Main content area

Autocatalytic Hydration of Dihydropyran to 1,5-Pentanediol Precursors via in situ Formation of Liquid- and Solid-Phase Acids

Barnett, Kevin J., McClelland, Daniel J., Huber, George W.
ACS sustainable chemistry 2017 v.5 no.11 pp. 10223-10230
acidity, byproducts, carboxylic acids, drying, gas chromatography-mass spectrometry, nuclear magnetic resonance spectroscopy, pH, tautomers, temperature
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×.