Thiourea and thioacetamide

Oxidation by aqueous cupric sulphate occurs slowly enough to be studied by conventional means at 25 °C giving a rate law  

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

The hydroxyl-ion dependences suggest oxidation of substrate anions. Alkali-catalysed enolisation is the slow step of the oxidation of thioacetamide but is a fast pre-equilibrium in the thiourea oxidation. 

The reaction between two polydentate complexes of Cu(II), CuY (YjH4 = ethylenediaminetetraacetic acid, Y2H4 = hydroxyethylethylenediaminetriacetic acid) and thiourea to give a Cu(I) complex of thiourea (this product was not identified), follows kinetics  

The mechanism postulated involves rapid, acid-catalysed ligand exchanges to give Cu(thiourea)2 which breaks down in the slow step. Activation energies are 

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In 1893 a third important regularity was observed by Nikolai Semenovich Kumakov (1860—1941).107 While investigating the substitution of ligands by thiourea and thioacetamide, Kumakov found that replacement occurs with all the ligands of the cis compound but only with the acid radicals of the trans compound (Scheme 2). Since the two isomers yield different products, this reaction, known as Kumakov s reaction or Kumakov s test, may be used to differentiate cis from trans isomers of dipositive platinum or palladium. Kumakov s classic reaction played a crucial role in Werner s proof of the square planar configuration of Pt11 and in Chemyaev s formulation of the trans effect. 

The kinetics of the potassium hexacyanoferrate(III)-catalysed oxidation of glucose with ammonium peroxodisulfate have been studied.82 The kinetics and mechanism of oxidation of some cycloalkanols by alkaline Fe(CN) have been reported.83 The same group has also studied the oxidation of cycloalkanones under comparable conditions and determined the order of reactivity as cyclohexanone > cyclopentanone > cyclo-octanone > cycloheptanone.84 Palladium(II) has been found to catalyse the oxidation of formaldehyde, thiourea, and thioacetamide by alkaline Fe(CN)g, whereas no effect is observed in the oxidation of acetaldehyde.85 The orders of reaction have been determined and a mechanism was proposed. 

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) ... 

Ahmed, A., K. K. Pillai, S. J. Ahmed, D. K. Balani, A. K. Najmi, R. Marwah, and A. Hameed. 1999. Evaluation of the hepato-protective potential of jigrine pre-treatment. Indian. J. Pharmacol. 31(6) 416-21. Akintonwa, D. A. A. 1985. High-pressure liquid chromatography separation of phenobarbitone, thiourea, and thioacetamide of toxicological interest. Ecotoxicol. Environ. Saf. 70(2) 145-49. 

H2S, Na2S, thiourea and thioacetamide are normally used as the S source [34-36, 52]. The major disadvantages of the method include poor crystallinity of as synthesized nanoparticles, large size distribution and invariably associated surface defects [61-67]. 

The increase in electrophilicity of coordinated ligands commonly leads to more favorable hydrolysis reactions. There are many reports on hydrolysis reactions of coordinated carboxamides, halogenated alkylamines, Schiff bases, thioamides, nitriles, etc. For example, thiourea and thioacetamide complexes of platinum metals decompose on heating in basic solution with formation of the corresponding metal sulfides, Eq. 1.26 and 1.27 ... 

The earliest CD processes were carried out using thiosulphate. Although thiourea (and to some extent thioacetamide) are now more commonly used to deposit sulphides, thiosulphate is still sometimes used. While the reaction pathways listed below are intended to suggest possibihties for reactions involving thiosulphate, it must be noted that the mechanism(s) for these reactions is (are) still not clear. Mechanisms have been proposed in the CD literature, but no convincing proof for any particular one has been forwarded. 

In an attempt to say something intelligent about these resistivities, there appears to be some correlation between the pH and resistivity, with low resistivity obtained when the pH is relatively low (only a few experiments have been carried out at relatively low values of pH also note Ref. 22, which describes an anomalously low resistivity even at normal values of pH). The bath described by Ito and Shiraishi [37] is very different from the previous ones, for three reasons the relatively low pH (= 8), the use of thioacetamide instead of thiourea, and the flow system used in this deposition. Very low values of dark resistivity were obtained with this bath and with an unusual temperature dependence (a minimum of 10 fi-cm was found at 63°C, which increased on either side of this temperature value). It was suggested that Cl, from the NH4CI buffer, acted as a dopant however, other chloride baths gave much higher resistivities. 

Nickel(II) complexes with thioacetamide (310) are similar to the corresponding ones with thiourea and were synthesized in a similar way. 

The reactions of [Ml2(CO)3(NCMe)2] with thiourea, A,A,A, /V -tetra-methylthiourea, and thioacetamide to give a number of seven-coordinate complexes have been described. A large series of 42 triphenylphos-phine oxide and triphenylphosphine sulfide complexes derived from [Ml2(CO)3(NCMe)2] have been prepared as shown in Scheme 5. Also, a series of tricyclohexylphosphinecarbondisulfide seven-coordinate complexes derived from the reactions of [MT(CO)3(NCMe)2], [MI,(CO)3(NC Me)L] L = PPhj, AsPhj, SbPhj, PCOPh),, and [Wl2(CO)3(PPh3)2] with PCy3CS2 have been reported. 

Porous silicon is under extensive study, largely due to its luminescence properties. For electroluminescence, however, some form of contact has to be made with the Si, and this necessitates deposition of another phase inside the pores of the Si in order to contact as much as possible of the internal area of the high-surface-area Si. With this in mind, CdS has been deposited inside the pores of porous silicon via a two-stage method [73]. Cd(OH)2 was deposited from an ammoniacal bath at pH 8, followed by conversion of the Cd(OH)2 to CdS by treatment with thioac-etamide at pH 8. This was repeated several times until the pores were essentially filled with CdS. The reason that this two-stage process was needed is that either the Si was unstable at the temperatures and pH values needed to deposit CdS from a thiourea solution, or CdS was formed in solution rather than on the Si surface using thioacetamide. 

To sum up, while there is too little information available to draw any firm conclusions, it appears that films deposited from most thiourea baths are weakly absorbing in the near-IR region and that films deposited from thiosulphate solutions (which are mildly acidic) may possess different optical properties in general than those deposited from (alkaline) thiourea baths. In this respect, and if this difference is real, it would be interesting to deposit PbS from thioacetamide baths, which can be both acidic and alkaline. 

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