Molecule of the Day

Many of you have this in your homes. If you have those slow-dissolving tablets that leave a bleachy smell in your water, there’s a good chance you have N-chloro-N-bromo-dimethylhydantoin in one of those giant tablets in your toilet tank.

The compound is almost entirely insoluble in water. However, water will slowly react with the surface of the tablet, and a few other compounds form, such as hypochlorous acid (chlorine bleach, more or less), and hypobromous acid, the bromine analogue of chlorine bleach.

As you’ve probably surmised, this is where the disinfecting power comes from. The cleaning power from the oxidizers (HOCl and HOBr) is probably marginal at this low concentration, so some manfacturers add a bit of detergent to help break up any errant, uh, detritus stuck to the walls of your toilet.

So, the lack of solubility (and slow hydrolysis) of BCDMH is used to modulate the rate of release (allowing the tablet to last more than a few hours). Neat, huh? Well, smart, at least.

See you tomorrow!