Abstract

Plant polyphenols can be used as reducing agents to prepare chrome tanning agents. The kinetics of the reaction between catechin, the precursor of condensed plant polyphenols, and dichromate play an important role in the study of this preparation. The factors which influence the redox between catechin and dichromate and its kinetic character were investigated under different conditions by spectrophotometry. The results show that redox may mainly be achieved in the first minute of the reaction. In this reaction, the concentration of catechin, solution acidity and reaction temperature are the main influences on the reaction rate. At 25°C the reaction rate equation may be expressed as follows:

-d[V(v)]/dt=k[Cr(VI)][catechin][H+]

When the temperature is over 35°C, there may be multi-radical reactions which may result in a more complex redox mechanism.