MECHANOCHEMISTRY OF LIGNIN .4. MECHANOCHEMICAL REACTIONS OF PHENYLCOUMARAN MODELS

Mechanochemical reactions of the phenylcoumaran units, important components of lignin, were investigated by use of four types of phenylcoumaran model compounds which were treated with a ceramic ball mill and/or a laboratory refiner. The results indicated that stilbene products were always formed, but phenylcoumarones were formed only from alpha-carbonyl-containing model compounds. On the basis of identification of stilbene products obtained by the treatment of model compounds with a laboratory by refiner, it was strongly suggested that phenylcoumaran units in lignin were also subjected to mechanochemical reactions in the course of mechanical pulping. The mechanisms involved in mechanochemical reactions of phenylcoumarans and the significance of these reaction products, stilbenes and phenylcoumarones, during light-induced color reversion of mechanical pulps were discussed.