Kinetics and Mechanism of Tetrahydrofuran Synthesis via 1,4-Butanediol Dehydration in High-Temperature Water

Abstract

We conducted an experimental investigation into the kinetics and mechanism of tetrahydrofuran synthesis from 1,4-butanediol via dehydration in high-temperature liquid water (HTW) without added catalyst at 200-350 degrees C. The reaction was reversible, with tetrahydrofuran being produced at an equilibrium yield of 84% (at 200 degrees C) to 94% (at 350 degrees C). The addition of CO2 to the reaction mixture increased the reaction rate by a factor of 1.9-2.9, because of the increase in acidity resulting from the formation and dissociation of carbonic acid. This increase was much less than that expected (factor of 37-60) from a previously suggested acid-catalyzed mechanism. This disagreement prompted experiments with added acid (HCl) and base (NaOH) to investigate the influence of pH on the reaction rate. These experiments revealed three distinct regions of pH dependence. At high and low pH, the dehydration rate increased with increasing acidity. At near-neutral pH, however, the rate was essentially insensitive to changes in pH. This behavior is consistent with a mechanism where H2O, in addition to H+, serves as a proton donor. This work indicates that the relatively high native concentration of + (large KW), which has commonly been thought to lead to the occurrence of acid-catalyzed reactions in HTW without added catalyst, does not explain the dehydration of 1,4-butanediol in HTW without catalyst. Rather, H2O serves directly as the proton donor for the reaction.

Solvothermal nanoYAG synthesis: Mechanism and particle growth kinetics

“…It has been reported that it transforms into tetrahydrofuron when the temperature and pressure exceed 250°C and 18 MPa [24]. In the present case, where the temperature exceeded the critical value but the pressure did not, the functional groups from the precursors were suspected to have reacted with the butanediol derivatives, possibly leading to a different reaction pathway (see GC-MS data) compared with the normal tetrahydrofuron transformation.…”

Metal phosphate catalyzed dehydration of sorbitol under hydrothermal conditions

“…The decrease of the pH from 5 to 3 during our tests indicates that high concentrations of protons are generated by self-ionization of water molecules under the chosen hydrothermal conditions [43]. That means the dehydration of sorbitol to isosorbide could be affected by the proton concentration.…”

Future Prospect of the Production of 1,3-Butadiene from Butanediols

“…c The sample is the same as that listed in Table 3 acidified conditions accelerate the reaction rate. 104 Richter and Vogel have reported that the THF selectivity is nearly 100% by the use of pure supercritical water as the reaction media. 106 Besides, several papers described that THF as the primary product from 1,4-BDO could be dehydrated into BD, even though the process needs strict conditions.…”