Thioacetamide metal complexes

At intermediate pH values, particularly in weakly acidic solutions (pH > 2), metal sulphide formation using thioacetamide may proceed through decomposition of a metal ion (or solid phase)-thioacetamide complex rather than through intermediate formation of sulphide [4] (see Sec. 3.3.3). Thioacetamide in pure water is fairly stable and does not readily hydrolyze at room temperature. 

Thioacetamide, MeC(=S)NH2 (taa), is isoelectronic with thiourea which it resembles by acting as a unidentate S-donor ligand. Thiobenzamide, PhC(=S)NH2 (tba), behaves similarly. Both thioamides form stable complexes with (b) class and borderline metals. Thioacetamide forms the tetrahedral complexes [MX2(taa)2] (M = Fe, Co, Zn X = Cl, Br, I, NCS).47,153-157 The v(M—S) frequency is rather low, ranging from 255 to 230cm, .14s The Mossbauer spectra of FeX2(taa)2 PC = Cl, Br) are consistent with a tetrahedral configuration.158... 

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) ... 

In aqueous solution, the DPD indicator is catalyti-cally oxidized by oxygen when trace metals are present. In the standard method, the DPD solution is mixed with a strong phosphate solution, buffered at pH 6.2, and ethylenediaminetetraacetate (EDTA) is added to complex trace metals. Thioacetamide (CH3CSNH2) can be added immediately following the addition of DPD to decrease the interference from monochloramine. Addition of mercury(II) chloride (HgCl2) to the phosphate buffer has also been found to reduce the interference from monochloramine, presumably by complexation of trace iodide by Hg" +. ... 

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 ... 

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