Armstrong's acid is a strong acid which is related to toluenesulfonic acid and is used in chemical synthesis. It was named for British chemist Henry Edward Armstrong

Henry Edward Armstrong

Henry Edward Armstrong FRS was an English chemist. Although Armstrong was active in many areas of scientific research, such as the chemistry of naphthalene derivatives, he is remembered today largely for his ideas and work on the teaching of science...

. It is sometimes used as a divalent

Divalent

In chemistry, a divalent ion or molecule has a valence of two and thus can form two bonds with other ions or molecules. An older term for divalent is bivalent....

 counterion

Counterion

A counterion is the ion that accompanies an ionic species in order to maintain electric neutrality. In table salt the sodium cation is the counterion for the chlorine anion and vice versa.In a charged transition metal complex, a simple A counterion is the ion that accompanies an ionic species in...

 for forming salts of basic

Base (chemistry)

For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...

 drug compounds, as an alternative to the related mesylate

Mesylate

In chemistry, a mesylate is any salt or ester of methanesulfonic acid . In salts, the mesylate is present as the CH3SO3− anion. When modifying the International Nonproprietary Name of a pharmaceutical substance containing the group or anion, the correct spelling is mesilate .Mesylate esters are a...

 or tosylate salts. When used in this way such a salt is called a naphthalenedisulfonate salt, as seen with the most common salt form of the stimulant drug CFT.