Synthesis of polyacenequinones via crossed aldol condensation in pressurized hot water in the absence of added catalysts
作者:Takenori Sawada、Shu Nakayama、Akiko Kawai-Nakamura、Kiwamu Sue、Hiizu Iwamura、Toshihiko Hiaki
DOI:10.1039/b914784p
日期:——
Phthalaldehyde and 1,4-cyclohexanedione react in the 2:1 molar ratio via a crossed aldol condensation in sub- and supercritical water to produce 6,13-pentacenequinone. The reaction conditions were optimized at 77% yield at 250 °C for 60 min with the starting molar ratio of 2:1:800 for phthalaldehyde, 1,4-cyclohexanedione and water, respectively. Whereas the initial rate of the reaction increased at higher pH, as suggested by earlier studies of the crossed aldol condensation of the two carbonyl compounds using a base catalyst in an organic solvent, the present results of successful reactions without the addition of any acid or base show the role of the increased solubility of the starting materials and the higher ion product in pressurized hot water. 6,13-Pentacenequinone was obtained as fine needles from the cooled reaction mixture just by filtration. Under similar conditions, 7,16-heptacenequinone and 5,12-naphthacenequinone were obtained in 46 and 70% isolated yields, respectively.
邻苯二甲醛和1,4-环己二酮在亚临界和超临界水中以2:1的摩尔比通过交叉阿尔多缩合反应生成6,13-五芳烯醌。反应条件经过优化,在250°C下反应60分钟,得到77%的产率,反应底物的摩尔比为邻苯二甲醛、1,4-环己二酮和水分别为2:1:800。尽管早期研究表明,在有机溶剂中使用碱催化剂进行的这两种羰基化合物的交叉阿尔多缩合反应,其初始反应速率随pH值升高而增加,但本研究的成功反应结果显示,即使没有添加任何酸或碱,反应仍然顺利进行,这体现了在加压热水中起始材料的溶解度增加及高离子产物的作用。通过简单过滤,从冷却的反应混合物中获得了细针状的6,13-五芳烯醌。在类似条件下,得到了46%和70%的纯化产率的7,16-七芳烯醌和5,12-萘烯醌。