Kinetic Studies on the Amination of Leucoquinizarin

Article abstract of DOI:10.1246/bcsj.55.1209

Leucoquinizarin reacts with amines to give mono- and diaminoanthraquinones.The amination mechanism of leucoquinizarin was investigated on the basis of the kinetics and structures of leuco compounds.The amination reaction of leucoquinizarin was characterized as follows.This amination proceeded in polar solvent but not in nonpolar solvent at all.The reaction rate was not influenced by the addition of a small amount of water (95percent ethanol) but enhanced largely in 80percent ethanol.This amination reaction has a low activation energy (ΔE^<*>=5.7-9.0 kcal mol^-1) and an extraordinarily small pre-exponential term (A=10³ - 10⁵ mol^-1min^-1).Leucoquinizarin was proposed to be aminated by the addition of amine to carboynl group at its 1,4-position.The oxidation of leuco monoaminohydroxyanthraquinone was also examined.