One-pot synthesis of menthol from citronellal or citral was summarized. Both batch and continuous reactors have been recently applied. This reaction is very complex and a bifunctional catalyst exhibiting especially Lewis acid sites for cyclisation of citronellal to isopulegol are needed, while metal particles are required for its hydrogenation to menthols. Typically, too mild acidity of the catalyst and small particles do not catalyze menthol formation. Furthermore, too high acidity causes catalyst deactivation and dehydration of menthol. Very high menthol yields have been obtained in batch reactor over nobel and transition metal supported bifunctional catalysts. Shape selectivity was demonstrated for Ni-supported on Zr-modified beta zeolite, which gave high diastereoselectivity to the desired L-menthol. Recently one-pot synthesis of menthol in a trickle bed reactor has been investigated. Catalyst suffers only minor deactivation in transformation of citronellal to menthol, while more severe catalyst deactivation occurred in transforming citral to menthols. Noteworthy from the industrial point of view is that the product distribution obtained with the same catalyst under kinetic regime or under diffusional limitations differs from each other. The metal location and synthesis method of extrudates can have a major effect on the catalyst performance. Kinetic modelling of the data obtained from the trickle bed reactor considering the effectiveness factor is discussed.

Graphical Abstract

The results from one-pot synthesis of menthol finding applications in pharmaceuticals and fragrances from citral and its hydrogenated product, citronellal over bifunctional catalysts metal–acid are summarized. The relationship between the catalyst properties and the performance is discussed. In the continuous mode catalyst deactivation becomes apparent and in such mode of operation the product distribution might differ from those obtained in a batch reactor.

中文翻译：

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柠檬醛和香茅醛在多相催化剂上一锅法合成薄荷醇

总结了从香茅醛或柠檬醛一锅法合成薄荷醇。最近应用了间歇式和连续式反应器。该反应非常复杂，需要具有特别是路易斯酸位点的双功能催化剂，用于将香茅醛环化为异胡薄荷醇，而金属颗粒则需要将其氢化为薄荷醇。通常，催化剂的酸性太弱和小颗粒不会催化薄荷醇的形成。此外，过高的酸度会导致催化剂失活和薄荷醇脱水。在诺贝尔和过渡金属负载的双功能催化剂上，在间歇反应器中已经获得了非常高的薄荷醇产率。在 Zr 改性的 β 沸石上负载 Ni 的形状选择性得到证实，这对所需的 L-薄荷醇具有高非对映选择性。最近研究了在滴流床反应器中一锅法合成薄荷醇。在香茅醛向薄荷​​醇的转化过程中催化剂仅发生轻微失活，而在柠檬醛向薄荷醇的转化中催化剂失活更为严重。从工业角度值得注意的是，在动力学机制或扩散限制下使用相同催化剂获得的产物分布彼此不同。挤出物的金属位置和合成方法会对催化剂性能产生重大影响。讨论了考虑有效性因素的从滴流床反应器获得的数据的动力学建模。而在将柠檬醛转化为薄荷醇的过程中发生了更严重的催化剂失活。从工业角度值得注意的是，在动力学机制或扩散限制下使用相同催化剂获得的产物分布彼此不同。挤出物的金属位置和合成方法会对催化剂性能产生重大影响。讨论了考虑有效性因素的从滴流床反应器获得的数据的动力学建模。而在将柠檬醛转化为薄荷醇的过程中发生了更严重的催化剂失活。从工业角度值得注意的是，在动力学机制或扩散限制下使用相同催化剂获得的产物分布彼此不同。挤出物的金属位置和合成方法会对催化剂性能产生重大影响。讨论了考虑有效性因素的从滴流床反应器获得的数据的动力学建模。

图形概要

总结了从柠檬醛及其氢化产物香茅醛在金属-酸双功能催化剂上发现薄荷醇在药物和香料中的应用的一锅法合成结果。讨论了催化剂性能与性能之间的关系。在连续模式中催化剂失活变得明显，并且在这种操作模式中，产物分布可能与在间歇反应器中获得的分布不同。