# Why do thiols have such a propensity for bonding with mercury?

Historically, thiols $\ce{-SH}$ were known as "mercapto-" due to their strong propensity to bond with mercury. Certain drugs still carry this designation, though mercaptopurine has an $\ce{=S}$ group instead of a thiol.

What makes the thiol group bond so strongly with mercury in particular? Why don't alcohols make such a strong bond with $\ce{Hg}$?

If it's known, was there any historical reason why it was important to be able to "capture" mercury?

• "...though mercaptopurine has an $\ce{=S}$ group instead of a thiol." - that would be the tautomerism at work. See this article for instance. – user95 Jul 7 '12 at 16:59
• @J.M. Ah, I see, definitely didn't think of that. Thank you, I'll have to download that later. – jonsca Jul 7 '12 at 17:04