746 7. MERCURIALS 



Reactions of the Mercurials with SH Groups 



The various types of mercaptide which can be formed are indicated in 

 the accompanying tabulation. The complexes formed under particular cir- 



cumstances will depend on the relative concentrations of thiol and mercurial, 

 the presence of ligands capable of complexing with the mercurials, the spa- 

 tial arrangement of the SH groups, the pH, and the nature of the R and R' 

 groups. Monofunctional mercurials, such as p-MB and PM, react with 

 cysteine, glutathione, and 2-mercaptoethanol in 1 : 1 molar ratio to form 

 R — S — Hg — R' type of complexes (Benesch and Benesch, 1952; Hoch and 

 Vallee, 1960). These reactions can be conveniently followed polarographi- 

 cally. Reactions with dithiols are more complex. The dimercaptide formed 

 from PM and dimercaprol (BAL) is insoluble, but if hydrophilic groups 

 occur on the mercurial the product is usually soluble. However, the in- 

 stability of the C — Hg bond may allow further reaction to form the cyclic 

 mercaptide, as occurs with mersalyl (Benesch and Benesch, 1952). This 

 reaction, where R = — CH2CONH — 9? — OCHgCOO", leads to the splitting 



CHp— OH CHp— OH 



I /OCH3 



CH— S-Hg-CHaCH^ _ + H 



I ^ 



I /OCH3 



CH2— S— Hg— CH2CH 



^R" 



Hg— CH2CH(OCH3)R 



CH2=:CHR" 



CH.OH 



