Generation and Reactivity of Ketyl Radicals with Lignin Related Structures. On the Importance of the Ketyl Pathway in the Photoyellowing of Lignin Containing Pulps and Papers
the photochemical studies ketyl radicals have been produced by charge-transfer (CT) photoactivation of the electron donor−acceptor salts of methyl viologen (MV2+) with α-hydroxy-α-phenoxymethyl-aryl acetates. This process leads to the instantaneous formation of the reduced acceptor (methyl viologen radical cation, MV+•), as is clearly shown in a laser flash photolysis experiment by the two absorption
通过辐射化学和光化学技术已经产生了具有木质素相关结构的酮基。在以前的研究中,酮基是通过α-羰基-β-芳基醚木质素模型与pH值为6.0的水溶液的脉冲辐射分解产生的溶剂化电子反应生成的。酮基的紫外-可见光谱的特征在于三个主要吸收带。当在碱性溶液(pH 11.0)中记录光谱时,这些谱带的形状和位置略有变化,现在将它们分配给了酮基自由基阴离子,并确定了1-(3,4,5-三甲氧基苯基)的ap K a = 9.5。 -2-苯氧基乙醇-1-基。发现酮基的衰变速率与剂量有关,在低剂量时,其范围为(1.7-2.7)×10 3 s- 1。在存在氧气的情况下,观察到酮基的快速衰变(k 2 = 1.8-2.7×10 9 M - 1 s - 1),伴随而来的是形成稳定的产物,即起始酮。在光化学研究中,已经通过α-羟基-α-苯氧基甲基-芳基乙酸酯的甲基紫精(MV 2+)的电子给体-受体盐的电荷转移(CT)光活化产生了