Photodimers of N-alkyl-3,4-dimethylmaleimides—Product ratios and reaction mechanism

详细信息	查看全文 | 推荐本文 |

• 作者：Xiuling Yu ; Cathrin Corten ; Helmut Gö ; rner ; Thomas Wolff ; Dirk Kuckling
• 关键词：Photodimerization ; Photo-cross-linking ; Flash photolysis ; Triplet state ; Reaction mechanism ; Selectivity
• 刊名：Journal of Photochemistry and Photobiology A ; Chemistry
• 出版年：2008
• 期刊代码：66_10106030
• 类别：ch
• 出版时间：5 July 2008
• 卷：198
• 期：1
• 页码：34-44
• 文件大小：1077 K

摘要

The photodimerization of three N-alkyl-3,4-dimethylmaleimides (DMI) – frequently used to form crosslinks in polymers – was examined. N-Isobutyl-3,4-dimethylmaleimide, N-(2-acetamido)ethyl-3,4-dimethylmaleimide, N-(3-propionic acid)-3,4-dimethylmaleimide were studied by steady-state and time-resolved photolysis in various solvents. Unexpectedly, under all conditions a single-bonded dimer distinct from the well-known cyclobutane fused cyclic dimer was identified. Depending on the solvent the single-bonded dimer amounts to 5–50%of the product yield, allowing for considerable selectivity. Dimerization quantum yields, Φ_dim, range from 0.01 to 0.5. Results from time-resolved experiments establish the involvement of the triplet state in the photodimerization mechanism, the quantum yield of singlet molecular oxygen formation accounts for the Φ_dim values. Electron transfer and hydrogen abstraction reactions of DMI in polar and protic solvents, in contrast to N-alkylmaleimides, are inefficient processes.