Selective Nitroaldol Condensations over Heterogeneous Catalysts in the Presence of Supercritical Carbon Dioxide
作者:Roberto Ballini、Marco Noè、Alvise Perosa、Maurizio Selva
DOI:10.1021/jo801650p
日期:2008.11.7
catalysts based on Al2O3, supercritical carbon dioxide not only acts as a good solvent for the reaction of aromatic and aliphatic aldehydes with 1-nitroalkanes but, most importantly, it also allows the selectivity to be tuned between the competitive formation of beta-nitroalcohols and nitroalkenes (from the Henry reaction and the nitroaldol condensation, respectively). In particular, when the pressure
在40-60摄氏度下,在基于Al2O3的非均相催化剂存在下,超临界二氧化碳不仅充当芳族和脂肪醛与1-硝基烷烃反应的良好溶剂,而且最重要的是,它还允许对在竞争形成β-硝基醇和硝基烯烃之间进行调节(分别来自亨利反应和硝基醛缩合)。特别地,当超临界相的压力(和密度)从80 bar增加到140 bar时,硝基烯烃的选择性平均从大约60%增加到> 90%。实验表明,在相同的压力范围内,反应物醛的浓度曲线急剧增加。相比之下,在无溶剂条件下,反应通常以更高的转化率进行,