LAUSR

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 fo...