Kinetics of Epimerization of (+)-Catechin and Its Rearrangement to Catechinic Acid

Article abstract of DOI:10.1021/jo00136a021

The rates of epimerization of (+)-catechin (1) to (+)-epicatechin (2) and of (-)-epicatechin to (-)-catechin in aqueous solution were measuredthe pH range 5.4-11.0 and the temperature range 34-100 deg C.The rate of conversion of (+)-catechin to catechinic acid (3) also was measured under these conditions.First-order kinetics were observed for all three processes.At low pH, k(epimerization) >> k(rearrangement), and epimerization approached an equilibrium in which (+)-catechin predominated(+)-epicatechin.Near pH 11 and at elevated temperatures,k(epimerization) was only slightly greater than k(rearrangement), and the rapid, irreversible formation of catechinic acid under these conditions determined product composition.Both the epimerization of catechin and its rearrangement to catechinic acid can be rationalized in terms of a quinone methide intermediate (4).