-thiadiazoles and 1,2,4-thiadiazolidines from thioureas are well known and have been summarized in three reviews those of Bambas, Sherman, and Kurzer. Contained in these reviews are discussions of the controversies that surrounded some of the products, notably Hector s bases, which resulted from oxidation of substituted thioureas.Subjects covered in the above reviews, but too extensive to outline in detail here, are the oxidation of amidinothioureas to 3,5-diamino-l,2,4-thiadiazoles (71), the oxidation of phenylthiourea and of substituted amidinothioureas to 3,5-diimino-1,2,4-thiadiazolidines (72, Hector s bases), the reaction of thiopseudoureas with trichloromethanesulfenyl chloride to form 3-alkylthio-5-chloro-l,2,4-thiadiazoles (73), the reaction of thiopseudoureas with sodium thiocyanate and bromine and the oxidation... 

The first recorded example of a 2,1,4-benzothiadiazine appears to be the 3-phenylamino-l//-derivative (49) which was obtained as a yellow crystalline solid by oxidative ring-closure of N- 2-aminophenyl)-V -phenylthiourea (48) with aqueous ferric chloride (Equation (6)) <29JICI81>. In a related manner, reduction of the V-(2-nitroaryl)-V -(methoxycarbonyl)thioureas (50) with sodium dithionite <7iGEP2l0846i, 88IJC(B)672> or with sodium hydrosulfide in DMF <72GEP2215733> affords the 3-methoxycarbonylamino-l//-2,l,4-benzothiadiazines (51) (Equation (7)), the 5-oxides of which (see Section 6.15.4.2) are useful anthelmintics (see Section 6.15.9). 

In conclusion, it is interesting that diaryldithioformamidine dihydrobromides, dissolved in acidified aqueous ethanol, may yield Hector s bases (14b) directly, without further addition of oxidants, according to Eq. (3). The dithioformamidine corresponding to 1-methyl-l-phenylthiourea similarly yields 40.34 Here the cyclization occurs under the influence of the excess of dithioformamidine, the oxidizing power of which is well established (e.g., liberation of iodine from iodide). Two moles of arylthiourea and one gram-atom of sulfur appear as by-products. 1-Phenylamidino-l-phenylthiourea is also oxidized by dithioformamidine to Hector s base nearly quantitatively.34... 

The 6-keto-cholestane (354) was also converted by a known pathway into the lactam (355). Oxidation to the ketone (356a), followed by treatment with phenyl-hydrazine. gave the indole derivative (357). Brominatioh of the 3-ketone (356a) with pyridinum hydrobromide perbromide afforded the 4-bromo-ketone (356b). which in turn was allowed to react with N-phenylthiourea to furnish the thiazol (358) (Scheme 17). ... 

Rates of oxidation of arylthioureas to the corresponding arylureas in AcOH are insensitive to substituents, have a negative fractional order in cetyltrimethyl ammonium dichromate (CTADC), fractional order in phenylthiourea, and second order in H+ ions. The effects of surfactant and polarity of the solvents have been reported and a mechanism has been proposed. ... 

Most organic corrosion inhibitors used in cleaning solutions will not prevent ferric ion corrosion. Special chemicals were developed to reduce this problem. Alfandry demonstrated that hexamethylenetetramine will protect steel in HCI, but the protection is reduced by the presence of Fe + ions. However, the protection provided to steel in sulfuric acid is improved by the addition of ferric ions to a solution inhibited by phenylthiourea. Streicher reported that ferric ion corrosion of steel in sulfuric acid can be reduced by a mixture of diorthotolylthiourea and an anionic surfactant, such as an alkyl-aryl sodium sulfonate. Sulfonium salts also were used as ferric ion inhibitors. These inhibitors are effective in a variety of mineral and organic acids, but they are most effective in acidic (pH of 5) EDTA solutions. The sulfonium salts were shown to electroreduce at the corrosion potential to form a hydrophobic product (hydrocarbon) that may enhance the protection of the steel from oxidation by the ferric ion. 

The reactivity of thioureas towards oxidants, however, has been more extensively studied. 1,3-Disubstituted thio- and seleno-ureas have been converted into the corresponding ureas by means of DMSO in the presence of an acidic catalyst. l,l-Dimethyl-3-phenylthiourea was oxidized by benzenesulphenyl chloride, thionyl chloride, sulphuryl chloride, and sulphur monochloride to the same product, (339). The oxidation of thioureas... 

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