Kinetics and mechanism of kappa number determination

The kinetics and mechanism involved in the kappa number determination have been studied using a spectrophotometric method to monitor the oxidation of pine kraft pulp as well as of model compounds for lignin and carbohydrates. It was found that, during the kappa number determination, the permanganate oxidation proceeds stepwise, forming manganese dioxide which is then reduce d to manganous ions. Lignin is oxidized by the addition of permanganate to all the double bonds in the aromatic rings followed by a rupture of the rin gs. The predominant part of the oxidation of lignin is completed within one minute whereas the oxidation of e.g. glucose is slow but proceeds at an ac celerating rate during the kappa number determination time (10 min). The sp ectrophotometric determination of per manganate remaining after the reactio n has advantages over the traditional iodometric method.