Showing papers on "Mechanochemistry published in 1991"

Mechanochemistry of lignin. V: An intensive chromophore in mechanical pulps bleached with alkaline hydrogen peroxide

Abstract: An intensive quinoid chromophore (IV-Q) was formed under daylight Irradiation of a hydroquinone derivative (IV—H), which was obtained by alkaline peroxide bleaching of a mechanochemical reaction product (IV—S) obtained from a phenylcoumaran lignin model. Chromophore IV—Q shows an absorption maximum at 460 nm in methanol and at 500 nm when impregnated in filter paper, both accompanied with a broad absorption in the ränge of 400—700 nm. Under Irradiation, chromophore IV—Q was bleached quickly with 1-thioglycerol to yield the corresponding hydroquinone (IV—H) and a Michaeltype addition product (IV-HT).The latter compounds were converted, however, readily into the corresponding quinones (IV-Q and IV-QT, respectively) in the absence of 1-thioglycerol. Based on these results, formation of a quinoid chromophore (11) was proposed in connection with the behavior of the lignin residue in peroxide bleached mechanical pulps.