Reaction of 1,2-naphthoquinone-4-sulfonate with aliphatic amines: Structure of the colored products and kinetics.

Substitution of the 4-sulfonate in sodium 1, 2-naphthoquinone-4-sulfonate (I) with many kinds of aliphatic amines (II) yields colored 4-substituted 1, 2-naphthoquinones (Q) : 4-morpholino-Q (IIIa), 4-piperidino-Q (IIIb), 4-pyrrolidino-Q (IIIc), 4-(1, 2, 4-triazol-1-yl)-Q (IIId), 4-(2-pyrrolyl)-Q (IIIe), 4-dimethylamino-Q (IIIf), 4-diethylamino-Q (IIIg), 4-isopropylamino-Q (IIIh), and 4-(4-amino-2-methyl-5-pyrimidylmethylamino)-Q (IIIi). The eliminated sulfite adds rapidly to the 4-position in I to form a colorless by-product, disodium 2-hydroxy-1-oxo-1, 4-dihydro-4, 4-naphthalenedisulfonate (IV). The rates of reactions were measured by polarography. The formations of IIIa and IV are successive second-order reactions. The pH profile of the rate constant, with a rounded peak at pH 10, suggests nucleophilic substitution of the free base (II) at the 4-carbon in the o-quinone form (I). The hydrolysis of IIIa to 2-hydroxy-1, 4-naphthoquinone (V) is an acid-base-catalyzed pseudo-first-order reaction. The best conditions for photometric determination of morpholine (IIa) were found to be reaction of IIa with excess I at pH 8 and 25°C for 30 min.