Mechanismus der protonkatalysierten gasphasendehydratisierung von furfurylalkohol

The gas phase proton catalysed water elimination of tetrahydrofurfuryl alcohol (1) gives exclusively the ring-enlarged oxonium-ion 12. There is no experimental indication for the generation of 11 via a [1.2]-hydrogen migration. From the analysis of appropriately ¹³C-labelled precursors in combination with collisional activation mass spectrometry the mechanism for the ring-enlargement has been derived, clearly indicating that the oxygen/carbon bond is cleaved. A comparison of the experimental results with computational investigation (ab initio molecular orbital calculations at the 4-31G level) suggests that free tetrahydrofurfuryl cation 7 is not generated in the gas phase solvolysis. The elimination of H₂O from the protonated molecule of 1 is a process characterised by anchimeric assistance of the ether oxygen 15.