Mercaptide thermolysis

Preliminary study of pure mercaptide thermolysis behavior by thermal analysis... 

The covalent mercaptide thermolysis takes place at quite moderate temperatures (150 to 250°C). Such mild thermal conditions are compatible with the thermal... 

METAL AND METAL SULFIDE SYNTHESIS BASED ON MERCAPTIDES 613 MERCAPTIDE THERMOLYSIS REACTIONS... 

PRELIMINARY STUDY OF PURE MERCAPTIDE THERMOLYSIS BEHAVIOR 619... 

The mercaptide thermolysis may behave differently in the presence or absence of polymers [Conte et al., 2007]. However, in most cases, the inorganic phase generated by the thermal degradation of mercaptide molecules dissolved in polymer corresponds exactly to that resulting from the thermal degradation of pure mercaptide. Consequently, a preliminary study of neat mercaptide thermolysis by thermal analysis approaches [differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA)] is usually performed before nanocomposite preparation and characterization. 

Conte, P., Carotenuto, G., Piccolo, A., Perlo, R, and Nicolais, L., NMR-investigation of the mechanism of silver mercaptide thermolysis in amorphous polystyrene, J. Mater. Chem., 17, 201-205 (2007). 

In this part of the chapter we discuss (a) the controlled thermolysis of thiolate solutions in polystyrene matrix at temperatures above the polymer glass transition temperature and (b) the reaction mechanism in the case of silver-polystyrene nanocomposite systems. However, the same reaction mechanism is probably involved in the thermolysis of other mercaptide-polystyrene systems. This technique has proven to be an excellent new preparative scheme for the generation of both metal and sulfide clusters in polymers. In particular, high-molecular-weight n-alkanethiolates have shown to be the most effective compound class since the low volatility of thermolysis by-products avoids film foaming during the annealing process. 

According to UV-Vis and DSC observations, the mechanism for zero-valence silver formation inside polystyrene matrices should involve a reduction of silver ions by hydrogen atoms generated from polystyrene during thermolysis. In particular, according to the DSC thermogram, the Ag-mercaptide... 

Thus, the reaction mechanism is influenced by the nature of the alkyl group, R , since mercaptides of secondary and thertiary thiols and thiophenols cannot provide nucleophilic substitution (SN2). Thiophenol thermolysis usually results in a metal sulfide with diphenyl molecule formation as a by-product. However, these ionic compounds melt and decompose at high temperatures and therefore are not adequate for nanocomposite synthesis. 

Thermolysis of covalent mercaptides (noble-metals and semimetals)... 

Etheroleptic mercaptides are much more soluble than the corresponding homolep-tic compounds, and their thermolysis takes place in two steps (1) imidazole ligand lost and (2) metal-sulfur bond cleavage at a higher temperature. 

The preparation of nanocomposite materials by thermolysis of mercaptide molecules dissolved in polymer represents quite a universal approach, and this reaction scheme is limited only by the ability to synthesize the mercaptide precursor. A short description of the most common mercaptide preparation routes follows. 

Thermogravimetric analysis (TGA) of pure mercaptides represents a simple way to establish the nature of the thermolysis product. In particular, since the organic... 

Carotenuto, G., Nicolais, L., and Perlo, R, Synthesis of polymer-embedded noble metal clusters by thermolysis of mercaptides dissolved in polymers, Polym. Eng. Sci., 46 (8), 1016-1020 (2006b). 

Nicolais, L. F., and Carotenuto, G., Synthesis of polymer-embedded metal, semi-metal, or sulfide clusters by thermolysis of mercaptide molecules dissolved in polymers. Recent patents on Material Science, 2008,1, 1-11. 

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