The acidity of the mercaptan is stronger than that of the corresponding alcohol, and a relatively stable salt is formed in the ethanol solution soluble in sodium hydroxide, and the carbon dioxide is returned to the mercaptan. Mercaptans can form water-insoluble thiolates with some heavy metal salts, which are soft and soft. Many heavy metal ions are toxic in the body because they bind to the sulfhydryl groups of biomolecules. On the other hand, thiols (such as dimercaptopropionic acid) can also be used to detoxify heavy metal ions from the urine by forming insoluble precipitates.