Dihydropyran (DHP) undergoes autocatalyzed hydration to 2-hydroxytetrahydropyran (2-HY-THP) by carboxylic acids formed in situ in both batch and continuous flow reactors. NMR, GC–MS, and pH analysis corroborate the presence of carboxylic acids in the hydration products. Carboxylic acids, likely in the form of 5-hydroxy-valeric acid, are made as low as 25 °C, increasing solution acidity and autocatalyzing DHP hydration. 1,5-Pentanediol precursors 2-HY-THP and C10 dimers are produced from DHP at ∼98% yields at temperatures ≤100 °C. At ≥140 °C, byproducts are formed, including acidic solid coke and a C10 dimer likely made via aldol condensation-cyclodehydration of the ring-opened tautomer of 2-HY-THP, 5-hydroxyvaleraldehyde. DHP hydration rates continuously increased up to 50 h time-on-stream in continuous reactors demonstrating that the acidic byproducts catalyze this reaction. Activation rates rose with temperature due to increased acidic solid coke formation. The coke formed is soluble in water and its formation is reversible. Solid coke formed at high temperatures and retained in the reactor upon drying increased DHP hydration rates by up to 28×.

中文翻译：

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通过原位形成液相和固相酸，将二氢吡喃自催化水合为1,5-戊二醇前体

二氢吡喃（DHP）通过原位形成的羧酸自动催化水合为2-羟基四氢吡喃（2-HY-THP）在间歇和连续流反应器中。NMR，GC-MS和pH分析证实了水合产物中羧酸的存在。可能以5-羟基戊酸形式存在的羧酸可降低至25°C，从而增加溶液的酸度并自动催化DHP的水合作用。1,5-戊二醇前体2-HY-THP和C10二聚体是由DHP在≤100°C的温度下以约98％的收率生产的。在≥140°C时，会生成副产物，包括酸性固体焦炭和可能通过2-HY-THP，5-羟基戊醛开环互变异构体的羟醛缩合-环脱水制得的C10二聚体。在连续反应器中，DHP水合速率连续提高至运行时间最多50小时，这表明酸性副产物可催化该反应。由于酸性固体焦炭形成的增加，活化率随温度升高。形成的焦炭可溶于水，并且其形成是可逆的。固态焦炭在高温下形成，干燥后保留在反应器中，使DHP水合速率提高了28倍。