用原位红外光谱研究氧化镁上甲醛与乙醛合成双季戊四醇反应的机理

In-Situ FT-IR Study on Reaction Mechanism for Synthesis of Dipentaerythritol from Formaldehyde and Acetaldehyde over MgO

以甲醛和乙醛为原料 ,研究了在碱性催化剂存在下合成双季戊四醇反应的机理和工艺 .结果表明 ,与液体碱NaOH的碱催化作用相比 ,固体碱MgO上的产物季戊四醇、双季戊四醇和三季戊四醇在收率方面水平相当 .用原位红外光谱研究了在MgO上甲醛和乙醛各自的吸附物种及甲醛 乙醛混合物的吸附物种 ,考察了这些吸附物种随温度的变化 .结果发现 ,吸附作用削弱了甲醛和乙醛分子中的C =O双键 ;甲醛与乙醛原位反应后表明有α ,β不饱和醛吸附物种生成 。

The synthesis of dipentaerythritol from HCHO and MeCHO in the presence of MgO catalyst was studied. When n(NaOH)/n(MeCHO) = 1 and n(MgO)/n(MeCHO) = 0.1, the reaction gave pentaerythritol, dipentacrythritol and tripentaerythritol with the yields of 36.0%, 41.5% and 12.5% respectively, while only with n(NaOH)/n(MeCHO) = 1.1 in the absence of MgO, their yields were 39.8%, 41.8% and 11.6% respectively. These experimental results showed that, compared with the liquid base catalyst, the solid base catalyst MgO had good performance in the catalytic reaction. Using in-situ FT-IR, the adsorption of HCHO or/and MeCHO on MgO was studied at different temperatures. It was found that the carbonyl double-bonds in HCHO and MeCHO were weakened substantially owing to the adsorption, and the carbonyl groups of a beta-unsaturated aldehyde were detected, which could be attributed to the presence of acrolein. Thus, with the supposition that acrolein acted as an intermediate in the reaction for synthesis of dipentaerythritol from HCHO and MeCHO, a mechanism accounting for the reaction over MgO was induced.