Two calcium-rich natural layered aluminosilicates containing 90–95 wt.% montmorillonite were chemically activated using 0.125–3.0 M HCl solutions. Structural and textural properties were characterized by X-ray diffraction, elemental analysis and N₂-adsorption/desorption analyses. According to infrared spectroscopy using pyridine as probe molecule, the amount of Brønsted acid sites increased when increasing HCl concentration. The catalytic performance of these materials was investigated in the Prins cyclization of (−)-isopulegol with vanillin to form octahydro-2H-chromen-4-ol, carried out in toluene at 35 °C. It was found that the amount of Brønsted acid sites and the microporosity of the catalysts are key factors for the control of the reaction rate and the selectivity towards octahydro-2H-chromen-4-ol.

中文翻译：

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在酸改性的蒙脱土上由香兰素和异薄荷醇合成八氢-2 H-铬-4-醇：酸度对Prins环化的影响

使用0.125-3.0 M HCl溶液化学活化了两种含90-95 wt。％蒙脱石的富钙天然层状铝硅酸盐。通过X射线衍射，元素分析和N ₂吸附/解吸分析来表征结构和质地特性。根据使用吡啶作为探针分子的红外光谱法，当增加HCl浓度时，布朗斯台德酸位点的数量增加。在（-）-异胡薄荷醇与香兰素的Prins环化反应中形成八氢-2 H的过程中，研究了这些材料的催化性能。-chromen-4-ol，在35°C的甲苯中进行。发现布朗斯台德酸位点的量和催化剂的微孔率是控制反应速率和对八氢-2 H-铬烯-4-醇的选择性的关键因素。