Molecules: You'd better learn to live with them.
There are a number of "strong" acids that are essentially completely dissociated in water - hydrochloric and sulfuric acid are two of the most common. Unfortunately, these are often volatile (as in HCl), insoluble, or otherwise ill-behaved in organic solvents. The organic sulfonic acids are quite strong - the functional group is essentially sulfuric acid with one of its valences occupied by a carbon functional group instead of another -OH. para-toluenesulfonic acid, or tosylic acid is probably the most common sulfonic acid used in the lab. Much stronger than carboxylic acids (the other organic acid), it's often used as an acid catalyst in nonaqueous systems.
Tosyl chloride, its "acid chloride" (the remaining -OH is replaced by -Cl, which will happily hop off and be replaced by most nucleophiles) is often used to create "tosylates," or esters of tosylic acid, from alcohols. This makes the alcohols more reactive to substitution. Tosyl chloride smells cloyingly like buttered popcorn, phenol, and rubber, in that order. I used to have a labmate who would always spill some when she used it, and it would give me a headache every time (and I'm not usually a candy-pants with chemical smells!).
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I have never verified it, but someone once claimed that the unpleasant smell of tosyl chloride actually comes from an impurity and that multiple recrystallizations will yield odorless stuff, though presumably it won't take long for it to start smelling again.
Posted by: barney | December 19, 2006 10:25 AM