A-Level Amines, amides and amino acids: worked solution

Question

Psilocin is a 4-hydroxy tryptamine bearing a -CH2CH2N(CH3)2 side chain, while the neurotransmitter serotonin (5-HT) is a 5-hydroxy tryptamine bearing a -CH2CH2NH2 side chain, so the two are closely related in structure. Apart from spectroscopic techniques, propose a chemical test that would distinguish serotonin from psilocin.

Serotonin has a primary amine side chain (-CH2CH2NH2) whereas psilocin has a tertiary amine (-CH2CH2N(CH3)2). A primary amine reacts with a suitable reagent that a tertiary amine cannot. Use warm ethanoyl chloride (or an acyl chloride/ethanoic anhydride): serotonin's primary -NH2 undergoes acylation, giving an amide and evolving misty white fumes of HCl (positive test), whereas psilocin's tertiary amine has no N-H and cannot form an amide, so no such reaction. (Alternatively, treatment with cold nitrous acid HNO2: the primary aromatic-side-chain amine can react while the tertiary amine gives a different/no stable result.)