一种新型松香基表面活性剂在芳香醇常温水相氧化反应中的应用

以松香为原料合成的表面活性剂具有良好的生态性能,符合“绿色化学”的要求。笔者设计合成了一种新型松香基表面活性剂(脱氢枞醇-聚乙二醇-550-琥珀酸单甲醚,DAPGS-550-M)。合成反应以脱氢枞醇为原料,分两步进行:脱氢枞醇在碱性条件下与琥珀酸酐反应得到脱氢枞醇琥珀酸酯,再与甲基聚乙二醇-550(PEG-550-M)进行酯化反应生成所需DAPGS-550-M。再利用DAPGS-550-M在水溶液中形成纳米胶束,分析各种芳香醇于室温水中的氧化反应,筛选获得最佳反应条件:室温下催化量为摩尔百分比2%的AgNO3和摩尔百分比0.5%的Bi(OTf)3,相同物质的量的K2S2O8,以及2% DAPGS-550-M的水溶液为反应介质。试验结果表明,在此反应条件下,反应底物适用性广,14种芳香醇顺利氧化得到较高产率的酮或醛产物,且均通过核磁共振进行了鉴定。此外,进一步对该新反应体系的E因子(废物与期望产物的质量比和原子经济性)以及催化体系的可循环性进行了研究,结果表明:E因子较低,且包括水、表面活性剂和催化剂在内的整个催化剂体系均易于回收利用,符合绿色化学要求。
The rosin-based surfactants, synthesized from rosin and modified rosin, have generally good ecological properties, meeting the requirements of “green raw materials” for surfactant. A novel rosin-based surfactant dehydroabietinol-polyethyleneglycol-550-succinate monomethyl ether(DAPGS-550-M)was prepared from dehydroabietinol in two steps: 1)synthesis of dehydroabietic alcohol succinate; and 2)synthesis of DAPGS-550-M. The mixture was refluxed using a Dean-Stark trap until completion. The synthesized surfactant DAPGS-550-M was then examined in the oxidatioin of aromatic alcohols in water at room temperature. After extensive screening with benzyl alcohol as a model substrate, the optimized oxidation reaction conditions were employing 2% AgNO3 and 0.5% Bi(OTf)3 together with a stoichiometric amount of K2S2O8 at room temperature. With the optimized conditions in hand, the substrate scope and generality of this oxidation methodology were further investigated under aqueous conditions at room temperature. Benzyl alcohol(1a)was completely oxidized within 20 min, delivering benzaldehyde(2a)in 96% yield. Notably, gram-scale oxidation of 1a furnished desired 2a in 89% yield. Excellent product yields were obtained within 2 h at room temperature in the oxidation of most benzylic alcohols bearing diverse substituents, including Cl(1b), Br(1c), MeO(1e and 1i), Me(1h), and diaryl(1l). Slower rates were observed with the highly electron-deficient(4-(trifluoromethyl)phenyl)methanol(1d)and 1-(4-nitrophenyl)ethan-1-ol(1k), which afforded the desired products in 8 h and 18 h respectively. The transformations of(2,6-dichlorophenyl)methanol(1f)and 9H-fluoren-9-ol(1m)were more sluggish, possibly because of the steric hindrance. Finally, 1-(thiophen-2-yl)ethan-1-ol(1n)proceeded smoothly in 17 h. Furthermore, the whole catalyst system including water, the surfactant and catalysts can be easily recycled leading to a very low E factor(the mass ratio of waste to desired product and the atom efficiency). In summary, we have introduced a new class of rosin-based surfactant DAPGS, which enabled a