Do the brackets in the formula imply that two molecules of amphetamine freebase would be required to produce one molecule of sulphate?
Yes, there are two amphetamine molecules for every one sulfate counterion in amphetamine sulfate. The sulfate ion (SO42-) has a
-2 charge that gets countered by the positively-charged amphetamine ions. In other words, each sulfate ion is surrounded by two protonated amphetamine
molecules that have an extra proton on their nitrogen and an overall charge of +1.
And by the way, while the salts of nitrogen-based drugs are commonly represented using formulas that seem to suggest that they exist as some sort of
seperate, unbound freebase·acid pair, in reality the acidic protons aren't actually on the acids, but are instead on the nitrogen atoms of the
freebase molecules. This creates opposite formal charges on the pair, causing strong electrostatic attractions between the protonated freebase
molecules and the deprotonated acid molecules. Put another way, the freebase and acid combine to give a single ionic compound where the cation is the
conjugate acid of the freebase, and the anion is the conjugate base of the acid.
Thus amphetamine sulfate, like any other sulfate salt, would more accurately be expressed as (C9H14
N)2SO4.
