OXIDATION OF LIGNIN MODEL COMPOUNDS CONTAINING AN ALPHA-CARBONYL GROUP AND A RING-CONJUGATED DOUBLE-BOND BY HYDROGEN PEROXIDE-UV PHOTOLYSIS

Studies were carried out on oxidation of lignin model compounds contai ning an alpha-carbonyl groups and a ring-conjugated double bond by hyd rogen peroxide/UV photolysis, The results showed that the reaction is strongly pH dependent. Under conditions studied, optimum disappearance rates of substrates were observed with molar ratio of substrate:hydro gen peroxide (1:8.8) at pH 10.6 with irradiation of 254 nm photons. Un der these conditions, acetovanillone was completely degraded into non- aromatic products after 2 hrs of irradiation. maleic acid and fumaric acid were found in trace amount in the reaction products, Under the sa me reaction conditions, trans-ferulic acid was appeared more stable th an acetovanillone, trans-cis isomerization was taken place, and maleic acid, fumaric acid and 4-hydroxybenzoic acid were also found in the r eaction products. These results indicate that oxidative cleavages or b oth aromatic ring, C-alpha-C-beta double bond, and demethoxylation hav e occurred during the hydrogen peroxide/UV photolysis. The possible pa thways for the degradation of the model compounds have been discussed.