Bismuth mercaptide

Most mercaptides are not available as commercial products, since large-scale applications of these chemical compounds are quite limited (only mercaptides of tin and antimony are used industrially as thermal stabilizers for poly(vinyl chloride) [de Sousa et al., 2000 Qu L. et al., 2002]). However, these compounds can be synthesized in a very simple way. Owing to their low water solubility, mercaptides can precipitate by reacting thiols (or thiophenols) with aqueous solutions of the corresponding metal salts. In addition to the well-known mercaptides of mercury, lead, zinc, and copper, many others, such as mercaptides of silver, gold, platinum, palladium, iridium, nickel, iron, cobalt, antimony, bismuth, and cadmium, have been prepared. 

Organometalhc compounds based on lead, tin, bismuth and zinc are also used to catalyse a urethane reaction. Bismuth and zinc carboxylates are used because of the toxicity and disposal problems of lead and tin. Nowadays, alkyl tin carboxylates, oxides and mercaptide oxides such as dibutyltin dUaurate (DBTDL),dioctyltin mercaptide, stannous octoate and dibutyltin oxide are used successfully in all types of polyurethane applications (Table 6.4), among which DBTDL was found to be the most widely used catalyst. The catalytic effect of organometaUic compounds is due to their capacity to form a complex with the isocyanates and polyols. The catalysis mechanism involves interaction of the metal cation with isocyanate and hydroxyl groups, followed by rearrangement of the resulting complex to yield the final urethane product. 

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